Cerebral Cortex Advance Access published online on September 16, 2009
Cerebral Cortex, doi:10.1093/cercor/bhp191
Population Response to Contextual Influences in the Primary Visual Cortex
1 Gonda Multidisciplinary Brain Research Center, Bar-Ilan University, 52900 Ramat Gan, Israel, 2 The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, 52900 Ramat Gan, Israel, 3 The Center for Brain and Behavior Research, University of Haifa, 31905 Haifa, Israel, 4 Math Department, Bar-Ilan University, 52900 Ramat Gan, Israel
Address correspondence to Hamutal Slovin. Email: slovinh{at}mail.biu.ac.il.
Collinear proximal flankers can facilitate the detection of a low-contrast target or generate false-alarm target detection in the absence of a target. Although these effects are known to involve subthreshold neuronal interactions beyond the classical receptive field, the underlying neuronal mechanisms are not fully understood. Here, we used voltage-sensitive dye imaging that emphasizes subthreshold population activity, at high spatial and temporal resolution and imaged the visual cortex of fixating monkeys while they were presented with a low-contrast Gabor target, embedded within collinear or orthogonal flankers. We found that neuronal activity at the target site in area primary visual cortex increased and response latency decreased due to spatial spread of activation from the flankers’ site. This increased activity was smaller than expected by a linear summation. The presentation of flankers alone induced strong spatial filling-in at the target site. Importantly, the increased neuronal activity at the target site was synchronized over time, both locally and with neuronal population at the flanker's site. This onset synchronization was higher for collinear than for orthogonal flankers. We further show that synchrony is a superior code over amplitude, for discriminating collinear from orthogonal pattern. These results suggest that population synchrony can serve as a code to discriminate contextual effects.
Key Words: collinear • monkey • striate cortex • visual perception • voltage-sensitive dye imaging