- Interhemispheric transfer
- The sharing of information between the two cerebral hemispheres, primarily via the corpus callosum. In normal cognition, sensory information arriving in one hemisphere is shared with the other within milliseconds, creating a unified perceptual experience. The corpus callosum has a rough topographic organisation: the genu carries frontal lobe fibres, the body carries motor and parietal fibres, and the splenium carries temporal and occipital (visual) fibres. Sectioning the splenium disconnects the visual cortices; sectioning the genu disrupts frontal communication. Modern diffusion tensor imaging (DTI) allows in-vivo mapping of callosal fibre tracts.
- Hemispheric lateralisation
- The functional specialisation of the two cerebral hemispheres for different cognitive processes. In most right-handed people (and the majority of left-handers), the left hemisphere is dominant for language production and comprehension, analytical reasoning, and sequential processing. The right hemisphere is typically superior for visuospatial processing, holistic face recognition, emotional prosody, and global pattern processing. Split-brain research made lateralisation amenable to experimental investigation by allowing each hemisphere to be tested in isolation.
- Split-brain experimental paradigm
- Gazzaniga and Sperry's method for studying each hemisphere independently. Stimuli are presented to one visual hemifield (which projects to the contralateral hemisphere) while the central fixation point is held steady to prevent eye movements that would transfer information to the other hemisphere. Because the corpus callosum is severed, the stimulus information is confined to the receiving hemisphere. Verbal responses (language is left-lateralised) reveal left hemisphere knowledge; the left hand (controlled by the right hemisphere) can point to, pick up, or draw what the right hemisphere perceived. This allowed dissection of each hemisphere's independent perceptual and cognitive abilities.
- Left-brain interpreter
- Gazzaniga's term for a left hemisphere system that generates post-hoc narrative explanations for behaviours, perceptions, and thoughts — even when the left hemisphere did not initiate them. When the right hemisphere was secretly instructed to perform an action (via words flashed to the left visual field), the left hemisphere — which had no access to the instruction — would immediately confabulate a plausible reason for why the action occurred. Gazzaniga proposed this as the normal basis of our sense of self: a narrator that retrospectively constructs a coherent story of our experiences and actions, sometimes with incomplete information.
- Agenesis of the corpus callosum (ACC)
- A congenital condition in which the corpus callosum fails to develop, either partially or completely. Occurs in approximately 1 in 4,000 births. When ACC occurs in isolation (without other brain malformations), it often produces no obvious cognitive deficits on standard neuropsychological testing, though subtle impairments in complex integrative and social tasks can be detected. This demonstrates remarkable developmental plasticity: the brain can reorganise interhemispheric communication through alternative routes (anterior commissure, mass intermedia) when callosal development fails. When ACC is part of a syndrome (chromosomal or structural), outcomes can be much more severe.
- Alien hand syndrome
- A phenomenon in which one hand (typically the non-dominant left hand) appears to act independently and contrary to the patient's stated intentions — reaching for objects, interfering with the other hand's actions, or undoing what the patient has done. Can occur after callosotomy (callosal alien hand) or after supplementary motor area lesions (frontal alien hand). In callosal alien hand, the right hemisphere's motor intentions cannot be monitored or inhibited by the language-dominant left hemisphere. The syndrome illustrates that unified voluntary control depends on continuous interhemispheric communication.