Spatial correlation of suppressive and excitatory receptive fields with direction selectivity of complex cells in cat...

The aim of the study was to account for direction selectivity of visual cortical neurons through systematic positional mismatch between excitatory and suppressive influences on each neuron. Direction-selective complex neurons were therefore recorded from striate cortex of cats lightly anaesthetized with halothane in nitrous oxide-oxygen. All but small residual eye movements were eradicated with intravenous gallamine triethiodide. Excitatory receptive field (ERF) dimensions and centring were quantified with optimal sine-wave grating stimuli, appropriately windowed to limit them to variable locations along and across the receptive field (RF) centre. Related suppressive receptive fields (SRFS) were similarly mapped during binocular conditioning, induced by an optimal grating applied to the other eye and drifting continuously in each neuron's preferred direction. Its purpose was to elevate ongoing levels of discharge to reveal often concealed null suppression. ERF and SRF profiles were systematically offset, especially along the line of preferred direction such that, for stimuli moving in the non-preferred direction, the SRF lay ahead of the ERF. Derivations of ERFS and SRFS during conditioning, within a single batch of trials, excluded eye movements as a source of positional mismatch. It is concluded that this mismatch may provide the basis for direction selectivity and the emergence of null suppression.