Les effets du vieillissement sur les réponses auditives et audiovisuelles des neurones du collicule supérieur chez le rat
Age-related physiological changes affect the peripheral auditory structures; this also applies to the superior colliculus (SC) auditory and visual processes. In aged rats, the peripheral hearing sensitivity decreases and at more central regions, particularly the first central node, in the ascending auditory projections, auditory processing of sounds is altered. Furthermore, at the level of the SC, spectral, temporal and directional properties of auditory neurons are also altered during aging. In addition, no systematic directional spatial arrangement is encountered among the neurons of aged rats, implying that the topographical organization of the auditory directional map is abolished in the deep layers of the SC. Moreover, in a condition where SC visual neurons are stimulated with looming concentric sinusoidal gratings (in the presence or in the absence of modulated audio signals), visual deficits in aged animals are particularly marked by a decrease in sensitivity to fast moving visual and audiovisual stimuli during self-motion. Given the links of age-related changes in the peripheral and in the central structures, inevitably, the mechanisms underlying the neuronal audiovisual plasticity, in the low-level (SC), are somehow disrupted. Specifically, in aged animals, the presence of the auditory stimulus when coupled with the visual signal did not enhance the response activity of the visual neurons. This seems to suggest that the mechanism that may serve to amplify the visual signal under weak or ambiguous and noisy conditions thus improving greater behavioral relevance of detecting rapidly approaching visual and audiovisual moving objects during self-motion is altered with aging. Overall, these results show that aging disrupts the SC neuronal activity that enables detection of relevant sensory information in a complex audiovisual environment.
rat Aging peripheral auditory system cochlear nucleus superior colliculus spectral and temporal auditory acuity directional hearing looming audiovisual integration