Inefficient visual search strategies in the first-episode schizophrenia spectrum.

BACKGROUND

Knowledge is lacking regarding deficits in selective attention and their underlying biological mechanisms during early stages of schizophrenia. The present study examined the N2pc, a neurophysiological index of covert spatial attention, and its cortical sources at first psychotic episode in the schizophrenia spectrum (FESz).

METHODS

Neurophysiological responses measured simultaneously with magnetoencephalography (MEG) and electroencephalography (EEG) during pop-out and serial search tasks were compared between 32 FESz and 32 matched healthy controls (HC). Mean scalp-recorded N2pc was measured from a cluster of posterior-lateral EEG electrodes. Cortical source-resolved MEG activity contributing to the N2pc signal was derived for the intraparietal sulcus (IPS) and lateral occipital complex (LOC).

RESULTS

Group differences in EEG N2pc varied by task demand. FESz exhibited reduced N2pc amplitude during pop-out (p < .01), but not serial search (p = .11). Furthermore, group differences in N2pc-related MEG cortical activity varied by task demand and cortical region. Compared to HC, FESz exhibited greater IPS during serial search (p < .01).

DISCUSSION

Reductions in EEG N2pc amplitude indicate an impairment of visuo-spatial attention evident at an individual's first psychotic episode, specifically during conditions emphasizing bottom-up processing. Examination of its cortical sources with MEG revealed that, compared to HC, FESz engaged parietal structures to a greater extent during the serial search condition. This pattern suggests a less efficient, more resource intensive strategy employed by FESz in response to a minimal demand on attention. The greater reliance on this controlled attentional network may negatively impact real-world functions with much greater complexity and attentional demands.