Altered neocortical tactile but preserved auditory early change detection responses in Friedreich ataxia

ObjectiveTo study using magnetoencephalography (MEG) the spatio-temporal dynamics of neocortical responses involved in sensory processing and early change detection in Friedreich ataxia (FRDA).MethodsTactile (TERs) and auditory (AERs) evoked responses, and early neocortical change detection responses indexed by the mismatch negativity (MMN) were recorded using tactile and auditory oddballs in sixteen FRDA patients and matched healthy subjects. Correlations between the maximal amplitude of each response, genotype and clinical parameters were investigated.ResultsEvoked responses were detectable in all FRDA patients but one. In patients, TERs were delayed and reduced in amplitude, while AERs were only delayed. Only tactile MMN responses at the contralateral secondary somatosensory cortex were altered in FRDA patients. Maximal amplitudes of TERs, AERs and tactile MMN correlated with genotype, but did not correlate with clinical parameters.ConclusionsIn FRDA, the amplitude of tactile MMN responses at SII cortex are reduced and correlate with the genotype, while auditory MMN responses are not altered.SignificanceSomatosensory pathways and tactile early change detection are selectively impaired in FRDA.