Neurocognitive functioning during symptomatic states and remission in bipolar disorder and schizophrenia: A comparative study

Bipolar disorders and schizophrenia: discrete disorders?

Background

With similarities in heritability, neurobiology and symptomatology, the question has been raised whether schizophrenia and bipolar disorder are truly distinctive disorders or belong to a continuum. This narrative review summarizes common and distinctive findings from genetics, neuroimaging, cognition and clinical course that may help to solve this ethiopathogenetic puzzle.

Methods

The authors conducted a literature search for papers listed in PubMed and Google Scholar, using the search terms "schizophrenia" and "bipolar disorder" combined with different terms such as "genes", "neuroimaging studies", "phenomenology differences", "cognition", "epidemiology". Articles were considered for inclusion if they were written in English or Spanish, published as full articles, if they compared subjects with schizophrenia and bipolar disorder, or subjects with either disorder with healthy controls, addressing differences between groups.

Results

Several findings support the hypothesis that schizophrenia and bipolar disorder are discrete disorders, yet some overlapping of findings exists. The evidence for heritability of both SZ and BD is obvious, as well as the environmental impact on individual manifestations of both disorders. Neuroimaging studies support subtle differences between disorders, it appears to be rather a pattern of irregularities than an unequivocally unique finding distinguishing schizophrenia from bipolar disorder. The cognitive profile displays differences between disorders in certain domains, such as premorbid intellectual functioning and executive functions. Finally, the timing and trajectory of cognitive impairment in both disorders also differs.

Conclusion

The question whether SZ and BD belong to a continuum or are separate disorders remains a challenge for further research. Currently, our research tools may be not precise enough to carve out distinctive, unique and undisputable differences between SZ and BD, but current evidence favors separate disorders. Given that differences are subtle, a way to overcome diagnostic uncertainties in the future could be the application of artificial intelligence based on BigData.

Limitations

Despite the detailed search, this article is not a full and complete review of all available studies on the topic. The search and selection of papers was also limited to articles in English and Spanish. Selection of papers and conclusions may be biased by the personal view and clinical experience of the authors.

Comparison of verbal fluency performance in Kannada-speaking adults with and without euthymic bipolar disorder type 1

Individuals with euthymic bipolar disorder (BD) type I exhibit deficits in executive functions. Although less explored in the BD population, the tasks of verbal fluency (VF) have shown great potential in understanding semantic organization. This study provides an extensive exploration across the letter and semantic VF tasks in 27 demographically matched euthymic BD-I and healthy controls (HC). The groups were compared on measures of the total number of correct words (TNCW), temporal pattern analysis, number of clusters (NC), mean cluster size (MCS), number of switches (NS), and error pattern. An overall reduction in letter fluency scores (the TNCW, number of switches, and NC) as compared to semantic fluency scores was noted for both groups, with a significantly greater decrease in the BD-1 group. The MCS and temporal pattern were relatively similar across the two groups. The influence of education with no gender difference was observed between groups with error types prevalent in both groups. The study findings call attention toward assessing the VF performance in persons with BD in terms of error production and the strategies employed (clustering-switching).

Social cognition and psychosocial functioning in schizophrenia and bipolar disorder: Theory of mind as a key to understand schizophrenia dysfunction

Functional impairment is a common symptom in schizophrenia (SZ) and bipolar disorder (BD). Pharmacological treatments have limited functional recovery in both disorders. Social cognition, a cognitive process, has been associated with functioning in mental disorders. Theory of mind (ToM) is considered a key factor in understanding the social cognitive deficits in SZ and BD. Our study aimed to investigate the relationship between ToM and functioning in SZ, BD, and healthy controls (HC) and compare ToM and functioning impairments between groups. A total of 208 participants (HC n = 69; BD n = 89; SZ n = 50) were evaluated with the Functioning Assessment Short Test (FAST), Reading the Mind in the Eyes Test (RMET), the Vocabulary subtest of the Wechsler Abbreviated Scale for Intelligence (WASI) and the Hopkins Verbal Learning Test - Revised (HVLT-R). Comparisons of RMET between low- and high-functioning individuals and multiple linear regression analyses were conducted for each group. Multiple regression analysis revealed that the association between ToM and psychosocial functioning was observed only in SZ (β = -1.352, p = 0.008). Low-functioning SZ participants showed a lower ToM performance compared to participants with high-functioning SZ (t = 1.80, p = 0.039, Cohen's d = 0.938). No significant associations were found in the other groups. ToM is essential to understand the functional impairment in SZ, more than in BD. Furthermore, ToM may be a primary target for intervention strategies in improving functioning in SZ.

Can neurological soft signs and neurocognitive deficits serve as a combined endophenotype for Han Chinese with bipolar disorder?

BACKGROUND

Bipolar disorder's (BD) potential endophenotypes include neurological soft signs (NSS) and neurocognitive disorders (ND). Few research, meanwhile, has coupled NSS and ND as combined endophenotypes of BD.

OBJECT

This study intends to investigate NSS and ND and compare their differences in euthymic patients with bipolar disorder (EBP), their unaffected first-degree relatives (FDR), and healthy controls (HC). Additionally, search for potential endophenotypic subprojects of NSS and ND and construct and verify a composite endophenotypic.

METHODS

The subjects were all Han Chinese and consisted of 86 EBP, 81 FDR, and 81HC. Cambridge Neurological Inventory and MATRICSTM Consensus Cognitive Battery tested NSS and ND independently.

RESULTS

All three groups displayed a trapezoidal distribution of NSS levels and cognitive abnormalities, with EBP having the most severe NSS levels and cognitive deficits, followed by FDR and HC. Among them, motor coordination in NSS and Information processing speed (IPS), Verbal learning (VL), and Working memory (WM) in neurocognitive function are consistent with the traits of the endophenotype of BD. The accuracy in differentiating EBP and HC or FDRs and HC was higher when these items were combined as predictor factors than in differentiating EBP and FDR.

CONCLUSION

These results provide more evidence that motor coordination, IPS, VL, and WM may be internal characteristics of bipolar disease. When these characteristics are combined into a complex endophenotype, it may be possible to distinguish BD patients and high-risk groups from normal populations.

Neurocognitive and social cognitive impairments in remission and symptomatic states of early-onset schizophrenia spectrum disorders

Previous studies demonstrated neurocognitive impairments in early-onset schizophrenia (EOS) and other psychotic spectrum disorders (PSD). This study aimed to compare remitted and symptomatic cases in terms of neurocognition and theory of mind (ToM). 50 healthy controls (HC) and 106 patients diagnosed schizophrenia in remission (EOS-R, n = 38), symptomatic schizophrenia (EOS-S, n = 34), and other PSD (n = 34) were included in our study. The Positive and Negative Symptom Scale, Columbia-Suicide Severity Rating Scale, Reactive and Proactive Aggression Questionnaire were used to evaluate psychopathology. A cognitive battery was conducted to measure verbal learning/memory, visual learning/memory, executive functions (EF), inhibition, processing speed (PS), verbal fluency skills. Reading Mind in Eyes Test (RMET) and Faux-Pas tests were implemented to assess ToM. Principal Component Analysis was used to identify cognitive domain scores. Patient groups had poorer performance in cognitive domains than the HC group. The cognitive impairment and psychopathology levels of EOS-R and the PSD groups were comparable for all cognitive domains. The EOS-S group also had poorer scores in Rey verbal learning score (d = 0.87), RMET (d = 0.72), verbal fluency (d = 0.66), PS/EF (d = 0.82) and visual learning/memory (d = 0.83) test scores than the PSD group. Only RMET (d = 0.72) and executive function/processing speed domain (d = 0.63) were significantly impaired in the EOS-S group than the EOS-R group Cognitive impairments seen in remitted psychotic disorders were on the same continuum. Impaired EF/PS and ToM skills could be a cognitive marker for symptomatic illness in youth.

Feasibility, Acceptability, and Preliminary Impact of Full-Body Interaction on Computerized Cognitive Training Based on Instrumental Activities of Daily Living: A Pilot Randomized Controlled Trial with Chronic Psychiatric Inpatients

Objective: To conduct a pilot randomized control trial to assess the feasibility and acceptability of full-body interaction cognitive training (FBI-CT) inspired by instrumental activities of daily living in chronic psychiatric inpatients and to explore its preliminary impact on cognitive and noncognitive outcomes. Materials and Methods: Twenty psychiatric inpatients met the inclusion criteria and were randomly allocated to the FBI-CT group (n = 10) or the tablet-based CT group (T-CT) (n = 10). Neuropsychological assessments were performed at baseline, postintervention, and 3-month follow-up. Results: Both groups presented high completion rates at postintervention and follow-up. Participants reported high satisfaction following the interventions, with the FBI-CT group exhibiting slightly higher satisfaction. A within-group analysis showed significant improvements in the FBI-CT group for processing speed and sustained attention for short periods (P = 0.012), verbal memory (P = 0.008), semantic fluency (P = 0.027), depressive symptoms (P = 0.008), and quality of life (P = 0.008) at postintervention. At 3-month follow-up, this group maintained verbal memory improvements (P = 0.047) and depressive symptoms amelioration (P = 0.026). The T-CT group revealed significant improvements in sustained attention for long periods (P = 0.020), verbal memory (P = 0.014), and executive functions (P = 0.047) postintervention. A between-group analysis demonstrated that the FBI-CT group exhibited greater improvements in depressive symptoms (P = 0.042). Conclusions: Overall, we found support for the feasibility and acceptability of both training approaches. Our findings show promise regarding the preliminary impact of the FBI-CT intervention, but due to study limitations such as the small sample size, we cannot conclude that FBI-CT is a more effective approach than T-CT for enhancing cognitive and noncognitive outcomes of chronic psychiatric inpatients. Clinical trials (number: NCT05100849).

The Role of Kynurenines in Cognitive Dysfunction in Bipolar Disorder

INTRODUCTION

Chronic low-grade inflammation is suggested to play a pathophysiological role in bipolar disorder (BD) and its related cognitive dysfunctions. Although kynurenine (KYN) pathway metabolites are key inflammatory mediators, studies investigating the association between KYN metabolism and cognition in BD are scarce. We aimed to explore the relationship between KYN metabolism and cognitive functioning across different mood states in BD.

METHODS

Sixty-seven patients with BD (35 depressed and 32 [hypo] manic) and 29 healthy controls were included. Cognitive functioning was assessed at 3 time intervals (baseline, 4, and 8 months) assessing processing speed, sustained attention, verbal memory, working memory, and response inhibition. Plasma samples for quantification of 3-hydroxykynurenine, quinolinic acid, and kynurenic acid (KYNA) were concurrently provided. Linear mixed models were used for statistical analysis.

RESULTS

The manic group showed deficits in all assessed cognitive domains with the exception of verbal memory at all test moments. The bipolar depression group showed deficits in the processing speed at all test moments. Throughout the whole follow-up period, KYNA was significantly lower in both patient groups than in controls. Only in the bipolar depression group, low KYNA was associated with worse global cognitive functioning (B = 0.114, p = 0.02) and slower processing speed in particular (B = 0.139, p = 0.03).

CONCLUSION

Only in the bipolar depression group, lower KYNA was associated with worse cognitive functioning. Future large-scale longitudinal studies are warranted to confirm the role of KYN metabolites in cognitive impairment in patients with BD and the possible therapeutic implications of this relationship.

Neurocognition, functional outcome, and quality of life in remitted and non-remitted schizophrenia: A comparison with euthymic bipolar I disorder and a control group

There are discrepancies about if the severity of the symptomatology in schizophrenia is related to neurocognitive performance, functional outcome, and quality of life (QoL). Also, there are controversial data about the comparison between euthymic bipolar patients and different subgroups of schizophrenia in neurocognition, functioning, and QoL level. The present study aimed to compare the neurocognitive performance, functional outcome, and QoL of remitted and non-remitted patients with SC with respect to a group of euthymic patients with BD, and a control group. It included 655 subjects: 98 patients with schizophrenia in remission (SC-R), 184 non-remitted patients with schizophrenia (SC-NR), 117 euthymic patients with bipolar I disorder (BD), and 256 healthy subjects. A comprehensive clinical, neurocognitive (six cognitive domains), functional, and QoL assessment was carried out. Remission criteria of Andreasen were used to classify schizophrenia patients as remitted or non-remitted. Compared with control subjects all groups of patients showed impaired neurocognitive performance, functioning and QoL. SC-R patients had an intermediate functioning between control subjects and SC-NR, all at a neurocognitive, functional, or QoL level. There were no significant differences between SC-R and BD. These results suggest that reaching clinical remission is essential to achieve a better level of psychosocial functioning, and QoL. Likewise, the results of this study suggest that euthymic patients with bipolar disorder and patients with schizophrenia in remission are comparable at the neurocognitive and functional levels, which might have implications in the pathophysiology of both disorders.

Graph Analysis of Verbal Fluency Tests in Schizophrenia and Bipolar Disorder

Verbal Fluency Tests (VFT) are one of the most common neuropsychological tasks used in bipolar disorder (BD) and schizophrenia (SZ) research. Recently, a new VFT analysis method based on graph theory was developed. Interpreting spoken words as nodes and every temporal connection between consecutive words as edges, researchers created graph structures, allowing the extraction of more data from participants’ speech, called Speech Graph Attributes (SGA). The aim of our study was to compare speech graphs, derived from Phonemic and Semantic VFT, between SZ, BD, and healthy controls (HC). Twenty-nine SZ patients, twenty-nine BD patients, and twenty-nine HC performed Semantic and Phonemic VFT. Standard measures (SM) and 13 SGA were analyzed. SZ patients’ Semantic VFT graphs showed lower total word count and correct responses. Their graphs presented less nodes and edges, higher density, smaller diameter, average shortest path (ASP), and largest strongly connected component than the HC group. SM did not differentiate BD and HC groups, and patients’ Semantic VFT graphs presented smaller diameter and ASP than HC. None of the parameters differentiated BD and SZ patients. Our results encourage the use of speech graph analysis, as it reveals verbal fluency alterations that remained unnoticed in the routine comparisons of groups with the use SM.

Early Recognition Method - Amplifying relapse management in community mental health care; a comprehensive study of the effects on relapse and readmission

This naturalistic multicenter study explored the relationship between participating in the Early Recognition Method (ERM) intervention and relapse, defined as spending at least one night at a psychiatric ward. The intervention was tailored to adult patients with schizophrenia or bipolar disorder in an outpatient mental health care setting. Before the intervention, the staff received training in application of the strategy. The ERM strategy is protocolized and includes identification and monitoring of individual early warning signs and development of a personal plan of action. The study showed a reduction in mean number and duration of readmissions during the period the patients participated in the intervention, compared to an equal pre-intervention period. For patients with bipolar disorder the reduction was statistical significant. The difference in outcome between the two diagnostic groups suggests that further tailoring of the application of the ERM strategy might improve the relapse prevention outcome.