Top-down processing mediated by interareal synchronization.
Perception and cortical responses are not only driven "bottom-up" by the external stimulus but are altered by internal constraints such as expectancy or the current behavioral goal. To investigate neurophysiological mechanisms of such top-down effects, we analyzed the temporal interactions of neurons on different levels of the cortical hierarchy during perception of stimuli with varying behavioral significance. We found that interareal interactions in a middle-frequency range (theta and alpha; 4-12 Hz) strongly depend on the associated behavior, with a phase relationship and a layer specificity indicating a top-down-directed interaction. For novel unexpected stimuli, presumably processed in a feed-forward fashion, no such interactions occurred but high-frequency interactions (gamma; 20-100 Hz) were observed. Thus corticocortical synchronization reflects the internal state of the animal and may mediate top-down processes.
von Stein
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A
Institute of Neuroinformatics, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland.
Chiang
C
C
König
P
P
D000818:Animals; D001522:Behavior, Animal; D002415:Cats; D010775:Photic Stimulation; D014793:Visual Cortex / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*