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Keywords:

  • directional hearing;
  • later plasticity;
  • development

Abstract

The auditory space map in the superior colliculus of the guinea-pig requires for its normal emergence at 32 days after birth (DAB) bimodal, auditory and visual experience during a 4-day crucial period (26–30 DAB) (Withington-Wray et al., Neurosci. Lett., 116, 280–286, 1990d). The need for auditory experience has been proposed to be linked to the rapid changes in the cues for auditory localization brought about by head growth. Head growth is particularly rapid during the first postnatal month but continues more slowly until ∼70 DAB. This suggests that sensory experience may be required beyond the initial crucial period to accommodate later growth. In this paper the role of auditory experience beyond the crucial period has been investigated. Deprivation of ordinary auditory experience was effected by placement of the animals in an environment in which continuous omnidirectional noise obscured the cues of sound direction. Animals deprived of auditory experience during the crucial period and then allowed normal experience showed limited ability to construct an auditory space map and the resulting map was less accurate than that found in normally reared animals. Auditory deprivation following normal experience during the crucial period caused a profound degradation, of both spatial tuning and topography, of auditory multi-unit receptive fields in the superior colliculus. The spatial tuning and topography of auditory fields from older animals (100 DAB) deprived of ordinary auditory cues for a 4-week period were normal. Thus, in the guinea-pig, susceptibility of the superior collicular space map to deprivation of auditory cues is limited by the age of the animal. The timing of the cessation of vulnerability may, in part, be due to the stabilization of directional cues affected by head growth.