The functional mechanisms of top-down attentional control

Abstract

Directing attention selectively to an expected event has already been known for a long time to recruit a network of frontal and parietal brain attentional control areas. In addition, this frontal-parietal control network has been hypothesized to signal stimulus-specific sensory (e.g. visual cortex) areas to increase preparatory (biasing) activity in an attempt to improve subsequent perceptual processing of the expected stimulus. The research presented in this thesis shows that there might actually be multiple, rather than one, frontal-parietal attentional control network, one being more medial-dorsal and the other being more lateral-dorsal in location. In addition, strong evidence was found for a frontal cortex initiation of top-down attentional control, rather than a parietal cortex initiation, as was hypothesized by some selective attention theories. Furthermore, it was found that the subsequently triggered sensory cortex biasing-related activity actually consisted of two different, coexisting, mechanisms: 1) a slow-wave baseline shift mechanism that can lower perceptual stimulus thresholds, and 2) an oscillatory alpha-frequency rhythm that can store an attentional trace (template), including both stimulus and response characteristics and their behavioral relevance. Finally, it was shown that voluntary choices in task strategies could selectively determine which frontal-parietal network would be activated (more medial-dorsal or more lateral-dorsal) and which sensory cortex mechanism would be selectively boosted. In short, an attention-for-perception based strategy recruits mostly a medial-dorsal frontal-parietal network and boosts most strongly the baseline shift mechanism, whereas an attention-for-action based strategy boosts more strongly the formation of an attentional template in sensory cortical areas. In conclusion, top-down attentional control is not a unitary mechanism, but includes multiple different processes that can be boosted selectively through voluntary choices in top-down task strategy.