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Curr Opin Neurobiol. 2001 Aug;11(4):488-97.

Processing in layer 4 of the neocortical circuit: new insights from visual and somatosensory cortex.

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Departments of Physiology and Otolaryngology, WM Keck Center for Integrative Neuroscience, Sloan-Swartz Center for Theoretical Neurobiology at UCSF, University of California, San Francisco, CA 94143-0444, USA.


Recent experimental and theoretical results in cat primary visual cortex and in the whisker-barrel fields of rodent primary somatosensory cortex suggest common organizing principles for layer 4, the primary recipient of sensory input from the thalamus. Response tuning of layer 4 cells is largely determined by a local interplay of feed-forward excitation (directly from the thalamus) and inhibition (from layer 4 inhibitory interneurons driven by the thalamus). Feed-forward inhibition dominates excitation, inherits its tuning from the thalamic input, and sharpens the tuning of excitatory cells. Recurrent excitation enhances responses to effective stimuli.

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