an autodidact meets a dilettante…

‘Rise above yourself and grasp the world’ Archimedes – attribution

Archive for the ‘neurology’ Category

what is autism and what causes it?

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Brain_Autism

The term ‘autism’ was coined in the 1940s by two physicians working independently of each other, Hans Asperger in Austria and Leo Kanner in the USA, to describe a syndrome the key feature of which was a problem with interacting with others in ‘normal’ ways. Sounds vague, but the problem was anything but wishy-washy to these individuals’ parents and families, and over time a more detailed profile has built up.

The term itself is from the Greek autos, or ‘self’, because those with the syndrome had clear difficulties in interpreting others’ moods and responses, resulting in a withdrawn, often antisocial state. Autistic kids often avoid eye contact and are all at sea over the simplest communication.

Already though, I feel I’m saying too much. When describing autism, it’s common to use words like ‘often’ or ‘sometimes’ or ‘some’, because the symptoms are seemingly so disparate. Much of what follows relies on the neurologist V S Ramachandran’s book The tell-tale brain, especially chapter 5, ‘Where is Steven? The riddle of autism’.

Autistic symptoms can be categorised in two major groups, social-cognitive and sensorimotor. The social-cognitive symptoms include mental aloneness and a lack of contact with the world of other humans, an inability to engage in conversation and a lack of emotional empathy. Also a lack of any overt ‘playfulness’ or sense of make-believe in childhood. These symptoms can be ‘countered’ by heightened, sometimes obsessive interest in the inanimate world – e.g. the memorising of ostensibly useless data, such as lists of phone numbers.

On the sensorimotor side, symptoms include over-sensitivity and intolerance to noise, a fear of change or novelty, and an intense devotion to routine. There’s also a physical repetitiveness of actions and performances, and regular rocking motions.

These two types of symptoms raise an obvious question – how are the two types connected to each other? We’ll return to that.

Another motor symptom, which Ramachandran thinks is key, is a difficulty in physically imitating the actions of others. This has led him to pursue the hypothesis that autism is essentially the result of a deficiency in the mirror neuron system.

In recent years there’s been a lot of excitement about mirror neurons – possibly too much, according to some neurologists. A mirror neuron is one that fires not only when we perform an action but also when we observe it being performed by others. They’ve been found to act in mammals and also, it seems, in birds, and in humans they’ve been found in the premotor cortex, the supplementary motor area, the primary somatosensory cortex and the inferior parietal cortex. It’s easier, however, to locate them than it is to determine their function. Clearly, to describe them as ‘responsible’ for empathy, or intention, is to go too far. As Patricia Churchland points out, ‘a neuron is just a neuron’, and what we describe as empathy or intention will likely involve a plethora of high-order processes and connections, in which mirror neurons will play their part.

With that caveat in mind, let’s continue with Ramachandran’s speculations on autism and mirror neurons. First, we’ll need to be reminded of the term ‘theory of mind’, used regularly in psychology. It’s basically the idea that we attribute to others the same sorts of intentions and desires that we have because of the assumption that they, like us, have that internal feeling and processing and regulating system we call a ‘mind’. A sophisticated theory of mind is one of the most distinctive features of the human species, one which gives us a unique kind of social intelligence. That autism would be related to theory-of-mind deficiencies seems a reasonable assumption, so what is the brain circuitry behind theory of mind, and how do mirror neurons fit into this picture?

Although neuro-imaging has revealed that autistic children have larger brains with larger ventricles (brain cavities) and notably different activity within the cerebellum, this hasn’t helped researchers much, because autism sufferers don’t present any of the usual symptoms of cerebellum damage. It could be that these changes are simply the side effects of genes which produce autism. Some researchers felt it was better to focus on mirror neurons straight-off, as obvious suspects, and to see how they fired and where they connected in particular situations. They used EEG (electroencephalography) as a non-invasive way to observe mirror neuron activity. They focused on the suppression of mu waves, a type of brain wave. It has long been known that mu waves are suppressed when a person makes any volitional movement, and more recently it has been discovered that the same suppression occurs when we watch others performing such movements.

So researchers used EEG (involving electrodes placed on the scalp) to monitor neuronal activity in a medium-functioning autistic child, Justin. Justin exhibited a suppressed mu wave, as expected, when asked to make voluntary movements. However, he didn’t show the same suppression when watching others perform those movements, as ‘neurotypical’ children do. It seemed that his motor-command system was functioning more or less normally, but his mirror-neuron system was deficient. This finding has been replicated many times, using a variety of techniques, including MEG (magnetoencephalography). fMRI, and TMS (transcranial magnetic stimulation). Reading about all these techniques would be a mind-altering experience in itself.

According to Ramachandran, all these confirmations ‘provide conclusive evidence that the [mirror neuron] hypothesis is correct.’ It certainly helps to explain why a subset of autistic children have trouble with metaphors and literality. They have difficulty separating the physical and the referential, a separation that mirror neurons appear to mediate somehow.

A well-developed theory of mind which can anticipate the behaviour of others is clearly a feature of understanding our own minds better. In Ramachandran’s words:

If the mirror-neuron system underlies theory of mind and if theory of mind in normal humans is supercharged by being applied inward, towards the self, this would explain why autistic individuals find social interaction and strong self-identification so difficult, and why so many autistic children have a hard time correctly using the pronouns ‘I’ and ‘you’ in conversation. They may lack a mature-enough self-representation to understand the distinction.

Of course, tons more can be said about the ‘mirror network’ and tons more research remains to be done, but there are many promising signs. For example, the findings about lack of mu wave suppression could be used as a diagnostic tool for the early detection of autism, and some interesting work is being done on the use of biofeedback to treat the disorder. Biofeedback is a process whereby physiological signals picked up by a machine from the brain or body of a subject are represented to the subject in such a way that he or she might be able to affect or manipulate that signal by a conscious change of behaviour or thinking. Experiments have been done to show that subjects can alter their own brain waves through this process. Some experimental work is also being done with drugs such as MDMA (otherwise known as the party drug ‘ecstacy’) which appear to enhance empathy through their action on neurotransmitter release.

So that’s a very brief introduction to autism. Hopefully I’ll come back to it in the future to explore the progress being made in understanding and treating the syndrome.

Written by stewart henderson

October 23, 2013 at 10:25 am

What do we currently know about the differences between male and female brains in humans?

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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.

Written by stewart henderson

October 6, 2013 at 9:30 am