Tonic organization of the inferior colliculi in the cat in conditions of simulated sound source motion.

Simulation of the motion of a sound source using a series of clicks with variable interaural delays was used to study movement effects as changes in the amplitude of sequential focal evoked potentials (EP) in series of EP arising in response to the signal. These experiments showed that a) in 25% of cases the movement effect depended on the direction of the simulated motion; b) the movement effect was better represented on the wide ipsilateral to the site of EP recording; left- and right-sided movement effects were identically dependent on the rate of motion; c) the phenomenon of the movement effect was associated with the dominance of contralateral afferentation compared with ipsilateral afferentation; d) the movement effect was accompanied by inhibitory manifestations consisting of suppression of monaural afferentation in conditions of binaural stimulation; e) marked movement effects were seen mainly in the ventrocentral part of the central nucleus, located very close to the positions of large multipolar neurons, while mild and moderate movement effects were distributed quite uniformly though the volume of the nucleus, following the distribution of the "basic" neurons; it is suggested that movement effects of different strengths are associated with differences in the ratios of the effectivenesses of ipsi- and contralateral stimulation, which depend on the properties of multipolar and "basic" neurons in the central nucleus of the inferior colliculus in relation to their responses to ipsi- and contralateral stimulation.