Origins of cross-orientation suppression in the visual cortex.
The response of a neuron in striate cortex to an optimally oriented stimulus is suppressed by a superimposed orthogonal stimulus. The neural mechanism underlying this cross-orientation suppression (COS) may arise from intracortical or subcortical processes or from both. Recent studies of the temporal frequency and adaptation properties of COS suggest that depression at thalamo-cortical synapses may be the principal mechanism. To examine the possible role of synaptic depression in relation to COS, we measured the recovery time course of COS. We find it too rapid to be explained by synaptic depression. We also studied potential subcortical processes by measuring single cell contrast response functions for a population of LGN neurons. In general, contrast saturation is a consistent property of LGN neurons. Combined with rectifying nonlinearities in the LGN and spike threshold nonlinearities in visual cortex, contrast saturation in the LGN can account for most of the COS that is observed in the visual cortex.
Li
Baowang
B
Group in Vision Science, School of Optometry, Helen Wills Neuroscience Institute, University of California, Berkeley, CA 94720-2020, USA.
Thompson
Jeffrey K
JK
Duong
Thang
T
Peterson
Matthew R
MR
Freeman
Ralph D
RD
D000818:Animals; D002415:Cats; D005074:Evoked Potentials, Visual / Q000502:physiology; D005829:Geniculate Bodies / Q000502:physiology; D036881:Long-Term Synaptic Depression / Q000502:physiology*; D009949:Orientation / Q000502:physiology*; D010470:Perceptual Masking / Q000502:physiology*; D013569:Synapses / Q000502:physiology; D013997:Time Factors; D014793:Visual Cortex / Q000502:physiology*; D014795:Visual Pathways / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology