Nancy Kanwisher: A neural portrait of the human mind

Summary

Nancy Kanwisher describes a worldwide effort to map the brain’s specialized components. Rather than acting as one general-purpose processor, the brain appears to combine specific systems for particular tasks with more general machinery that supports many kinds of demanding mental activity.

Key findings and concepts

• Prosopagnosia, or face blindness, can result from damage to a particular brain area. People with prosopagnosia may see faces clearly but be unable to recognize them, while other abilities remain intact.
• Functional magnetic resonance imaging (fMRI) detects changes in blood flow associated with neural activity. Because blood flow is regulated locally, fMRI can show which brain areas respond more during particular tasks. It measures activity indirectly and cannot, by itself, prove that a region is necessary for a mental function.
• Kanwisher’s research identified a brain region that responds more to faces than to objects. The team tested many kinds of images and found that the region responded strongly to faces but much less to non-face images.
• Evidence that this region contributes causally to face perception came from electrical stimulation during clinical monitoring of a patient with epilepsy. Stimulation temporarily altered the patient’s perception of a face.
• Other specialized regions are involved in:
  • Color, places, visual motion, and bodies or body parts
  • Hearing pitched sounds and processing speech sounds
  • Understanding language
  • Thinking about what other people are thinking (“mentalizing”)
• A proposed “food-detection” region turned out not to be food-specific: it responded similarly to non-food images matched for color and shape. This illustrates why researchers need carefully designed comparisons before assigning a function to a brain area.
• Some regions respond across several kinds of difficult mental tasks, suggesting that specialized systems work alongside general-purpose cognitive machinery.
• These functional patterns occur in broadly similar locations across people, although their exact locations and sizes vary.

Methods and open questions

To test whether a brain region is selective, researchers can:

• Compare its response to a target stimulus with its responses to varied alternatives.
• Repeat measurements and test across multiple participants.
• Use carefully matched comparison images to rule out simpler explanations, such as color or shape.

Brain imaging alone is insufficient to determine whether a region is necessary for a function. Researchers need evidence from interventions, such as electrical stimulation, or from brain damage.

Major unanswered questions include what each region does precisely, why some functions involve multiple areas, how brain regions connect, and how this organization develops in childhood and evolved across species.

Diffusion imaging can trace bundles of connections between brain areas. Methods for tracing individual neurons may eventually contribute to a detailed brain wiring diagram. Researchers are also studying other animals and human infants.

Kanwisher emphasizes that understanding the brain is valuable in its own right, in addition to its potential relevance to treating disorders such as Alzheimer’s disease and autism.

Researchers and sources featured

• Nancy Kanwisher — speaker and researcher.
• Kanwisher’s colleagues and laboratory team — including unnamed researchers involved in the imaging and stimulation studies.
• An unnamed patient with epilepsy and the unnamed neurologist and clinical team involved in the electrical-stimulation demonstration.
• Production credits: Joseph Geni (transcriber) and Madeleine Aronson (reviewer).