RESEARCH FOCUS 15-1 SPLIT BRAIN

15-1 THE NATURE OF THOUGHT

CHARACTERISTICS OF HUMAN THOUGHT

NEURAL UNIT OF THOUGHT

COMPARATIVE FOCUS 15-2 ANIMAL INTELLIGENCE

EXPERIMENT 15-1 QUESTION: HOW DO INDIVIDUAL NEURONS MEDIATE COGNITIVE ACTIVITY?

15-2 COGNITION AND THE ASSOCIATION CORTEX

KNOWLEDGE ABOUT OBJECTS

MULTISENSORY INTEGRATION

SPATIAL COGNITION

ATTENTION

EXPERIMENT 15-2 QUESTION: CAN NEURONS LEARN TO RESPOND SELECTIVELY TO STIMULI?

PLANNING

IMITATION AND UNDERSTANDING

RESEARCH FOCUS 15-3 THE RISE AND FALL OF MIRROR NEURONS

15-3 EXPANDING FRONTIERS OF COGNITIVE NEUROSCIENCE

CLINICAL FOCUS 15-4 NEUROPSYCHOLOGICAL ASSESSMENT

MAPPING THE BRAIN

COGNITION AND THE CEREBELLUM

SOCIAL NEUROSCIENCE

NEUROECONOMICS

15-4 CEREBRAL ASYMMETRY IN THINKING

ANATOMICAL ASYMMETRY

FUNCTIONAL ASYMMETRY IN NEUROLOGICAL PATIENTS

FUNCTIONAL ASYMMETRY IN THE HEALTHY BRAIN

FUNCTIONAL ASYMMETRY IN THE SPLIT BRAIN

EXPERIMENT 15-3 QUESTION: WILL SEVERING THE CORPUS CALLOSUM AFFECT THE WAY IN WHICH THE BRAIN RESPONDS?

EXPLAINING CEREBRAL ASYMMETRY

EXPERIMENT 15-4 (A) QUESTION: HOW CAN THE RIGHT HEMISPHERE OF A SPLIT-BRAIN SUBJECT SHOW THAT IT KNOWS INFORMATION? (B) QUESTION: WHAT HAPPENS IF BOTH HEMISPHERES ARE ASKED TO RESPOND TO COMPETING INFORMATION?

LEFT HEMISPHERE, LANGUAGE, AND THOUGHT

15-5 VARIATIONS IN COGNITIVE ORGANIZATION

SEX DIFFERENCES IN COGNITIVE ORGANIZATION

HANDEDNESS AND COGNITIVE ORGANIZATION

CLINICAL FOCUS 15-5 SODIUM AMOBARBITAL TEST

SYNESTHESIA

CLINICAL FOCUS 15-6 A CASE OF SYNESTHESIA

15-6 INTELLIGENCE

CONCEPT OF GENERAL INTELLIGENCE

MULTIPLE INTELLIGENCES

DIVERGENT AND CONVERGENT INTELLIGENCE

INTELLIGENCE, HEREDITY, EPIGENETICS, AND THE SYNAPSE

15-7 CONSCIOUSNESS

WHY ARE WE CONSCIOUS?

EXPERIMENT 15-5 QUESTION: CAN PEOPLE ALTER THEIR MOVEMENTS WITHOUT CONSCIOUS AWARENESS?

WHAT IS THE NEURAL BASIS OF CONSCIOUSNESS?

Split Brain

Epileptic seizures may begin in a restricted region of one brain hemisphere and spread through the fibers of the corpus callosum to the corresponding location in the opposite hemisphere. To prevent the spread of seizures that cannot be controlled through medication, neurosurgeons sometimes sever the 200 million nerve fibers of the corpus callosum.

The procedure is medically beneficial for many people with epilepsy, leaving them virtually seizure free, with only minimal effects on their everyday behavior. In special circumstances, however, the aftereffects of a severed corpus callosum become more readily apparent, as extensive psychological testing by Roger Sperry, Michael Gazzaniga, and their colleagues (Sperry, 1968; Gazzaniga, 1970) has demonstrated.

On close inspection, such split-brain patients reveal a unique behavioral syndrome that offers insight into the nature of cerebral asymmetry. Cortical asymmetry is essential for such integrative tasks as language and body control.

One split-brain subject was presented with several blocks. Each block had two red sides, two white sides, and two half-red and half-white sides, as illustrated. The task was to arrange the blocks to form patterns identical with those shown on cards.

When the subject used his right hand to perform the task, he had great difficulty. His movements were slow and hesitant. In contrast, when he performed the task with his left hand, his solutions were not only accurate but also quick and decisive.

Findings from studies of other split-brain patients have shown that, as tasks of this sort become more difficult, left-hand superiority increases. Participants whose brain is intact perform equally well with either hand, indicating the intact connection between the two hemispheres. But in split-brain subjects, each hemisphere works on its own.

Apparently, the right hemisphere, which controls the left hand, has visuospatial capabilities that the left hemisphere does not.