[Functional magnetic resonance imaging in patients with long-term unilateral hearing loss]

To evaluate the potential functional reorganization by functional magnetic resonance imaging (MRI) to measure the brain activation in responses to stimulation to healthy ears in patients with long-term unilateral hearing loss (UHL).

From June 1998 to December 2009, 23 patients with serious UHL (15 left, 8 right) were recruited along with 15 matched normal hearing subjects. Laterality index (LI) for activated voxel in primary auditory cortex (PAC) was calculated. And the activations outside auditory cortex were also evaluated.

The data were discarded in 3 patients with left-ear UHL and 1 normal subject because of head motion. All control subjects showed contralateral dominant activation of PAC in group analysis. However, the group data of UHL patients showed that the activation was more symmetrical and the contralateral dominance diminished versus the control group. As compared with normal subjects outside PAC, heightened activation in left prefrontal cortex, bilateral inferior parietal lobule and left occipital/precuneus was found in UHL patients while reduced activation in left superior temporal gyrus was also found.

The diminished contralateral dominance in PAC and heightened activation in non-auditory region suggest the reduction of interhemispheral inhibition and general increase in brain excitation in long-term UHL patients potentially occur as a result of functional reorganization adaptive to UHL. However, the reduced activation in superior temporal gyrus may be correlated with the deterioration of speech perception in these patients.