Mechanisms of top-down attention.

Attention exhibits characteristic neural signatures in brain regions that process sensory signals. An important area of future research is to understand the nature of top-down signals that facilitate attentional guidance towards behaviorally relevant locations and features. In this review, we discuss recent studies that have made progress towards understanding: (i) the brain structures and circuits involved in attentional allocation; (ii) top-down attention pathways, particularly as elucidated by microstimulation and lesion studies; (iii) top-down modulatory influences involving subcortical structures and reward systems; (iv) plausible substrates and embodiments of top-down signals; and (v) information processing and theoretical constraints that might be helpful in guiding future experiments. Understanding top-down attention is crucial for elucidating the mechanisms by which we can filter sensory information to pay attention to the most behaviorally relevant events.