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406 pp Price £20 ISBN 0-333-781872 (h/b)
London: Macmillan .
DH Wilkinson once calculated, rather whimsically, that an average human life lasts about 109 seconds whereas an average sensory trace lasts less than one second (pace Buddha, St John of the Cross and an extremely select group of others). Confined though I am within my own solipsistic nutshell, I know I am more than the sum of a billion-odd parts, and suspect that the same might be true of my fellow humans as well. But between sensation and experience yawns a dreadful gap, long lamented by philosophers, and latterly by neuroscientists too. Joseph LeDoux has made yet another attempt to span this chasm (here scaled to the dimensions of the synaptic cleft) in Synaptic Self: How Our Brains Become Who We Are. His book is a well-written and commendably comprehensive survey of many of the big ideas in modern neuroscience. It is manifestly not an answer to the question posed by its title.
LeDoux's central concern is nothing less than the synaptic interface between the ancient emotional circuitry of the limbic brain and the neocortical apparatus of cognition and motivation. The operation of this interface in emotional and goal directed behaviours and the mechanisms by which it is changed by experience are the great themes of his book. His expositions have an easy charm that belies their author's eminence. As one of the pioneers of emotional cognition, LeDoux is entitled to his dauntless vision of the brain as the canvas of our evolutionary and personal past. He has stripped away the filmy varnish of our sentience to reveal the ancient triptych of cognition, emotion and motivation. Neuroanatomy, cellular neurophysiology, neurotransmitter pharmacology, systems physiology, behavioural psychology, functional brain imaging, clinical neurology and psychiatry are all duly painted in. There is a ghost, though, at this glorious banquet of the brain: the inner life, the ‘something-it-is-like-to-be-me’-ness that has leapt, raucous and uninvited, out of the dense synaptic thicket in our heads.
LeDoux maintains that ‘consciousness’ is an overvalued idea in modern neuroscience, and it is difficult to argue with this. And yet, when all's said and done, our intricate inner lives are very probably unique, quite different in kind as well as in degree from those enjoyed by the many animal species that populate LeDoux's book. The subjective quality of sensory traffic, those notorious ‘qualia’ that have exercised philosophers from Plato to David Chalmers, may yet turn out to be fundamental to the operation of brains, rather than inconvenient epiphenomena. We know what it is to be human: we cannot imagine what it is like to be a bat, or even whether it is like ‘something’ at all. LeDoux's sweeping definition of the self (‘the totality of the living organism’) acknowledges our common mammalian heritage even as it sidesteps the problem of conscious awareness; but will this really do? In his final chapter, LeDoux rightly rejects the notion of a coordinating homunculus, crouched somewhere inside the skull, in favour of a set of seven organizational principles that confer plasticity on parallel synaptic networks and permit the brain to reinvent itself as it learns. And yet, his principles leave oddly untouched the central paradox of our experience of the grainy and chaotic world—its seamless perceptual unity in time and space.
It may indeed turn out that a sense of extension in time is fundamental to the idea of self, at least as far as human brains go; it is not at all clear that animals possess such a sense, for it anticipates a future no less than it reanimates a past. It is evidently not dependent on any single memory mechanism, as we now understand them. For the present, it remains a true mystery; and to his credit LeDoux refuses to explain it away by resorting to neurophysiological legerdemain. The problem is, this mystery lies at the very core of human selfhood; it is the biological sine qua non upon which the existential angst of Sartre and friends is built. Our own existence cannot fill us with nausea, ecstasy, or perverse and peculiarly human mixtures of both, unless we first apprehend that we exist. The neural machinery that LeDoux describes would be blind and mute if something about the human brain did not insist on this ontogenetic Catch-22. The problem is no less acute in the case of our perceived spatial integrity. For LeDoux, the paradigm of a self divided is the schizophrenic patient, or perhaps the callosotomy patient with inter-manual conflict; but the clinical neurologist might point to wards filled with stroke patients who refuse even to own their left arms.
To paraphrase JBS Haldane, the brain is surely queerer than we imagine, though I trust not queerer than we can imagine. Turn to any page of Wilder Penfield's neurosurgical ancient history and you will quickly reacquaint yourself with the appalling strangeness of an organ that has stored a faithful record of all the banalities it has ever suffered, alongside all its transports of delight. LeDoux's magnificently intelligible joining of parts is most seductive; but I am still bothered by niggling doubts.
All the same, his book has a refreshing humility. He acknowledges at the outset that his is not the whole story. Like the Danaids of Greek myth, neuroscientists may never finish this particular job with the tools they now have at their disposal: the leaking vessels of our present paradigms cannot contain the self in its brain. Getting inside our own qualia is proving much more difficult than getting inside the atom, but that is no reason to abandon the attempt—or worse still, to convince ourselves that we have already succeeded. Non intellego, ergo sum.