Auditory Cortical Spatial Receptive Fields

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Abstract
Neurons in the primary auditory cortex (AI) of anesthetized cats were studied for their sensitivity to directions of transient sounds in virtual acoustic space under a variety of conditions. An effective transient sound evokes a single spike or short burst of spikes with a precisely timed onset. The aggregate of effective directions forms a spatial receptive field. Typically, spatial receptive fields are large, often occupying a quadrant or more of acoustic space. Within the receptive field onset latency varies systematically with direction thereby providing information about source direction. This receptive field structure is highly robust, remaining relatively stable under conditions of competing sounds. Maximum likelihood analysis suggests that psychophysical spatial acuity can be achieved with a relatively small ensemble of AI neurons with broad receptive fields having response gradients of latency. Using reverse correlation and white-noise analysis receptive fields were mapped in space and time. This analysis revealed that spatial receptive fields of AI neurons need not be static but may exhibit marked temporal dynamics. This suggests a sensitivity for direction and speed of moving sound sources.