Active touch exploration of extrapersonal space elicits specific electrogenesis in the right cerebral hemisphere of intact right-handed man.

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Abstract
Language and analytic processing are currently thought to be represented in the left hemisphere, whereas spatial and holistic processing involve primarily the right hemisphere in man. An experimental paradigm for engaging the nonlanguage hemisphere (generally the right) was described. This involved active touch exploration with the index finger to identify the orientation of a ridge with respect to the subject''s body. The task was compatible with the electronic averaging of transient event-related cerebral potentials recorded from the intact scalp. A consistent positive electrogenesis of 1-5 .mu.V and about 0.5-1.5 s in duration was recorded over the nonlanguage hemisphere, regardless of whether the left or the right index finger performed the tactile scanning. The lateralized specific electrogenesis did not extend to the midline, and it was differentiated from the decision P300 component. This is a new procedure for analyzing, in intact man, measurable focal potentials associated with unique processor subsystems during cognitive behavior. The method will make it possible to investigate the dynamic distribution of processing tasks between the 2 hemispheres in normal man in whom the commissural integration is normal, thereby adding to the data collected on patients with unilateral brain lesions or with surgical transection of the corpus callosum.