ACOUSTIC RESPONSE PROPERTIES OF SINGLE NEURONS IN THE CENTRAL POSTERIOR NUCLEUS OF THE THALAMUS OF THE GOLDFISH, CARASSIUS-AURATUS

Acoustic responses were recorded extracellularly from single neurons i n the thalamic central posterior nucleus (CP). Spontaneous activity, b est sensitivity, and sharpness of tuning (Q(10dB)) of CP neurons range d from 0 to 36 spikes/s, -40 to 5 dB re: 1 dyne/cm(2), and 0.18 to 1.8 0, respectively. The distribution of characteristic frequency (CF) was nonuniform with a mode at 195 Hz. Temporal response patterns of CP ne urons (N = 60) were categorized into three groups: phasic (25%), tonic chopper-like (22%), and tonic nonchopper-like (53%) on the basis of p eri-stimulus time and inter-spike interval histograms. Most CP neurons (90%) did not phase-lock to tones, and none phase-locked strongly. Th e properties of CP neurons are similar to those of the midbrain torus semicircularis neurons in spontaneous rates, best sensitivities, nonun iform CF distributions, and in exhibiting level-independent best frequ encies. Both CP and toral neurons show a diversity of response pattern s resembling those found in the mammalian central auditory system. How ever, CP neurons have broader tuning and less phase-locking than toral neurons, suggesting different roles in auditory processing. While per ipheral frequency analysis is enhanced at the midbrain level, the inte gration of frequency-selective channels in the thalamus may function i n the processing of wideband spectra characteristic of natural sound s ources.