Temporospatial characterization of brain oscillations (TSCBO) associated with subprocesses of verbal working memory in schizophrenia

The studies of the neural correlates of verbal working memory in schizophrenia are somewhat inconsistent. This could be related to experimental paradigms that engage differentially working memory components or methodological limitations in terms of characterization of brain activity. Magnetoencephalographic recordings were obtained on 10 schizophrenia patients and 11 healthy controls while performing a modified Sternberg paradigm to investigate subprocesses of verbal working memory. A new method for temporospatial characterization of brain oscillations was applied to whole head recordings and a 1-48 Hz frequency range. Patients differed from controls in event-related synchronization/ desynchronization (ERS/ERD) patterns during the encode phase, the mid-maintain phase, and the end of the maintain phase. During the encode phase, patients did not show 1-4 Hz ERS in the left anterior frontal and left parietal lobes. In the mid-maintain phase, the left anterior frontal and left parietal lobes 1-4 Hz ERS, and the bilateral occipital lobes 8-32 Hz ERS were not observed in patients. At the end of the maintain phase, patients did not exhibit 12-48 Hz ERD in the left frontal and parietal lobes. The behavioral data showed reduced primacy effect. In schizophrenia, the encode and maintain subprocesses were associated with less ERS and less ERD, respectively. These ERS/ERD abnormalities had specificity in terms of frequency and spatial location. Less ERD reflects reduced complexity of the neural activity, while reduced ERS reflects failure of the neural systems to resume idle state. The impaired primacy effect appears related to specific ERS/ERD patterns in the encode and maintain phases.