Tonotopic cortical changes following stapes substitution in otosclerotic patients: A magnetoencephalographic study

The aim of the study was to investigate and follow up the tonotopic organiz ation of the primary auditory cortex in otosclerotic patients before and af ter corrective surgery. The characteristics of primary auditory cortex acti vation were studied in ten otosclerotic patients (i.e., subjects suffering from a conductive hearing loss, prior to and following stapes substitution) . Magnetoencephalographic recordings of auditory evoked fields by tone-burs t stimulation at octave frequencies between 250 and 2000 Hz were performed during monaural stimulation. The brain topography of the main cortical resp onse (N100m) generators at different tones was studied in patients and comp ared with ten healthy controls; pre-post-surgical changes were also correla ted to their clinical outcome following corrective surgery. A significant d ecrease of the tonotopic extension in the cortical region responsive to the four explored frequencies was found in patients before surgery with respec t to the control population At the time of postsurgical follow-up, the tono topic representation had enlarged and was approaching the dimensions seen i n normal subjects, although with higher variability. The extent of the enla rgement of the postoperative tonotopically organized area was directly corr elated with the postsurgery period duration. Our findings indicate that aud itory cortical areas of human adults undergo functional reorganization foll owing peripheral alteration of the sensory input entering the CNS. The rest riction of the cortical tonotopic region caused by the long-term reduction of acoustic input is followed by a reorganization within the usual boundari es following the recovery of auditory function; this process is taking plac e in a time scale of a few weeks. Hum. Brain Mapping 10:28-38, 2000. (C) 20 00 Wiley-Liss, Inc.