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13 years ago
Tracking the tell-tale signs of pure genius
A leading neuroscientist on the intriguing case studies that are revealing the powerful, adaptive potential of the human brain  A 70-year-old engineer who has just retired confesses that he has had a life-long urge to have his left arm amputated below the elbow. He has the arm removed and feels much better.
Another man loses his arm in a car accident, but still feel its ghostly presence; this phantom limb is clenched in a painfully awkward position.
A third man, a student of mine, makes a remarkable recovery from a coma, only to become convinced that his mother and father are impostors.
All three case studies are fascinating. Yet as I argue in my new book, The Tell-Tale Brain, they can also teach us a great deal about how the brain does its near-miraculous work.
This is an organ of staggering complexity: a 3lb lump of jelly that can contemplate the meaning of infinity, the idea of God, and even its own existence.
How all this is produced by 100 billion of the little wisps known as neurons is surely one of the last great mysteries in science.
Yet, by studying the behaviour of people who have undergone a change in a tiny part of the brain, whether from injury, stroke, or malfunctioning genes, you can pin down the functions that this small region governs, and begin to figure out how it works and how it interacts with other regions.
What this means is that strange neurological symptoms have the potential to take our understanding in a new direction.
The classic example is the work by the British scientist Brenda Milner with a patient whose initials were "HM". She found that damage to the hippocampus in the brain's temporal lobes had led to HM's inability to form new memories.
So instead of asking vague questions such as, "How is memory stored in the brain?" she could pin the process down to the hippocampus. Other scientists were then able to use this to explore the cellular and molecular mechanisms of memory formation.
One principle that often crops up is the importance of evolution, especially the notion that a brain mechanism that evolved for one function can be hijacked for another. As the great biologist Theodosius Dobzhansky said, "Nothing in biology makes any sense except in the light of evolution."
Take that 70-year-old engineer who wanted to amputate his arm – a classic case of apotemnophilia [a neurological disorder in which a sane and rational individual wants a healthy limb or limbs to be amputated].
Many far-fetched Freudian ideas have been proposed to explain this condition (including the idea that the amputation stump would resemble a large penis). But the real answer is genetic. It turns out that the right hemisphere of the brain contains a complete representation of your body – a genetically specified "body image".
Our brain-imaging experiments showed that with this particular patient, the hand on this genetic map was missing – so the sensory impulses from the arm had nowhere to go to, and the patient experienced it as "over-present". Similar changes in body images might even explain the desire that transsexuals have to have their penis amputated.
Phantom limbs [the limb has been removed, but the patient feels its presence] are more common – and in some cases, the ghostly arm is paralysed, and fixed in a very painful position.
Often, this can be solved surprisingly simply: propping up a mirror in front of the patient enabled us to use the reflection of his intact arm to create the optical illusion that the phantom limb had been resurrected and was obeying the brain's command. In many cases, this relieves the pain.
Astonishingly, even real pain in a paralysed arm – after a stroke, for example – can be relieved by techniques such as visual feedback, demonstrating the brain's ability to reorganise itself.
In the case of the patient who failed to recognise his parents – a victim of what is called Capgras syndrome – the explanation was also anatomical: the fibres that connected his amygdala [an area of the brain linked to mental and emotional state] to his fusiform gyrus, part of the temporal lobe where faces are first identified from visual input, had been partially damaged.
He still recognised his mother – but link between emotion and visual perception had been severed. Failing to feel the expected warmth, his brain had concluded that she had to be an impostor. Put her on the phone, and he recognised her immediately.
Or consider a fourth condition: synaesthesia, when otherwise normal people get their senses muddled up, seeing vivid colours when looking at printed numbers or listening to musical tones. The condition runs in families and is seven or eight times more common among artists, poets, novelists and other creative people. But why?
Well, it turns out that the colour area and the number area in the brain are very close to each other; we found that synaesthetes get "cross-wires".
The explanation is that the brain of a foetus contains a florid excess of connections, which are pruned to create the architecture of the adult brain. If these "pruning genes" fail, it leaves excess connections, which cause cross-activation between number and colour.
If the same genes are diffusely expressed, the result is excess connectivity throughout the brain – even between far–flung regions. Assuming that high-level concepts are represented in different parts of the brain, such excess connections would create an opportunity for linking seemingly unrelated ideas.
This would explain the sevenfold higher incidence of synaesthesia in arty types compared to the rest of us – and also the wide prevalence of the apparently useless synaesthesia gene, given the creativity it stirs up it outlying members of the population.
Another of the many areas in which anatomy, evolution and genetics collide is the issue of "mirror neurons". When you reach for a chocolate bar or pull a lever, motor command neurons in your frontal lobes issue instructions for and orchestrate this semi-skilled movement. But some of these cells – mirror neurons – will fire even when you watch someone else execute the same action; allowing the neuron to perform a sort of virtual reality simulation of the action: "The same neuron is firing in my brain as would fire if I myself were to reach for a peanut."
In order for us to empathise with each other – visually and, I would argue, metaphorically – such neurons play a crucial role. In particular, they are a
prerequisite for imitating another person's sequence of skilled actions, something humans excel at.
A polar bear might have taken a few hundred thousand years to evolve a fur coat through natural selection, but a human child can acquire the skill by watching its mother hunt such a bear down and skin it.
He can then transmit the skill "vertically" (to his own offspring) or "horizontally", to his peers. Indeed, it was this kind of sophisticated imitation that
accelerated the emergence of culture in early hominids.
This kind of research can help explain why the human brain is unique, especially in its simultaneous capacity for grasp of self-awareness and "other awareness".
Apes, for example, have mirror neurons too, but they may not be sophisticated enough or connected adequately to other brain structures to permit the imitation of complex skills and accurately view others (and oneself) as beings with minds and intentions.
Based on the cases I have seen, I would argue that there are anatomical structures unique to the human brain; especially the left angular gyrus and supramarginal gyrus, which split off from the more ancient inferior parietal lobule as it grew during our evolution.
These two areas are involved, respectively, in understanding and performing skills, such as hafting an axe or opening a champagne bottle, and in human abilities such as reading, writing, arithmetic and linguistic comprehension.
Given the state of the research, this is the most speculative theory I have put forward. But even if it were to prove false, it should provide a starting point as we attempt to decipher some of the more elusive and enigmatic aspects of the human mind.
As Darwin said: "False views, if supported by some evidence, do little harm, for everyone takes a salutary pleasure in proving their falseness; and when this is done, one path towards error is closed and the road to truth is often at the same time opened".
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