VISUAL EXPERIENCE DURING A SENSITIVE PERIOD PLAYS A CRITICAL ROLE IN VESTIBULAR COMPENSATION - NEURONAL SUBSTRATES WITHIN DEITERS NUCLEUS IN THE ALERT CAT

In a previous study [31], we showed that Deiters' neurons ipsilateral to a vestibular neurectomy temporarily exhibit increased sensitivity t o visual cues about fast movement. It was proposed that this change in the deafferented vestibular neuron response observed only during the first 3 weeks post-lesion plays an important role in the vestibular co mpensation process. The present study was aimed at analyzing the poten tial influence over the first 2 weeks post-lesion of visual motion cue deprivation (cats housed in stroboscopic light) and passive visual ex perience (visual information not correlated to head or body movement) on the visually induced activity of Deiters' cells. The extra-cellular response of single units was recorded during sinusoidal translation o f a whole field optokinetic stimulus in six alert cats. Following the deprivation of visual motion cues, vestibular unit responses were foun d to be tuned to low frequencies of visual stimulation, as in intact c ats, and to display a phase lag re. velocity during rapid visual stimu lation. Passive visual stimulation was also found to impede the increa se in neuronal sensitivity to visual input, although the cats had bene fited from normal vision from the 15th day post-lesion. These results are discussed in relation to the functional implication of interactive visual experience within the early stages (sensitive period) of the v estibular compensation process.