The 21st-Century Brain:
Explaining, Mending and Manipulating the Mind
By Richard Lewontin
In their attempts to make the mysterious complexities of the natural world understandable, scientists have over and over again used metaphors. Descartes likened the animal body to a machine, and physicists tell us that if we are to understand the way molecules of a gas behave we should think of them as billiard balls that, unlike any real ball, undergo perfectly elastic collisions.
Hanging on the wall of my study is a German scroll from the 1920s, The Human Factory, which depicts the inner workings of the human torso below the neck as an interconnected series of assembly lines, supply pipes, spray guns, crushers, storage vats, wheels, and pulleys. Then, as one’s gaze rises to the head, the form of the metaphor changes. At the base of the skull, connecting the factory floor to the offices on the upper stories, is a telephone exchange with women operators plugging and unplugging wires in a switchboard. And in those offices, labeled “Willpower,” “Intelligence,” and “Judgement” are men sitting at tables and desks arguing, consulting, and—thinking. Even the electric line metaphor of pathways of communication requires operators to decide whom to connect with whom. The metaphor for thought is just more thought. Technology had not yet provided devices that could serve as models for memory, consciousness, and rationality.
We have changed all that. In the three-quarters of a century since Fricke and Company produced The Human Factory, science has produced elaborate devices for the manipulation and storage of information, and these have been seized upon by scientists desperate to make the mental concrete. There are computer models in which various regions of the brain are analogized to disk memory, in which both data and program instructions are stored, chip processors that manipulate the information and modify the programs, and input-output circuits for connections to the rest of the body. When it became clear that much mental information is diffusely located rather than concentrated at discrete spots, the brain as hologram was substituted for brain as electronic computer.
But these devices have not succeeded in capturing what is now known about mental processes. The optimism that we will understand the brain as just another form of some object we have already invented has given way to a renewed puzzlement about how to connect the mental with the physical. The naive reductionist 20th-century Mental Machine has given way to the undoubtedly physical yet mysterious entity, The 21st-Century Brain.
Steven Rose, an accomplished investigator of the neurobiology of memory and producer of careful essays and books on what is surely biology’s most difficult question, has not fallen into the temptation that has ensnared so many “big thinkers” about thinking. Rose does not try to produce the sort of grand theory that has been so attractive to scientists anxious to be remembered as the Newton of the mind.
Rather, he presents us with the outcome of experiments, recorded anatomical traumata, and surgical interventions in human beings and other animals that have led us to reject simple mechanical models, and he makes clear what phenomena must be incorporated (in both senses of that word) in a correct physical picture of mental processes. In so doing, Rose necessarily destroys the basis for every simple physical model of mental function that has been constructed and leaves us hanging where we belong for the present, in perplexity.
So what are the essential facts? First, the brain as a whole is broadly regionally differentiated and brain imaging studies certainly show specific areas of the brain that light up when specific mental functions are in process. However, the relation between these areas and particular functions is complex. There is, for example, no “memory bank” corresponding to a computer memory.
Damage to the hippocampus interferes with the ability to retain new long-term memories, but those memories are not encoded in specific neuronal connections. Over time other brain regions and connections become involved in specific memories.
Second, there is no process of the build-up and then slow loss of fixed wiring connections of neurons in the brain that corresponds to fixed mental states. Certainly new neurons and synaptic connections are being produced and are dying throughout life with, alas, a preponderance of losses as we grow older, but these births and deaths are not in some one-to-one connection with events remembered or individual mental processes. There is not some fixed physical module corresponding to the ability to do long division or remembering Pi to six decimal places.
Third, just as new neurons become physically involved in old functions and memories, neurons that are already present can increase the number of connections to other neurons over time, and thus become involved in a new multiplicity of pathways. We do not have neuron-by-neuron catalogues that relate particular cells to particular mental states, so it may well be that such multiple pathways are not related in any categorization that makes logical sense.
Could the dozens of synaptic connections that a single neuron makes with dozens of other different neurons be involved in such diverse functions as remembering a telephone number and an instant ability to construct a grammatically correct sentence in French? As the most common phrase in The 21st-Century Brain has it, “Nobody knows.”
Among the curiosities discussed by Rose is the finding that when long-term memories are recalled, it is not the original memory of the event that is being referenced, but the most recent recall of it. We have memories of memories. I have a vivid pictorial memory of having shared the stage with Carl Sagan at a debate about evolution with some creationists. I also have indisputable documentary and eye-witness evidence that Sagan and I appeared on different days of the event and did not overlap. Although convinced of the historical fact, I am unable to expunge from my memory that image of our joint appearance. The implications of such a phenomenon for the validation of false memories are considerable.
The 21st-Century Brain takes up, in its last chapters, the problem of the reification of behaviors as concrete psychological pathologies. One of the best-known cases is attention deficit/hyperactivity disorder. Is there a common neuroendocrinological phenomenon that lies at the basis of this claimed entity? The belief that it has a corporeal, rather than a purely definitional, existence invites chemical intervention. Rose is skeptical of its physical reality and the reality of various other newly defined behavioral pathologies. But, then again, he may not be a disinterested observer. The behavior that he and I engaged in during the days of the American invasion of Vietnam could easily be seen as a manifestation of the disease now listed in the authoritative Diagnostic and Statistical Manual of Mental Disorders as “oppositional defiance disorder.”
After finishing The 21st-Century Brain, the reflective readers may find themselves seriously considering the possibility that the human species may be extinct before we understand the central nervous system.
—Lancet, March 12 2005