Memory systems in schizophrenia: Modularity is preserved but deficits are generalized

• Published in: Schizophrenia research 2015-10, Vol.168 (1), p.223-230
• Main Authors: Haut, Kristen M, Karlsgodt, Katherine H, Bilder, Robert M, Congdon, Eliza, Freimer, Nelson B, London, Edythe D, Sabb, Fred W, Ventura, Joseph, Cannon, Tyrone D
• Format: Article
• Language: English
• Subjects: Adult; Attention Deficit Disorder with Hyperactivity - psychology; Bipolar disorder; Bipolar Disorder - psychology; Cognition; Episodic memory; Female; Humans; Male; Memory Disorders - complications; Memory, Episodic; Memory, Short-Term; Middle Aged; Neuropsychological Tests; Principal Component Analysis; Psychiatric Status Rating Scales; Psychiatry; Psychosis; Schizophrenia - complications; Schizophrenic Psychology; Working memory; Young Adult
• ISSN: 0920-9964; 1573-2509
• DOI: 10.1016/j.schres.2015.08.014

Abstract Objective Schizophrenia patients exhibit impaired working and episodic memory, but this may represent generalized impairment across memory modalities or performance deficits restricted to particular memory systems in subgroups of patients. Furthermore, it is unclear whether deficits are unique from those associated with other disorders. Method Healthy controls (n = 1101) and patients with schizophrenia (n = 58), bipolar disorder (n = 49) and attention-deficit–hyperactivity-disorder (n = 46) performed 18 tasks addressing primarily verbal and spatial episodic and working memory. Effect sizes for group contrasts were compared across tasks and the consistency of subjects' distributional positions across memory domains was measured. Results Schizophrenia patients performed poorly relative to the other groups on every test. While low to moderate correlation was found between memory domains ( r = .320), supporting modularity of these systems, there was limited agreement between measures regarding each individual's task performance (ICC = .292) and in identifying those individuals falling into the lowest quintile (kappa = 0.259). A general ability factor accounted for nearly all of the group differences in performance and agreement across measures in classifying low performers. Conclusions Pathophysiological processes involved in schizophrenia appear to act primarily on general abilities required in all tasks rather than on specific abilities within different memory domains and modalities. These effects represent a general shift in the overall distribution of general ability (i.e., each case functioning at a lower level than they would have if not for the illness), rather than presence of a generally low-performing subgroup of patients. There is little evidence that memory impairments in schizophrenia are shared with bipolar disorder and ADHD.