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Original Investigation
February 2016

Psychotic Experiences and Neuropsychological Functioning in a Population-based Sample

Author Affiliations
  • 1Department of Psychosis Studies, Institute of Psychiatry, Psychology, and Neuroscience, King’s College London, London, England
  • 2Department of Health Services and Population Research, Institute of Psychiatry, Psychology, and Neuroscience, King’s College London, London, England
  • 3Department of Psychological Medicine, Institute of Psychiatry, Psychology, and Neuroscience, King’s College London, London, England
  • 4Department of Psychiatry, Yale University, New Haven, Connecticut
  • 5Department of Psychiatry, Icahn School of Medicine at Mount Sinai, New York, New York
  • 6Department of Preventive Medicine, Icahn School of Medicine at Mount Sinai, New York, New York
  • 7Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, New York
JAMA Psychiatry. 2016;73(2):129-138. doi:10.1001/jamapsychiatry.2015.2551
Abstract

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.

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