Left- and right-side unilateral spatial neglect: Hemispheric differences.

Neglect of one side of space, typically contralateral to a lesion of one cerebral hemisphere, is a multicomponent neurologic syndrome. In humans, left neglect after right brain damage is more frequent, severe, or both, than right neglect after left brain damage. Right neglect is behaviorally like left neglect. In the monkey, such a functional asymmetry is not present. In humans, left hemisphere-based spatial systems are weaker, likely due to the coexistence of language and spatial processes. This may account for the lateral asymmetry of neglect, which is present at birth. Except in a few patients, there is no global functional reversal of language and spatial cognition. Left brain-damaged patients often show both aphasia and right neglect, as many right brain-damaged patients with crossed aphasia show left neglect. Lateralized sensory stimulations temporarily improve both left and right neglect. Damage to the posterior parietal lobe (inferior parietal lobule), the temporo-parietal junction, the superior and middle temporal, and to the premotor and prefrontal cortices is associated with contralateral neglect; also, lesions in white matter fiber tracts and subcortical nuclei bring about neglect, with no definite left-right asymmetries.