SOUND FREQUENCY AND BINAURAL RESPONSE PROPERTIES OF SINGLE NEURONS IN RAT INFERIOR COLLICULUS

Sound frequency and binaural response properties were determined for single neurons in the rat's inferior colliculus. Nerve cell responses in the central nucleus of the inferior colliculus were narrowly tuned and had clearly defined characteristic frequencies (CF). The central nucleus was tonotopically organized with low frequencies represented dorsolaterally and high frequencies ventromedially from 0.87 to 45 kHz. Sharpness of tuning, as indicated by Q10, covered a wide range of values for neurons with the same CF, but the maximum Q10 at each frequency increased monotonically with CF. Maximum Q10s were larger than previously reported for auditory cortex at the same CF. Binaural responses were classified as either suppression, summation or mixed. Most of the units encountered exhibited binaural suppression but there were substantial numbers of both summation and mixed responses. Each major binaural response type was distributed broadly across sound frequencies within the rat's hearing range. Binaural suppression responses were most numerous at high frequencies and summation responses at low frequencies. The binaural response types, their relative proportions and their distribution by CF were similar for neurons in the central nucleus of inferior colliculus and primary auditory cortex of the albino rat.