Role of structural plasticity in the human brain for multisensory compensation following unilateral peripheral vestibular lesion

Peripheral vestibular deafferentation is known to elicit functional brain plasticity which may be related to vestibular compensation. We examined whether and how structural (morphological) changes in the human brain might contribute to central vestibular compensation following peripheral vestibular lesions.

We compared structural grey matter changes in patients with a severe unilateral peripheral vestibular lesion with age-matched control subjects. We hypothezised morphometric changes in insular and temporo-parietal multisensory cortices which may be related to functional disability.

Subjects were examined with a battery of neuro-otological tests (audiometry, acoustic evoked potentials, subjective visual vertical, caloric irrigation) and clinical scores (Gardner, Cohen) to assess vestibulo-cochlear disability. Using voxel-based morphometry (VBM, SPM2) grey matter changes of subjects were examined within defined regions of interest according to the a priori hypothesis and correlated with scores of functional/clinical impairment.

Categorical comparisons (ANOVA) revealed grey matter volume (GMV)-increases in patients bilaterally in primary somatosensory cortices and motion sensitive areas in the medial temporal gyrus (MT) when compared to age-matched normal control subjects. Regression analysis revealed GMV changes (i) in contralesional parietoinsular vestibular cortex (PIVC) correlating with caloric hyporesponsiveness, and (ii) in the contralesional posterior insula/superior temporal gyrus which correlated with clinically assessed vestibular deficits; i.e., the larger vestibular impairment the smaller was the change of GMV.

In conclusion, these data suggest structural cortical plasticity in multisensory areas which is related to functional vestibular impairment. More specifically, change of GMV was related to an improvement of vestibular function suggesting that structural alterations are related to central vestibular compensation.