Auditory evoked potentials in multiple sclerosis: alpha responses are reduced in amplitude, but theta responses are not altered.

Auditory evoked potentials (EPs) were measured in a group of 16 multiple sclerosis (MS) patients and in a control group of 20 subjects. In vertex recordings, response amplitudes were reduced in the MS group. Remarkably, EP frequency components computed from the averaged EPs showed different degrees of amplitude reduction in different frequency channels: alpha (7-12 Hz) components were reduced whereas theta (4-7 Hz) responses were not altered. Our interpretation takes into account results of our companion paper (Başar-Eroglu et al., this issue) on similar results in the visual modality and is based on considering MS as a disease with disturbed sensory input to the brain. The fact that in this disorder alpha responses are reduced while theta responses are not altered can be interpreted as follows: alpha components might be mainly dependent on sensory input and thus reflect primary sensory processing. Theta responses, being unaltered in MS, might mainly reflect associative processing. The results are in accordance with conclusions drawn from investigations of topographic differences of evoked electric and magnetic brain responses.