Mind

Cognitive neuroscience, which focuses on how the mind emerges from the brain, first developed as a discipline in the 1960s. Unlike Willis or Broca, contemporary cognitive neuroscientists can build on the extraordinary advances in the understanding of the brain that took place in the late nineteenth and twentieth centuries. For example, it is now accepted that the brain is composed of several billion neurons, which project a trillion branches to contact other neurons. Neurons carry information as electrical impulses, and communicate with other neurons by releasing a variety of chemicals known as neurotransmitters.

Cognitive neuroscience has also gained great strength from new technologies that provide high-resolution information about brain activity. Consider one technology known as functional magnetic resonance imaging (fMRI). fMRI represents a modern twist on the investigative methods of Willis, Broca, and Donders. A human subject lies with head surrounded by a large, doughnut-shaped magnet. The magnet's powerful field causes some molecules in the subject's brain to release radio waves. Detectors pick up these signals, which a computer uses to reconstruct the structure of the brain. Additional analysis of this data can reveal movements of blood in the brain, which reliably indicate highly active regions of the brain.

A complex cognitive task, such as reading or recalling a person's face, involves many regions of the brain. In order to isolate components specific to these tasks, scientists borrow Donders's subtraction method. They scan the brains of their subjects as they perform one task, and then have them perform second task that is almost—but not quite—identical to the first. The scientists then study the fMRI scans for brain activity produced by the second task that are not produced by the first task as well.

Consider, for example, the ability to understand other people's thoughts and intentions (known as mentalizing). Psychologists and neuroscientists are fascinated by this ability because it appears to be unique to humans and may therefore represent a crucial innovation in the social evolution of the human species. Psychologists have also demonstrated that autistic people do a poor job of mentalizing. Yet despite this deficit, they can still develop other skills such as mathematics and music. This pattern suggests that mentalizing is not the result of a general-purpose intelligence, but is instead a distinct, modular function of the brain that can be selectively disabled.

In 2001, British researchers found support for this hypothesis with the help of fMRI. They designed an experiment based on the game of "rock, scissors, paper." In each round, two players simultaneously choose one object. Rock beats scissors, scissors beat paper, and paper beats rock. The subjects lay in a brain scanner and played the game on a computer screen. In some cases, they were told they were playing against a computer; in other cases, they thought their opponent was a person. In fact, the researchers generated a random sequence of choices. The only difference lay in the attitude of the subjects. As the researchers confirmed in interviews after the study, when subjects thought they were playing against a person, they tried to figure out their opponent's strategy.

Scans revealed some regions that became active in both versions of the game. But the researchers also found a handful of small regions in the brain that were only active when the subjects thought they were playing against a person. One region has been shown in other studies to integrate information from face and hand movements. Another region is active during emotional experiences, and a third distinguishes self from non-self.

These results illuminate a general lesson of cognitive neuroscience: Most complex functions of the mind, such as mentalizing, are not carried out in a single region of the brain. Instead, a network of regions works together, integrating their activities. This realization has immediate practical implications. The deficit in mentalizing found in autistic people, for example, may not be the result of a lesion to a particular region of the brain. Instead, it may result from damage to the connections between the components of the mentalizing network.