Brain food

Issue: 109

John Parrington

bq. A review of Steven Rose, The 21st Century Brain (Jonathan Cape, 2005), £25, and Terrence Deacon, The Symbolic Species (Norton, 1998), £8.99

Understanding how the human brain works is one of the biggest unsolved questions in biology, and it is also the subject of Steven Rose’s most recent book. The 21st Century Brain is a book of two halves. In the first half Rose maps out the current state of the neurosciences, and in particular he discusses how new
developments in genetics and brain imaging techniques are affecting our understanding of the processes going on within the brain. In the second half he takes up the question of whether this new found knowledge is leading to new cures and treatments for brain disorders, or to new, possibly sinister, ways to control
human behaviour.

For Rose the past is the key to understanding the present. In the case of the brain, this means taking us through a tour of human evolution starting from the origins of life in the primeval soup that
existed on this planet 4 billion years ago, through to the changes in brain structure that accompanied our divergence from the
apes. There are a variety of alternate explanations for how life or iginally evolved. Some favour the idea that it all started with DNA, or its chemical cousin RNA, because of the roles these molecules play as the so-called ‘blueprint’ of life.

But as Rose points out, it is far more likely that life began within a protective bubble, the precursor to the cells that are the building blocks of our bodies. It is a pertinent point to make in the context of a discussion about the brain because it stresses the importance that cell membranes play in creating a specialised microenvironment that is different both in its chemical composition and its electrical potential from the surrounding fluid that bathes the cell. It is the dynamic changes in these two components, powered by movements of charged atoms, or ions, that underlie the electrical impulses that sweep across the brain when we think a thought, or move a muscle, or indulge in any other activity that requires the action of nerves.

In adopting an evolutionary perspective, Rose is very careful to distinguish himself from a recent school of thought,
spearheaded by people such as the linguist Steven Pinker, called ‘evolutionary psychology’, which sees human behaviour as being rigidly determined by the genes. Two defining features of evolutionary psychology are firstly that it sees the mind as being composed of a series of modules, each one mediating a different facet of human behaviour, and secondly that these modules, and the resulting behaviour, are presumed to have originated, and become fixed, in the early Stone Age, anywhere from 600,000 to 100,000 years ago. Under such a guiding philosophy its exponents have sought to explain everything from rape and aggression, through why women tend not to rise to the top in large corporations, to children’s tendency to dislike spinach, in terms of genes and natural selection

There is much that is laughable about evolutionary psychology, not least the fact that the picture it paints of early huntergatherer
society as one where hunter-dad brings home the sabre-toothed tiger steaks, while gatherer-mum tidies the cave and looks after the children, seems more based on The Flintstones than on any
serious anthropological studies. But the most serious problem from a scientific point of view is evolutionary psychology’s
complete unwillingness, or inability, to relate its proposed mental modules to the biology of the brain.

In fact, recent studies suggest that, while there is undoubtedly some localisation of function at the lowest levels of brain activity, the more sophisticated and complex the behaviour, the more likely it is to be a global process involving many different brain regions. While it is not something Rose spells out in his book, the scientific findings emerging from the human genome project, and those of other organisms such as the chimp, also argue against the idea that different aspects of human behaviour, even something as apparently clearly defined as language, originate in specific brain modules, each one determined by a different gene. If such were the case, then one might expect that humans would have a much greater number of genes than so-called ‘simpler’

Indeed, this was originally thought to be the case, with estimates prior to the human genome project predicting 100,000 genes. It was quite a shock when the ‘first draft’ of the human genome,
completed in 2001, indicated that there were only likely to be 30,000 to 40,000 genes. This figure has since been revised
downwards even more dramatically, with current estimates suggesting that we have only have 20,000 to 25,000 genes, about
the same as a mouse or a rat, and hardly more than the lowly nematode worm, which has 19,000. Most recently the
sequencing of the chimp genome has indicated that the differences between ourselves and our closest relative are unlikely to be due to gross differences in the genes themselves, but instead probably represent alterations in the way certain
genes are turned on or off during embryo development.

So if the evolutionary psychologists are wrong, how does the human brain work? Currently neuroscience draws on two main resources. We have learned much about the human brain from studying how its thought processes are affected by injury and disease, or even by stimulating brain regions during surgery and seeing how this affects the behaviour of the person who has volunteered to take part in such an experiment. However, these
are all very indirect routes to knowledge. By necessity, most of what we know about basic brain processes comes from
experiments on animals. Rose himself studies the process of memory in chicks. Much of the rest of neuroscience involves
experiments on mice or rats, or to a lesser extent on primates, while important insights about the development of the brain and nervous system have emerged from studies of fruit flies and zebrafish.

Rose’s descriptions of the similarities in brain chemistry between different species show that animal rights supporters’ arguments against the value of animal experiments for the study of such
processes are not based upon any valid scientific premise. However, Rose does have reservations about the ‘reductionism’
that guides many such studies.

Rose describes how there is currently a great deal of excitement in the neurosciences because of new technologies, byproducts
of the human genome project, that allow scientists for the first time to study which genes are turned on or off within brain cells on a global scale. He mentions proteomics, which allows
scientists to make a catalogue of all the proteins within a particular cell, but there are also DNA microchips, which can be
used to create such a catalogue for the RNA messages that act as an intermediary between the genes and the proteins that they code for. In addition, there now increasingly sophisticated ‘imaging’ techniques that allow the chemical changes taking place in brain cells to be visualised in real time. Finally, a large number of mutant mice have been created that have defects in genes involved in important cellular processes. By studying such mice, scientists hope to decipher their function within the brain, as well as gaining insights into how defects in these genes in humans might underlie certain types of mental illness or degenerative brain disorders.

According to Rose, one of the problems with proteomic approaches is that they only provide a static snapshot of the
proteins in the brain, not their changes and interactions over time. In this respect, he may be unaware of important new
developments in proteomics that mean it is now possible to record not just the presence or absence of a particular protein
in the cell, but also the chemical changes that modify its activity in response to cellular signals. Meanwhile, in what can be seen as a fusion of genetic engineering and imaging technology, it is becoming possible to add fluorescent ‘tags’ to proteins of interest so that their interactions within the living brain cell can be studied in real time. Another exciting development is that genetically
engineered mice are being created in which the control region of a gene of interest is fused to the gene coding for a fluorescent ‘reporter’ protein, so that when the normal gene is turned on within the brain this registers as a fluorescent signal that can be studied in the living animal.

Rose also has some serious criticisms of mutant mouse studies—for instance, that the effects of such mutations are often masked by the redundancy and plasticity of the developing brain which ensures that the gene defect is compensated for by other genes. Conversely, he argues that because many genes are involved in a
variety of different processes, deleting them from the genome may result in a vast range of diffuse consequences. These are valid criticisms, but I feel that here Rose overstates his case.

Firstly, despite their deficiencies, scientists have learned an enormous amount about some of the basic cellular processes taking place in the brain from studying such mutants. Secondly, increasingly sophisticated genetic engineering techniques mean that it is now possible to delete genes in only a small subset of cells in the brain, or even to turn selected genes on and off by the addition of a special chemical, thus allowing neuroscientists to
avoid some of the problems of redundancy and compensation inherent in traditional mutant mouse studies.

Nevertheless, despite the increasing sophistication of such research tools, I would agree with Rose that a key
unsolved problem for neuroscience is how to integrate the increasing amounts of information emerging from such studies
into a coherent global picture of how the brain works as a whole. According to Rose, this is because we lack an appropriate theoretical framework to accommodate all the mountains of new
data. As a consequence, while we may increasingly know which genes are turned on where and when in the brain, and even the cellular signals that regulate them, we still lack the basic concepts to explain such fundamental properties of the brain as learning and memory, even in animals

Undoubtedly the biggest unsolved question about the brain is that of our own human consciousness, the material roots that it springs from, and what it is that makes us unique compared to other animals. Surprisingly, some neuroscientists seem to have a problem recognising that human consciousness is a unique
phenomenon in its own right, and instead have defined it by such narrow limits that it makes you wonder whether they have ever really sat down and thought about the miraculous events going on in their own heads. So Rose describes how one brain researcher has compared consciousness to an electrical dimmer switch, brightening as more neurons are engaged, darkening when fewer are active, while another believes that consciousness is what abandons you every night and returns to you next morning upon

What these scientists seem to be confusing is the ability that we share with other complex animals of being able to feel and be aware of the world around us, and even to unconsciously react back upon it to an extent, with the specifically human attribute of self-conscious awareness that allows us to reflect upon the world around us, rationalise and analyse it in abstract terms, and having made sense of the world in this way, use the information to
plan and carry out future actions, as well as communicating what we have discovered to other human beings. Some scientists have grasped this point but, having recognised that there is something
unique about human consciousness, they then try and model it as analogous to a computer.

But as Rose points out, this misses another crucial feature of the human brain. Unlike a computer, it has not been designed but has evolved over millions of years. This has the consequence that
sophisticated and specifically human forms of cognitive processing are present together in the brain with far more
primitive functions that we share with less complex organisms, the two existing together in a complex, layered manner.
Another important reason why we can’t just consider brains as ‘wetware’, analogous to the hardware of a computer, is the role of emotional responses in mediating the functions of the brain. Negative emotions such as concern, stress, fear and alarm, but also positive ones such as contentment, joy and euphoria, are
conveyed by hormones, which interact with receptors in the brain as well as in other parts of the body. The importance of emotions for cognitive responses is illustrated by a study described by Rose in which a set of volunteers listened to stories, some of which contained fearful elements. The stories that were best
remembered were the scary ones, but not when volunteers were also given a drug that blocked their response to adrenaline. The steroid hormones that regulate sex and stress also seem to have important effects upon cognition.

Any explanation of human consciousness will have to incorporate all these different elements. But before such an explanation can even begin, surely a crucial remaining step is to identify what it is within the human brain that underlies our specifically human form of consciousness.

One of the distinctive features about human beings is our capacity for language. Is this where the key to human consciousness lies? Rose has some thoughts on this matter, primarily in reference to the work of Terrence Deacon, who has carried out some important studies in this area. In his book The Symbolic Species, Deacon made the important point that what is distinctive about human language is its reliance upon symbolic representation,
words being abstract symbols with no need to reflect the properties of the objects they represent. It is by manipulating this system of abstract symbols that we rationalise the world around us. In many ways Deacon is merely updating the insights of Lev
Vygotsky, the psychologist who did so much to develop a theory of the mind along Marxist principles in postrevolutionary Russia. What is exciting about Deacon’s work is that he is exploring a similar explanatory framework to Vygotsky but within the context of modern neuroscience.

A key issue that now needs to be addressed is how the emergence of language during human evolution has affected the other functions of the brain. One of the important points that Deacon makes is that because language is not just a means of communication, but also a way of symbolically representing the world around us, it has the potential to transform all aspects of the ways in which we interact with the world, for instance our emotional responses. Although emotions have an important role to play in shaping cognitive function, it is equally true that it is very hard to imagine a human emotion that is not deeply affected
by the social context in which it occurs, whether this be sex, or hunger, or fear. This raises the question of what physical changes in the brain underlie such a transformative capacity.

The ease with which children learn to speak suggests that innate biological features must underlie our language abilities. However, in terms of evolutionary timescales, the evolution of language is still a very recent phenomenon. This means that the differences that exist between our brains and those of our closest relative, the
chimpanzee, may be incredibly subtle. What most surprised Deacon when he first began to study the regions of the human brain thought to be involved in language was that the same regions in the brains of other primates seemed to be incredibly similar. In his book, Rose mentions some examples of genes that
appear to be involved in language formation in humans. However, there is no clear evidence for a ‘language gene’ as such, but rather the suggestion that language in humans is the result of a
variety of genes subtly affecting the position of certain nerve cells and the time at which they appear in the developing brain.

We might have more idea about how language shapes human consciousness if we knew more about what factors triggered the emergence of language during evolution. Rose doesn’t really
address this issue, while Deacon suggests that it was due to the increasing size of the human social group. But this doesn’t
explain why language only evolved in humans and not other apes. For me a far better explanation is that put forward by
Frederick Engels in his essay ‘The Part Played by Labour in the Transition from Ape to Man’, which he wrote in 1876. Engels saw the development of the use of tools for social labour as being one of the key moments in our evolution. For him, language was the next major development because social labour ‘brought society
closer together by increasing cases of mutual support and joint activity and by making clear the advantage of this joint activity to each individual. In short, men in the making arrived at the point where they had something to say to each other.’

Recent studies have shown that not only humans but also apes and even some birds can make and use tools, and this has led to
the argument that there is nothing unique about our capabilities in this area. However, this argument misses the fact that these instances of animal tool use are all deeply rooted in the innate biological responses of the animal. In contrast, human tool use became both all-pervasive as our way of interacting with the world, and at the same time is constantly revolutionising itself, so that over a period of only a few hundred thousand years we have progressed from living in caves to sending rockets into outer space. Obviously this must have involved an interactive process between tool use and language, with each one stimulating the
evolution of the other.

The final part of Rose’s book is concerned with how our increasing knowledge of the brain, but also our continuing confusion about how it really works, has influenced the development of new drugs and treatments for mental disorders. He describes how unusual and abnormal mental conditions have been recognised since ancient times, but only began to be classified as distinct ‘illnesses’ with the start of the industrial age. While acknowledging the advances that have been made in the diagnosis of neurological conditions such as Huntington’s, Parkinson’s and Alzheimer’s
diseases, what also emerges from Rose’s account is how little we still know about many disorders of the mind.

This is particularly true of personality disorders such as manic depression and schizophrenia. It has become very fashionable recently to claim that schizophrenia is caused by a genetic defect.
However, despite successive claims that a new gene ‘for’ schizophrenia has been discovered, there is little in the way of
evidence to suggest any of these supposed genetic determinants have anything but the loosest of associations with the condition. Meanwhile, as Rose points out, one of the more str iking features of schizophrenia is how much it is influenced by social conditions, with the consequence that working class people are twice as
likely to be diagnosed as schizophrenic as those who are middle class. Even more striking is the fact that black people of
Caribbean origin living in Britain are far more likely to suffer from schizophrenia than in their country of origin.

Rose is critical of many of the drug treatments for mental disorders. He mentions the examples of Ritalin, which is being increasingly used to control the behaviour of children in the classroom, and Prozac, used to treat depression. It is clear that these drugs do change behaviour in some quite drastic ways, but whether they are anything more than chemical straitjackets remains to be shown. Children treated with Ritalin are said to be suffering from attention deficit/hyperactivity disorder and it is claimed that they have a defect in the response to dopamine, a
neurochemical in the brain, rather than the other possibility which is that they are rebelling against a rigid and unstimulating school system. Yet since 2004 a new drug, Strattera, has been marketed as a cure for this supposed disorder, despite the fact that it has an entirely different target site in the brain, with no explanation provided for the discrepancy.

In this context, it is difficult to know how seriously to regard some of the future possibilities that Rose discusses at the end of his book, of the development of methods for mind control by the military, or the use of gene therapy to treat disorders of the brain. What does seem clear is that while we lack a proper
framework for how the mind works we will be stumbling in the dark. Equally, as long as the pharmaceutical industry is
primarily guided in its research activities simply by how much money it can make from its drugs, we are likely to see more
reliance on chemical straitjackets rather than any real attempt to treat the real, actual basis of disorders of the mind.