Impaired relational memory in the early stage of psychosis

Abstract

Background: Humans constantly take in vast amounts of information, which must be filtered, flexibly manipulated, and integrated into cohesive relational memories in order to choose relevant behaviors. Relational memory is impaired in chronic schizophrenia, which has been linked to hippocampal dysfunction. It is unclear whether relational memory is impaired in the early stage of psychosis.

Methods: We studied eye movements during a face-scene pairs task as an indirect measure of relational memory in 89 patients in the early stage of psychosis and 84 healthy control participants. During testing, scenes were overlaid with three equally-familiar faces and participants were asked to recall the matching (i.e. previously-paired) face. During Match trials, one face had been previously paired with the scene. During Non-Match trials, no faces matched the scene. Forced-choice explicit recognition was recorded as a direct measure of relational memory.

Results: Healthy control subjects rapidly (within 250-500 ms) showed preferential viewing of the matching face during Match trials. In contrast, preferential viewing was delayed in patients in the early stage of psychosis. Explicit recognition of the matching face was also impaired in the patient group.

Conclusions: This study provides novel evidence for a relational memory deficit in the early stage of psychosis. Patients showed deficits in both explicit recognition as well as abnormal eye-movement patterns during memory recall. Eye movements provide a promising avenue for the study of relational memory in psychosis, as they allow for the assessment of rapid, nonverbal memory processes.

Keywords: Associative memory; Eye movements; First episode; Hippocampus; Schizophrenia.

Figure 1.

Average viewing times by group of faces (A-B) and background scenes (C). During Match trials (A), healthy control subjects spent most of the 10 s trial viewing the matching face, relative to the non-matching faces. This preferential viewing was reduced in early psychosis patients. During Non-Match trials (B), a control condition where none of the three faces had been previously matched with the background scene, both groups viewed each of the three displayed faces similarly, suggesting preferential viewing during Match trials was indicative of memory processes. When there were no matching faces on which to fixate, healthy control subjects spent more time viewing the background scene than early psychosis patients (C; Non-Match trials). Error bars show the 95% confidence interval. Match face (M); Non-Match face (NM); Upper Left face (UL); Upper Right face (UR); Bottom face (B).

Figure 2.

Average proportion of viewing time for display elements by group over the 10 s trial (A) and during the initial 2 s of each trial (B). Shaded regions show the 95% confidence interval. Asterisks denote viewing greater than chance (33%) for each individual time bin during the first 2 s of display, p < 0.05, Bonferroni-corrected. Preferential viewing of the matching face was stronger in healthy control subjects compared to early psychosis patients (70 - 85% vs. 50 - 70%, respectively), with healthy control subjects showing a faster onset of preference compared to early psychosis patients (250 ms vs. 1000 ms, respectively).

Figure 3.

Correct trials only analysis. Average proportion of viewing time for display elements for all correct trials by group over the entire 10 s trial (A) and the first 2 s of each trial (B). Error bars show the 95% confidence interval. Asterisks denote viewing greater than chance (33%) for each individual time bin during the first 2 s of display, p < 0.05, Bonferroni-corrected. Similar to the analysis of all trials, healthy control subjects showed rapid preferential viewing (250 ms) of the matching face (B), with consistent preference for the matching face at 75% to 85% throughout the 10 s trial (A). For early psychosis patients, preferential viewing occurred earlier than in all trials (750 ms; B), and although consistent at 60% to 80% throughout the 10 s trial, remained lower than the healthy control group (A). These data indicate that for the early psychosis group, eye movement measures of relational memory are abnormal relative to healthy control subjects, even for trials on which the face-scene pair is successfully identified during a subsequent recognition memory test.