The comparison of neurocognition and neuroimaging in bipolar disorder patients with and without psychotic symptoms: A controlled study with schizophrenia patients

Objective: This study aims to investigate the neurophysiopathology of schizophrenia (Sch) and bipolar disorder (BD), which are considered to exist on a continuum in terms of their neurodevelopmental origins. It seeks to reveal developmental differences in the brain while considering the role of the central nervous system (CNS). Materials and Methods: The research group included patients diagnosed with remitted bipolar disorder with psychotic features (P-BD) according to DSM-5 criteria. The control group consisted of remitted schizophrenia (Sch) patients and bipolar disorder patients without psychotic features (NP-BD). Mood symptoms in BD patients were assessed using the Hamilton Depression Rating Scale (HAM-D-17) and the Young Mania Rating Scale (YMRS), while psychotic symptoms in Sch patients were evaluated using the Positive and Negative Syndrome Scale (PANSS). The neurocognitive test battery included the WAIS Digit Symbol and Digit Span Tests, Stroop Test, Wisconsin Card Sorting Test (WCST), Continuous Performance Test (CPT), Trail Making Test (TMT), Rey Auditory Verbal Learning Test, Facial Emotion Recognition and Discrimination Tests, and the WAIS-R Vocabulary Subtest. T1-weighted volumetric magnetic resonance images of all participants were acquired at the Radiology Department of Manisa Celal Bayar University (MCBU) using a 1.5 Tesla GE Signa HDxt device. Structural imaging analyses were conducted using the vol2Brain software. Statistical analyses were performed with the R statistical software package via the Jamovi platform. Results: 130 No significant differences were found between the groups in terms of sociodemographic data, except for age. The 'TMT A Completion Time' was significantly longer in the Sch group compared to the NP-BD group. The 'TMT B Completion Time' was significantly longer in the Sch group compared to the P-BD group. In terms of the 'Rey 1-5 Total Recall' and 'Rey 6 Recall' scores, the Sch group recalled significantly fewer words compared to the NP-BD group. The P-BD group scored significantly higher than the Sch group on the CPT 'Correct Rejections' and 'Hit Rate' scores. When 'Commission Errors' were examined, the Sch group made significantly more errors than the P-BD group. In terms of brain structure volumes, the P-BD group had significantly larger volumes in the total anterior insula, right anterior insula, total vermis, cerebellar vermal lobules I-V and VIII-X, and total occipital pole compared to the Sch group. The right parietal operculum volume was statistically significantly larger in the NP-BD group compared to the P-BD group. The parameters that were found to be significant were subjected to multinomial logistic regression analysis, considering confounding factors such as patient age, illness duration, number of hospitalizations, and history of electroconvulsive therapy (ECT). After the analysis, the significance of the TMT A, Rey 1-5 Total Recall, Rey 6 Recall tests, and the volumes of the total vermis, total occipital pole, cerebellar vermal lobules VIII-X, total anterior insula, right anterior insula, and right parietal operculum remained significant. Conclusion: Our findings suggest that the central nervous system (CNS) is not sufficiently effective in differentiating between schizophrenia (Sch) and bipolar disorder (BD). Instead, they highlight neurobiological differences between these two disorders, indicating that their neurodevelopmental processes follow distinct pathways, independent of the CNS. This supports the hypothesis that Sch and BD are part of a broader psychotic spectrum. In conclusion, this study makes a significant contribution to understanding the neurobiological differences between Sch and BD and provides a foundation for future research. Keywords: Bipolar Disorder, Schizophrenia, Schneiderian First-Rank Symptoms, Neuroimaging, Neurocognition