THE STRUCTURE OF SPATIAL RECEPTIVE-FIELDS OF NEURONS IN PRIMARY AUDITORY-CORTEX OF THE CAT

Transient broad-band stimuli that mimic in their spectrum and time wav eform sounds arriving from a speaker in free space were delivered to t he tympanic membranes of barbiturized cats via sealed and calibrated e arphones. The full array of such signals constitutes a virtual acousti c space (VAS). The extracellular response to a single stimulus at each VAS direction, consisting of one or a few precisely time-locked spike s, was recorded from neurons in primary auditory cortex. Effective sou nd directions form a virtual space receptive field (VSRF). Near thresh old, most VSRFs were confined to one quadrant of acoustic space and we re located on or near the acoustic axis. Generally, VSRFs expanded mon otonically with increases in stimulus intensity, with some occupying e ssentially all of the acoustic space. The VSRF was not homogeneous wit h respect to spike timing or firing strength. Typically, onset latency varied by as much as 4-5 msec across the VSRF. A substantial proporti on of recorded cells exhibited a gradient of first-spike latency withi n the VSRF. Shortest latencies occupied a core of the VSRF, on or near the acoustic axis, with longer latency being represented progressivel y at directions more distant from the core, Remaining cells had VSRFs that exhibited no such gradient. The distribution of firing probabilit y was mapped in those experiments in which multiple trials were carrie d out at each direction. For some cells there was a positive correlati on between latency and firing probability.