The Relationship Between Intrinsic Motivation and Neurocognition in Individuals with Schizophrenia and Comorbid Substance Use Disorders

Purpose: Schizophrenia is characterized by deficits in intrinsic motivation (IM) and decrements in neurocognition that span across functional subdomains such as vigilance, verbal memory, working memory, reasoning, and processing speed.  While recent studies show deficits in IM and neurocognition exact functional consequences in schizophrenia, not one of these investigations has examined relations between IM and neurocognition in individuals with schizophrenia and comorbid substance use disorders (SUDs). Examining such relations in adults with schizophrenia and comorbid SUDs is critical as this comorbidity impedes recovery and little is known about the impact of IM on neurocognitive performance in this population.  For a sample of adults with schizophrenia and comorbid SUD, we examined whether IM is a salient predictor of neurocognitive performance, and then explored whether this relationship varied across SUD subgroups.

Method:  Five hundred thirty five (n = 119 alcohol use disorder; n = 183 substance use disorder; n = 233 alcohol/substance use disorder) adults with schizophrenia and comorbid SUD completed a neuropsychological battery at baseline of the Clinical Antipsychotic Trials of Intervention Effectiveness. IM was measured by summing two items (purpose and motivation) of the Quality of Life Scale.  Mixed-effects models examined relations between IM and neurocognition (composite and subdomains: vigilance, verbal memory, working memory, reasoning, and processing speed). Hochberg’s correction adjusted for multiple inference testing.

Results:  In the overall sample, a significant positive prediction of neurocognition composite scores was observed by IM scores (corrected, p < .001).  This pattern of significant results was observed across all neurocognition subdomain scores by IM scores (all corrected, p < .004), except no significant positive prediction of reasoning scores was observed by IM scores (corrected, p = .219) in the overall sample.  Variability in this pattern of results was subsequently observed across SUD subgroups. No significant positive prediction of neurocognition composite or subdomain scores was observed by IM scores in the subgroup with alcohol/substance use disorders (all corrected, p > .090). Such a pattern of null results was largely observed in the subgroup with alcohol use disorders for relations between IM and neurocognition composite/ subdomain scores (all corrected, p > .143), except a significant positive prediction of processing speed scores was observed by IM scores (corrected, p = .020). Finally, in the subgroup with substance use disorders, a significant positive prediction of neurocognition composite scores and all subdomain scores by IM scores was observed (corrected, p < .021), except no significant positive prediction of reasoning scores was observed by IM scores (corrected, p = .475).

Implications:  Results revealed IM is a salient predictor of neurocognitive performance in schizophrenia and comorbid SUD.  Post-hoc analyses showed neurocognitive outcomes varied by SUD diagnosis, such that the subgroup with substance use disorders largely accounted for the significant prediction of neurocognition composite/subdomain scores by IM scores observed. Social workers should focus on treatment development efforts that seek to improve the low base rates of IM in those with alcohol use disorders and alcohol/substance use disorders, which may lessen the impact neurocognitive deficits have on this population.