Two neural systems for visual orienting and the pathophysiology of unilateral spatial neglect

This chapter critically assesses current neurobiological models of attention and unilateral spatial neglect, particularly in relation to neuroimaging results acquired over the last decade. It highlights that these models do not account for significant discrepancies between lesion studies and neuroimaging results. It then reports a new experiment that clarifies some of these discrepancies and proposes a revision of current models. It is noted that lesions causing neglect in the frontal lobe do not match with frontal areas of activation during visuospatial attention; rather, they better match the location of regions mediating alerting/vigilance. Moreover, the current evidence supports a role for human anterior cingulate cortex (AC) in response evaluation and monitoring, and not stimulus selection or motivation. It is also shown that temporoparietal junction (TPJ) plays a critical role in alerting. The proposed model clarifies some of the discrepancies between neuropsychological studies of neglect and brain imaging studies of visuospatial attention, and provides novel information on the pathophysiology of neglect.