Auditory evoked cortical potentials after lesions of brachium of inferior colliculus.

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Abstract
A study was made of the effects of acute and chronic section of the classical auditory pathways at the level of the brachium of the inferior colliculus (BIC) on the distribution of cortical evoked potentials. Animals were anesthetized with a-chloralose. It was found that lesions which section the BIC and are confined to the lateral quadrant of the midbrain may abolish the evoked responses recorded from classical auditory cortex without affecting the potentials obtained from the association and sensorimotor cortex. In some cases, lesions which sectioned the BIC, while resulting in a restricted distribution of the evoked activity in auditory cortex, did not eliminate such activity. It is concluded that the normal pattern of evoked responses seen in auditory cortex is dependent upon the integrity of the BIC, but that other pathways within the lateral part of the midbrain may also transmit activity to auditory cortex and, moreover, that there are midbrain pathways leading to the association and sensorimotor cortex which are located medial to the great afferent pathways and which are independent of the routes leading to the classical auditory fields.