Mémoire émotionnelle et activités électrocorticales en schizophrénie Emotional Memory and Electrocortical Activity in Schizophrenia

Résumé

Contexte L’altération des fonctions émotionnelles ainsi que de la mémoire des personnes atteintes de schizophrénie est connue depuis plus d’un siècle. Toutefois, les structures cérébrales touchées ainsi que les stades de traitement affectés restent encore mal compris.

Objectif Approfondir de quelles façons la valence et l’activation émotionnelle affectent la mémoire épisodique et l’activité cérébrale associée chez des patientes atteintes de schizophrénie.

Hypothèse L’activité des régions frontales associées à certains types de stimuli émotifs sera généralement affectée dans la population clinique, et ce, en réponse aux stimuli à fortes activations émotionnelles.

Participantes Seize patientes atteintes de schizophrénie dans une phase stable de leur maladie furent appariées à 17 participantes contrôles sur la base de l’âge, de la dominance manuelle et du statut socio-économique.

Instrument et mesures L’EEG a été enregistré à partir de 60 électrodes fixées dans un casque en lycra élastique. Ces signaux ont été moyennés pour obtenir les composantes N200, P300, ainsi que la LPC afin de cibler les processus mnésiques et émotionnels.

Résultats Pour la N200 et la P300 frontale, la magnitude de l’effet de mémoire observé chez les patientes schizophrènes est augmentée significativement dans l’hémisphère frontal droit en réponse aux stimuli à valences déplaisantes, alors que l’augmentation de cet effet s’effectue dans les deux hémisphères chez les participantes contrôles.

Conclusion Une altération électrocorticale précoce reflétant la familiarité et la mémoire aux stimuli déplaisants est présente chez les patientes, alors que les processus tardifs de récollection consciente (LPC pariétale) ne seraient pas atteints.

Mots-clés :

• mémoire,
• émotions,
• potentiels évoqués cognitifs,
• schizophrénie,
• ERP

Abstract

Context Abnormal emotion processing is frequent in schizophrenia and affects social and functional outcome. Past event-related potential (ERP) research investigating processing of affective stimuli in schizophrenia was done mainly with facial expressions and revealed impaired facial emotion recognition in patients relative to control subjects. Experimentations involving fMRI with this group of patients, showed alteration of limbic and frontal regions in response to emotional unpleasant images, compared to neutral stimuli during a memory task. Other studies have also noted an increase in brain activity when the activation of the stimuli was high compared to low arousal stimuli. This may indicate a different sensitivity threshold to emotional arousal and emotional valence involving frontal pathways in these patients. But very few studies attempted to separate the contributions of emotional valence and arousal within an episodic memory protocol with ERP, in that population.

Goal The aim of the current research is to investigate brain electro-cortical activity in schizophrenia in response to emotional images during an episodic memory task.

Method ERP components were analyzed in 16 schizophrenic and 17 control participants matched for age, sex and intelligence. ERPs were obtained from 56 EEG electrodes. The tasks consisted in a classical episodic memory task that presented 100 repeated old and 100 new photographic images divided into four categories (unpleasant-high arousal, unpleasant-low arousal, pleasant-high arousal and pleasant-low arousal) selected from the International Affective Picture System. The N200, P300 and late positive component (LPC) mean amplitude, were analyzed using repeated-measure analyses of variance (MANOVA).

Results Patients with schizophrenia and control subjects gave comparable subjective evaluations of arousal and valence. However, the frontal N200 and the P300 both showed an interaction of the group x memory x valence x hemisphere (F [1.32]=8.36; p <.01). Thus, this complex interaction denotes an increase of the episodic memory effect in the right hemisphere in response to unpleasant stimuli, with schizophrenic patients. With respect to the control group, there is also an increase of this memory effect in the right hemisphere, but in response to pleasant stimuli. The schizophrenic patients presented a smaller LPC memory effect, especially at the frontal region. More specifically, the frontal LPC was reduced, and the clinical group was less reactive to the emotional arousal content, compared to the control group.

Discussion Altogether, our results revealed that while the subjective evaluation of emotional pictures is equivalent across groups, cerebral differences are present in schizophrenic patients during emotional recognition. N200 and P300 results in the frontal region suggest impaired selective attention and episodic memory to unpleasant stimuli in patients, while later processes related to conscious recollection (parietal LPC) are not affected with patients affected with schizophrenia.

Conclusion This finding provides further support for the notion of a possible discrepancy between the subjective experience and the physiological expression of emotions in schizophrenia patients. Those results could open the door to new clinical research investigations in psychiatry, particularly in the comprehension of a relationship between frontal cortex vulnerability and episodic memory often present in psychosis.

Keywords:

• schizophrenia,
• psychosis,
• event-related potentials,
• memory,
• emotion,
• valence,
• arousal