Structural plasticity in the human brain following unilateral peripheral vestibulo-cochlear neurectomy

Peripheral vestibular deafferentation is known to elicit functional brain plasticity which may be related to vestibular compensation. We examined (i) whether there are structural (morphological) changes in the human brain following peripheral vestibulo-cochlear neurectomy due to acoustic neuroma (AN), and (ii) how they might contribute to central compensation. We compared grey matter changes in AN patients with age and gender-matched control subjects. We hypothezised that morphometric changes in vestibular and auditory cortex as well as temporo-parietal multisensory cortices are related to functional disability/recovery.

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. Simple regression analysis revealed GMV increase (i) in the contralesional superior temporal gyrus/posterior insula to be correlated with decreasing clinically assessed vestibular deficits; (ii) in the contralesional inferior parietal lobe with decreasing functional impairment of daily living activities; and (iii) in the contralesional auditory cortex (Heschl gyrus) with decreasing hearing impairment.

In conclusion, these data suggest structural cortical plasticity in multisensory vestibular and auditory cortex areas of patients following unilateral irreversible vestibular deafferentation which is related to functional vestibular and auditory function. More specifically, increase of GMV was related to better vestibular and auditory function suggesting that structural alterations are related to central mechanisms of compensation.