In Who’s in Charge: Free Will and the Science of the Brain Michael Gazzaniga puts forward a powerful case against neurological determinism, arguing that even given current insights into the physical workings of the brain there is no reason to downgrade human free will or moral responsibility.

In chapter 1 Gazzaniga offers a concise overview of theories of brain development and functioning which serves as a prolegomenon to the rest of the work. Gazzaniga begins his account with Karl Lashley’s theory of equipotentiality – that any part of the brain can perform the function of any other – which supported a view of the human mind as a blank slate. This he suggests was the consensus view in the first half of the twentieth century. He then outlines how this idea was challenged in the second half of the twentieth century by the pioneering research of Donald Hebb into neural connectivity and Roger Sperry into neurospecificity. Their work, along with that of others, led to the currently prevailing view of the brain not as an undifferentiated mass capable of learning anything but as a highly specified and constrained system. In terms of the old nature-versus-nurture paradigm Gazzaniga suggests that both play an important role. While the global structure of the brain is genetically determined and many of its mechanisms are evolutionary preprogrammed, the formation of specific connections and networks at a local level has been revealed as strongly dependent on activity. In particular he suggests that neuroscientists have come to understand the human brain as a complex modular system with no one overall command centre.

In chapter 2 Gazzaniga begins to show how the understanding of the human brain as modular has led neuroscientists to deconstruct the view of a unified centre of consciousness. Here he focuses on what he calls ‘the parallel and distributed brain’, confronting the crucial question of how the many different and highly specified brain modules are able to function as an integrated whole. As Gazzaniga suggests, nineteenth-century research revealed two important features of the human brain: the extreme localization of cerebral functions and its dependence on unconscious processes. In the twentieth century, he says, the importance of both of these has been borne out by research into split-brain patients carried out by himself and others. In patients with a separated right and left hemisphere of the brain Gazzaniga was able to show that there existed, effectively, two streams of consciousness. While initially this suggested the theory of a dichotomous brain, further research demonstrated that there exist within each brain a constellation of centers of consciousness all interacting with each other. In these terms conscious experience may be understood as the feeling engendered by multiple modules, each of which has specialized capacities. It may be understood as a result of the evolution of the human brain which was only able to retain its efficiency as it expanded by decentralizing into multiple interconnected modules.

In chapter 3 Gazzaniga moves on to discuss the way in which the brain unifies the experience of these multiple modules into one stream of consciousness. It does this, he argues, citing the most recent developments in neuroscience, through a form of post hoc interpretation which often distorts the truth. Thus while we may think that we jumped back because we saw a snake, in actual fact our jumping was an automatic evolutionary fight-or-flight response made before we were conscious of the snake’s presence. Through Gazzaniga’s own research into split-brain patients it has even become possible to isolate the part of the left hemisphere which is responsible for explaining our actions and he calls this the interpreter module. It is this interpreter module which explains all the behaviors, thoughts and emotions arising from the rest of the brain. However, what this research also revealed was that the interpreter’s account is only as good as the information it receives, a fact which can be used to explain many otherwise puzzling neurological disorders. What is most striking, however, is the implications of the interpreter theory for questions of consciousness and free will. As Gazzaniga outlines, the role of the interpreter is to make sense of all things which we become aware of, but since consciousness is a slow process whatever has made it into our consciousness has in fact already happened. This inevitably leads to the question of whether we have any conscious control over our actions or whether in fact we are neurologically determined constructing our self-consciousness post hoc.

In chapter 4 Gazzaniga explores more of the implications of this new theory of consciousness as simply the post hoc interpretation of events. The current consensus, he suggests, is that free will is an illusion created by the interpreter module. Yet while Gazzaniga himself agrees that our notion of consciousness and agency is constructed by the interpreter, he does not see this as entailing the denial of human responsibility. Instead he suggests the need for a radical shift in our understanding of freedom and responsibility, corresponding to our new understanding of the physical world and its mechanisms. As he points out, chaos theory and quantum physics have together undermined a classically deterministic view of the universe. Moreover, detailed studies of emergent phenomena have suggested that higher-order properties are irreducible to their constituent parts and may operate under very different rules. Taken together, Gazzaniga argues, these developments suggest the inadequacy of both neurological determinism – the view that free will is an illusion – and neurological reductionism – the view that every mental state is identical to and thus reducible to some neural state. Instead, he argues that conscious thought is most likely an emergent property. In this sense mind can be viewed as a somewhat independent property of brain while simultaneously being wholly dependent upon it, a relation which he suggests is something like that of hardware and software. While he is cautious about describing the detailed causal interaction of mind and brain, Gazzaniga is insistent that the two are complementary.

In chapter 5 Gazzaniga moves on to consider what he calls the ‘social mind’, the way in which social conditions effect and constrain individual behavior. This, he suggests, should be understood in terms of social hard-wiring – the neural circuits in human brains that recognize and facilitate social behavior – and the dynamic relationship between individual minds. It is not enough to consider a single mind in isolation, abstracted from its social environment, since the behavior of one person affects that of another. Indeed in evolutionary terms, as primate research has indicated, it seems to have been the existence of social groups which catalyzed the development of complex brains. In this process both social competition and social cooperation played a key role. Gazzaniga distinguishes two stages in this evolutionary development: the first primitive stage, which lasted until humans abandoned their nomadic lifestyle and began to settle in fixed locations, and the second stage of a coevolution with emerging civilization which still continues to shape our social minds. Coevolution relates to the way in which acquired traits can evolve – not in the sense that acquired traits can themselves be inherited, but in the sense that we can inherit a tendency to acquire particular traits which subsequently becomes honed over multiple generations. The implication of this is that sometimes the direction and rate of evolutionary change by natural selection can be effected by acquired behaviours. In this way individuals can be said to coevolve with their social environment, each constraining and shaping the development of the other. 

Fundamental to this process of coevolution is the human capacity to understand the mental states of others. As Gazzaniga outlines, recent groundbreaking research has located this capacity in what are called mirror neurons. What was discovered, in monkeys first and later in humans, was that when we observe someone carrying out a particular action the very same neurons fire in us as in the person themselves. Indeed, it turns out that it is through this process of mirroring that we come to understand the actions and intentions of other persons, gaining a crucial insight into their own mental state. It has also been suggested that such mirror neurons may be the basis of our understanding of other people’s emotions, allowing us through the interpreter module to construct an account of their own inner life. Through understanding the lives of others we also make moral evaluations of their behavior. Drawing on new evidence Gazzaniga suggests that many of the moral judgments and choices we make are in fact intuitive and unconscious, programmed into us through evolution. In this light he argues that it is in fact the interpreter module that seeks to make sense of these innate reactions in moral terms through interpreting them retrospectively. In this way morality too may be regarded as part of this dynamic process of coevolution in which individual choices and social environment are mutually constraining.

In his sixth and final chapter Gazzaniga moves on to a discussion of moral accountability in light of modern neuroscience. As he outlines, the whole notion of human responsibility is something which has come under increasing attack by many neuroscientists. The prevailing view of neurological determinism has even led a number to argue that humans are never accountable for their actions, something he points out has radical implications for law and society. Others who have not gone to this extreme have still argued that neuroscience shows that some people are not responsible for their actions, which has led to neuroscientific evidence – such as brain scans – playing a prominent role in the courtroom. On a merely practical level Gazzaniga has a number of objections to this stance, all based on the fact that the current state of scientific knowledge is not strong enough to bear the burden of proof demanded of it. He suggests, therefore, that there is a real danger in using brain scans in court because every brain is individual and cannot be normalized to the standards of others. Likewise he worries about the status of the scientific expert as someone who possesses far too much power to sway court decisions. Yet his real objections go deeper than this. He suggests that it is only as we come to think about ourselves that we shape the rules that we live by. In this sense ‘we are the law’. It follows for him that the process of coevolution – in which individuals are constrained by society and society by individuals – is crucial for understanding our current legal system. Responsibility is therefore not something that can be isolated in individuals but is a kind of emergent property within society. In this sense, Gazzaniga wants to argue, neurological determinism has nothing to do with the question of justice or responsibility. 

In an afterword Gazzaniga returns to the fundamental question of human identity. As he summarizes: ‘we are people not brains – we are that abstraction that occurs when a mind which emerges from a brain interacts with a brain’. It is thus the interaction of mind and brain which provides our conscious reality, but this interaction is itself constrained by the personal and social environment that we exist in. The challenge that lies ahead of us is to develop a vocabulary for these ‘layered interactions’ of mind and brain from which so many things of fundamental value to us are emergent. This, he concludes, will be the scientific problem of the twenty-first century.