Evidence of peripheral auditory activity modulation by the auditory cortexin humans

At the auditory periphery, the medial olivocochlear system is assumed to be involved in complex sound processing and may be influenced by feedback fro m higher auditory nuclei. Indeed, the descending auditory pathway includes fibers coming from the auditory cortex that are anatomically well positione d to influence the superior olivary complex, and thus the medial efferent s ystem. The aim of the present study was to verify the hypothesis of an impl ied influence of the auditory cortex on the peripheral auditory system. In three rare cases of patients presenting with intractable temporal lobe epil epsy, Heschl's gyrus (i.e, the temporal superior gyrus) was surgically remo ved in the right hemisphere in two patients and in the left hemisphere in a third patient, in order to minimize epilepsy attacks; as preoperative ster eo-encephalography had shown the epileptic focus or tumor to be situated in those locations. In all three cases, several weeks after the operation the medial olivocochlear system was clearly less functional on both sides, but especially on the side contralateral to the resection, In healthy controls , no such pattern was obtained. In four other epileptic patients, who were operated unilaterally at the anterior temporal pole, amygdala and hippocamp us with the temporal gyrus partially spared, efferent suppression grew stro nger in the ear ipsilateral to surgery. These results revealed that, in humans, the primary and secondary auditory cortex play a role in modulating auditory periphery activity through direct or indirect efferent fibers. In accordance with previous findings, this de scending influence may improve the auditory afferent message by adapting th e hearing function according to cortical analysis of the ascending input. ( C) 2001 IBRO. Published by Elsevier Science Ltd. All rights reserved.