Neural models of schizophrenia

The Therapeutic Role of Intermittent Theta Burst Stimulation in Schizophrenia: A Systematic Review and Meta-analysis

ABSTRACT

Schizophrenia affects approximately 1% of the population worldwide. Multifactorial reasons, ranging from drug resistance to adverse effects of medications, have necessitated exploring further therapeutic options. Intermittent theta burst stimulation (iTBS) is a novel high-frequency form of transcranial magnetic stimulation, a safe procedure with minor adverse effects with faster and longer-lasting poststimulation effects with a potential role in treating symptoms; however, the exact target brain regions and symptoms are still controversial. Therefore, we aimed to systematically investigate the current literature regarding the therapeutic utilities of iTBS using Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines. Twelve studies were included among which 9 found iTBS effective to some degree. These studies targeted the dorsolateral prefrontal cortex and the midline cerebellum. We performed a random-effects meta-analysis on studies that compared the effects of iTBS on schizophrenia symptoms measured by the Positive and Negative Syndrome Scale (PANSS) to sham treatment. Our results showed no significant difference between iTBS and sham in PANSS positive and negative scores, but a trend-level difference in PANSS general scores ( k = 6, P = 0.07), and a significant difference in PANSS total scores ( k = 6, P = 0.03). Analysis of the studies targeting the dorsolateral prefrontal cortex showed improvement in PANSS negative scores ( k = 5, standardized mean difference = -0.83, P = 0.049), but not in PANSS positive scores. Moderators (intensity, pulse, quality, sessions) did not affect the results. However, considering the small number of studies included in this meta-analysis, future works are required to further explore the effects of these factors and also find optimum target regions for positive symptoms.

Hippocampal Network Dysfunction in Early Psychosis: A 2-Year Longitudinal Study

Background

Hippocampal abnormalities are among the most consistent findings in schizophrenia. Numerous studies have reported deficits in hippocampal volume, function, and connectivity in the chronic stage of illness. While hippocampal volume and function deficits are also present in the early stage of illness, there is mixed evidence of both higher and lower functional connectivity. Here, we use graph theory to test the hypothesis that hippocampal network connectivity is broadly lowered in early psychosis and progressively worsens over 2 years.

Methods

We examined longitudinal resting-state functional connectivity in 140 participants (68 individuals in the early stage of psychosis, 72 demographically similar healthy control individuals). We used an anatomically driven approach to quantify hippocampal network connectivity at 2 levels: 1) a core hippocampal-medial temporal lobe cortex (MTLC) network; and 2) an extended hippocampal-cortical network. Group and time effects were tested in a linear mixed effects model.

Results

Early psychosis patients showed elevated functional connectivity in the core hippocampal-MTLC network, but contrary to our hypothesis, did not show alterations within the broader hippocampal-cortical network. Hippocampal-MTLC network hyperconnectivity normalized longitudinally and predicted improvement in positive symptoms but was not associated with increasing illness duration.

Conclusions

These results show abnormally elevated functional connectivity in a core hippocampal-MTLC network in early psychosis, suggesting that selectively increased hippocampal signaling within a localized cortical circuit may be a marker of the early stage of psychosis. Hippocampal-MTLC hyperconnectivity could have prognostic and therapeutic implications.

Axonal transport deficits in neuropsychiatric disorders

Axonal transport is a major cellular process that mediates bidirectional signaling between the soma and synapse, enabling both intracellular and intercellular communications. Cellular materials, such as proteins, RNAs, and organelles, are transported by molecular motor proteins along cytoskeletal highways in a highly regulated manner. Several studies have demonstrated that axonal transport is central to normal neuronal function, plasticity, and memory storage. Importantly, disruptions in axonal transport result in neuronal dysfunction and are associated with several neurodegenerative disorders. However, we do not know much about axonal transport deficits in neuropsychiatric disorders. Here, we briefly discuss our current understanding of the role of axonal transport in schizophrenia, bipolar and autism.

Disease Modeling of Neurodegenerative Disorders Using Direct Neural Reprogramming

Understanding the pathophysiology of CNS-associated neurological diseases has been hampered by the inaccessibility of patient brain tissue to perform live analyses at the molecular level. To this end, neural cells obtained by differentiation of patient-derived induced pluripotent stem cells (iPSCs) are considerably helpful, especially in the context of monogenic-based disorders. More recently, the use of direct reprogramming to convert somatic cells to neural cells has emerged as an alternative to iPSCs to generate neurons, astrocytes, and oligodendrocytes. This review focuses on the different studies that used direct neural reprogramming to study disease-associated phenotypes in the context of neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis.

Relationship between motor function and psychotic symptomatology in young-adult patients with schizophrenia

Motor abnormalities have been indicated to be a core manifestation of schizophrenia and not just motor side-effects of antipsychotics. However, little is known about whether all of the complete motor function, including fine motor function, muscle strength, and balance is linked to psychotic symptoms. Therefore, this study was to investigate association between complete motor function and psychotic symptoms in young-adult schizophrenia patients who had no extrapyramidal motor symptoms, which were assessed using the Extrapyramidal Symptom Rating Scale. Seventy schizophrenia patients were recruited. Fine motor function, muscle strength, and balance were assessed using The McCarron Assessment of Neuromuscular Development. Psychotic symptoms were assessed using the Positive and Negative Syndrome Scale. Given gender differences in muscle power, the correlation between muscle strength and psychotic symptoms was analyzed by gender separately. Partial correlation controlling for effects of the chlorpromazine equivalent dosage of antipsychotics was conducted. Better fine motor function was correlated with less-severe negative symptoms (r = - 0.49, p < 0.001) in the total sample. In men, better muscle strength was correlated with more severe positive symptoms and less-severe negative symptoms (r = 0.41, p = 0.008; r = - 0.55, p < 0.001). The link between motor function and psychotic symptoms may support the cerebellar and basal ganglia hypotheses of schizophrenia, proposing that diverse schizophrenia symptoms may share the same neural deficiency, that is, dysfunction of cerebellum or basal ganglia. Considering the moderate-to-strong association between muscle strength and psychotic symptoms, muscle strength might be a powerful physical predictor of psychotic progression.

Correlation Between Levels of Delusional Beliefs and Perfusion of the Hippocampus and an Associated Network in a Non-Help-Seeking Population

BACKGROUND

Delusions are a defining and common symptom of psychotic disorders. Recent evidence suggests that subclinical and clinical delusions may represent distinct stages on a phenomenological and biological continuum. However, few studies have tested whether subclinical psychotic experiences are associated with neural changes that are similar to those observed in clinical psychosis. For example, it is unclear if overactivity of the hippocampus, a replicated finding of neuroimaging studies of schizophrenia, is also present in individuals with subclinical psychotic symptoms.

METHODS

To investigate this question, structural and pulsed arterial spin labeling scans were collected in 77 adult participants with no psychiatric history. An anatomical region of interest approach was used to extract resting perfusion of the hippocampus, and 15 other regions, from each individual. A self-report measure of delusional ideation was collected on the day of scanning.

RESULTS

The level of delusional thinking (number of beliefs [r = .27, p = .02]), as well as the associated level of distress (r = .29, p = .02), was significantly correlated with hippocampal perfusion (averaged over right and left hemispheres). The correlations remained significant after controlling for age, hippocampal volume, symptoms of depression and anxiety, and image signal-to-noise ratio, and they were confirmed in a voxelwise regression analysis. The same association was observed in the thalamus and parahippocampal, lateral temporal, and cingulate cortices.

CONCLUSIONS

Similar to patients with schizophrenia, non-help-seeking individuals show elevated perfusion of a network of limbic regions in association with delusional beliefs.

Four-way multimodal fusion of 7 T imaging data using an mCCA+jICA model in first-episode schizophrenia

Acquisition of multimodal brain imaging data for the same subject has become more common leading to a growing interest in determining the intermodal relationships between imaging modalities to further elucidate the pathophysiology of schizophrenia. Multimodal data have previously been individually analyzed and subsequently integrated; however, these analysis techniques lack the ability to examine true modality inter-relationships. The utilization of a multiset canonical correlation and joint independent component analysis (mCCA + jICA) model for data fusion allows shared or distinct abnormalities between modalities to be examined. In this study, first-episode schizophrenia patients (n_SZ =19) and matched controls (n_HC =21) completed a resting-state functional magnetic resonance imaging (fMRI) scan at 7 T. Grey matter (GM), white matter (WM), cerebrospinal fluid (CSF), and amplitude of low frequency fluctuation (ALFF) maps were used as features in a mCCA + jICA model. Results of the mCCA + jICA model indicated three joint group-discriminating components (GM-CSF, WM-ALFF, GM-ALFF) and two modality-unique group-discriminating components (GM, WM). The joint component findings are highlighted by GM basal ganglia, somatosensory, parietal lobe, and thalamus abnormalities associated with ventricular CSF volume; WM occipital and frontal lobe abnormalities associated with temporal lobe function; and GM frontal, temporal, parietal, and occipital lobe abnormalities associated with caudate function. These results support and extend major findings throughout the literature using independent single modality analyses. The multimodal fusion of 7 T data in this study provides a more comprehensive illustration of the relationships between underlying neuronal abnormalities associated with schizophrenia than examination of imaging data independently.

A mathematical and biological plausible model of decision-execution regulation in "Go/No-Go" tasks: Focusing on the fronto-striatal-thalamic pathway

Discovering factors influencing the speed and accuracy of responses in tasks such as "Go/No-Go" is one of issues which have been raised in neurocognitive studies. Mathematical models are considered as tools to identify and to study decision making procedure from different aspects. In this paper, a mathematical model has been presented to show several factors can alter the output of decision making procedure before execution in a "Go/No-Go" task. The dynamic of this model has two stable fixed points, each of them corresponds to the "Press" and "Not-press" responses. This model that focuses on the fronto-striatal-thalamic direct and indirect pathways, receives planned decisions from frontal cortex and sends a regulated output to motor cortex for execution. The state-space analysis showed that several factors could affect the regulation procedure such as the input strength, noise value, initial condition, and the values of involved neurotransmitters. Some probable analytical reasons that may lead to changes in decision-execution regulation have been suggested as well. Bifurcation diagram analysis demonstrates that an optimal interaction between these factors can compensate the weaknesses of some others. It is predicted that abnormalities of response control in different brain disorders such as attention deficit hyperactivity disorder may be resolved by providing treatment techniques that target the regulation of the interaction. The model also suggests a possible justification to show why so many studies insist on the important role of dopamine in some brain disorders.