ERP/CSD indices of impaired verbal working memory subprocesses in schizophrenia

To disentangle subprocesses of verbal working memory deficits in schizophrenia, long EEG epochs (410 s) were recorded from 13 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 to sharpen 31-channel topographies. Patients showed poorer performance and reduced left inferior parietotemporal P3 source. Build-up of mid-frontal negative slow wave (SW) in controls during 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. Midfrontal SW sinks (encoding and retention periods) and posterior SW sinks and sources (encoding only) were related to performance in controls only. Data suggest disturbed processes in a frontal-parietotemporal network in schizophrenia, affecting encoding and early item storage. Descriptors: Schizophrenia, Working memory, Event-related potential (ERP), Principal components analysis (PCA), Current source density (CSD), Laplacian, Slow wave (SW)