Prolonged cortical silent period among drug-naive subjects at ultra-high risk of psychosis

Excitation/inhibition imbalance in schizophrenia: a meta-analysis of inhibitory and excitatory TMS-EMG paradigms

Cortical excitation-inhibition (E/I) imbalance is a potential model for the pathophysiology of schizophrenia. Previous research using transcranial magnetic stimulation (TMS) and electromyography (EMG) has suggested inhibitory deficits in schizophrenia. In this meta-analysis we assessed the reliability and clinical potential of TMS-EMG paradigms in schizophrenia following the methodological recommendations of the PRISMA guideline and the Cochrane Handbook. The search was conducted in three databases in November 2022. Included articles reported Short-Interval Intracortical Inhibition (SICI), Intracortical Facilitation (ICF), Long-Interval Intracortical Inhibition (LICI) and Cortical Silent Period (CSP) in patients with schizophrenia and healthy controls. Meta-analyses were conducted using a random-effects model. Subgroup analysis and meta-regressions were used to assess heterogeneity. Results of 36 studies revealed a robust inhibitory deficit in schizophrenia with a significant decrease in SICI (Cohen's d: 0.62). A trend-level association was found between SICI and antipsychotic medication. Our findings support the E/I imbalance hypothesis in schizophrenia and suggest that SICI may be a potential pathophysiological characteristic of the disorder.

The pathobiology of psychomotor slowing in psychosis: altered cortical excitability and connectivity

Psychomotor slowing is a frequent symptom of schizophrenia. Short-interval intracortical inhibition assessed by transcranial magnetic stimulation demonstrated inhibitory dysfunction in schizophrenia. The inhibitory deficit results from additional noise during information processing in the motor system in psychosis. Here, we tested whether cortical inhibitory dysfunction was linked to psychomotor slowing and motor network alterations. In this cross-sectional study, we included 60 patients with schizophrenia and psychomotor slowing determined by the Salpêtrière Retardation Rating Scale, 23 patients without slowing and 40 healthy control participants. We acquired single and double-pulse transcranial magnetic stimulation effects from the left primary motor cortex, resting-state functional connectivity and diffusion imaging on the same day. Groups were compared on resting motor threshold, amplitude of the motor evoked potentials, as well as short-interval intracortical inhibition. Regression analyses calculated the association between motor evoked potential amplitudes or cortical inhibition with seed-based resting-state functional connectivity from the left primary motor cortex and fractional anisotropy at whole brain level and within major motor tracts. In patients with schizophrenia and psychomotor slowing, we observed lower amplitudes of motor evoked potentials, while the short-interval intracortical inhibition/motor evoked potentials amplitude ratio was higher than in healthy controls, suggesting lower cortical inhibition in these patients. Patients without slowing also had lower amplitudes of motor evoked potentials. Across the combined patient sample, cortical inhibition deficits were linked to more motor coordination impairments. In patients with schizophrenia and psychomotor slowing, lower amplitudes of motor evoked potentials were associated with lower fractional anisotropy in motor tracts. Moreover, resting-state functional connectivity between the primary motor cortex, the anterior cingulate cortex and the cerebellum increased with stronger cortical inhibition. In contrast, in healthy controls and patients without slowing, stronger cortical inhibition was linked to lower resting-state functional connectivity between the left primary motor cortex and premotor or parietal cortices. Psychomotor slowing in psychosis is linked to less cortical inhibition and aberrant functional connectivity of the primary motor cortex. Higher neural noise in the motor system may drive psychomotor slowing and thus may become a treatment target.

Cortical inhibition on TMS-EEG: interstimulus interval effect on short-interval paired-pulse

In mental disorders, paired-pulse (PP) transcranial magnetic stimulation and electroencephalography (TMS-EEG) recordings usage is increasing to directly evaluate the cortical inhibition of motor and nonmotor regions. One of the most common measures to assess the inhibition is the short-interval cortical inhibition (SICI), which depends on the interstimulus interval (ISI). This measure has been widely used in the motor cortex. However, the number of studies that evaluate other nonmotor regions, such as the dorsolateral prefrontal cortex (DLPFC), are increasing and there is still little knowledge on how the ISI affects those areas.In this pilot study, six subjects underwent a SICI protocol over the DLPFC using ISI values of 2 and 4ms with the aim of comparing them. TMS-EEG signals for both ISIs were characterized regarding the amplitude and latency of the TMS-evoked potentials (TEP) P60 and N100. Whereas the variation of cortical inhibition between ISIs is almost significant for N100, with higher inhibition for an ISI of 2ms, for TEP P60 the variation was not appreciable. Findings are in accordance with the ones in the state-of-the-art obtained in the motor cortex and suggest that a greater inhibition is likely to be produced with an ISI of 2ms.Clinical relevance- This pilot study indicates that cortical inhibition might be better assessed when DLPFC is stimulated with an ISI of 2ms in the SICI protocol.

The cortical silent period in schizophrenia: A systematic review and meta-analysis focusing on disease stage and antipsychotic medication

BACKGROUND

Although numerous studies reported some changes of cortical silent period (CSP), an indicator of gamma-aminobutyric acid (GABA) function in central nervous system, in schizophrenia patients, it has been unknown how the disease stage and antipsychotic medication affect CSP values.

METHODS

The present study conducted a systematic review of previous literature comparing CSP between schizophrenia patients and healthy subjects, and then performed meta-analysis on the effects of (1) the disease stage and (2) antipsychotics on CSP.

RESULTS

(1) In the comparison of the disease stage comprising a total of 17 reports, there was no significant difference in CSP between patients under drug-naïve first-episode psychoses and healthy controls, or between patients with antipsychotic medication and healthy controls. (2) In the comparison of the antipsychotic class, patients treated with clozapine were longer in CSP compared to healthy controls. Patients treated with olanzapine/quetiapine or with other type of antipsychotics were not different from healthy controls. Regarding other type of antipsychotics, the iteration analysis after leaving out one literature showed that patients were shorter in CSP than healthy controls.

CONCLUSION

The results showed that clozapine seems to surely prolong CSP, indicating the enhancement of GABA transmission via GABA_B receptors, suggesting the possible relationship between the CSP prolongation by clozapine and its high efficacy in psychopathology. The finding of shorter CSP in patients with other type of antipsychotics was distinct from clozapine/olanzapine/quetiapine, but was difficult to interpret since this group included a variety of transcranial magnetic stimulation (TMS) methodologies and patients' background.

A systematic review of TMS and neurophysiological biometrics in patients with schizophrenia

BACKGROUND

Transcranial magnetic stimulation can be combined with electromyography (TMS-EMG) and electroencephalography (TMS-EEG) to evaluate the excitatory and inhibitory functions of the cerebral cortex in a standardized manner. It has been postulated that schizophrenia is a disorder of functional neural connectivity underpinned by a relative imbalance of excitation and inhibition. The aim of this review was to provide a comprehensive overview of TMS-EMG and TMS-EEG research in schizophrenia, focused on excitation or inhibition, connectivity, motor cortical plasticity and the effect of antipsychotic medications, symptom severity and illness duration on TMS-EMG and TMS-EEG indices.

METHODS

We searched PsycINFO, Embase and Medline, from database inception to April 2020, for studies that included TMS outcomes in patients with schizophrenia. We used the following combination of search terms: transcranial magnetic stimulation OR tms AND interneurons OR glutamic acid OR gamma aminobutyric acid OR neural inhibition OR pyramidal neurons OR excita* OR inhibit* OR GABA* OR glutam* OR E-I balance OR excitation-inhibition balance AND schizoaffective disorder* OR Schizophrenia OR schizophreni*.

RESULTS

TMS-EMG and TMS-EEG measurements revealed deficits in excitation or inhibition, functional connectivity and motor cortical plasticity in patients with schizophrenia. Increased duration of the cortical silent period (a TMS-EMG marker of γ-aminobutyric acid B receptor activity) with clozapine was a relatively consistent finding.

LIMITATIONS

Most of the studies used patients with chronic schizophrenia and medicated patients, employed cross-sectional group comparisons and had small sample sizes.

CONCLUSION

TMS-EMG and TMS-EEG offer an opportunity to develop a novel and improved understanding of the physiologic processes that underlie schizophrenia and to assess the therapeutic effect of antipsychotic medications. In the future, these techniques may also help predict disease progression and further our understanding of the excitatory/inhibitory balance and its implications for mechanisms that underlie treatment-resistant schizophrenia.

Assessment of Cortical Plasticity in Schizophrenia by Transcranial Magnetic Stimulation

Neural plasticity refers to the capability of the brain to modify its structure and/or function and organization in response to a changing environment. Evidence shows that disruption of neuronal plasticity and altered functional connectivity between distinct brain networks contribute significantly to the pathophysiological mechanisms of schizophrenia. Transcranial magnetic stimulation has emerged as a noninvasive brain stimulation tool that can be utilized to investigate cortical excitability with the aim of probing neural plasticity mechanisms. In particular, in pathological disorders, such as schizophrenia, cortical dysfunction, such as an aberrant excitatory-inhibitory balance in cortical networks, altered cortical connectivity, and impairment of critical period timing are very important to be studied using different TMS paradigms. Studying such neurophysiological characteristics and plastic changes would help in elucidating different aspects of the pathophysiological mechanisms underlying schizophrenia. This review attempts to summarize the findings of available TMS studies with diagnostic and characterization aims, but not with therapeutic purposes, in schizophrenia. Findings provide further evidence of aberrant excitatory-inhibitory balance in cortical networks, mediated by neurotransmitter pathways such as the glutamate and GABA systems. Future studies with combining techniques, for instance, TMS with brain imaging or molecular genetic typing, would shed light on the characteristics and predictors of schizophrenia.

An Open-label Trial of Adjuvant High-frequency Left Prefrontal Repetitive Transcranial Magnetic Stimulation for Treating Suicidal Ideation in Adolescents and Adults With Depression

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) offers promise for the treatment of depression, yet its potential impact on suicidal ideation (SI), particularly in adolescents, has not been well studied. This study aimed to investigate the efficacy of add-on rTMS for reducing SI in a large clinical sample experiencing an acute phase of depression.

METHODS

This study included 146 patients with a score of ≥14 on the 17-item Hamilton Rating Scale for Depression (HAMD). Among them, 97 had a HAMD-SI (3-item) score of 1 or greater and were pooled into the analysis. Symptoms of depression and SI were measured using the HAMD total score and HAMD-SI score. Comparisons of clinical improvement for both SI and rates of remission were made between adolescent (n = 29) and adult patients (n = 68), as well as between high-frequency (HF) rTMS on the left dorsolateral prefrontal cortex (DLPFC) (80 trains, 30 pulses per train, 12 s intertrain interval, 2400 pulses per session) and low-frequency (LF) rTMS on the right DLPFC protocol (2 trains, 700 pulses per train, 1 s intertrain-interval, 1400 pulses per session), power (intensity) level of 120% of motor threshold (MT), and 5 sessions per week for 2 weeks.

RESULTS

Add-on rTMS treatment showed significant clinical improvement in SI, and was also well tolerated, with no adverse events reported. The SI improvements and remission rates were more significant in adolescents treated with the HF left DLPFC rTMS protocol, compared with adults treated with the LF right DLPFC rTMS protocol (remission rates: adolescent with LF right DLPFC, 50%; adolescent with HF left DLPFC, 94%; adult with LF right DLPFC, 65%; adult with HF left DLPFC, 57%). A positive association between improvement in the HAMD total score and HAMD-SI score was found in adults, but not in adolescents.

CONCLUSIONS

Add-on rTMS treatment for SI associated with depression is promising with respect to safety and feasibility. Our preliminary evidence supports an extension of the application of rTMS to adolescent patients with SI during the acute phase of depression, in addition to its use in adult treatment-resistant depression.

Effect of Electroconvulsive Therapy on Medial Prefrontal γ-Aminobutyric Acid Among Schizophrenia Patients: A Proton Magnetic Resonance Spectroscopy Study

OBJECTIVE

Electroconvulsive therapy (ECT) has often been applied to augment antipsychotics for schizophrenia patients. However, the underpinning mechanism is still unclear. Previous studies of major depressive disorder reported an increase in γ-aminobutyric acid (GABA) after ECT. The present study investigated the effects of ECT on medial prefrontal GABA in schizophrenia using a proton magnetic resonance spectroscopy.

METHODS

Inpatients fulfilling the diagnostic criteria for schizophrenia (Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition) were assigned to 2 groups, ECT group (n = 14) receiving ECT plus antipsychotic drugs (APD) and drug group (n = 17) only receiving antipsychotic drugs. Medial prefrontal GABA+/Cr concentrations of all patients were measured with magnetic resonance spectroscopy at baseline and after 4-week treatment. Sex- and age-matched healthy comparisons (n = 19) were scanned at baseline.

RESULTS

γ-Aminobutyric acid level did not show a significant difference among 3 groups. However, when 2 patient groups were combined, their GABA level was significantly lower than that in healthy comparisons group. For schizophrenia patients, repeated measures analysis of variance revealed that both the group effect and group × time interaction were insignificant, but the time effect of baseline versus after treatment was significant. Exploratory post hoc paired t test found a significant increase of GABA only in ECT group, but not in drug group. No correlation was found between GABA change and clinical symptom improvement in either group.

CONCLUSIONS

γ-Aminobutyric acid level in the medial prefrontal lobe was reduced in schizophrenia patients. An increase in GABA concentration in the medial prefrontal cortex is more significantly associated with ECT plus antipsychotics than antipsychotics alone, possibly supporting the hypothesis of ECT augmentation for GABA mediated neural inhibition.

Towards a neurodynamical understanding of the prodrome in schizophrenia

The identification of biomarkers for the early diagnosis of schizophrenia that could inform novel treatment developments is an important objective of current research. This paper will summarize recent work that has investigated changes in oscillatory activity and event-related potentials with Electro/Magnetoencephalography (EEG/MEG) in participants at high-risk for the development of schizophrenia, highlighting disruptions in sensory and cognitive operations prior to the onset of the syndrome. Changes in EEG/MEG-data are consistent with evidence for alterations in Glutamatergic and GABAergic neurotransmission as disclosed by Magnetic Resonance Spectroscopy and brain stimulation, indicating changes in Excitation/Inhibition balance parameters prior to the onset of psychosis. Together these data emphasize the importance of research into neuronal dynamics as a crucial approach to establish functional relationships between impairments in neural circuits and emerging psychopathology that together could be fundamental for early intervention and the identification of novel treatments for emerging psychosis.

Reduced γ-Aminobutyric Acid and Glutamate+Glutamine Levels in Drug-Naïve Patients with First-Episode Schizophrenia but Not in Those at Ultrahigh Risk

Altered γ-aminobutyric acid (GABA), glutamate (Glu) levels, and an imbalance between GABAergic and glutamatergic neurotransmissions have been involved in the pathophysiology of schizophrenia. However, it remains unclear how these abnormalities impact the onset and course of psychosis. In the present study, 21 drug-naïve subjects at ultrahigh risk for psychosis (UHR), 16 drug-naïve patients with first-episode schizophrenia (FES), and 23 healthy controls (HC) were enrolled. In vivo GABA and glutamate+glutamine (Glx) levels in the medial prefrontal cortex were measured using proton magnetic resonance spectroscopy. Medial prefrontal GABA and Glx levels in FES patients were significantly lower than those in HC and UHR, respectively. GABA and Glx levels in UHR were comparable with those in HC. In each group, there was a positive correlation between GABA and Glx levels. Reduced medial prefrontal GABA and Glx levels thus may play an important role in the early stages of schizophrenia.

The role of white matter microstructure in inhibitory deficits in patients with schizophrenia

BACKGROUND

Inhibitory-excitatory (I-E) imbalance has increasingly been proposed as a fundamental mechanism giving rise to many schizophrenia-related pathophysiology. The integrity of I-E functions should require precise and rapid electrical signal transmission.

OBJECTIVE/HYPOTHESIS

We hypothesized that part of the I-E abnormality in schizophrenia may originate from their known abnormal white matter connectivity that may interfere the I-E functions.

METHODS

We test this using short-interval intracortical inhibition (SICI) vs. intracortical facilitation (ICF) which is a non-invasive measurement of I-E signaling. SICI-ICF from left motor cortex and white matter microstructure were assessed in schizophrenia patients and healthy controls.

RESULTS

Schizophrenia patients showed significantly reduced SICI but not ICF. White matter microstructure as measured by fraction anisotropy (FA) in diffusion tensor imaging had a significant effect on SICI in patients, such that weaker SICI was associated with lower FA in several white matter tracts, most strongly with left corona radiata (r = -0.68, p = 0.0002) that contains the fibers connecting with left motor cortex. Left corticospinal tract, which carries the motor fibers to peripheral muscular output, also showed significant correlation with SICI (r = -0.54, p = 0.005). Mediation analysis revealed that much of the schizophrenia disease effect on SICI can be accounted for by mediation through left corona radiata. SICI was also significantly associated with the performance of processing speed in patients.

CONCLUSION

This study demonstrated the importance of structural circuitry integrity in inhibitory signaling in schizophrenia, and encouraged modeling the I-E dysfunction in schizophrenia from a circuitry perspective.

Altered Motor-Striatal Plasticity and Cortical Functioning in Patients with Schizophrenia

Patients with schizophrenia undergo changes in brain plasticity. In the present study, we characterized motor cortical-striatal plasticity in such patients. Compared with the potentiation following high-frequency repetitive transcranial magnetic stimulation in the control group, the patients demonstrated impaired plasticity of corticostriatal motor-evoked potentials recorded from hand muscles. Notably, the loss of cortical plasticity was correlated with impaired motor learning in a rotary pursuit task. Moreover, the loss of plasticity was correlated with the symptoms of schizophrenia. The results suggest that the progression of schizophrenia is accompanied by altered cortical plasticity and functioning.