SOME DISCHARGE CHARACTERISTICS OF SINGLE NEURONS IN THE INFERIOR COLLICULUS OF THE CAT. I. TONOTOPICAL ORGANIZATION, RELATION OF SPIKE-COUNTS TO TONE INTENSITY, AND FIRING PATTERNS OF SINGLE ELEMENTS

Abstract

Discharges of single units in response to pure tones were studied in the inferior colliculus of anesthetized cats. A tonotopical organization of single neurons is described. There is a low-high sequence of best frequencies in the central nucleus; and probably a high-low sequence in the external nucleus. For many neurons the number of spikes first increases with increasing intensity of the tone and then decreases with further increase in tone intensity. Such functions occur usually over a restricted range of the effective spectrum. Individual neurons differ in their firing patterns. The patterns range from pure onset patterns[long dash]in which the onset burst is the oniy sign of activity[long dash]to sustained patterns which are usually characterized by an onset burst, a silent period, and a period of sustained firing. The effect of systematic change in the frequency and intensity of the tone on the firing patterns is described. The manner in which the pattern may be affected by stimulus rate, variation in tone duration, or a change in the route of the stimulus is also scrutinized. Some implications of the findings as to the organization of the neural network are discussed.