Abnormal resting-state functional connectivity underlies cognitive and clinical symptoms in patients with schizophrenia

Brain Network Resilience and Cognitive Function in Patients with First Episode Schizophrenia Spectrum Disorders

BACKGROUND

First-episode schizophrenia spectrum disorders (FESSDs) are associated with significant cognitive impairment that affects daily functioning. While these deficits are well-documented, the neural mechanisms underlying the cognitive impairment in FESSDs remain limited. As the structure robustness and resilience of the brain network in healthy population are reported to be associated with cognitive function, we examined these associations in FESSDs.

METHODS

This study investigated the relationships of the structure robustness and resilience of the core brain network with cognitive function and psychopathology in patients with FESSDs (n = 340) using data from two independent cohorts in South Korea and China. Age- and sex-matched HC (n = 420) were also recruited. We applied advanced k-shell decomposition techniques to functional brain networks and estimated various measures of structure robustness and resilience.

RESULTS

Patients with FESSDs had brain networks with a less robust structure and resilience than those of HC. Resilience measures were positively correlated with executive function in patients. Core brain network structure and k-core resilience were negatively correlated with the Positive and Negative Syndrome Scale scores. Subgroup analysis showed that structure robustness and resilience at each site matched the main analysis, but correlations with cognitive function and psychopathology were observed only in the South Korea cohort.

CONCLUSIONS

Better preservation of brain network structure and resilience is associated with higher cognitive function and milder clinical symptoms in patients with FESSDs. This highlights potential targets for therapeutic interventions aimed at enhancing cognitive function and improving the symptoms of FESSDs.

Aberrant Functional Connectivity and Brain Network Organization in High-Schizotypy Individuals: An Electroencephalography Study

BACKGROUND AND HYPOTHESIS

Oscillatory synchrony plays a crucial role in establishing functional connectivity across distinct brain regions. Within the realm of schizophrenia, suggested to be a neuropsychiatric disconnection syndrome, discernible aberrations arise in the organization of brain networks. We aim to investigate whether the resting-state functional network is already altered in healthy individuals with high schizotypy traits, highlighting the pivotal influence of brain rhythms in driving brain network alterations.

STUDY DESIGN

Two-minute resting-state electroencephalography recordings were conducted on healthy participants with low and high schizotypy scores. Subsequently, spectral Granger causality was used to compute functional connectivity in theta, alpha, beta, and gamma frequency bands, and graph theory metrics were employed to assess global and local brain network features.

STUDY RESULTS

Results highlighted that high-schizotypy individuals exhibit a lower local efficiency in theta and alpha frequencies and a decreased global efficiency across theta, alpha, and beta frequencies. Moreover, high schizotypy is characterized by a lower nodes' centrality and a frequency-specific decrease of functional connectivity, with a reduced top-down connectivity mostly in slower frequencies and a diminished bottom-up connectivity in faster rhythms.

CONCLUSIONS

These results show that healthy individuals with a higher risk of developing psychosis exhibit a less efficient functional brain organization, coupled with a systematic decrease in functional connectivity impacting both bottom-up and top-down processing. These frequency-specific network alterations provide robust support for the dimensional model of schizophrenia, highlighting distinctive neurophysiological signatures in high-schizotypy individuals.

Impaired speaking-induced suppression predicts degraded agency and hallucination severity in schizophrenia

Background

Agency is the awareness of being the originator of one's own thoughts and actions. Patients with schizophrenia (SZ) show deficits in agency that contribute to distortions in reality-monitoring (distinguishing self-generated from externally-produced information) and result in psychotic symptoms. Agency is also critical for speech-monitoring (monitoring what we hear ourselves say while speaking). For example, disruptions in agency that manifest as hallucinations are thought to result from the misattribution of the source of patients' inner thoughts/speech as external voices.

Methods

We used magnetoencephalography (MEG) to assay assess agency during reality-monitoring (RM) and speech-monitoring (SM) tasks. In healthy controls (HC) during SM, the auditory cortical (A1) response is smaller while speaking (speak condition) compared to listening to the same speech (listen condition). This is known as speaking-induced suppression (SIS) M100 response which is measured using MEG 100ms after speech onset.

Results

During RM, SZ (N=30) showed impairments in both self-agency (identification of self-generated information) and external-agency (identification of externally-produced information), compared to HC (N=30). During SM, SZ failed to enhance M100 A1 responses during the listen condition and suppress M100 A1 responses while speaking, revealing impaired SIS. Weakened SIS predicted worsening hallucination severity.

Conclusions

SZ showed degraded neural M100 responses in A1 during the listen condition which drove impaired suppression of M100 SIS during highly-predictable self-generated speech. Impaired SIS induced noisier auditory sensory predictions, making it more likely for SZ to misattribute the source of inner thoughts/speech as externally-derived, giving rise to disruptions in agency during RM and more severe hallucinations.

Cerebellar dysconnectivity in schizophrenia and bipolar disorder is associated with cognitive and clinical variables

BACKGROUND

Abnormal cerebellar functional connectivity (FC) has been implicated in the pathophysiology of schizophrenia (SCZ) and bipolar disorder (BD). However, the patterns of cerebellar dysconnectivity in these two disorders and their association with cognitive functioning and clinical symptoms have not been fully clarified. In this study, we examined cerebellar FC alterations in SCZ and BD-I and their association with cognition and psychotic symptoms.

METHODS

Resting-state functional magnetic resonance imaging (rs-fMRI) data of 39 SCZ, 43 BD-I, and 61 healthy controls from the Consortium for Neuropsychiatric Phenomics dataset were examined. The cerebellum was parcellated into ten functional networks, and seed-based FC was calculated for each cerebellar system. Principal component analyses were used to reduce the dimensionality of the diagnosis-related FC and cognitive variables. Multiple regression analyses were used to assess the relationship between FC and cognitive and clinical data.

RESULTS

We observed decreased cerebellar FC with the frontal, temporal, occipital, and thalamic areas in individuals with SCZ, and a more widespread decrease in cerebellar FC in individuals with BD-I, involving the frontal, cingulate, parietal, temporal, occipital, and thalamic regions. SCZ had increased within-cerebellum and cerebellar frontal FC compared to BD-I. In BD-I, memory and verbal learning performances, which were higher compared to SCZ, showed a greater interaction with cerebellar FC patterns. Additionally, patterns of increased cortico-cerebellar FC were marginally associated with positive symptoms in patients.

CONCLUSIONS

Our findings suggest that shared and distinct patterns of cortico-cerebellar dysconnectivity in SCZ and BD-I could underlie cognitive impairments and psychotic symptoms in these disorders.

Causal role of medial superior frontal cortex on enhancing neural information flow and self-agency judgments in the self-agency network

Self-agency is being aware of oneself as the agent of one's thoughts and actions. Self-agency is necessary for successful interactions with the outside world (reality-monitoring). Prior research has shown that the medial superior prefrontal gyri (mPFC/SFG) may represent one neural correlate underlying self-agency judgments. However, the causal relationship remains unknown. Here, we applied high-frequency 10Hz repetitive transcranial magnetic stimulation (rTMS) to modulate the excitability of the mPFC/SFG site that we have previously shown to mediate self-agency. For the first time, we delineate causal neural mechanisms, revealing precisely how rTMS modulates SFG excitability and impacts directional neural information flow in the self-agency network by implementing innovative magnetoencephalography (MEG) phase-transfer entropy (PTE) metrics, measured from pre-to-post rTMS. We found that, compared to control rTMS, enhancing SFG excitability by rTMS induced significant increases in information flow between SFG and specific cingulate and paracentral regions in the self-agency network in delta-theta, alpha, and gamma bands, which predicted improved self-agency judgments. This is the first multimodal imaging study in which we implement MEG PTE metrics of 5D imaging of space, frequency and time, to provide cutting-edge analyses of the causal neural mechanisms of how rTMS enhances SFG excitability and improves neural information flow between distinct regions in the self-agency network to potentiate improved self-agency judgments. Our findings provide a novel perspective for investigating causal neural mechanisms underlying self-agency and create a path towards developing novel neuromodulation interventions to improve self-agency that will be particularly useful for patients with psychosis who exhibit severe impairments in self-agency.