[Deficit of cognitive event-related potentials during a working task in patients with major depression]. / Déficit de los potenciales evocados cognitivos durante una tarea de memoria en pacientes con depresión mayor.

INTRODUCTION: To study working memory function in major depression using identification and memory tests with event-related potentials (ERP). METHODS: We compared behavioral performance and event-related potentials during the processing of the Sternberg working memory task in 26 patients with major depression and 64 healthy matched control subjects. RESULTS: Depressed patients had more errors and had an increase in reaction time that was superior to the control subjects during the memory test of 5 letters presented. The depressive patients showed increased event-related potentials (P300 and N400) between 300-700 milliseconds registered in Pz. The prolonged positive activity in the patients ERPs suggests specific deficit in cortical activity and the large prolonged negativity activity in the patients' ERPs suggests abnormal activation of additional neuronal assemblies than those normally participating in the memory task. These data could reflect either compensatory mechanisms of dysfunction of inhibitory systems. CONCLUSIONS: This study provides objective evidence that major depression significantly affects working memory. The ERP changes in depression could be accounted for by cortical activity dysfunction of the central executive control of working memory.

[Cortical processing of visual and auditory stimuli in depressive patients: a study with event related potentials]. / Procesamiento cortical e estímulos visuales y auditivos en pacientes depresivos: estudio mediante potenciales evocados.

Event related Potentials, which seem to be an objective parameter reflecting cognitive functions, have been examined in depression. To evaluate the influence of visual and auditory stimuli on the P300 latency we studied 42 patients with major depression and 21 normal subjects. The experimental tasks applied were first a series of 300 auditory stimuli [255 (85%) were tones of 1000 Hz, and considered the frequent stimulus, whereas 45 (15%) were tones of 2000 Hz and referred to as the rare stimulus and second a series of 300 visual stimuli 255 (85%) were black circles on a white background, and considered the frequent stimulus, 9 cm diameter, 200 ms duration whereas 45 (15%) were back squares on a white background and referred to as the rare stimulus, 9 cm diameter, 200 ms duration] in the center of a computer screen. The results shown an increase of P300 latency in depressive patients during auditory and visual tasks. Non differences were found in reaction time to visual or auditory stimuli. 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.