Plasticity of binaural interaction. II. Critical period and changes in midline response

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Abstract
Units in the inferior colliculus were activated by contralateral clicks. Suppression of this activity by ipsilateral clicks that were of equal or greater intensity is the commonly observed indication of binaural interaction in adult rats. Such binaural interaction was evident in the unit activity of young rats during the 1st wk after the initial indications of hearing appear at about 10 days after birth. Monaural deprivation begun at 10 days after birth and continued for 3-5 mo. abolished this binaural interaction. The same duration of deprivation had much less effect if begun at 30 days, and no effect if begun at 60 days. Unit responses, averaged as a population, and distributions of midline responses from individual units demonstrated these changes. Apparently the neural mechanisms of binaural analysis require experiential validation during the 4-7 wk after hearing begins.