Archive for the ‘brain’ Category
this one’s for the birds
Canto: If anybody doesn’t appreciate the beauty and complexity and general magnificence of birds they should pee off and never darken this blog again.
Jacinta: Right. Now what brought that on, mate?
Canto: Oh just a general statement of position vis-à-vis other species. Charles Darwin, an old friend of mine, was pretty disdainful of human specialness in his correspondence, but he kept a low profile – on this and everything else – in public. I want to be a bit more overt about these things. And one of the things that really amazes me about birds, apart from their physical beauty, is how much goes on in those teeny noggins of theirs.
Jacinta: Yes, but what really brought this on? I haven’t heard you rhapsodising about birds before.
Canto: You haven’t been inside my vast noggin mate. Actually I’ve been taking photos – or trying to – of the bird life around here; magpies, magpie-larks, crows, rainbow lorikeets, honeyeaters, galahs, corellas, sulphur-crested cockies, as well as the pelicans, black swans, cormorants, moorhens, coots and mallard ducks by the river, not to mention the ubiquitous Australian white ibis and the masked lapwing.
Jacinta: Well I didn’t know you cared. Of course I agree with you on the beauty of these beasties. Better than any tattoo I’ve seen. So you’re becoming a twitcher?
Canto: I wouldn’t go that far, but I’ve been nurturing my fledgling interest with a book on the sensory world of birds, called, appropriately, Bird sense, by a British biologist and bird specialist, Tim Birkhead. It’s divided into sections on the senses of birds – a very diverse set of creatures, it needs to be said. So we have vision, hearing, smell, taste, touch, and that wonderful magnetic sense that so much has been made of recently.
Jacinta: So we can’t generalise about birds, but I know at least some of them have great eyesight, as in ‘eyes like an eagle’.
Canto: Well, as it happens, our own Aussie wedge-tailed eagle has the most acute sense of vision of any creature so far recorded.
Jacinta: Well actually it isn’t ours, it just happens to inhabit the same land-form as us.
Canto: How pedantic, but how true. But Birkhead points out that there are horses for courses. Different birds have vision adapted for particular lifestyles. The wedge-tail’s eyes are perfectly adapted to the clear blue skies and bright light of our hinterland, but think of owl eyes. Notice how they both face forward? They’re mostly nocturnal and so they need good night vision. They’ve done light-detection experiments with tawny owls, which show that on the whole they could detect lower light levels than humans. They also have much larger eyes, compared with other birds. In fact their eyes are much the same size as ours, but with larger pupils, letting in more light. They’ve worked out, I don’t know how, that the image on an owl’s retina is about twice as bright as on the average human’s.
Jacinta: So their light-sensitivity is excellent, but visual acuity – not half so good as the wedge-tailed eagle’s?
wedge-tailed eagle – world’s acutest eyes
Canto: Right – natural selection is about adaptation to particular survival strategies within particular environments, and visual acuity isn’t so useful in the dark, when there’s only so much light around, and that’s why barn owls, who have about 100 times the light-sensitivity of pigeons, also happen to have very good hearing – handy for hunting in the dark, as there’s only so much you can see on a moonless night, no matter how sensitive your eyes are. They also learn to become familiar with obstacles by keeping to the same territory throughout their lives.
face of a barn owl – ‘one cannot help thinking of a sound-collecting device’, quoth researcher Masakazu Konishi
Jacinta: So they don’t echo-locate, do they?
Canto: No, though researchers now know of a number of species, such as oilbirds, that do. Barn owls, though, have asymmetrical ear-holes, one being higher in the head than the other, which helps them to pinpoint sound. It was once thought that they had infra-red vision, because of their ability to catch mice in apparently total darkness, but subsequent experiments have shown that it’s all about their hearing, in combination with vision.
Jacinta: Well you were talking about those amazing little brains of birds in general, and I must say I’ve heard some tales about their smarts, including how crows use cars to crack nuts for them, which must be true because it was in a David Attenborough program.
Canto: Yes, and they know how to drop their nuts near pedestrian crossings and traffic lights, so they can retrieve their crushed nuts safely. The genus Corvus, including ravens, crows and rooks, has been a fun target for investigation, and there’s plenty of material about their impressive abilities online.
seeing is believing
Jacinta: So what other tales do you have to tell, and can you shed any light on how all this cleverness comes in such small packages?
Canto: Well Birkhead has been studying guillemots for years. These are seabirds that congregate on cliff faces in the islands around Britain, and throughout northern Europe and Canada. They’re highly monogamous, and get very attached to each other, and thereby hangs another fascinating tale. They migrate south in the winter, and often get separated for lengthy periods, and it’s been noted that when they spot their partner returning, as a speck in the distance, they get highly excited and agitated, and the greeting ceremony when they get together is a joy to behold, apparently – though probably not as spectacular as that of gannets. Here’s the question, though – how the hell can they recognise their partner in the distance? Common guillemots breed in colonies, butt-to-butt, and certainly to us one guillemot looks pretty well identical to another. No creature could possibly have such acute vision, surely?
Jacinta: Is that a rhetorical question?
Canto: No no, but it has no answer, so far. It’s a mystery. It’s unlikely to be sight, or hearing, or smell, so what is it?
Jacinta: What about this magnetic sense? But that’s only about orientation for long flights, isn’t it?
Canto: Yes we might discuss that later, but though it’s obvious that birds are tuned into their own species much more than we are, the means by which they recognise individuals are unknown, though someone’s bound to devise an ingenious experiment that’ll further our knowledge.
Jacinta: Oh right, so something’s bound to turn up? Actually I wonder if the fact that people used to say that all Chinese look the same, which sounds absurd today, might one day be the case with birds – we’ll look back and think, how could we possibly have been so blind as to think all seagulls looked the same?
Canto: Hmmm, I think that would take a lot of evolving. Anyway, birds are not just monogamous (and anyway some species are way more monogamous than others, and they all like to have a bit on the side now and then) but they do, some of them, have distinctly sociable behaviours. Ever heard of allopreening?
Jacinta: No but I’ve heard the saying ‘birds of a feather flock together’ and that’s pretty sociable. Safety in numbers I suppose. But go on, enlighten me.
Canto: Well, allopreening just means mutual preening, and it usually occurs between mates – and I don’t mean in the Australian sense – but it’s also used for more general bonding within larger groups.
Jacinta: Like, checking each other out for fleas and such, like chimps?
Cant: Yeah, though this particular term is usually reserved for birds. Obviously it serves a hygienic purpose, but it also helps calm ruffled feathers when flocks of colonies live beak by jowl. And if you ever get close enough to see this, you’ll notice the preened bird goes all relaxed and has this eyes half-closed, blissed-out look on her face, but we can’t really say that coz it’s anthropomorphising, and who knows if they can experience real pleasure?
Jacinta: Yes, I very much doubt it – they can only experience fake pleasure, surely.
Canto: It’s only anecdotal evidence I suppose, but that ‘look’ of contentment when birds are snuggling together, the drooping air some adopt when they’ve lost a partner, as well as ‘bystander affiliation’, seen in members of the Corvus genus, all of these are highly suggestive of strong emotion.
Jacinta: Fuck it, let’s stop beating about the bush, of course they have emotions, it’s only human vested interest that says no, isn’t it? I mean it’s a lot easier to keep birds in tiny little cages for our convenience, and to burn their beaks off when they get stressed and aggressive with each other, than to admit they have feelings just a bit like our own, right? That might mean going to the awful effort of treating them with dignity.
Canto: Yyesss. Well on that note, we might make like the birds and flock off…
how the flock do they do that?
distributed consciousness – another nail in the coffin of human specialness
for more on this, the whole conference is available online
I wrote a piece here called ‘Animals R Us’ a few years ago because I was annoyed at certain contemptuous remarks directed at animals – a rather large set to be contemptuous of – and also because I’ve always disliked the idea of human specialness so beloved of some of our religious co-habitants. I was also thinking of the remarks of Marilyn Robinson on consciousness, which I critiqued even more years ago. Atheists, she argued (wrongly) don’t take enough account of consciousness (with the inference that if they did, they’d be more accepting of a supernatural being, presumably). So I’m happy to briefly revisit the complexities and the consciousness of non-humans here.
The latest research reveals more and more the distributed nature of consciousness, and some of this research is summarised in ‘Triumph of the zombie killers’, chapter 1 of Michael Brooks’s book At the edge of uncertainty: 11 discoveries taking science by surprise. He brings up philosopher David Chalmers’s 20-year-old claim about the ‘hard problem’ of consciousness, that it doesn’t appear to be reducible to material processes. In fact, Chalmers went further, saying ‘No explanation given wholly in physical terms can ever account for the emergence of conscious experience.’ Well, forever is a long long time and I wonder what Chalmers would have to say now (I’ll have to check out his more recent pronouncements). In 1994 he used a zombie analogy, suggesting that you couldn’t know whether we were surrounded by zombies, or ‘pretend’ humans, since the sense of self-awareness essential to consciousness cannot be identified or described by methodological naturalism. It’s been difficult to provide a coherent theory to account for this subjective feeling, and Daniel Dennett took the view a couple of decades ago that consciousness is essentially an illusion, or rather an evolved way of dealing with the world which captures the elements of reality we need to get by, and then some. That’s why we can so often be fooled by our brains. We have perceptual glitches and blind spots. An obvious example is the human eye, which only focuses sharply on a tiny area, using the fovea centralis, a patch of densely packed photoreceptor cells only a millimetre in diameter. The rest of our visual field is seen in much lower resolution, and without colour. But we’re not aware of this because of the eye’s movements, or saccades, which average 3 per second. The time between one sharp focus and the next is ‘blacked-out’ of consciousness, creating an illusion of seamlessly moving vision. The analogy with film is obvious.
This evolved use of sight to be ‘good enough’ helps explain our ‘change blindness’, which has been highlighted by a number of recent experiments, and which has been exploited for decades by professional magicians. It also helps explain why we don’t notice mistakes in editorial continuity in films, which are even overlooked by editors, because they involve ‘irrelevant’ background details. This evolved use of eyesight to help us to make enough sense of the world as we need to, as economically as possible, is something shared by many other creatures, as researchers have declared. Consciousness researchers gathered together at Cambridge in July 2012 and issued a ‘declaration on consciousness’, summarising recent findings on consciousness in non-human animals and in infant humans:
Non-human animals have the neuroanatomical, neurochemical, and neurophysiological substrates of conscious states along with the capacity to exhibit intentional behaviours… humans are not unique in possessing the neurological substrates that generate consciousness. Non-human animals, including all mammals and birds, and many other creatures, including octopuses, also possess these neurological substrates
It’s a vitally important point that’s being made here. Even to call consciousness an emergent property is misleading, as it suggests that we’re still hung up on the consciousness label, and on detecting the point at which this phenomenon has ‘emerged’. Previous tests for consciousness are gradually being found wanting, as what they test has little to do with the more expansive understanding of consciousness that our research is contributing to, more and more. What’s more, serious damage to, and indeed the complete loss of, such areas of the human brain as the insular cortex, the anterior cingulate cortex, and the medial prefrontal cortex, all vital to our self-awareness according to previous research, haven’t prevented subjects from articulating clear signs of consciousness and self-reflection. There’s no ‘place’ of consciousness in the human or mammalian brain, and signs of intentionality and individual personality are cropping up in a whole range of species.
Early researchers on chimpanzees and other highly developed animals were often dismissive of claims that they were being cruel, citing ‘anthropomorphism’ as a barrier to scientific progress. We can now see that we don’t have to think of animals as ‘human-like’ to recognise their capacity for suffering and a whole range of other negative and positive experiences and emotions. And we’re only at the beginning of this journey, which, like the journey initiated by Copernicus, Kepler and others, will take us far from the hubristic sense of ourselves as singular and central.
What do we currently know about the differences between male and female brains in humans?
Having had an interesting conversation-cum-dispute recently over the question of male-female differences, and having then listened to a podcast, from Stuff You Should Know, on the neurological differences between the human male and the human female, which contained some claims which astonished me (and for that matter they astonished the show’s presenters), I’ve decided to try and satisfy my own curiosity about this pretty central question. Should be fun.
The above link is to How Stuff Works, which I think is the written version of the Stuff You Should Know podcast, that’s to say with more content and less humour (and less ads), but I do recommend the podcast, because the guys have lots of fun with it while still delivering plenty of useful and thought-provoking info. Anyway, the conversation I was talking about was one of those kitchen table, wine-soaked bullshit sessions in which one of the participants, a woman, was adamant that nurture was pretty well entirely the basis for male-female differences. I naturally felt sympathetic to this view, having spent much of my life trying to blur the distinctions between masculinity and femininity, having generally been turned off by ultra-masculine and ultra-feminine traits and wanting to push for blended behaviour, which obviously suggests we can control these things through nurturing such a blending. However, I had just enough knowledge of what research has revealed about the matter to say, ‘well no, there are distinct neurological differences between males and females’, but I didn’t have enough knowledge to give more than a vague idea of what these differences were. The podcast further whetted my appetite, but writing about it here should pin things down in my mind a bit more, here’s hoping.
I’ve chosen the title of this post reasonably carefully, with apologies for its clunkiness. For the fact is, we still know little enough about our brains. I’ve mentioned humans, but I expect there are gender differences in the brains of all mammals, so I’m particularly interested in that part of the brain that distinguishes us, though not completely, from other mammals, namely the prefrontal cortex.
Here’s an interesting summary, from a blurb on a New Scientist article by Hannah Hoag from 2008;
Research is revealing that male and female brains are built from markedly different genetic blueprints, which create numerous anatomical differences. There are also differences in the circuitry that wires them up and the chemicals that transmit messages between neurons. All this is pointing towards the conclusion that there is not just one kind of human brain, but two. …
Men have bigger brains on average than women, even accounting for sexual dimorphism, but the two sexes are bigger in different areas. A 2001 Harvard study found that some frontal lobe regions involved in problem-solving and decision-making were larger in women, as well as regions of the limbic cortex, responsible for regulating emotions. On the other hand, areas of the parietal cortex and the amygdala were larger in men. These areas regulate social and sexual behaviour.
The really incredible piece of data, though, is that men have about 6.5 times more grey matter (neurons) than women, while women have about ten times more white matter (axons and dendrites, that’s to say connections) than men. These are white because they’re sheathed in myelin, which allows current to flow much faster. On the face of it, I find this really hard, if not impossible, to believe. I mean, that’s one effing huge difference. It comes from a study led by Richard Haier of the University of California, Irvine and colleagues from the University of New Mexico, but this extraordinary fact appears to be of little consequence for male performance in intellectual tasks as compared to female. What appears to have happened is that two different ‘brain types ‘ have evolved alongside and in conjunction with each other to perform much the same tasks. Other research appears to confirm this amazing fact, finding that males and females access different parts of the brain for performing the same tasks. In an experiment where men and women were asked to sound out different words, Gina Kolata reported on this back in early 1995 in the New York Times:
The investigators, who were seeking the basis of reading disorders, asked what areas of the brain were used by normal readers in the first step in the process of sounding out words. To their astonishment, they discovered that men use a minute area in the left side of the brain while women use areas in both sides of the brain.
After lesions to the left hemisphere, men more often develop aphasia (problems with understanding and formulating speech) than women.
While I’m a bit sceptical about the extent of the differences between grey and white matter in terms of gender, it’s clear that these and many other differences exist, but they’re difficult to summarise. We can refer to different regions, such as the amygdala, but there are also differences in hormone activity throughout the brain, and so many other factors, such as ‘the number of dopaminergic cells in the mesencephalon’, to quote one abstract (it apparently means the number of cells containing the neurotransmitter dopamine in the midbrain). But let me dwell a bit on the amygdala, which appears to be central to neurophysiological sex differences.
Actually, there are 2 amygdalae, located within the left and right temporal lobes. They play a vital role in the formation of emotional memories, and their storage in the adjacent hippocampus, and in fear conditioning. They’re seen as part of the limbic system, but their connections with and influences on other regions of the brain are too complex for me to dare to elaborate here. The amygdalae are larger in human males, and this sex difference appears also in children from age 7. But get this:
In addition to size, other differences between men and women exist with regards to the amygdala. Subjects’ amygdala activation was observed when watching a horror film. The results of the study showed a different lateralization of the amygdala in men and women. Enhanced memory for the film was related to enhanced activity of the left, but not the right, amygdala in women, whereas it was related to enhanced activity of the right, but not the left, amygdala in men.
This right-left difference is significant because the right amygdala connects differently with other brain regions than the left. For example, the left amygdala has more connections with the hypothalamus, which directs stress and other emotional responses, whereas the right amygdala connects more with motor and visual neural regions, which interact more with the external world. Researchers are of course reluctant to speculate beyond the evidence, but as a non-scientist, but as a pure dilettante I don’t give a flock about that – just don’t pay attention to my ravings. It seems to me that most female mammals, who have to tend offspring, would be more connected to the flight than the fight response to danger than the unencumbered males would be??? OMG, is that evolutionary psychology?
It’s interesting but hardly surprising to note that studies have shown this right-left amygdala difference is also correlated to sexual orientation. Presumably – speculating again – it would also relate to those individuals who sense from early on that they’re born into ‘the wrong gender’.
Neuroimaging studies have found that the amygdala develops structurally at different rates in males and females, and this seems to be due to the concentration of sex hormone receptors in the different genders. Where there’s a size difference there appears to be a big difference in number of sex hormones circulating in the area. Again this is difficult to interpret, and it’s early days for this research. One brain structure, the stria terminalis, a bundle of fibres that constitute the major output pathway for the amygdala, has become a focus of controversy in the determination of our sense of gender and sexual orientation. As a dilettante I’m reluctant to comment much on this, but the central subdivision of the bed nucleus of the stria terminalis is on average twice as large in men as in women, and contains twice the number of somatostatin neurons in males. Somatostatin is a peptide hormone which helps regulate the endocrine system, which maintains homeostasis.
What all this means for the detail of sex differences is obviously very far from being worked out, but it seems that the more we examine the brain, the more we find structural and process differences between the male and female brain in humans. And it’s likely that we’ll find similar differences in other mammals.
It’s important to note, though, that these differences, as in other mammals, exist in the same species, in which the genders have evolved to be codependent and to work in tandem towards their survival and success. Just as it would seem silly to say that female kangaroos are smarter/dumber than males, the same should be said of humans. The terms smart/dumb are not very useful here. The two genders, in all mammals, perform complementary roles, but they’re also also both able to survive independently of one another. The amazing thing is that such different brain designs can be so similar in output and achievement. It’s more impressive evidence of the enormous diversity of evolutionary development.
where does our alphabet come from?
Etruscan ink-holder, with alphabet, from the early 7th century BCE
I’m currently reading Lost languages: the enigma of the world’s undeciphered scripts, by Andrew Robinson, a pretty demanding work in parts, though designed for the general reader. It’s looking at the difficulty of scripts of which we have too few examples, and too few connected languages – either descended from or ancestral to these extant fragments – to be able to get a handle on them. However it also looks at famous decipherings of the past – of the Egyptian and the Mayan hieroglyphs, and of Linear B (Mycenean, the earliest form of Greek), as well as at written languages in general, which inevitably makes a fellow think of his own taken-for-granted language, its origins and its ‘type’, among all the types of writing we have.
Robinson informs us of a consensus among scholars, arrived at though much struggle – that all written languages contain phonemic and semantic, or logographic, elements. A dummy’s way of presenting this is that they contain both sounds and signs. Our alphabet is, of course, largely phonemic, but in writing we also use signs, such as full stops, question marks, apostrophes, quotation marks, etc. We also use capitals. For example B represents the same sound as b, but it also signifies the beginning of a sentence or (the beginning of) a name of something. It follows that b also has a sign value, in contrast to the sign value of B. Apparently Finnish is the most purely phonemic language we have these days, while Chinese and Japanese are very heavily sign based.
So what about the English language, or more strictly, the alphabet we share with many other European languages. It’s generally known as the Latin alphabet, and it was introduced to England by Christian missionaries in about the 7th century, replacing Anglo-Saxon runes that date back at least another couple of hundred years. These runes may also be traced back to the Latin alphabet – we don’t have enough extant examples to be sure.
The alphabet has evolved over the years. Wikipedia tells us that back in the year 1011 a polymath named Byrhtferth set down the alphabet as it was understood at the time. It comprised 23 of our modern letters (J, U and W had not yet emerged), the ampersand & and five other letter/symbols no longer recognised, or at least formally recognised, as alphabetical. One was the ligature æ, called ash. In the fourteenth century the letters uu, often used together, were merged to make w, still called ‘double u’ today. The alphabet became fixed in the sixteenth century, when j and u emerged as distinct from i and v.
So it would seem that the Latin alphabet evolved, much like humans evolved from earlier forms, with little mutations along the way, so that if you go back far enough it’ll be barely recognisable. What is called the classical Latin or Roman alphabet derived from a western variant of the Greek alphabet, used in southern Italian colonies such as Cumae in modern-day Campania. This was in turn modified by the Etruscans (800-100BCE) before being taken up and modified further by the Romans.
It’s an enormously complicated story of interaction and modification. The English alphabet isn’t exactly the Latin alphabet, which itself changed as the Romans developed and advanced their civilization, incorporating more territories and their cultural influences. It’s not something you can trace in an obvious linear way. The Romans were influenced linguistically by both the southern colonies and the northern Etruscans. After the Roman conquest of Greece in the first century BCE, the Greek letters Y and Z were added to their alphabet, giving them 23 letters during the ‘classical’ period (the period of the late republic and the empire). Our number system – obviously a part of our written language, but I won’t get too much into mathematical symbology here – is often described as Arabic, but the Arabs and Persians adopted it from the Hindus, who apparently developed the place-value notation in the fifth century, adding zero a century later.
If we want to go back to the origin of writing systems and writing itself, it seems not to have had a single origin. I’ve mentioned the ancestor of Latin, the Greek alphabet, which has been around since the eighth century BCE and is still in use. It consists of 24 letters from alpha to omega, and of course many of its symbols, including pi, are used in mathematical notation. The Greek alphabet in turn derives from the Phoenician. There is some dispute or at least conjecture as to how far back the Phoenician alphabet can be dated – a bit like putting a date on the first humans, who after all had parents who were much the same as they were. Scholars generally put the date back to 1050 BCE, and inscriptions with Phoenician elements before that date are attributed to ‘parent scripts’. To quote the Wikipedia article:
The oldest known inscription that goes by the name of Phoenician is the Ahiram epitaph, engraved on the sarcophagus of King Ahiram from c. 1200 BCE.[5]
However, the immediate predecessor to Phoenician is conventionally referred to as Proto-Canaanite. Ancestral to this was the Proto-Sinaite script, used by Canaanites in the Sinai region from about 1850 BCE. We don’t have too many examples of it, but it’s claimed by some to be the first ever alphabetic writing system. Most of the inscriptions using this language, generally accepted as Semitic, were found among Egyptian hieratic and hieroglyphic inscriptions, and there are graphic similarities to the hieratic script, which is less elaborate than hieroglyphics, but little headway has been made in deriving the Semitic script from Egyptian hieratic.
Egyptian hieroglyphics can be dated back to 2700 BCE. They’re complex beasties that can be used as phonograms, logograms or determinatives; in other words as sounds or sound sequences, as pictorial representations, or as clues to meaning neither clearly pictorial nor phonological (in earlier times hieroglyphics were doggedly construed as almost entirely logographic, and this hindered a full decoding). It’s quite possible, apparently, that the Proto-Sinaite script was influenced by the phonological (hence alphabetical) elements of hieroglyphics.
The Meroitic script, again probably derived from hieroglyphics, is an alphabetic script used in the Nubian Kingdom of Meroe in what is now northern Sudan. It first appeared in the second century BCE and flourished at the height of Nubian power (750 to 300 BCE). It appears to have developed independently of the Greek alphabet, though some scholars claim a connection.
One of the earliest known writing systems, Cuneiform, emerged in Sumer in the late 4th millennium BCE . The term ‘cuneiform’ means wedge-shaped, and was so named by its wedge-shaped markings left on clay tablets. The earliest Cuneiform was pictorial, but over time it became more stylized, simplified and abstract. The Cuneiform of the early bronze age contained about 1000 characters, but this was down to 400 by the late bronze age, some 1500 years later. Sumerian is not really recognised as a fully fledged language by scholars until about the 31st century BCE.
So is there an earlier form of writing than Cuneiform? I suspect that there were innumerable forms of proto-writing, symbols used with a shared, tribal meaning indecipherable to outsiders, and that this could have gone on for millennia. It just happened that with early Sumerian civilization we had a larger clot of people together than ever before, and with that, language took a further step towards codification and regularisation.
So I’ve gone a bit further back than our alphabet, but I’ve barely scratched the surface of language development. Tracing all the connections is an endless and ongoing task, and we’re continuing to make headway, but the key to all this is human ingenuity in finding such a variety of more or less efficient systems to communicate and preserve increasingly complex ideas, which whole regions of our developing brains are devoted to. There’s so much more to say on this subject.
the latest on dolphin language
I wrote, or semi-podcasted, on the brain of the dolphin a while back, and much of my focus was on language, often described as the sine qua non of cerebral complexity and intelligence. In that piece, posted about eight months ago, I reported that there there was little clear evidence of any complex language in dolphins, but there had been some interesting research. Allow me to quote myself:
Dolphins do sometimes mimic the whistles of other dolphins too, particularly those of their closest relatives, but signature whistles as a form of recognition and differentiation, are a long way from anything like language. After all, many species can recognise their own mates or kin from the distinctive sounds they make, or from their specific odour, or from visual cues. However, a clever experiment carried out more recently, which synthesised these whistles through a computer, so that the whistle pattern was divorced from its distinctive sound, found that the dolphins responded to these patterns even when produced via a different sound. It seemed that they were recognising names. It’s undoubtedly intriguing, but clearly a lot more research is required.
So it was with some interest that I heard, on a recent SGU podcast, an account of what seemed an elaboration of the experiments conducted above, further confirming that dolphins recognised names. Or were they just reporting the same experiments? Having re-listened to the SGU segment, I find that they didn’t give any details of who did the study they were talking about, the only mention was to a news article. So I’ll just report on anything I can find, because it’s such a cool subject.
There’s a nice TED talk, from February 2013, on dolphin language and intelligence here, which is about researches over many years in the Bahamas with Atlantic spotted dolphins. As always, I suggest you listen to the talk and do the ‘research on the research’ yourself, as I’m not a scientist and I’m only doing this to educate myself, but hopefully I can also engage your interest.
Dolphins have a brain- to-body ratio (a rough but not entirely reliable guide to intelligence) second only to humans, they pass the mirror self-awareness test (another standard for intelligence that’s been questioned recently), they can be made to understand very basic artificial human language tests, and they’re at least rudimentary tool users. But the real interest lies in their own, obviously complex, vocal communication systems.
I probably misrepresented the information on signature whistles before: they’re only what we humans have been able to isolate from all the ‘noise’ dolphins make, because they’re recognisable and interpretable to us. Denise Herzing, in her TED talk, refers to ‘cracking the code’ of dolphins’ communication systems. She and her team have been working with the dolphins over the summer months for 28 years. They work with underwater cameras and hydrophones to correlate the sounds and behaviours of their subjects. This particular species is born without spots, but is fully black-and-white spotted by age 15. They go through distinct developmental phases making them easy to track over the years (dolphins live into their early 50s). The distinctive spotted patterns make them easy to track individually. Females are sexually mature by about age 9, males at around 15. Dolphins are very sexually active with multiple partners, so paternity is not always easy to determine, so this is worked out by collecting fecal matter and analysing its DNA. So, over 28 years, three generations have been tracked.
What really interests me about the dolphin communication question is their relation to sound and their use of sound compared to ours. Herzing describes them as ‘natural acousticians’ who make and hear sounds ten times as high as humans do. They also have highly developed vision, so they communicate via bodily signals, and they have taste and touch. Sound is of course a wave or vibration which can be felt in water, the acoustic impedance of tissue in water being much the same as on land. Tickling, of a kind, does occur.
Signature whistles are the most studied dolphin sounds, as the most easily measured. They’re used as names, in connecting mothers and calves for example. But there are many other vocalisations, such as echo-location clicks (sonar), used in hunting and feeding, and also socially, in tightly-packed sound formations – buzzes, which can be felt in the water. They’re used regularly by males courting females. Burst-pulse sounds are used in times of conflict, and they are the least studied, most hard to measure of dolphin sounds.
Interestingly, Herzing notes that there’s a lot of interaction and co-operation in the Bahamas between spotted and bottle-nose dolphins, including baby-sitting each others’ calves, and combining to chase away sharks, but little mention is made, in this talk at least, of any vocal communication between the two species. When she goes on to talk about synchrony, I think she’s only talking about within-species rather than between species. Synchrony is a mechanism whereby the dolphins co-ordinate sounds and body postures to create a larger, stronger social unit.
As I’ve mentioned, dolphins make plenty of sounds beyond the range of human hearing. Underwater equipment is used to collect these ultrasonic sounds, but we’ve barely begun to analyse them. Whistle complexity has been analysed through information theory, and is highly rated even in relation to human languages, but virtually nothing is known about burst-pulse sounds, which, on a spectrogram, bear a remarkable similarity to human phonemes. Still, we have no Rosetta Stone for interpreting them, so researchers have developed a two-way interface, with underwater keyboards, with both visual and audible components. In developing communication, they’ve exploited the dolphins’ natural curiosity and playfulness. Dolphins, for example, are fond of mimicking the postures and vocalisations of humans, and invite the researchers into their play. Researchers have developed artificial whistles to refer to dolphins’ favourite toys, including sargassum, a kind of seaweed, and ropes and scarves, so that they can request them via the keyboard interface. These whistles were outside the dolphins’ normal repertoire, but easily mimicked by them. The experiment has been successful, but of course it isn’t known how much they understand, or what’s going through their minds with all this. What is clear, however, is that the dolphins are extremely interested in and focused on this type of activity, which sometimes goes on for hours.
This research group has lately been using an underwater wearable computer, known as CHAT (cetacean hearing and telemetry), which focuses on acoustic communication. Sounds are created via a forearm keyboard and an underwater speaker for real-time Q and A. This is still at the prototype stage, but it uses the same game-playing activity, seeking to empower dolphins to request toys, as well as human game-players, through signature whistles. It’s hoped that the technology will be utilisable for other species too in the future.
All of this is kind of by way of background to the research reported on recently. This was really about dolphin memory rather than language – or perhaps more accurately, memory triggered by language. Dolphins recognise the sounds of each others’ signature whistles, but would they recognise the whistle of a dolphin they’d not been in contact with for years. And for how many years? Researcher Jason Bruck tested this by collecting whistles of dolphins in captive facilities throughout the US. Dolphins are moved around a lot, and lose contact with friends and family. Sounds a bit like the foster-care system. Bruck found that when dolphins heard the signature whistles of old companions played to them through an underwater speaker, they responded with great attention and interest. One dolphin was able to recognise the whistle of a friend from whom he was separated at age two, after twenty years’ separation. As biologist Janet Mann put it, this is a big breakthrough but not so surprising, as dolphins are highly social animals whose lives, like ours, are criss-crossed by profound connections with others, with effects positive, negative and equivocal. It’s important, too, for what it suggests – the capacity to remember so much more, in the same coded way. in other words, a complex language, perhaps on a level with ours. Will we ever get to crack this code? Why not. Hopefully we won’t stop trying.
some thoughts on hypnotism
hmm, are those waves or particles, or both, or neither?
Today I want to write about a subject I know bugger all about but which has always fascinated me – hypnotism. The first encounter with it that made an impression on me was as a schoolkid coming home for lunch, as we did every day – our parents were both at work – and catching some of the midday variety show, which regularly featured a bearded and mildly exotic hypnotist who, with nothing more, apparently, than snappings of fingers, intense gazes and a voice of calm command, got ordinary people to crawl on all fours and bark like dogs, or some other form of mild humiliation, to the incredibly complacent amusement of the studio audience – or so it seemed to me.
This was all very flummoxing to my nascent scepticality. Could this really be real? If so, the consequences, it seemed to me, were enormous for a person’s autonomy, or sense of self-ownership. More important, could this ever be done to me? My impulse would be to fight such an outrageous invasion of, indeed takeover of, what I held to be more dear to me than anything else – my independence of thought and action.
So I drew two conclusions from these observations. First, that it couldn’t be real – that there must be at least some fakery involved. Second, that if it was real, I, if not the entire human population, needed to be protected from such outrages, by law. If we could be made to bark like dogs, why couldn’t we be made, by an evil genius, to rip out each others’ throats, to murder our loved ones, to fly planes into buildings or to press nuclear buttons? In fact, if this power to control minds was real, no human law could prevent it from being abused. It followed, according to the Law of Wishful Thinking, that this power couldn’t be real.
But as life went on, the urgency of this issue receded, though the questions raised were never resolved. A lot of nasty things happened, people ripped each other apart, either physically or psychologically, and people murdered those they loved, and flew planes into buildings and declared wars that slaughtered thousands, but the motives seemed all too clear and basic and perennially human. No evil geniuses needed to be posited. Manipulation might be suspected at times, but of the common and garden type. Hypnosis appeared surplus to requirements, so much that I never really considered it.
The old questions resurfaced on listening to Brian Dunning, of skeptoid.com, presenting a podcast on hypnosis, which provided some interesting historical background, for example that the term ‘hypnosis’ was coined by an English surgeon, James Braid, in the 1840s. Braid became obsessed with the practice after seeing a stage performance, and worked on utilising it for medical purposes. He even wrote a book about hypnotism which, according to Dunning, still stands up well today.
Dunning also addresses an issue that has always vexed me – that of susceptibility to hypnosis. In the 50s, Stanford University developed a rough measure of susceptibility which they named the Stanford Hypnotic Susceptibility Scales. Here’s Dunning’s description:
It’s a series of twelve short tests to gauge just how hypnotized you really are, scored on a scale of 0 (not at all) to 12 (completely). They are responses to simple suggestions like immobilization, simple hallucinations, and amnesia. Most people score somewhere in the middle, and nearly everyone passes at least one of the tests. There’s even a script you can follow to hypnotize anyone and put them through the scales, with a little bit of practice.
Not only do people score very differently, there’s been little progress made in predicting what types of people are most susceptible. Subjects’ suppositions about their own susceptibility don’t correlate at all with test scores. Supposed predictors like intelligence, creativity, desire to become hypnotized, and imaginativeness also have no correlation. Most likely, you yourself are a decent candidate who will score near the middle of the scale, regardless of whether you think you will or not.
These findings are not reassuring. Maybe it’s a male thing (and one of the reasons males are less willing to visit the doctor), but I’ve always wanted to be, and so felt myself to be, ‘in control’ of my physical and mental health. For example, I didn’t need a doctor to tell me I was creeping up in weight towards obesity, with all the attendant health issues. I realised it myself, took control, reduced my general food intake, introduced an exercise regime, and brought my weight back to normal. Similarly, with issues of getting older, such as the possibility of dementia, I reckon that keeping mentally active, learning new things, firing up new pathways, is the self-help solution, and with hypnotism, the defence is a strong mind and a profound unwillingness to be hoodwinked by any evil geniuses out there. But I’m not silly, and I’ve always known that I’m at least partially kidding myself, and that I can’t fully bullet-proof myself against cancer, dementia, or even mind control. So maybe I should subject myself to the above-mentioned susceptibility scales, and face the facts.
For the susceptible ones, there are certainly medical benefits in the application of hypnosis, in relieving stress, in pain management, and in preparing patients for, and managing them through, surgery. Attempts have made to use hypnotherapy, and to analyse its success, in weight loss programs and in treating addictive behaviour, with mixed results.
But what of that worst-case scenario, where the susceptible are manipulated into performing dastardly deeds? Dunning’s conclusions on this seemed reassuring. The susceptible clients certainly reported losing their memory of actions performed under hypnosis, and they certainly did perform those actions, or ‘see’ things they were commanded to see, but, according to Dunning ‘only so long as they were consciously willing to go along.’ He ends with a recommendation to try hypnotism, saying ‘you can’t lose control’ and that ‘you might just have a really wild ride’, two statements that might seem to contradict each other.
But these reassurances were all blown away by Derren Brown’s program on hypnotism, one of a series he presented on how the human mind can be made to believe things and do things that aren’t always in its best interest. Brown is a thorough-going sceptic and an atheist, and so on the side of the angels. I was primed for a dose of debunking, but, frankly, was left with far more questions than answers. I have to rely on my memory here, but the program began with some references to Sirhan Sirhan, the killer of Robert Kennedy in the sixties. Sirhan’s lack of remorse over the years has told against him at parole board hearings and the like, but since he bizarrely claims to have no recollection of the act, his lack of remorse would in that sense be consistent. Without going into too much detail about the assassination (conspiracy theories abound), Brown plants in our minds the germ of an idea that this could’ve been a mind-control event. The rest of the program involves an elaborate set-up in which Brown hypnotises a susceptible subject into ‘killing’ Stephen Fry, with a gun, while Fry is performing onstage, and the hypnotised subject is in the audience. Fry, who’s in on the act, plays dead, and the audience – well, here’s where my memory fails me. I seem to remember shock and confusion, but I don’t recall any heroes grappling with the gunman, or reacting as the gunman stood up and took aim at Fry. Maybe that’s just the behaviour of well-primed security guards. After all, shooting someone when they’re onstage, though theatrical, is hardly a real-life scenario. In fact I don’t recall it ever having happened.
More importantly – in fact far more importantly – the scenario, if we’re to believe it, completely disproves Dunning’s claim that you can’t be persuaded to do something entirely uncharacteristic when under hypnosis. The young man who ‘shoots’ Fry seems to be a pleasant, gentle soul. In an after-event interview with Brown, at which Fry is also present, he has no recollection of firing the gun, though he does remember attending the show (if my memory serves me correctly).
I was really shaken by all this. I tried to wriggle out of the conclusions. Obviously the shooter was using a toy gun – or maybe a real gun with blank bullets. Could it be that he wouldn’t have gone through with it had it been a real gun? That didn’t make sense, really – the gun was in its own case, and looked real enough to me, inexpert though I am (I truly loathe guns). It was no water-pistol or cap-gun. But maybe the whole set-up was a sham? In this and in other Brown shows I found it incredible that subjects could be so easily put into a hypnotised state. In fact ‘ludicrous’ is the word that springs to mind. There’s a part of me – quite a big part in fact – that just wants to dismiss the whole thing as arrant bullshit, a kind of sick joke. How can the human brain, the most complex 1300g entity on the planet, be so easily hijacked?
Well, apparently it can. One has to accept the evidence, however reluctantly. And of course it’s not accurate to say that the entire brain is hijacked. Or rather, just as you don’t have to have complete control of every aspect of a plane in order to hijack it, you just have to control the pilot, so hypnotism must involve control of some kind of consciousness-controller in the brain. Something like what we describe as ‘the self’, no less. A big problem, especially when some psychologists, neurologists and philosophers deny the very existence of the self.
But I’ll leave an exploration of how hypnotism works from a neurophysiological perspective for another post. I suspect, though, that not much progress has been made in that area. Meanwhile, I’m left with a much greater concern about hypnotism than ever before. As if there wasn’t enough to worry about!
how to debate William Lane Craig, or not – part 6, intentional states
mind of god, exclusive pic
Dr Craig’s next argument is that his god is the best explanation of intentional states of consciousness in the world. This is a weird one, and I can only assume that he’s put his best forces in the vanguard in the hope of blowing the opposition out of the water, and that these rather piddling forces in the rear weren’t really meant to be exposed to the light of reason, and were just added to give a scarey sense of bulk or weight to the Doctor’s position. Never mind the quality, feel the width, as they say.
Dr Craig starts by ‘informing’ us that ‘philosophers are puzzled’ by states of intentionality. He doesn’t tell us which philosophers, but the clear intimation is that all philosophers are puzzled in this way – and by the way, this is a very typical piece of deceptiveness from Dr Craig, and your sceptical antennae should be stretched to their outermost limits by offhand remarks such as these. Dr Craig’s presentation here is very thin, but he’s trying, I think to convince you that philosophers are baffled by the non-materiality of intentionality or consciousness generally, and this is a massive misrepresentation of a complex area in the philosophy of mind. It’s true that there’s a lot of interesting debate, and has been for some decades, on the explanation of consciousness in material terms, but there are virtually no philosophers who consider that intentional states are without material cause. That’s to say, that you could have an intentional state without a brain – or something like it, such as a super-computer of some sort. Dr Craig makes the absurd claim that he can think about things, or of things, but a physical object cannot. But I see Dr Craig as a physical object, albeit one with intentions and consciousness. Dr Craig seems to want to make a distinction between objects and conscious subjects, but he doesn’t make this explicit in his rather clumsy argument. I have no difficulty with this distinction, seeing him, as I see myself, and my cat, as both object and conscious subject. In other words I see consciousness as necessarily embodied. Now, what the term ’embodied’ means is really too complex to be gone into here, but I would strongly argue that, while philosophers debate the connection between consciousness and embodiment, and are perhaps especially interested in what embodiment entails, I don’t know of any who are interested in considering consciousness as entirely non-material.
Dr Craig claims that Dr Rosenberg, an atheist, takes the view that ‘there really are no intentional states’, and that ‘we never really think about anything’. I’m not familiar with Dr Rosenberg’s views, but to say that I suspect they’ve been vastly over-simplified and misrepresented by Dr Craig’s characterization of them would be too weak a statement by far. Furthermore Craig claims that Rosenberg’s views, whatever they are, represent atheism. This is nonsense. Philosophers hold vastly different views on the so-called ‘hard problem’ of consciousness, including the view that there is no hard problem. The vast majority of philosophers who debate these issues are, in fact, atheists.
Dr Craig ends this fifth point with another formal argument, which, for the readers’ convenience, I’ll put here.
1. If God did not exist, intentional states of consciousness would not exist.
2. But intentional states of consciousness do exist.
3 Therefore God exists.
However, this argument is so paltry and pathetic that it isn’t worth commenting on further, except perhaps to say that it doesn’t deserve to be called an argument.
revisiting that old chestnut, the separate spheres of science and religion
In any case, a most excellent book
It always surprises me when I hear scientists who are otherwise extremely stimulating and admirable taking up the old S J Gouldian position on religion. I have in mind here V S Ramachandran, in his recent book The tell-tale brain:
When I make remarks of this nature about God… I do not wish to imply that God doesn’t exist; the fact that some patients develop such delusions doesn’t disprove God – certainly not the abstract God of Spinoza or Shankara [an Indian mystic philosopher of the eighth century]. Science has to remain silent on such matters. I would argue, like Erwin Schrodinger and Stephen Jay Gould, that science and religion (in the nondoctrinaire philosophical sense) belong to different realms of discourse and one cannot negate the other.
Mmmm. Always a bit of a problem when science is told what it ‘has to’ do. Or is it just me that doesn’t like being told that? I do, though, take Ramachandran’s point that science has nothing directly to say about the supernatural, the realm of the ‘non-evidential’. To say that there’s no evidence for the non-evidential seems rather beside the point. And yet…
The whole point of religion is supernatural agency, and this, it seems to me, involves these other-worldly agents acting in this world; answering prayers, performing miracles and so forth. After all, a god who does nothing is, arguably, not worth worshipping. Worshipping a god is, it seems to me, a quid pro quo sort of thing, though this is rarely made explicit. We expect something from these gods, they made us for a purpose, hence their obsession with us, their fatal flaw, it might seem. I’m talking about monotheistic gods of course, the ones without siblings or goddy communities to distract them from being our eternal lords and masters.
How these issues can be claimed to belong to different orders of discourse is beyond me. To me, as I’ve written, science is born of relentless questioning, with two aspects, curiosity and scepticism. And one of the biggest questions, obviously, is – how did we come to be here? It’s a question that science relentlessly explores – the origin of life, the origin of matter, the origin of universal laws and forces. It’s also a question that religion, particularly monotheistic religion, purports to answer. The answer being, a deity is responsible. A deity far too complex and ineffable for us to be capable of understanding or even beginning to explore.
I don’t see any difficulty in treating this as a theory, or more accurately a hypothesis, like any other, to be treated with the same sceptico-curious questioning as any other claim about our world and our experience.
I note that Ramachandran isolates religion ‘in the nondoctrinaire philosophical sense’ as the only religious ‘type’ that’s beyond the realm of scientific inquiry. Or perhaps he means beyond scientific proof, as I’m sure he agrees that the areas and pathways of the brain associated with religious or spiritual feeling are well worth probing. In fact, quite a bit of headway has been made in recent years in neurophysiology and in experimental psychology, in teasing out the forces contributing to religious belief. So such belief does fall within the scientific ‘realm of discourse’ or purview. When I first encountered the concept of a god in Sunday School as a seven or eight year old, the first thing that came to me was a whole heap of questions. Questions in which, as always, you can’t disentangle curiosity from scepticism. Who? What? Where? Says who? Can you really be serious? What are you getting out of this? How can this idea be possible? Where did it come from? Why is he male? What do you mean that he’s our father – isn’t one more than enough?
I believe these to be scientific questions, but then maybe I have a broader definition of science than most. I certainly hope so. And maybe these questions can’t negate gods, or belief in them, but they can certainly make it hot for this whole bizarro world of ‘faith’.
The other side of Ramachandran’s argument, though, I certainly agree with. Whatever religious discourse is, it has no hope of negating science.
fountains 4: what’s a glial cell?
Here’s the transcript for the next podcast, which I won’t be putting online for another week or so, when I can afford to buy space to host podcasts directly from this site. Then I’ll be able to stick all the fountains podcasts in one place, with the new logo created by a friend of mine, Stuart Rose:
What’s a glial cell?
Today, I’m going to make my first, but hopefully not last, foray into neurobiology. And since neurobiology is about the most complicated subject imaginable, I’ve decided to enter it sideways, so to speak, by looking at glial cells, or neuroglia, as they’re sometimes called. Not that this will make it any easier.
Glial cells – ‘glia’ means glue in Greek – perform a whole range of tasks apart from holding neurons together. They also come in many different varieties, and there’s still a lot we don’t know about them. They make up about half the mass of the brain, and they outnumber neurons many times over, making up between 85% and 90% of brain cells.
Considering the great varieties of roles glial cells play in the central nervous system (CNS), the peripheral nervous system (PNS) and in neurogenesis or the development of the brain, it’s hard to start with a summary or overview. They’re generally a lot smaller than neurons, and the glia/neuron ratio varies greatly between species, with the human brain near the top end. Elephants, though, are much higher with 97% glial cells.
Glial cells emerge from the multipotent precursor cells of the neural crest and neural tube. Radial glial cells act as progenitors and also as scaffolding for the growth and migration of neurons in the brain. They play a role in the development and maintenance of synaptic plasticity in the cerebellum. This function of supporting neurons is typical of all glial cells, with some of them having their own quasi-neuronal tasks. In the vertebrate retina, for example, Muller cells or Muller glia have been found, quite recently, to play a role in the formation of synapses. They’ve also been shown, when the retina is damaged, to re differentiate into progenitor cells which can then become photoreceptor cells.
But I’m galloping forward a bit here. The three main types of glial cells in the CNS are the astrocytes, the oligodendrocytes and the microglia, and some of their functions have long been known, though the detail, as well as a growing number of other roles and functions, are only now being focused on, in what some are describing as a revolution in neurobiology. Dr. Douglas Fields, chief of the Nervous System Development & Plasticity Section of the National Institutes of Health in the USA, argues that our understanding of the brain has been overly influenced by what he calls ‘the neuron doctrine’, that’s to say, a relentless focus on the electrical activity of the brain in the form of action potentials between neurons. The fact that glial cells don’t communicate electrically has meant that their role in brain activity has been largely overlooked for the best part of a century, according to Dr Fields. My layman’s perspective suggests to me that, not being electrical, glial cells just aren’t as flashy or sexy as neurons. ‘I sing the body electric’, Walt Whitman memorably wrote, and maybe he wasn’t thinking about neurons, but he definitely wasn’t thinking about glial cells.
So let’s have a look at some of those glial cell types. Astrocytes – so-called because of their star-like shape and projections – perform lots of functions within the CNS, including providing physical support to neurons through the formation of a matrix, cleaning up chemical debris within the brain, and replenishing chemicals within neurons and so keeping them healthy and well-nourished. This clearly requires communication between neurons and glia. Astrocytes also monitor the fluid surrounding neurons and keep it chemically well maintained. They get rid of the flotsam and jetsam through a process called phagocytosis, which involves engulfing the unwanted particles and essentially digesting them, a process performed by dedicated cells throughout the body.
looks like an astrocyte
Astrocytes nourish the neurons by first obtaining glucose from capillaries, then breaking it down into lactate, the first product of glucose metabolism. The lactate is then released into the fluid surrounding the neurons. The neurons take up this lactate and transport it, as an energy source, to their mitochondria. Astrocytes also maintain a store of glycogen from this process, which may be used in times of high neuronal metabolism.
One of the essential functions of oligodendrocytes is myelination. Now I’m sorry for the polysyllabification there, but I’m talking about the production of myelin sheath, the insulating material that protects the axons of the CNS as well as substantially improving their electrical activity. Myelin is white in colour, and accounts for the white colour of the brain. It’s made up of 80% lipid and 20% protein and it increases, many times over, the strength and efficiency of electrical conduction down the axon. The axon is generally the only part of the neuron sheathed in myelin. The oligodendrocytes are able to sheath as many as 40 axons at once in myelin.
Microglia, the smallest of the glial cells, also engage in phagocytosis to clean up debris, but their most important role is immunological. The brain’s main protection against pathogens is the blood-brain barrier, a layer of endothelial cells similar to the types of cells that line blood vessels and internal organs. When somehow pathogens cross the blood-brain barrier or are introduced into the brain directly, microglia, which are ultra-sensitive to chemical imbalances in the brain, and particularly to extra-cellular potassium levels, move swiftly into action. Microglia perform a similar role in the CNS to that of macrophages in the blood system, but are not as easily replaceable as macrophages, due to the blood-brain barrier. However microglia are extremely plastic which allows them to perform a variety of immunological functions at short notice while also maintaining homeostasis in the brain.
Another type of glia, the Schwann cells, provide support to the nerve cells of the peripheral nervous system (PNS). They wrap themselves around axons, as with oligodendrocytes in the CNS, and in so doing produce myelin, though the process of myelin production is substantially different in the PNS, with one cell producing only one segment of myelin. Schwann cells also clean up debris and play a major role in the regrowth of PNS axons. They arrange themselves into cylinders which guide the tendrils of regenerating axons. When a functioning tendril comes into contact with one of these cylinders it will grow inside it a rate of up to 4mm a day.
There are other types of glia, and the glial cells already mentioned have their subsets and their developmental phases, which all play their part in the development and maintenance of the brain and the nervous systems, yet for a long time neurophysiologists considered the ‘white matter’ of the brain – the glia, predominantly – as passive, with the grey neuronal matter being the active component.
With the renewed interest in glia however, experiments are being conducted that show that when you remove or ablate relevant glial cells, it has a profound effect on an animal’s ability to sense its surroundings. This has been shown in worms and other creatures, and it raises many questions as to how glial cells communicate with neurons in facilitating an effective sense of our environment, without which, we wouldn’t last long.
We now know that the activation of calcium ions provides the principal means of chemical communication between neuroglia and neurons. An increase in calcium ions signals the release of what are now being called gliotransmitters, molecules that travel between cells in a manner similar to neurotransmitters. All this communication has a variety of purposes but it’s the immunological role of neuroglia that has researchers really excited. The neuroglia are able to pick up signals between neurons and respond by controlling neuronal activity, inhibiting or stimulating or refining the action potentials between nerve cells. All of this was completely unsuspected until recently. Their role in such diseases as Parkinson’s, Alzheimer’s, Lou Gehrig’s disease, cancer and AIDS, and even such disorders as OCD (Obsessive-Compulsive Disorder) are now being uncovered through a lot of experimental work. Communication between astrocytes and microglia and neurons are substantially altered in specific ways in each of these diseases. So important have glia become in contemporary neuro-research that there’s talk of ‘the other brain’ or ‘the glial brain’ as opposed to the neural brain. They of course work in tandem, but the point is that we have a lot of catching up to do in researching glia.
It’s worth noting that, though neurons in invertebrate animals are not substantially different from those in vertebrates, glial cells are far less numerous, in proportion to neurons, in invertebrates, where they don’t have the same myelin-producing role. Investigating the increasingly vital and diverse roles played by glia and how they came to evolve in more complex animals will no doubt be a focus of future research.