Reorganization of auditory cortex in tinnitus

TLDR

The study used magnetic source imaging to determine whether tonotopy in the auditory cortex of individuals with tinnitus diverges from normative functional organization. Using magnetic source imaging and magnetoencephalography, ten tinnitus subjects and fifteen healthy controls were presented with four tone sets while recordings were obtained from both hemispheres. The results revealed a marked shift of the tinnitus frequency representation toward an adjacent cortical area, a larger Euclidean distance than controls (5.3 mm vs 2.5 mm), a strong positive correlation between tinnitus loudness and cortical reorganization (r = 0.82), and evidence that tinnitus is linked to plastic changes in auditory cortex, analogous to phantom limb pain.

Abstract

Magnetic source imaging was used to determine whether tonotopy in auditory cortex of individuals with tinnitus diverges from normative functional organization. Ten tinnitus subjects and 15 healthy controls were exposed to four sets of tones while magnetoencephalographic recordings were obtained from the two cortical hemispheres in sequence. A marked shift of the cortical representation of the tinnitus frequency into an area adjacent to the expected tonotopic location was observed. The Euclidean distance of the tinnitus frequency from the trajectory of the tonotopic map was 5.3 mm (SD = 3.1) compared with a distance of 2.5 mm (SD = 1.3) of a corresponding frequency in the healthy controls ( t = 3.13, P < 0.01). In addition, a strong positive correlation was found between the subjective strength of the tinnitus and the amount of cortical reorganization ( r = 0.82, P < 0.01). These results demonstrate that tinnitus is related to plastic alterations in auditory cortex. Similarities between these data and the previous demonstrations that phantom limb pain is highly correlated with cortical reorganization suggest that tinnitus may be an auditory phantom phenomenon.