Event-related oscillations during working memory tasks in schizophrenic patients and healthy controls

Schmiedt, C.1,2, Brand, A.3, Hildebrandt, H.4, and Basar-Eroglu, C.2
1Department of Neuropsychology and Behavioral Neurobiology, University of Bremen, Germany; 2Institute of Psychology and Cognition Research, University of Bremen, Germany; 3General Hospital Bremen-Ost, Center for Psychiatry and Psychotherapie, Germany; 4General Hospital Bremen-Ost, Clinic for Neurology, Germany
E-mail: cschmiedt@uni-bremen.de

Recent findings substantiate the view that event-related oscillations (EROs) are functionally involved in cognitive processing [1,2,3]. For example there are many observations that imply a connection between especially frontal theta oscillations, information coding and function of working memory (WM). In order to examine differences in neurophysiological changes associated with WM-load between schizophrenic patients (n=10) and matched controls (n=10), we recorded ERPs (Fz,Cz,Pz,Oz,F3,F4,T5,T6) during a n-back WM task, and a control task for simple actions. The data were analysed by means of Fast Fourier Transform (FFT) and digitally filtered in different frequency bands.

The behavioral data showed that the patients had longer reaction times in all tasks as well as poorer performance accuracy in the one- and two-back tasks. The results of the EROs analyses presented a gradual increase of theta and gamma oscillations after stimulus onset with WM-load in controls, whereas in the schizophrenics patients reduced fronto-central theta was observed. However, gamma oscillations with high amplitude values were found without any specific topographic differences, which remained constant over all task conditions.

Our results show a selectively distributed, task-related oscillatory system in controls during WM demand. Therefore, the observed task-unrelated distribution of oscillatory activity in patients can be interpreted as a disorder of this system and this may be one of the possible explanations for a general brain dysfunction in schizophrenia.

[1] Basar E., et al. (2001) Int. J. Psychophys., 39, 241-248. [2] González-Hernández J., et al. (2003) Int. J. Psychophys., 48, 11-24. [3] Klimesch W. (1999) Brain Res. Rev., 29, 169-195.