Decreased amplitude of auditory event-related delta responses in Alzheimer's disease

The present study assessed auditory event-related potentials in patients with Alzheimer's disease (AD). Delta responses of 21 mild probable AD subjects according to NINCDS-ADRDA criteria, and 16 healthy elderly controls were evaluated by an active oddball paradigm. Averaged and single sweep potentials were analyzed during target tone processing. As far as time domain averaged event-related potentials (ERPs) are concerned, no significant group differences were observed for N100 and P200 components (both latency and amplitude); also, N200 and P300 amplitude did not differ between groups, whilst N200 and P300 latency were significantly prolonged in AD patients. Concerning delta frequency component of the averaged ERPs, no significant differences between groups were obtained for delta response amplitude as well as delta response topography (Fz, Cz, Pz). Analysis of delta responses was performed for single sweep maximal peak-to-peak amplitude. Significant between groups differences were revealed at the level of single sweep amplitude at the 3 midline sites (Fz, Cz, Pz), during target tone processing. In particular, the difference between healthy controls and AD subjects was at the level of stimulus-related delta amplitude changes: in all locations a significant enhancement of the delta response is recorded in healthy subjects (especially at the frontal location), whilst this delta reactivity was not detectable in AD patients. From a clinical point of view, the lack of delta reactivity might relate to a decision-making function impairment since mild Alzheimer's disease.