Spatial Receptive Fields of Single Neurons of Primary Auditory Cortex of the Cat

Abstract

Neurons in the primary auditory cortical field (AI) have been shown to be sensitive to the direction of a sound when the source is either in an anechoic free field (Middle- brooks et al, 1980; Rajan et al, 1990; Imig et al, 1990) or in anechoic virtual acoustic space (Brugge et al, 1994; 1996a,b). The spatial receptive fields obtained under these stimulus conditions are typically large in size at suprathreshold levels, often exceeding an acoustic hemifield; close to threshold their centers tend to lie on or near the acoustic axis. How large receptive fields centered around the acoustic axis enable AI neurons to encode information about sound direction is not well understood, although it would appear that the time structure of the neuronal discharge within the receptive field plays a role (Mid- dlebrooks et al, 1994; Brugge et al, 1996). In this paper we review and extend our findings on directional sensitivity of isolated AI neurons to transient sound, employing conventional extracellular recording methods (Brugge et al, 1994,1996a) and a technique by which synthesized signals that mimic sounds coming from particular directions in space are delivered at the eardrums of Nembutal-anesthetized cats through a sealed and calibrated sound delivery system (Chan et al, 1993; Reale et al, 1996).