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. 2020 Oct:224:126-132.
doi: 10.1016/j.schres.2020.09.015. Epub 2020 Oct 21.

Inefficient visual search strategies in the first-episode schizophrenia spectrum

Alfredo L Sklar  1 , Brian A Coffman  1 , Gretchen Haas  2 , Avniel Ghuman  3 , Raymond Cho  4 , Dean F Salisbury  5
Affiliations

Inefficient visual search strategies in the first-episode schizophrenia spectrum

Alfredo L Sklar et al. Schizophr Res. 2020 Oct.

Abstract

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.

Keywords: First-episode; Magnetoencephalography; N2pc; Schizophrenia spectrum; Selective attention; Visual search.

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Conflict of interest statement

Declaration of competing interest None of the authors reported any biomedical financial interests or potential conflicts of interest.

Figures

Figure 1.
Figure 1.
Target detection task depicting pop-out and serial search conditions. Participants were instructed to identify the target annulus based on the color cue then indicate via button-press the side on which the gap appears on the target.
Figure 2.
Figure 2.
N2pc Difference waveforms for healthy control (HC) and first-episode psychosis (FESz) participants derived from pop-out and serial search conditions (A). Un-subtracted, grand average waveforms elicited in response to ipsilateral and contralateral targets for HC (B) and FESz (B) participants. The grey box indicates the 225 – 275ms N2pc mean amplitude time-window.
Figure 3.
Figure 3.
(A) The intraparietal sulcus (IPS) and lateral occipital complex (LOC) ROIs selected for analysis of cortical source reconstructions. N2pc-related activity during pop-out (HC (B); FESz (C)) and serial search (HC (D); FESz (E)). Due to the subtraction used to generate N2pc-related activity (i.e., LVF – RVF), negative (blue) values on LH and positive (red) values on RH reflect greater activity. LH values were inverted in the quantification for purposes of comparison. dSPM values reflect averages over the 225–275ms time-window.
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