Keith Sutherland reviews an important work that corrects media distortions about the science of consciousness
In 1995, The THES published a debate on the causes of the recent revival of interest in consciousness studies. According to Francis Crick, consciousness was put back on the curriculum when Nobel laureates like himself became active in the field, hitherto the province of New Age flakes. This prompted the neurologist Semir Zeki, in true Marxist fashion, to debunk Crick's great-man theory of history and suggest a material cause: the improvements in brain-imaging technology. The following week I proffered a sociological explanation: the students of the 1960s, who enjoyed a rich extra-curricular approach to "consciousness studies" (even if some of them didn't inhale), are now running the science departments.
Susan Greenfield went up to Oxford in 1969 to read classics. Although Brain Story contains an interesting chapter on the effects of drugs on brain chemistry, she does not let slip whether her own interest in consciousness and the brain was ever influenced by recreational pursuits. However her background in the humanities is apparent throughout the book: chapter two starts with a Shakespearean meditation on the human condition, when she recalls the first time she dissected a human brain. But unlike Hamlet, who had only an empty skull, Greenfield was intrigued whether a tiny sliver of cortex accidentally scraped under her fingernail might contain a particular memory, fear or dream.
The interweaving of such anecdotes with scientific material shows that this book is clearly intended for a wide audience. Brain Story is delightfully written, lavishly illustrated and is targeted at anyone with even a casual interest in the workings of the brain. But why should Joe Public be concerned with the difference between LTP and LGN? Given that everyone knows that our experiences are mediated by brain events, why should we bother opening the black box? Although it is important for a practising neurosurgeon to know which cortical areas are involved in, say, speech production, does this knowledge represent any progress beyond 19th-century phrenology so far as the general public is concerned?
In fact, there are several reasons why this book should be read by a wide range of people (not just those who switched off the accompanying BBC series because they were so irritated by the intrusive incidental music). Over the past few decades, the public has been presented with a highly misleading caricature of brain science by the media, and Brain Story goes a long way towards correcting these distortions.
Ask any non-specialist for a view on the mind and the chances are you will hear some version of the old yarn "mind is to brain as computer software is to hardware". Although this myth has its origins in the Faustian pact between psychology and artificial intelligence, neuroscientists have not been entirely free of culpability. In the 1960s, even John Eccles fell victim to the infectious meme that the neuron was a binary switch that permitted only two states (excited and inhibited). Greenfield pours scorn on this by outlining more recent evidence on the modulatory role of neurotransmitters. Neurons are exquisitely complex and brains are integrated into bodies and are subject to all manner of hormonal and visceral influences.
Bodies are also situated in a social and cultural milieu. Greenfield reports research showing that the same drug (amphetamine) can produce markedly different emotions, depending on the social context. It is refreshing to find a pharmacologist who is disinclined to explain sophisticated states of mind "exclusively in terms of mere molecules".
One of the reasons for the dominance of the computational theory of mind is the cross-infection between work in the neurophysiology of vision and computer-vision systems. This has led to the simplistic view that the human visual system operates on an input-driven model. Greenfield points out that vision is a highly active system and even endorses Rodolfo Llin s's radical constructivist view that waking is just dreaming with the eyes open and without sensory constraints.
Seeing as no one has the faintest idea how human memory works, the temptation has been to borrow words like "store", "retrieve" and "memory trace" from the computer-science literature. But whereas computer memory is localised, Wilder Penfield famously discovered that in humans there is no reliable correlation between the cortical area stimulated and the specific memory evoked. If cognitive science is in need of an appropriate metaphor for memory then holography might be a more fruitful source. A study reported recently in Nature showed that, unlike computer memory, long-term memory in human subjects is surprisingly labile - every time a memory is recalled it is modified and "reconsolidated".
If the authors of the recent Department of Trade and Industry Foresight report had read Greenfield's book, they might not have blurted out the widely reported statement that "neuro-chemical technology may provide greater access to the memories of the living and possibly deceased". The main value of Brain Story is as an antidote to futuristic trash such as this.
The computational model of the mind-brain has recently been combined with a Darwinism-inspired theory of origins to form the new discipline of "evolutionary psychology". According to EP, there is no such thing as "general intelligence", rather what we call "mind" is a bolted-together system of modules that developed in the "environment of evolutionary adaptedness". Evolutionary psychology has been much encouraged by the modularity evidence uncovered by lesion studies.
Lawrence Weiskrantz's famous blindsight patient GY is "outed" in Brain Story as Graham Young. Let us leave aside the issue of whether the reports of a single patient, a "superstar in the field of consciousness research", can really be trusted. Fortunately, most of the other examples of selective cortical damage (prosopagnosia, motion blindness and so on) are robust and might be interpreted as supporting the modularity hypothesis.
Although this all makes for good prime-time television, in the book Greenfield is a lot more cautious about extrapolations from lesion studies and cautions the reader against "inferring function from dysfunction". There is a growing wave of scepticism about the research methodology in cognitive neuroscience, with its built-in theoretical bias towards localisation. Friedmann Pulvermuller has pointed out that the cognitive processing of word meanings has been "located" in all of the major lobes of the brain! Greenfield agrees with Jerry Fodor's new book The Mind Doesn't Work That Way that the evidence for modularity just is not available. Unfortunately, Fodor concludes, even if the modular theory is wrong we simply do not possess a better theory.
Greenfield proffers her own dynamic hypothesis, according to which transient assemblies of tens of millions of brain cells compete with each other to generate moments of consciousness, as a candidate to replace modularism. She speculates that deeper levels of anaesthesia could be associated with smaller neuronal assemblies, whereas higher consciousness means larger, more complex assemblies, in which sensory input, emotion, rationality and past experience all combine.
Unfortunately for Greenfield, there is no evidence for her theory of neuronal groupings. Just as Victorian photography could not register moving objects, current imaging technology is too slow to capture such transient neural ensembles. She speculates that Benjamin Libet's discovery of the half-second delay involved in the generation of conscious experience might indicate the time needed to recruit a sufficiently large neuronal assembly. As human subjects can respond to stimuli much faster than this, what is the purpose of consciousness? If Pete Sampras can return a tennis ball before he consciously perceives it, could a zombie win at Wimbledon? These questions are, sadly, left unanswered.
A further reason why this book is so timely is as a contribution to the debate on medical ethics. Greenfield has recently expressed her doubts over the need for brain-dead organ donors to receive anaesthetics prior to organ removal. On the other hand she has suggested that foetuses might possibly undergo pain during abortion. The spectrum of opinion regarding the "threshold" of consciousness currently ranges from panexperientialism to the view that only creatures that possess language are sentient. Developments in medical science mean that pinpointing the onset of consciousness will become increasingly important, and Greenfield's book provides a useful background to the ethical entailments.
However, I think another reason this book might be widely read is that, given the decline in the status and plausibility of mainstream religion, the public increasingly looks to science to fill the gap. The first episode of Greenfield's television series was devoted to the scientific examination of religious experience and endorsed Crick's view that we are all "just a bunch of neurons". Greenfield took delight in explaining both van Gogh's creative use of colours and religious experience in terms of temporal lobe epilepsy. But does this tell us anything other than the pre-theoretical intuitions of a philosophical materialist? Are attempts to investigate the truth claims of religion through the study of the brain any better founded than William Paley's attempts to prove the existence of God through the argument from design?
Greenfield acknowledges the so-called hard problem of consciousness - "how a subjective, inner world is generated from a lump of neuronal sludge". But she then seeks to get round the problem using John Searle's idiosyncratic notion that the problem of phenomenal consciousness and the problem of free will are one and the same. She then executes a quick segue to a discussion with Libet on his discovery that the brain develops a "readiness potential" a full half second before the experience of a "free" volition. "If consciousness and free will are mere illusions, where does this leave personal responsibility and accountability?"
Indeed. But Greenfield has left out half the story. In the book I co-edited with Libet ( The Volitional Brain: Towards a Neuroscience of Free Will ), he claims that we can always veto a "voluntary" act and there is no evidence to suggest that the veto is anything other than an act of free will. (Libet informed me that his interview for Greenfield's book was a long one and this aspect was edited out.) I am afraid editing Libet and Searle will not get Greenfield off the hook. The seeming intractability of the hard problem of consciousness has driven many good scientists to metaphysical extremes. Although she is happy to cite Roger Penrose's views on artificial intelligence, she fails to mention his controversial theory that experience is a fundamental property of space-time.
No doubt these metaphysical problems are left locked in the closet in order not to frighten the horses. If, as Greenfield declared in a newspaper, "the brain is her religion", then the last thing the new convert needs is doctrinal disputes among the high priests.
Keith Sutherland is executive editor, Journal of Consciousness Studies.
Author - Susan Greenfield
ISBN - 0 563 55108 9
Publisher - BBC Worldwide
Price - £17.99
Pages - 208