The term attention refers to the preferential allocation of cognitive and neural resources to events that have become behaviorally relevant. Attention is modulated by the bottom-up influence of the ascending reticular activating system and the top-down influence of association and limbic cortices. Focal lesions that interfere with the bottom-up or top-down regulation of attention, or multifocal partial lesions that interrupt multiple domain-specific processing pathways, can disrupt the attentional matrix and give rise to the acute confusional state syndrome.