Deficit in sensory motor processing in depression and Alzheimer's disease: a study with EMG and event related potentials.

Event related potentials have been examined in depression and Alzheimer disease like clinical utility. To evaluate the influence of visual and auditory stimuli on the P300 latency we studied 12 patients with major depression, 12 patients with Alzheimer disease and 12 normal subjects. The experimental tasks applied was, first a series of 300 auditory stimuli, 255 (85%), with tones of 1,000 Hz, and considered as the frequent stimulus, whereas 45 (15%) were tones of 2,000 Hz and referred as the rare stimulus. A second series of 300 visual stimuli, 255 (85%) that were black circles on a white background, and considered the frequent stimulus (9 cm diameter, 200 ms duration), whereas 45 (15%) were black squares on a white background and referred as the rare stimulus (9 cm diameter, 200 ms duration) in the centre of a computer screen. The results show an increase of P300 latency in depressive and Alzheimer patients during auditory and visual tasks. Differences were found in reaction time to visual or auditory stimuli in Alzheimer disease. These results are consistent with an impairment in brain function in depressive patients that is associated with cortical hypoactivity and deficits in perceptive, auditory or visual, functions, whereas deterioration in Alzheimer's disease is sensorymotor, according to the slowness latency in the reaction time.