Top-down processing mediated by interareal synchronization

^*Institute of Neuroinformatics, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland; and ^†Neurosciences Institute, 10634 J. J. Hopkins Drive, San Diego, CA 92121

Edited by John J. Hopfield, Princeton University, Princeton, NJ, and approved September 6, 2000 (received for review September 16, 1999)

Abstract

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 (θ and α; 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 (γ; 20–100 Hz) were observed. Thus corticocortical synchronization reflects the internal state of the animal and may mediate top-down processes.

Footnotes

↵ ‡ To whom reprint requests should be addressed. E-mail: peterk{at}ini.phys.ethz.ch.
This paper was submitted directly (Track II) to the PNAS office.
↵ § Because the indirect connections between area 17 and area 7 via area 18 and 21a are presumably at least as important as the direct connections between these two areas, it can be argued that they should be placed two levels apart (48).