Representation of cochlear innervation patterns in single auditory nerve fiber responses

Unit responses of auditory afferent fibers in the monkey could be classified into two distinct populations according to two criteria: (i) the shape of the response area (in particular, the sharpness of tuning, "Q(10)," and high frequency cutoff), and (ii) the impulse rate-sound intensity functions at different frequencies. These two populations have different log-normal distributions of the Q (10)s The smaller population has a relatively rounded (smaller Q(10)) response area with a slow high frequency cutoff and rate-intensity functions with ramps of different slopes. The larger population has a sharp (larger Q (10)) response area and rate functions with parallel ramps. These differences in discharge properties give reasonable grounds to suppose that the smaller and the larger populations correspond to the outer spiral and inner radial fibers in the cochlea, respectively.