ERP/CSD Indices of Impaired Verbal Working Memory Subprocesses in Schizophrenia

Jürgen Kayser^1,2, Craig E. Tenke^1,2, Nathan A. Gates², Chris J. Kroppmann², Roberto B. Gil^1,3, Gerard E. Bruder^1,2

¹Department of Psychiatry, College of Physicians and Surgeons of Columbia University, USA; ²Department of Biopsychology and ³Clinical Psychobiology, New York State Psychiatric Institute, New York, USA

Received 12 October 2005; revised 27 January 2006; accepted 10 March 2006. 

Abstract

To disentangle cognitive subprocesses of verbal working memory deficits in schizophrenia, long EEG epochs (>10 s) were recorded from 13 schizophrenia patients and 17 healthy adults during a visual Word Serial Position Test. ERP generator patterns were summarized by temporal PCA from reference-free current source density (CSD) waveforms so as to sharpen 31-channel topographies. Patients showed poorer performance and reduced left inferior parietotemporal P3 source activity after each word presentation. Build-up of mid-frontal negative slow wave (SW) in controls during the initial word series, which requires item encoding, integration and active maintenance, was absent in patients, whereas a sustained mid-frontal SW sink during the retention interval was comparable across groups. Mid-frontal SW sinks during retention and encoding periods and posterior SW sinks and sources during the encoding interval were significantly related to performance in controls but not patients. Data suggest verbal working memory deficits in schizophrenia involve disturbed processes in a frontal-parietotemporal network, affecting encoding and early item storage.

Key Words: schizophrenia; working memory; event-related potential (ERP); Principal Components Analysis (PCA); Current Source Density (CSD)