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The Journal of Neuroscience, December 27, 2006, 26(52):13537-13547; doi:10.1523/JNEUROSCI.3723-06.2006

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Behavioral/Systems/Cognitive
Luminance-Evoked Inhibition in Primary Visual Cortex: A Transient Veto of Simultaneous and Ongoing Response

Thomas R. Tucker and David Fitzpatrick

Department of Neurobiology, Duke University Medical Center, Durham, North Carolina 27710

Correspondence should be addressed to David Fitzpatrick, Duke University Medical Center Box 3209, Department of Neurobiology, Durham, NC 27710. Email: fitzpat{at}neuro.duke.edu

Large-scale changes in luminance are known to exert a significant suppressive or masking effect on visual perception, but the neural substrate for this effect remains unclear. In this report, we describe the results of experiments using in vivo intracellular recording to explore the impact of luminance transients on the responses of orientation-selective neurons in layer 2/3 of tree shrew primary visual cortex. By measuring changes in excitatory and inhibitory conductances, we find that instantaneous changes in luminance evoke strong cortical inhibition. When combined with visual stimuli that would otherwise yield strong excitatory responses, luminance transients produce significant reductions in excitation as well as increases in inhibition. As a result, luminance transients significantly delay the emergence of orientation tuned cortical responses, and virtually eliminate ongoing responses to effective stimuli. We conclude that cortical inhibition is a critical factor in luminance-evoked cortical suppression and the likely substrate for luminance-induced visual masking phenomenon.

Key words: visual cortex; physiology; inhibition; luminance; neural circuits; synaptic conductance

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Received Aug. 25, 2006; revised Nov. 8, 2006; accepted Nov. 22, 2006.

Correspondence should be addressed to David Fitzpatrick, Duke University Medical Center Box 3209, Department of Neurobiology, Durham, NC 27710. Email: fitzpat{at}neuro.duke.edu

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