Working memory dysfunction in schizophrenia patients with obsessive-compulsive symptoms: an fMRI study

BACKGROUND

A substantial proportion of schizophrenia patients also meets DSM-IV criteria for obsessive-compulsive disorder (OCD). Schizophrenia with OCD ("schizo-obsessive") patients are characterized by distinct clinical characteristics, treatment response and prognosis. Whether schizo-obsessive patients exhibit a distinct pattern of brain activation is yet unknown. To address this question, the present functional magnetic resonance imaging (fMRI) study explicitly compared alterations in brain activation and functional connectivity (FC) underlying a working memory deficit in schizophrenia patients with and without OCD.

METHODS

fMRI was applied during the N-back working memory (WM) task in three groups: schizo-obsessive (n=16), schizophrenia (n=17) and matched healthy volunteers (n=20). WM-related activation in the right dorsolateral prefrontal cortex (DLPFC) and the right caudate nucleus, brain areas relevant to schizophrenia and OCD, and FC analysis were used for the evaluation.

RESULTS

The two schizophrenia groups with and without OCD exhibited a similar reduction in activation in the right DLPFC and right caudate, as well as decreased FC compared to the healthy controls. Notably, reduced regional brain activation was not related to severity of schizophrenic or OCD symptoms.

CONCLUSIONS

Schizo-obsessive patients do not differ from their non-OCD schizophrenia counterparts in brain activation patterns during the N-back WM task. Cognitive paradigms taping alternative neural networks (e.g., orbitofrontal cortex) particularly relevant to OCD, are warranted in the search for potential distinctive brain activation patterns of the schizo-obsessive subgroup.

Neural modulations in processing of natural information in patients with schizophrenia and their unaffected siblings

Recent studies in healthy populations have shown a hierarchical network of brain areas to process information over time. Specifically, we revealed that the capacity to accumulate information changes gradually from the early sensory areas toward high-order perceptual and cognitive areas. Previous research in schizophrenia pointed to impairment in comprehension of information. Yet, the neural mechanisms underlying the breakdown of information processing are poorly known. Better understanding of the neural circuits involved in information processing may assist in early identification of predisposition to the disease. Using fMRI, we examined different levels of information comprehension elicited by naturally presented stimuli. Healthy participants, patients with first episode schizophrenia and their undiagnosed siblings listened to a real-life narrated story and scrambled versions of it. To estimate the level of synchronization in response time courses, we calculated inter-subject correlation (inter-SC) across the entire stimuli within each group. The time-scale gradients found in healthy and siblings groups were consistent with our previous findings. Within the schizophrenia group, the reliability patterns obtained for the shortest and intermediate temporal scales were similar to patterns observed in healthy groups. However, the analysis of responses to story condition (long temporal scale) revealed robust and widespread disruption of the inter-SC. In comparison to healthy groups, the response time courses to the story were highly variable within the schizophrenia group, although some significant inter-SCs in the TPJ and precuneus were found. The hierarchical temporal deficit is a fundamental trait that may be a better target for the study of the etiology and pathophysiology of the disease.

Disclosure of interest

The authors have not supplied their declaration of competing interest.