The syndrome of spatial neglect is typically associated with focal injury to the temporoparietal or ventral frontal cortex. This syndrome shows spontaneous partial recovery, but the neural basis of both spatial neglect and its recovery is largely unknown. We show that spatial attention deficits in neglect (rightward bias and reorienting) after right frontal damage correlate with abnormal activation of structurally intact dorsal and ventral parietal regions that mediate related attentional operations in the normal brain. Furthermore, recovery of these attention deficits correlates with the restoration and rebalancing of activity within these regions. These results support a model of recovery based on the re-weighting of activity within a distributed neuronal architecture, and they show that behavioral deficits depend not only on structural changes at the locus of injury, but also on physiological changes in distant but functionally related brain areas.

We report an endogenous signal that has a widespread cortical distribution and is time-locked to the termination of a sustained state of task-readiness. In three event-related functional magnetic resonance imaging (fMRI) experiments, subjects saw an arrow cue that predicted either the direction of motion or the location of a subsequent test stimulus. A reactivation of the BOLD (blood oxygenation level-dependent) signal occurred at the termination of the state of readiness in occipital regions that were transiently activated by the cue and in frontal-parietal regions that maintained an attentional set over the trial. Moreover, a delayed activation occurred in prefrontal and temporo-parietal regions that did not initially respond to the cue and that have been implicated in re-orienting attention to novel sensory events. These latter regions may have generated control signals that ended the state of readiness in regions active during the cue period. These results indicate that terminating a state of readiness produces a widely distributed cortical signal and suggest that areas involved in a preparatory state may be maintained as a network which can be modulated as a whole.

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.

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