The Mind and the Brain (40 page)

Study after study has indeed found a primary role for the prefrontal cortex in freely performed volitional activity. “That aspect of free will which is concerned with the voluntary selection of one action rather than another critically depends upon the normal functioning of the dorsolateral prefrontal cortex and associated brain regions,” Sean Spence and Chris Frith concluded in “The Volitional Brain.” Damage to this region, which lies just behind the forehead and temples and is the most evolutionarily advanced brain area,
seems to diminish one’s ability to initiate spontaneous activity and to remain focused on one task rather than be distracted by something else. These symptoms are what one would predict in someone unable to choose a particular course of action. Large lesions of this region turn people into virtual automatons whose actions are reflexive responses to environmental cues: such patients typically don spectacles simply because they are laid before them, or eat food presented to them, mindlessly and automatically. (This is what those who have had prefrontal lobotomy do.) And studies in the 1990s found that when subjects are told they are free to make a particular movement at the time of their own choosing—in an experimental protocol much like Libet’s—the decision to act is accompanied by activity in the dorsolateral prefrontal cortex. Without inflating the philosophical implications of this and similar findings, it seems safe to conclude that the prefrontal cortex plays a central role in the seemingly free selection of behaviors, choosing from a number of possible actions by inhibiting all but one and focusing attention on the chosen one. It makes sense, then, that when this region is damaged patients become unable to stifle inappropriate responses to their environment: a slew of possible responses bubbles up, as it does in all of us, but brain damage robs patients of the cerebral equipment required to choose the appropriate one.

Typical of the new breed of neuroscientists intrepid enough to investigate the existence and efficacy of will is Dr. David Silbersweig. As a philosophy major at Dartmouth College, in 1980 he wrote his senior thesis on the philosophy of mind. A slight man with an intense manner (perhaps a side effect of the caffeine he was substituting for sleep, thanks to his newborn, on the summer day in 2000 when we met), Silbersweig chose not to hole up in a garret and think deep thoughts about Mind. Instead, he enrolled in medical school. But after training at Cornell Medical Center and working at the Medical Research Council in London, Silbersweig returned to the passion of his youth. At the functional neuroimaging lab at Cornell that he runs with his wife, Emily Stern, he looks for the
neural footprints that volition leaves as it darts through the brain. As he puts it, “We are now in an era where you can address questions of volition through neuroscience.”

Silbersweig and Stern do that with PET scans, testing how volition affects conscious perception. Sensory input, of course, does not necessarily produce conscious sensory awareness: if it did, people would be aware of every sight that their visual system takes in, and we plainly aren’t. (To test this, ask yourself what lies at the extreme right of your peripheral vision this very second, but without concentrating on it.) In such a case, sensory information is clearly being processed—one can trace the sequence of activation along the visual pathway—yet conscious perception of it is absent. To investigate the role of volition in sensory disturbances, Silbersweig and Stern study, among other conditions, schizophrenia. When schizophrenics hear voices, the brain is constructing a simulacrum of reality. The patient is conscious of sounds that are not there, suggesting that a brain state underlying the mental state (“I hear voices!”) is sufficient for conscious awareness. But no volition is involved; the patient does not wish to hear voices. So here we have conscious sensory perception in the absence of both sensory stimuli and volition.

Volition can coexist with conscious perception, but in the absence of sensory stimuli. This is the well-known case of mental imagery. One can voluntarily (volitionally) evoke a sensory experience, calling up the image of a giraffe or the voice of Dr. Martin Luther King, Jr., delivering his “I Have a Dream” speech. If you just did either of these, then your visual association cortex almost certainly became active in the first case, your auditory association cortex in the second. Imagery thus presents a neat comparison to schizophrenic hallucinations: the same lack of sensory input, a similar albeit internally experienced conscious percept—but with volition.

For another example of how volition can affect sensation, fortune sent Stern and Silbersweig a young man known as S. B., who was eighteen when they began studying him in 1992. S. B. had suf
fered two strokes of the middle cerebral artery, in 1990 and 1991. The strokes had produced lesions that left him cortically deaf: although his ear and the rest of the peripheral components of his auditory system are fine, S. B. fails to hear environmental sounds—a door closing, a car backfiring. But cortical deafness is more nuanced than this. When S. B. concentrates hard, he can make out simple sounds—when they begin and when they cease, as well as their volume. So in experiments with S. B., volition alone is responsible for conscious perception.

PET scans pick out striking differences in brains receiving or not receiving external auditory stimuli, with or without awareness, with or without volition. In one unmedicated schizophrenic’s brain, Stern and Silbersweig found, auditory-language association cortices in the temporal lobe became more active at the very moment he reported hearing voices. There was, as expected, no activity in the primary auditory cortex, the region that processes input from the ear. Among five schizophrenic patients who were on medication but still heard voices, the active regions included those generally believed to retrieve contextual information (the hippocampus), integrate emotional experience with perception (ventral striatum), and help maintain conscious awareness (thalamus). These regions, together, probably generate complex, emotionally charged hallucinations. But just as Sherlock Holmes solved a mystery by noting that a dog had failed to bark, it was the brain region that remained dark that offered the tantalizing clue to volition, which is absent during schizophrenic hallucinations. The frontal cortex remained quiet.

Silbersweig and Stern compared this pattern to that in healthy patients who were asked to imagine sounds. “There was a preponderance of activity in the frontal lobes,” Silbersweig said. When S. B. became aware of sounds to which he was otherwise deaf—sounds that he could hear only if he willed himself to do so—the same frontal regions lit up. What they were seeing, Silbersweig believes, “was an effect of volition and attention on perceptual
function, a top-down modulation of activity.” The PET results support the hypothesis that these prefrontal systems play a role in “volitional control of conscious sensory experience,” Silbersweig and Stern conclude.

One of the more striking hints of the reality, and power, of will came from experiments in the late 1990s on patients with “locked-in syndrome.” In this terrifying condition, a patient’s cognitive and emotional capacities are wholly intact, but he is completely paralyzed. He cannot point, nod, whisper, smile, or perform any other voluntary motor function. (Occasionally some muscles around the eye are spared, allowing the patient to blink voluntarily and so achieve a rudimentary form of communication.) Such a patient’s muscles are deaf to the wishes of his mind. Locked-in syndrome is generally caused by stroke or other brain injury; it can also result from Lou Gehrig’s disease, amyotrophic lateral sclerosis (ALS). The damage blocks the pathways by which the brain initiates voluntary movement. For decades scientists despaired of ever helping these patients. But then a few groups began investigating a long shot: might they somehow bypass the muscles and enable the patients to communicate through computers controlled by the brain alone?

Johnny Ray had been locked-in ever since a brainstem stroke in December 1997. His powers of reason, cognition, emotion all remained intact. But his brain could no longer communicate with his body, for those messages run through the brainstem, where the neuronal wires were no more functional than electric utility lines after Hurricane Andrew. He could no longer move or talk. So in a twelve-hour operation the following March, Johnny, a Vietnam veteran, had electrodes implanted into the region of his motor cortex that controlled the movement of his left hand. The electrodes, encased in glass cones, contained growth-promoting substances that caused some of the patient’s functioning brain cells to grow into the cones. When they did, an electric signal passing along an axon in the part of the cortex controlling the left hand excited the
minuscule gold contacts in the electrodes, which amplified and transmitted the signal through a gold wire to a receiver in Johnny’s pillow at the Veterans Affairs Medical Center in Decatur, Georgia, and from there to a computer. Soon, Johnny was imagining moving his left hand, causing a wave of action potentials to sweep through his motor cortex. By altering the frequency of the signals, he managed to move a cursor to various icons (“help,” “pain”). He stared at the computer monitor, focusing on the imagined movement of his paralyzed hand, willing the cursor to move. He eventually learned to control the cursor well enough to spell, choosing letters from the screen one at a time. In a few months, he got up to three characters per minute. And then he skipped the middle step: rather than imagine moving his hand, he simply concentrated on moving the cursor. And it moved. He had willed the cursor to move.

The herculean mental effort required to operate the cursor system provides strong evidence that what is involved here is real, volitional effort. As such, it mirrors the tremendous mental effort that OCD patients must make to veto the urge to execute some compulsion. In the absence of effort the OCD pathology drives the brain’s circuitry, and compulsive behaviors result. But mental effort, I believe, generates a directed mental force that produces real physical effects: the brain changes that follow cognitive-behavioral therapy for OCD. The heroic mental effort required underlines the power of active mental processes like attention and will to redirect thoughts and actions in a way that is detectable on brain scans. Let me be clear about where mental effort enters the picture. The OCD patient is faced with two competing systems of brain circuitry. One underlies the passively experienced, pathological intrusions into consciousness. The other encodes information like the fact that the intrusions originate in faulty basal ganglia circuits. At first the pathological circuitry dominates, so the OCD patient succumbs to the insistent obsessions and carries out the compulsions. With practice, however, the conscious choice to exert effort to resist the pathological messages, and attend instead to the
healthy ones, activates functional circuitry. Over the course of several weeks, that regular activation produces systematic changes in the very neural systems that generate those pathological messages—namely, a quieting of the OCD circuit. Again quoting James, “
Volitional effort is effort of attention
….
Effort of attention is thus the essential phenomenon of will
.”

I propose, then, that “mental force” is a force of nature generated by volitional effort, such as the effort required to refocus attention away from the obsessions of OCD and onto an actively chosen healthy behavior. Directed mental force, I suggest, accounts for the observed changes in brain function that accompany clinical improvement among OCD patients who have been successfully treated with the Four Steps. The volitional effort required for Refocusing can, through the generation of mental force, amplify and strengthen alternative circuitry that is just beginning to develop in the patient’s brain. The results are a quieting of the OCD circuit and an activation of healthy circuits. Through directed mental force, what begin as fragile, undependable processes—shifting attention away from the OCD obsessions and onto less pathological behaviors—gradually become stronger. This is precisely the goal of the therapy: to make the once-frail circuits prevail in the struggle against the OCD intruder. The goal is to become, as Gotama Buddha termed it, “a master of the course of thought.” Volitional effort and attentional Refocusing generate a mental force that changes brain circuitry, thus resulting in a lessening of OCD symptoms—and, over time, produces a willfully induced change in the very circuitry of the brain.

One should not, needless to say, posit the existence of a new force of nature lightly. The known forces—gravity, electromagnetism, and the strong and weak forces that, respectively, hold atomic nuclei together and cause radioactive decay—do a pretty good job of explaining a dizzying range of natural phenomena, from the explosion of a supernova to the photosynthesis of a leaf, from the flight of a falling autumn leaf to the detonation of the Hiroshima
bomb. But mental force, its name notwithstanding, is not strictly analogous to the four known forces. Instead, I am using
force
to imply the ability to affect matter. The matter in question is the brain. Mental force affects the brain by altering the wave functions of the atoms that make up the brain’s ions, neurotransmitters, and synaptic vesicles. By a direct action of mind, the brain is thus made to behave differently. It is in this sense of a direct action of mind on brain that I use the term
mental force
. It remains, for now, a hypothetical entity. But explaining phenomena like the self-directed neuroplasticity observed in OCD patients undergoing Four Steps therapy, like the brain changes detected in those of Alvaro Pascual-Leone’s piano players who only imagined practicing a keyboard exercise, like the brain changes in Michael Merzenich’s monkeys who paid attention to incoming sensory stimuli—explaining all of these phenomena and more requires a natural force of this kind. Mental force is the causal bridge between conscious effort and the observed metabolic and neuronal changes.

Let me anticipate an objection. Materialists may argue that although the experience of effort is caused by the brain’s activity (as are all mental experiences, in this view), it has no effect on the brain. If the brain changes, according to this argument, it is because the same brain events that generate the feeling of mental effort also act back on (other parts of) the brain; this intervening thing called “the feeling of mental effort,” they might argue, is a mere side effect with no causal power of its own. But this sort of reasoning is inconsistent with evolutionary theory. The felt experience of willful effort would have no survival value if it didn’t actually
do something
. Therefore, positing that the feeling is the mere empty residue of neuronal action is antibiological reasoning and an unnecessary concession to the once-unquestioned but now outdated tenet that all causation must reside in the material realm. Moreover, the “brain changes itself” hypothesis fails to account for the observed clinical data, in which OCD patients describe making a concerted
mental effort to master the task that changes their brain. Denying the causal efficacy of mental effort, then, means ignoring the testimony of individuals who describe the enormous exertion of will required to wrestle their obsessions into submission. (Of course, psychology has a long history of dismissing such verbal reports as a misleading source of data. But as James pointed out in 1890, that dismissal reflects the “strange arrogance with which the wildest materialist speculations persist in calling themselves ‘science.’”) To those of us without a constitutional aversion to the idea of an active role for the mind in the real world, the facts speak loud and clear: there are no rational grounds for denying that conscious mental effort plays a
causal role
in the cerebral changes observed in these OCD patients.