Cortical evoked auditory responses are abnormal in Down syndrome: an MEG-study

Pekkonen, E.1,2,3, Osipova, D.2,3, Sauna-Aho, O.4, and Arvio, M.5
1Department of Neurology, University of Helsinki, Finland; 2BioMag laboratory, Helsinki University Central Hospital, Finland; 3Cognitive Brain Research Unit, Department of Psychology, Finland; 4Päijät-Häme Central Hospital, Lahti, Finland; 5Pääjärvi Centre, Pääjärvi Inter-Municipal Association, Lammi, Finland

Introduction. Patients with Down syndrome (DS) usually have an extra copy of chromosome 21, accompanied by later mental retardation. Brain pathology in DS have similar features than that of Alzheimer’s disease (AD); accumulation of senile plaques and neurofibrillary tangles, accompanied by destruction of ascending cholinergic neurons. Existing event-related potential (ERP) studies in DS have shown accelerated signal processing at the level of brainstem, with delay of later cortical responses N1 and P3. Studies with magnetoencephalography (MEG) indicate that patients with AD have impaired parallel auditory processing between the hemispheres. It has not been studied with MEG, whether patients with DS have similar functional abnormalities of auditory processing as observed in AD.

Material and methods. Whole-head MEG-measurements were performed to six patients with DS, and six age-matched healthy controls. Monaural auditory tones were presented to all subjects with stimulus interval of 1 s, and auditory evoked fields (AEF) were measured with 306-channel MEG-system.

Results. Magnetic P50 response was significantly delayed, but not attenuated in the DS group. The subsequent N100m was significantly attenuated contralaterally in the patient group, whereas the latency difference of N100m was not significant.

Discussion. This is the first MEG-study in patients with Down syndrome suggesting that parallel auditory processing between the hemispheres is impaired in DS. In addition, our preliminary results suggest that P50m and N100m generators have different sensitivity to Down pathology. An abnormal auditory processing might be linked to cholinergic deficiency observed in DS.