Psychotic Experiences and Neuropsychological Functioning in a Population-based Sample

Importance: Psychotic experiences in early life are associated with neuropsychological impairment and the risk for later psychiatric disorders. Psychotic experiences are also prevalent in adults, but neuropsychological investigations spanning adulthood are limited, and confounding factors have not been examined rigorously.

Objective: To characterize neuropsychological functioning in adults with psychotic experiences while adjusting for important sociodemographic characteristics and familial factors and investigating the effect of age.

Design, Setting, and Participants: The South East London Community Health (SELCoH) study is a population-based household survey of physical and mental health in individuals 16 years or older conducted from June 1, 2008, to December 31, 2010, in 2 London boroughs. The study included 1698 participants from 1075 households. Data were analyzed from May 6, 2014, to April 22, 2015.

Exposures: Psychotic experiences measured using the Psychosis Screening Questionnaire.

Main Outcomes and Measures: Neuropsychological functioning measured using tests assessing verbal knowledge (Wechsler Test of Adult Reading), working memory (Spatial Delayed Response Task), memory (Visual Object Learning Task), and processing speed (digit symbol coding task). A composite IQ score of general cognitive ability was calculated.

Results: A total of 1677 participants with a mean (SD) age of 40 (17) years were included in the analysis. Compared with the group without psychotic experiences, the 171 (9.7%) adults with psychotic experiences did not show a statistically significant impairment on mean (SD) measures of IQ (95.25 [16.58] vs 100.45 [14.77]; Cohen d, -0.22; P = .06) or processing speed (40.63 [13.06] vs 42.17 [13.79]; Cohen d, -0.03; P = .73) but were impaired on measures of verbal knowledge (31.36 [15.78] vs 38.83 [12.64]; Cohen d, -0.37; P = .003), working memory (20.97 [4.12] vs 22.51 [3.26]; Cohen d, -0.34; P = .005), and memory (43.80 [8.45] vs 46.53 [7.06]; Cohen d, -0.28; P = .01). Only participants 50 years and older with psychotic experiences showed medium to large impairments in neuropsychological functioning (mean [SD]) on measures of IQ (81.22 [15.97] vs 91.28 [14.31]; Cohen d, -0.70), verbal knowledge (28.31 [13.83] vs 38.51 [11.50]; Cohen d, -0.88), working memory (19.11 [4.77] vs 21.99 [3.42]; Cohen d, -0.82), and memory (39.17 [8.23] vs 44.09 [6.51]; Cohen d, -0.45) after adjusting for socioeconomic status, cannabis use, and common mental disorders. Medium impairments (mean [SD]) on measures of working memory (21.27 [3.64] vs 22.62 [2.97]; Cohen d, -0.45) and memory (44.32 [5.84] vs 46.91 [5.74]; Cohen d, -0.45) were seen in those aged 35 to 49 years and on a measure of verbal knowledge (30.81 [14.17] vs 37.60 [10.48]; Cohen d, -0.62) in those aged 16 to 24 years. First-degree relatives of adults with psychotic experiences showed a small impairment on a measure of verbal knowledge (34.71 [12.10] vs 38.63 [10.97]; Cohen d, -0.36; P = .02), and unrelated cohabitants showed no neuropsychological impairment.

Conclusions and Relevance: The profile of cognitive impairment in adults with psychotic experiences differed from that seen in adults with psychotic disorders, suggesting important differences between subclinical and clinical psychosis.