VOLTAGE-CLAMP MEASUREMENT OF VISUALLY-EVOKED CONDUCTANCES WITH WHOLE-CELL PATCH RECORDINGS IN PRIMARY VISUAL-CORTEX

Whole cell patch recordings have been realized in the primary visual c ortex of the anesthetized and paralyzed cat, in order to better charac terize input resistance and time constant of visual cortical cells in vivo. Measurements of conductance changes evoked by visual stimulation were derived from voltage clamp recordings achieved in continuous mod e at two or more different subtreshold holding potentials. They show t hat the magnitude of the conductance increase can reach up to 300% of the mean conductance at rest. The observation of similar changes for t he preferred and antagonist responses, when flashing ON and OFF a test stimulus in pure ON and OFF subfields supports the hypothesis of a ro le for shunting inhibition in the spatial organization of simple recep tive fields.