Abstract

Background: Reduced WM is a primary cognitive deficit in schizophrenia. To better determine its functional and neuroanatomical origin (cortical activation during encoding, retention, or retrieval), advanced analytic techniques (current source density, CSD; principal components analysis, PCA; CSD animations) were used to exploit the high temporal resolution underlying 31-channel ERP topographies obtained during a verbal WM task based on the Word Serial Position Test (Wexler et al. 1998). Methods: Long EEG epochs (> 10 s; 0.01 Hz high pass) were recorded from 13 schizophrenic (9 male) and 17 healthy adults (8 male) during 128 visual trials consisting of 4 initial words (500 ms exposure, 1,500 ms SOA), a retention period requiring storage of the word sequence (4,500 ms), a probe word (500 ms), and a delayed button press to indicate its correct position. Reference-free CSDs of ERP waveforms were submitted to unrestricted, covariance-based, and Varimax-rotated PCA to identify and measure relevant neuronal generator patterns. Results: Poorer performance in patients (72.9±14.3% vs. 88.2±10.8% correct, p<0.01) was paralleled by reduced stimulus-related, left-lateralized (inferior-parietal) P3 source asymmetry (p<0.01) and amplitude (p<0.05) during encoding and retrieval. Healthy adults evidenced a sustained increase in mid-frontal sink activity during word encoding (up to 6 s), which was absent in patients (p<0.01). In contrast, a sustained frontocentral sink during the retention period and early, left-lateralized (inferior-parietal) N1 sinks were similar across groups. Conclusions: Electrophysiologic correlates of visual verbal WM deficits in schizophrenia suggest a complex disturbance in functional neuronal network processes, primarily affecting the encoding of successive stimuli.

Reference

Wexler BE, Stevens AA, Bowers AA, Sernyak MJ, Goldman Rakic PS (1998). Word and tone working memory deficits in schizophrenia. Arch Gen Psychiatry 55(12):1093-1096.