Dysfunctional long-term potentiation-like plasticity in schizophrenia revealed by transcranial direct current stimulation

New clues for the role of cerebellum in schizophrenia and the associated cognitive impairment

Schizophrenia (SZ) is a complex neuropsychiatric disorder associated with severe cognitive dysfunction. Although research has mainly focused on forebrain abnormalities, emerging results support the involvement of the cerebellum in SZ physiopathology, particularly in Cognitive Impairment Associated with SZ (CIAS). Besides its role in motor learning and control, the cerebellum is implicated in cognition and emotion. Recent research suggests that structural and functional changes in the cerebellum are linked to deficits in various cognitive domains including attention, working memory, and decision-making. Moreover, cerebellar dysfunction is related to altered cerebellar circuit activities and connectivity with brain regions associated with cognitive processing. This review delves into the role of the cerebellum in CIAS. We initially consider the major forebrain alterations in CIAS, addressing impairments in neurotransmitter systems, synaptic plasticity, and connectivity. We then focus on recent findings showing that several mechanisms are also altered in the cerebellum and that cerebellar communication with the forebrain is impaired. This evidence implicates the cerebellum as a key component of circuits underpinning CIAS physiopathology. Further studies addressing cerebellar involvement in SZ and CIAS are warranted and might open new perspectives toward understanding the physiopathology and effective treatment of these disorders.

L-carnitine Modulates Cognitive Impairment Induced by Doxorubicin and Cyclophosphamide in Rats; Insights to Oxidative Stress, Inflammation, Synaptic Plasticity, Liver/brain, and Kidney/brain Axes

Chemotherapy-induced cognitive impairment in cancer patients is known as "chemobrain". Doxorubicin and Cyclophosphamide are two chemotherapeutic agents used in combination to treat solid tumors. L-carnitine was reported for its anti-oxidant and anti-inflammatory activities. The goal of the present study was to elucidate the neuroprotective effect of L-carnitine against chemobrain induced by Doxorubicin and Cyclophosphamide in rats. Rats were divided into five groups: Control group; Doxorubicin (4mg/kg, IV) and Cyclophosphamide (40mg/kg, IV)-treated group; two L-carnitine-treated groups (150 and 300mg/kg, ip) with Doxorubicin and Cyclophosphamide; and L-carnitine alone-treated group (300mg/kg). Doxorubicin and Cyclophosphamide induced histopathological changes in rats' hippocampi and prefrontal cortices, as well as reduced memory as evidenced by behavioural testing. L-carnitine treatment showed opposite effects. In addition, chemotherapy treatment enhanced oxidative stress via reducing catalase and glutathione levels, and inducing lipid peroxidation. By contrast, L-carnitine treatment showed powerful antioxidant effects reversing chemotherapy-induced oxidative damage. Moreover, chemotherapy combination induced inflammation via their effect on nuclear factor kappa B (p65), interleukin-1β, and tumor necrosis factor-α. However, L-carnitine treatment corrected such inflammatory responses. Furthermore, Doxorubicin and Cyclophosphamide reduced synaptic plasticity via hindering expression of brain-derived neurotrophic factor, phosphorylated cyclase response element binding protein, synaptophysin, and postsynaptic density protein 95 whereas protein expression of such synaptic plasticity biomarkers was enhanced by L-carnitine treatment. Finally, acetylcholinesterase activity was found to be enhanced by chemotherapy treatment affecting rats' memory while L-carnitine treatment reduced acetylcholinesterase activity. L-carnitine also showed hepatoprotective and renal protective effects suggesting liver/brain and kidney/brain axes as possible mechanisms for its neuroprotective effects.

Smoking status ameliorates cholinergic impairments in cortical inhibition in patients with schizophrenia

Rationale Modulation of cortical excitability, in particular inhibition, is impaired in patients with schizophrenia. Chronic nicotine consumption, which is prevalent in this group, has been shown to alter cortical excitability in healthy individuals and to increase inhibitory activity. Thus, beneficial effects of smoking on impaired cortical excitability in patients with schizophrenia have been proposed, though direct experimental evidence is still lacking.

OBJECTIVES

We aimed to explore the effect of chronic smoking on cortical excitability by comparing smoking and non-smoking patients with schizophrenia.

METHOD

Twenty-six smoking and 19 non-smoking patients diagnosed with schizophrenia were included. Transcranial magnetic stimulation (TMS) applied to the primary motor cortex served as experimental paradigm for measuring corticospinal and intracortical excitability as follows: Resting motor threshold (RMT) and the input/output curve (I/O curve) were obtained to assess corticospinal excitability. Intracortical excitability was explored using paired-pulse TMS techniques (intracortical facilitation (ICF), short-latency intracortical inhibition (SICI) and short-latency afferent inhibition (SAI)).

RESULTS

A significantly stronger inhibition in the cholinergically driven SAI protocol was observed in smokers compared to non-smokers. All other measures did not show significant differences between groups.

CONCLUSION

Our results suggest an increased inhibition within cholinergic circuits due to chronic nicotine consumption in schizophrenia. This increase may compensate impaired cholinergic neurotransmission and could explain the high rate of smokers in schizophrenia.

Natural Oscillatory Frequency Slowing in the Premotor Cortex of Early-Course Schizophrenia Patients: A TMS-EEG Study

Despite the heavy burden of schizophrenia, research on biomarkers associated with its early course is still ongoing. Single-pulse Transcranial Magnetic Stimulation coupled with electroencephalography (TMS-EEG) has revealed that the main oscillatory frequency (or "natural frequency") is reduced in several frontal brain areas, including the premotor cortex, of chronic patients with schizophrenia. However, no study has explored the natural frequency at the beginning of illness. Here, we used TMS-EEG to probe the intrinsic oscillatory properties of the left premotor cortex in early-course schizophrenia patients (<2 years from onset) and age/gender-matched healthy comparison subjects (HCs). State-of-the-art real-time monitoring of EEG responses to TMS and noise-masking procedures were employed to ensure data quality. We found that the natural frequency of the premotor cortex was significantly reduced in early-course schizophrenia compared to HCs. No correlation was found between the natural frequency and age, clinical symptom severity, or dose of antipsychotic medications at the time of TMS-EEG. This finding extends to early-course schizophrenia previous evidence in chronic patients and supports the hypothesis of a deficit in frontal cortical synchronization as a core mechanism underlying this disorder. Future work should further explore the putative role of frontal natural frequencies as early pathophysiological biomarkers for schizophrenia.

Transcranial cortex-wide Ca2+ imaging for the functional mapping of cortical dynamics

Visualization and tracking of the information flow in the broader brain area are essential because nerve cells make a vast network in the brain. Fluorescence Ca²⁺ imaging is a simultaneous visualization of brain cell activities in a wide area. Instead of classical chemical indicators, developing various types of transgenic animals that express Ca²⁺-sensitive fluorescent proteins enables us to observe brain activities in living animals at a larger scale for a long time. Multiple kinds of literature have reported that transcranial imaging of such transgenic animals is practical for monitoring the wide-field information flow across the broad brain regions, although it has a lower spatial resolution. Notably, this technique is helpful for the initial evaluation of cortical function in disease models. This review will introduce fully intact transcranial macroscopic imaging and cortex-wide Ca²⁺ imaging as practical applications.

Abnormal synaptic plasticity and impaired cognition in schizophrenia

Schizophrenia (SCZ) is a severe mental illness that affects several brain domains with relation to cognition and behaviour. SCZ symptoms are typically classified into three categories, namely, positive, negative, and cognitive. The etiology of SCZ is thought to be multifactorial and poorly understood. Accumulating evidence has indicated abnormal synaptic plasticity and cognitive impairments in SCZ. Synaptic plasticity is thought to be induced at appropriate synapses during memory formation and has a critical role in the cognitive symptoms of SCZ. Many factors, including synaptic structure changes, aberrant expression of plasticity-related genes, and abnormal synaptic transmission, may influence synaptic plasticity and play vital roles in SCZ. In this article, we briefly summarize the morphology of the synapse, the neurobiology of synaptic plasticity, and the role of synaptic plasticity, and review potential mechanisms underlying abnormal synaptic plasticity in SCZ. These abnormalities involve dendritic spines, postsynaptic density, and long-term potentiation-like plasticity. We also focus on cognitive dysfunction, which reflects impaired connectivity in SCZ. Additionally, the potential targets for the treatment of SCZ are discussed in this article. Therefore, understanding abnormal synaptic plasticity and impaired cognition in SCZ has an essential role in drug therapy.

NMDA receptor-related mechanisms of dopaminergic modulation of tDCS-induced neuroplasticity

Dopamine is a key neuromodulator of neuroplasticity and an important neuronal substrate of learning, and memory formation, which critically involves glutamatergic N-methyl-D-aspartate (NMDA) receptors. Dopamine modulates NMDA receptor activity via dopamine D1 and D2 receptor subtypes. It is hypothesized that dopamine focuses on long-term potentiation (LTP)-like plasticity, i.e. reduces diffuse widespread but enhances locally restricted plasticity via a D2 receptor-dependent NMDA receptor activity reduction. Here, we explored NMDA receptor-dependent mechanisms underlying dopaminergic modulation of LTP-like plasticity induced by transcranial direct current stimulation (tDCS). Eleven healthy, right-handed volunteers received anodal tDCS (1 mA, 13 min) over the left motor cortex combined with dopaminergic agents (the D2 receptor agonist bromocriptine, levodopa for general dopamine enhancement, or placebo) and the partial NMDA receptor agonist D-cycloserine (dosages of 50, 100, and 200 mg, or placebo). Cortical excitability was monitored by transcranial magnetic stimulation-induced motor-evoked potentials. We found that LTP-like plasticity was abolished or converted into LTD-like plasticity via dopaminergic activation, but reestablished under medium-dose D-cycloserine. These results suggest that diffuse LTP-like plasticity is counteracted upon via D2 receptor-dependent reduction of NMDA receptor activity.

Distribution of Aquaporin-4 channels in hippocampus and prefrontal cortex in mk-801-treated balb/c mice

Functional disorders of the glymphatic system and Aquaporin-4 (AQP-4) channels take part in the pathophysiology of neurodegenerative disease. The aim of this study was to describe the distribution of AQP-4 channels in the prefrontal cortex and hippocampus in a mouse model of NMDA receptor blocking agent-induced schizophrenia-like behavior model. NMDA receptor antagonist MK-801 was used to produce the experimental schizophrenia model. MK-801 injections were administered for eleven days to Balb/c mice intraperitoneally. Beginning from the sixth day of injection, the spatial learning and memory of the mice were tested by the Morris water maze (MWM) task. A group of mice was injected with MK-801 for ten days without the MWM task. Hippocampus and prefrontal specimens were collected from this group. Tissue samples were stained immunohistochemically and AQP-4 channels were examined by electron microscope. Time to find the platform was significantly longer at MK-801 injected group than the control group at the MWM task. Also, time spent at the target quadrant by the MK-801 group was shorter compared to the control group. AQP-4 expression increased significantly at MK-801 group glial cells, neuronal perikaryon, perineuronal and pericapillary spaces. In the MK-801 group, there was remarkable damage in neurons and glial cells. Increased AQP-4 channel expression and neurodegeneration at the MK-801 group induced with schizophrenia-like behavior model. MK-801 induced NMDA receptor blockade causes a decline in cognitive and memory functions. Increased AQP-4 expression at the prefrontal cortex and hippocampus to elicit and transport products of synaptic neurotransmitters and end metabolites is suggested.

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.

Memory Disorders Related to Hippocampal Function: The Interest of 5-HT4Rs Targeting

The hippocampus has long been considered as a key structure for memory processes. Multilevel alterations of hippocampal function have been identified as a common denominator of memory impairments in a number of psychiatric and neurodegenerative diseases. For many years, the glutamatergic and cholinergic systems have been the main targets of therapeutic treatments against these symptoms. However, the high rate of drug development failures has left memory impairments on the sideline of current therapeutic strategies. This underscores the urgent need to focus on new therapeutic targets for memory disorders, such as type 4 serotonin receptors (5-HT₄Rs). Ever since the discovery of their expression in the hippocampus, 5-HT₄Rs have gained growing interest for potential use in the treatment of learning and memory impairments. To date, much of the researched information gathered by scientists from both animal models and humans converge on pro-mnesic and anti-amnesic properties of 5-HT₄Rs activation, although the mechanisms at work require more work to be fully understood. This review addresses a fundamental, yet poorly understood set of evidence of the potential of 5-HT₄Rs to re-establish or limit hippocampal alterations related to neurological diseases. Most importantly, the potential of 5-HT₄Rs is translated by refining hypotheses regarding the benefits of their activation in memory disorders at the hippocampal level.

Cognitive outcomes after tDCS in schizophrenia patients with prominent negative symptoms: Results from the placebo-controlled STARTS trial

Cognitive deficits and negative symptoms in schizophrenia are associated with poor functional outcomes and limited in terms of treatment. The Schizophrenia Treatment With Electric Transcranial Stimulation (STARTS) trial has shown efficacy of transcranial direct current stimulation (tDCS) for improving negative symptoms. In this secondary analysis, we investigate its effects on cognitive performance. In STARTS, a double-blinded, sham-controlled, randomized clinical trial, patients were treated with twice-daily, 20-min, 2-mA fronto-temporal tDCS over 5 days or sham-tDCS. In 90 patients, we evaluated the cognitive performance up to 12 weeks post-treatment. We found that active-tDCS showed no beneficial effects over sham-tDCS in any of the tests. Based on a 5-factor cognitive model, improvements of executive functions and delayed memory were observed in favor of sham-tDCS. Overall, the applied active-tDCS protocol, primarily designed to improve negative symptoms, did not promote cognitive improvement. We discuss possible protocol modification potentially required to increase tDCS effects on cognition. ClinicalTrials.gov identifier: NCT02535676.

The Imbalanced Plasticity Hypothesis of Schizophrenia-Related Psychosis: A Predictive Perspective

A considerable number of studies have attempted to account for the psychotic aspects of schizophrenia in terms of the influential predictive coding (PC) hypothesis. We argue that the prediction-oriented perspective on schizophrenia-related psychosis may benefit from a mechanistic model that: 1) gives due weight to the extent to which alterations in short- and long-term synaptic plasticity determine the degree and the direction of the functional disruption that occurs in psychosis; and 2) addresses the distinction between the two central syndromes of psychosis in schizophrenia: disorganization and reality-distortion. To accomplish these goals, we propose the Imbalanced Plasticity Hypothesis - IPH, and demonstrate that it: 1) accounts for commonalities and differences between disorganization and reality distortion in terms of excessive (hyper) or insufficient (hypo) neuroplasticity, respectively; 2) provides distinct predictions in the cognitive and electrophysiological domains; and 3) is able to reconcile conflicting PC-oriented accounts of psychosis.

Towards a global investigation of transcriptomic signatures through co-expression networks and pathway knowledge for the identification of disease mechanisms

We attempt to address a key question in the joint analysis of transcriptomic data: can we correlate the patterns we observe in transcriptomic datasets to known interactions and pathway knowledge to broaden our understanding of disease pathophysiology? We present a systematic approach that sheds light on the patterns observed in hundreds of transcriptomic datasets from over sixty indications by using pathways and molecular interactions as a template. Our analysis employs transcriptomic datasets to construct dozens of disease specific co-expression networks, alongside a human protein-protein interactome network. Leveraging the interoperability between these two network templates, we explore patterns both common and particular to these diseases on three different levels. Firstly, at the node-level, we identify most and least common proteins across diseases and evaluate their consistency against the interactome as a proxy for their prevalence in the scientific literature. Secondly, we overlay both network templates to analyze common correlations and interactions across diseases at the edge-level. Thirdly, we explore the similarity between patterns observed at the disease-level and pathway knowledge to identify signatures associated with specific diseases and indication areas. Finally, we present a case scenario in schizophrenia, where we show how our approach can be used to investigate disease pathophysiology.

Proteome Analysis of PC12 Cells Reveals Alterations in Translation Regulation and Actin Signaling Induced by Clozapine

Although antipsychotics are routinely used in the treatment of schizophrenia for the last decades, their precise mechanism of action is still unclear. In this study, we investigated changes in the PC12 cells’ proteome under the influence of clozapine, risperidone, and haloperidol to identify protein pathways regulated by antipsychotics. Analysis of the protein profiles in two time points: after 12 and 24 h of incubation with drugs revealed significant alterations in 510 proteins. Further canonical pathway analysis revealed an inhibition of ciliary trophic factor signaling after treatment with haloperidol and showed a decrease in acute phase response signaling in the risperidone group. Interestingly, all tested drugs have caused changes in PC12 proteome which correspond to inhibition of cytokines: tumor necrosis factor (TNF) and transforming growth factor beta 1 (TGF-β1). We also found that the 12-h incubation with clozapine caused up-regulation of protein kinase A signaling and translation machinery. After 24 h of treatment with clozapine, the inhibition of the actin cytoskeleton signaling and Rho proteins signaling was revealed. The obtained results suggest that the mammalian target of rapamycin complex 1 (mTORC1) and 2 (mTORC2) play a central role in the signal transduction of clozapine.

Visual cortical plasticity and the risk for psychosis: An interim analysis of the North American Prodrome Longitudinal Study

BACKGROUND

Adolescence/early adulthood coincides with accelerated pruning of cortical synapses and the onset of schizophrenia. Cortical gray matter reduction and dysconnectivity in schizophrenia are hypothesized to result from impaired synaptic plasticity mechanisms, including long-term potentiation (LTP), since deficient LTP may result in too many weak synapses that are then subject to over-pruning. Deficient plasticity has already been observed in schizophrenia. Here, we assessed whether such deficits are present in the psychosis risk syndrome (PRS), particularly those who subsequently convert to full psychosis.

METHODS

An interim analysis was performed on a sub-sample from the NAPLS-3 study, including 46 healthy controls (HC) and 246 PRS participants. All participants performed an LTP-like visual cortical plasticity paradigm involving assessment of visual evoked potentials (VEPs) elicited by vertical and horizontal line gratings before and after high frequency ("tetanizing") visual stimulation with one of the gratings to induce "input-specific" neuroplasticity (i.e., VEP changes specific to the tetanized stimulus). Non-parametric, cluster-based permutation testing was used to identify electrodes and timepoints that demonstrated input-specific plasticity effects.

RESULTS

Input-specific pre-post VEP changes (i.e., increased negative voltage) were found in a single spatio-temporal cluster covering multiple occipital electrodes in a 126-223 ms time window. This plasticity effect was deficient in PRS individuals who subsequently converted to psychosis, relative to PRS non-converters and HC.

CONCLUSIONS

Input-specific LTP-like visual plasticity can be measured from VEPs in adolescents and young adults. Interim analyses suggest that deficient visual cortical plasticity is evident in those PRS individuals at greatest risk for transition to psychosis.

Functional Dysregulations in CA1 Hippocampal Networks of a 3-Hit Mouse Model of Schizophrenia

For a better translation from treatment designs of schizophrenia to clinical efficiency, there is a crucial need to refine preclinical animal models. In order to consider the multifactorial nature of the disorder, a new mouse model associating three factors (genetic susceptibility-partial deletion of the MAP6 gene, early-life stress-maternal separation, and pharmacological treatment-chronic Δ-9-tetrahydrocannabinol during adolescence) has recently been described. While this model depicts a schizophrenia-like phenotype, the neurobiological correlates remain unknown. Synaptic transmission and functional plasticity of the CA1 hippocampal region of male and female 3-hit mice were therefore investigated using electrophysiological recordings on the hippocampus slice. While basal excitatory transmission remained unaffected, NMDA receptor (NMDAr)-mediated long-term potentiation (LTP) triggered by theta-burst (TBS) but not by high-frequency (HFS) stimulation was impaired in 3-hit mice. Isolated NMDAr activation was not affected or even increased in female 3-hit mice, revealing a sexual dimorphism. Considering that the regulation of LTP is more prone to inhibitory tone if triggered by TBS than by HFS, the weaker potentiation in 3-hit mice suggests a deficiency of intrinsic GABA regulatory mechanisms. Indeed, NMDAr activation was increased by GABAA receptor blockade in wild-type but not in 3-hit mice. This electrophysiological study highlights dysregulations of functional properties and plasticity in hippocampal networks of 3-hit mice, one of the mechanisms suspected to contribute to the pathophysiology of schizophrenia. It also shows differences between males and females, supporting the sexual dimorphism observed in the disorder. Combined with the previously reported study, the present data reinforce the face validity of the 3-hit model that will help to consider new therapeutic strategies for psychosis.

Neurobiological After-Effects of Low Intensity Transcranial Electric Stimulation of the Human Nervous System: From Basic Mechanisms to Metaplasticity

Non-invasive low-intensity transcranial electrical stimulation (tES) of the brain is an evolving field that has brought remarkable attention in the past few decades for its ability to directly modulate specific brain functions. Neurobiological after-effects of tES seems to be related to changes in neuronal and synaptic excitability and plasticity, however mechanisms are still far from being elucidated. We aim to review recent results from in vitro and in vivo studies that highlight molecular and cellular mechanisms of transcranial direct (tDCS) and alternating (tACS) current stimulation. Changes in membrane potential and neural synchronization explain the ongoing and short-lasting effects of tES, while changes induced in existing proteins and new protein synthesis is required for long-lasting plastic changes (LTP/LTD). Glial cells, for decades supporting elements, are now considered constitutive part of the synapse and might contribute to the mechanisms of synaptic plasticity. This review brings into focus the neurobiological mechanisms and after-effects of tDCS and tACS from in vitro and in vivo studies, in both animals and humans, highlighting possible pathways for the development of targeted therapeutic applications.

Impaired Potentiation of Theta Oscillations During a Visual Cortical Plasticity Paradigm in Individuals With Schizophrenia

Long-term potentiation (LTP) is a form of experience-dependent synaptic plasticity mediated by glutamatergic transmission at N-methyl-D-aspartate receptors (NMDARs). Impaired neuroplasticity has been implicated in the pathophysiology of schizophrenia, possibly due to underlying NMDAR hypofunction. Analogous to the high frequency electrical stimulation used to induce LTP in vitro and in vivo in animal models, repeated high frequency presentation of a visual stimulus in humans in vivo has been shown to induce enduring LTP-like neuroplastic changes in electroencephalography (EEG)-based visual evoked potentials (VEPs) elicited by the stimulus. Using this LTP-like visual plasticity paradigm, we previously showed that visual high-frequency stimulation (VHFS) induced sustained changes in VEP amplitudes in healthy controls, but not in patients with schizophrenia. Here, we extend this prior work by re-analyzing the EEG data underlying the VEPs, focusing on neuroplastic changes in stimulus-evoked EEG oscillatory activity following VHFS. EEG data were recorded from 19 patients with schizophrenia and 21 healthy controls during the visual plasticity paradigm. Event-related EEG oscillations (total power, intertrial phase coherence; ITC) elicited by a standard black and white checkerboard stimulus (~0.83 Hz, several 2-min blocks) were assessed before and after exposure to VHFS with the same stimulus (~8.9 Hz, 2 min). A cluster-based permutation testing approach was applied to time-frequency data to examine LTP-like plasticity effects following VHFS. VHFS enhanced theta band total power and ITC in healthy controls but not in patients with schizophrenia. The magnitude and phase synchrony of theta oscillations in response to a visual stimulus were enhanced for at least 22 min following VHFS, a frequency domain manifestation of LTP-like visual cortical plasticity. These theta oscillation changes are deficient in patients with schizophrenia, consistent with hypothesized NMDA receptor dysfunction.

Transcranial Direct Current Stimulation and Cognition in Neuropsychiatric Disorders: Systematic Review of the Evidence and Future Directions

Transcranial direct current stimulation (tDCS) has been implemented in neuropsychiatric disorders characterized by cognitive impairment. However, methodological heterogeneity challenges conclusive remarks. Through a critical analysis of previous conflicting findings and in the light of current neurobiological models of pathophysiology, we qualitatively assessed the effects of tDCS in neuropsychiatric disorders that share neurobiological underpinnings, as to evaluate whether stimulation can improve cognitive deficits in patients' cohorts. We performed a systematic review of tDCS studies targeting cognitive functions in mental disorders and pathological cognitive aging. Data from 41 studies, comprising patients with diagnosis of mood disorders, schizophrenia-spectrum disorders, Alzheimer's disease (AD), and mild cognitive impairment (MCI), were included. Results indicate that tDCS has the capacity to enhance processing speed, working memory, and executive functions in patients with mood and schizophrenia-spectrum disorders. The evidence of a positive effect on general cognitive functioning and memory is either inconclusive in AD, or weak in MCI. Future directions are discussed for developing standardized stimulation protocols and for translating the technique therapeutic potential into effective clinical practice.

The Neuroprotective Effects of Astragaloside IV against H2O2-Induced Damage in SH-SY5Y Cells are Associated with Synaptic Plasticity

The aim of this study was to investigate whether the neuroprotective effects of astragaloside IV (AS-IV) against hydrogen peroxide (H2O2)-induced damage on human neuroblastoma cell line (SH-SY5Y) are associated with synaptic plasticity. The concentration screening of AS-IV and H2O2 on SH-SY5Y cells and the protective effects of AS-IV on SH-SY5Y cells under H2O2 stress were all determined by MTT assay. The expression of postsynaptic density 95 (PSD-95) and growth-associated protein 43 (GAP-43) were measured by western blot (WB) and inmunofluorescence staining assay under the same treatment conditions. According to the MTT results, the concentration of H2O2 at 50 μmol/L for 3 h was used for the cell damage model, and various concentrations of AS-IV (0.1, 0.2, 0.3, and 0.4 μmol/L) were used to affect SH-SY5Y cells. The MTT results showed that pretreatment of SH-SY5Y cells with AS-IV (0.1, 0.2, 0.3, and 0.4 μmol/L) attenuated the damage induced by H2O2 (50 μmol/L, 51.62% cell viability) and increased cell viability to 64.19, 63.48, 65.86, and 65.81%, respectively. Western blot analysis and immunofluorescence staining showed that the protective effects of AS-IV against SH-SY5Y cell damage caused by H2O2 resulted in reduced expression of PSD-95 and increased expression of GAP-43 in comparison with the H2O2 treatment group. The conclusion shows that AS-IV protected SH-SY5Y cells and enhanced their viability under H2O2 stress. AS-IV may facilitate presynaptic and postsynaptic plasticity to exert protective effects against oxidative damage of SH-SY5Y cells.

Synaptic Plasticity Shapes Brain Connectivity: Implications for Network Topology

Studies of brain network connectivity improved understanding on brain changes and adaptation in response to different pathologies. Synaptic plasticity, the ability of neurons to modify their connections, is involved in brain network remodeling following different types of brain damage (e.g., vascular, neurodegenerative, inflammatory). Although synaptic plasticity mechanisms have been extensively elucidated, how neural plasticity can shape network organization is far from being completely understood. Similarities existing between synaptic plasticity and principles governing brain network organization could be helpful to define brain network properties and reorganization profiles after damage. In this review, we discuss how different forms of synaptic plasticity, including homeostatic and anti-homeostatic mechanisms, could be directly involved in generating specific brain network characteristics. We propose that long-term potentiation could represent the neurophysiological basis for the formation of highly connected nodes (hubs). Conversely, homeostatic plasticity may contribute to stabilize network activity preventing poor and excessive connectivity in the peripheral nodes. In addition, synaptic plasticity dysfunction may drive brain network disruption in neuropsychiatric conditions such as Alzheimer's disease and schizophrenia. Optimal network architecture, characterized by efficient information processing and resilience, and reorganization after damage strictly depend on the balance between these forms of plasticity.

Neuroprotective effect of levetiracetam in mouse diabetic retinopathy: Effect on glucose transporter-1 and GAP43 expression

AIMS

Retinopathy is a neurodegenerative complication associating diabetes mellitus. Diabetic retinopathy (DR) is the primary reason of visual loss during early adulthood. DR has a complicated multifactorial pathophysiology initiated by hyperglycaemia-induced ischaemic neurodegenerative retinal changes, followed by vision-threatening consequences. The main therapeutic modalities for DR involve invasive delivery of intravitreal antiangiogenic agents as well as surgical interventions. The current work aimed to explore the potential anti-inflammatory and retinal neuroprotective effects of levetiracetam.

MAIN METHODS

This study was performed on alloxan-induced diabetes in mice (n: 21). After 10 weeks, a group of diabetic animals (n: 7) was treated with levetiracetam (25 mg/kg) for six weeks. Retinal tissues were dissected and paraffin-fixed for examination using (1) morphometric analysis with haematoxylin and eosin (HE), (2) immunohistochemistry (GLUT1, GFAP and GAP43), and (3) RT-PCR-detected expression of retinal inflammatory and apoptotic mediators (TNF-α, IL6, iNOS, NF-κB and Tp53).

KEY FINDINGS

Diabetic mice developed disorganized and debilitated retinal layers with upregulation of the gliosis marker GFAP and downregulation of the neuronal plasticity marker GAP43. Additionally, diabetic retinae showed increased transcription of NF-κB, TNF-α, IL6, iNOS and Tp53. Levetiracetam-treated mice showed downregulation of retinal GLUT1 with relief and regression of retinal inflammation and improved retinal structural organization.

SIGNIFICANCE

Levetiracetam may represent a potential neuroprotective agent in DR. The data presented herein supported an anti-inflammatory role of levetiracetam. However, further clinical studies may be warranted to confirm the effectiveness and safety of levetiracetam in DR patients.

Motor cortical plasticity in schizophrenia: A meta-analysis of Transcranial Magnetic Stimulation - Electromyography studies

BACKGROUND

Several lines of investigations converge upon aberrant synaptic plasticity as a potential pathophysiological characteristic of schizophrenia. In vivo experiments using neuromodulatory perturbation techniques like Transcranial Magnetic and Direct Current Stimulation (TMS & tDCS) have been increasingly used to measure 'motor cortical plasticity' in schizophrenia. A systematic quantification of cortical plasticity and its moderators in schizophrenia is however lacking.

METHOD

The PubMed/MEDLINE database was searched for studies up to December 31st, 2017 that examined case-control experiments comparing neuromodulation following single-session of TMS or tDCS. The primary outcome was the standardized mean difference for differential changes in motor evoked potential (MEP) amplitudes measured with single-pulse TMS (MEP Δ) between patients and healthy subjects following TMS or tDCS. After examining heterogeneity, meta-analyses were performed using fixed effects models.

RESULTS

A total of 16 datasets comparing cortical plasticity (MEP Δ) between 189 schizophrenia patients and 187 healthy controls were included in the meta-analysis. Patients demonstrated diminished MEP Δ with effect sizes (Cohen's d) ranging from 0.66 (LTP-like plasticity) to 0.68 (LTD-like plasticity). Heterosynaptic plasticity studies demonstrated a greater effect size (0.79) compared to homosynaptic plasticity studies (0.62), though not significant (P = 0.43). Clinical, perturbation protocol- and measurement-related factors, and study quality did not significantly moderate the aberrant plasticity demonstrated in schizophrenia.

CONCLUSIONS

Schizophrenia patients demonstrate diminished LTP- and LTD-like motor cortical plasticity, which is not influenced by the various clinical and experimental protocol related confounders. These consistent findings should encourage the use of perturbation-based biomarkers to characterize illness trajectories and treatment response.

Critical period plasticity-related transcriptional aberrations in schizophrenia and bipolar disorder

Childhood critical periods of experience-dependent plasticity are essential for the development of environmentally appropriate behavior and cognition. Disruption of critical periods can alter development of normal function and confer risk for neurodevelopmental disorders. While genes and their expression relevant to neurodevelopment are associated with schizophrenia, the molecular relationship between schizophrenia and critical periods has not been assessed systematically. Here, we apply a transcriptome-based bioinformatics approach to assess whether genes associated with the human critical period for visual cortex plasticity, a well-studied model of cortical critical periods, are aberrantly expressed in schizophrenia and bipolar disorder. Across two dozen datasets encompassing 522 cases and 374 controls, we find that the majority show aberrations in expression of genes associated with the critical period. We observed both hyper- and hypo-critical period plasticity phenotypes at the transcriptome level, which partially mapped to drug candidates that reverse the disorder signatures in silico. Our findings indicate plasticity aberrations in schizophrenia and their treatment may need to be considered in the context of subpopulations with elevated and others reduced plasticity. Future work should leverage ongoing consortia RNA-sequencing efforts to tease out the sources of plasticity-related transcriptional aberrations seen in schizophrenia, including true biological heterogeneity, interaction between normal development/aging and the disorder, and medication history. Our study also urges innovation towards direct assessment of visual cortex plasticity in humans with schizophrenia to precisely deconstruct the role of plasticity in this disorder.

Changes in motor cortical excitability in schizophrenia following transcranial direct current stimulation

Schizophrenia is a disorder associated with cortical inhibition deficits. Transcranial direct current stimulation (tDCS) induces changes in cortical excitability in healthy subjects and individuals with neuropsychiatric disorders depending on the stimulation parameters. Our aim was to investigate whether a previously published tDCS protocol associated with symptomatic improvement in schizophrenia would induce changes in motor cortical excitability, assessed by transcranial magnetic stimulation paradigms, i.e., short-interval intracortical inhibition (SICI) and intra-cortical facilitation (ICF). We assessed cortical excitability measurements in 48 subjects with schizophrenia before and after a single session of active tDCS (20 min, 2 mA, anode over left dorsolateral prefrontal cortex, cathode over left temporoparietal cortex) or sham. Those who received active tDCS had a significant increase of SICI in the left motor cortex compared to those who received sham stimulation (Cohen's d = 0.54, p = .019). No changes were observed for ICF. In addition, lower SICI was associated with higher age (β = -0.448, p < .01). Increase in intracortical inhibition may indicate a mechanism of action of tDCS in this population. Future studies should investigate whether this finding is a biomarker of treatment response for schizophrenia.

Altered Functional Connectivity of the Default Mode Network in Patients With Schizo-obsessive Comorbidity: A Comparison Between Schizophrenia and Obsessive-compulsive Disorder

Clinical and neuroimaging data support the idea that schizo-obsessive comorbidity (SOC), similar to obsessive-compulsive disorder (OCD) and schizophrenia (SCZ), may be a distinct brain disorder. In this study, we examined the strength of resting-state functional connectivity (rsFC) between 19 subregions of the default mode network (DMN) and whole brain voxels in 22 patients with SOC features, 20 patients with SCZ alone, 22 patients with OCD, and 22 healthy controls (HC). The main results demonstrated that patients with SOC exhibited the highest rsFC strength within subregions of the DMN and the lowest rsFC strength between the DMN and subregions of the salience network (SN) compared with the other 3 groups. In addition, compared with HCs, all 3 patient groups exhibited increased rsFC between subregions of the DMN and the executive control network (ECN). The SOC and SCZ group both exhibited increased rsFC between subregions of the DMN and the middle temporal gyrus, but the OCD group exhibited decreased rsFC between them. These findings highlight a specific alteration in functional connectivity in the DMN in patients with SOC, and provide new insights into the dysfunctional brain organization of different mental disorders.

Aberrant Middle Prefrontal-Motor Cortex Connectivity Mediates Motor Inhibitory Biomarker in Schizophrenia

BACKGROUND

Inhibitory deficits in motor cortex in schizophrenia have been well demonstrated using short-interval intracortical inhibition (SICI) by transcranial magnetic stimulation. However, it remains unknown whether these deficits originate from dysfunction of motor cortex itself or reflect abnormal modulations of motor cortex by other schizophrenia-related brain areas.

METHODS

The study was completed by 24 patients with schizophrenia spectrum disorders and 30 healthy control subjects. SICI was obtained by delivering transcranial magnetic stimulation over the left motor cortex. Resting-state functional magnetic resonance imaging and diffusion tensor imaging fractional anisotropy were used to measure functional connectivity (FC) and white matter microstructures, respectively. Stimulation sites for SICI at motor cortex were used as the seeds to obtain whole-brain FC maps. Clinical symptoms were assessed with the Brief Psychiatric Rating Scale.

RESULTS

In schizophrenia, left prefrontal cortex-motor cortex FC was inversely associated with SICI but positively associated with the underlying white matter microstructure at the left corona radiata and also associated with overall symptoms (all corrected p < .05). Mediation analysis showed that the prefrontal-motor cortex FC significantly mediated the corona radiata white matter effects on SICI (p = .007).

CONCLUSIONS

Higher resting-state left prefrontal-motor cortex FC, accompanied by a higher fractional anisotropy of left corona radiata, predicted fewer inhibitory deficits, suggesting that the inhibitory deficits in motor cortex in schizophrenia may in part be mediated by a top-down prefrontal influence. SICI may serve as a robust biomarker indexing inhibitory dysfunction at anatomic as well as circuitry levels in schizophrenia.

Beneficial effects of anodal transcranial direct current stimulation (tDCS) on spatial working memory in patients with schizophrenia

Schizophrenia is a severe and often detrimental psychiatric disorder. The individual patients' level of functioning is essentially determined by cognitive, particularly working memory (WM), deficits that are critically linked to dysfunctional activity of the dorsolateral prefrontal cortex (dlPFC). Transcranial direct current stimulation (tDCS) can transiently modulate activity of the dlPFC and remote areas and has been shown to improve WM functions. It may therefore provide a new, targeted treatment option. For this aim, the present study investigated the effect of anodal tDCS of different intensities on spatial WM in patients with schizophrenia. In two experiments, 32 patients performed a spatial n-back task with increasing WM load (1-, 2-, and 3-back) at baseline and in two sessions with anodal or sham tDCS (EXP I [n = 16]: 1 mA; EXP II [n = 16]: 2 mA) to the right dlPFC (cathode: left m. deltoideus). With 1 mA anodal tDCS, no effect on WM performance could be detected. However, 2 mA anodal tDCS increased accuracy (measured by d') of the task with the highest WM load (3-back). This effect was larger in patients with a lower level of general neurocognitive functioning. These results demonstrate a beneficial effect of 2 mA anodal tDCS on deficient WM accuracy in patients with schizophrenia particularly under challenging conditions and in subjects with higher cognitive impairments. This data will inform future clinical trials on tDCS-enhanced cognitive training to improve treatment of schizophrenia.

Diverse definitions of the early course of schizophrenia-a targeted literature review

Schizophrenia is a debilitating psychiatric disorder and patients experience significant comorbidity, especially cognitive and psychosocial deficits, already at the onset of disease. Previous research suggests that treatment during the earlier stages of disease reduces disease burden, and that a longer time of untreated psychosis has a negative impact on treatment outcomes. A targeted literature review was conducted to gain insight into the definitions currently used to describe patients with a recent diagnosis of schizophrenia in the early course of disease ('early' schizophrenia). A total of 483 relevant English-language publications of clinical guidelines and studies were identified for inclusion after searches of MEDLINE, MEDLINE In-Process, relevant clinical trial databases and Google for records published between January 2005 and October 2015. The extracted data revealed a wide variety of terminology and definitions used to describe patients with 'early' or 'recent-onset' schizophrenia, with no apparent consensus. The most commonly used criteria to define patients with early schizophrenia included experience of their first episode of schizophrenia or disease duration of less than 1, 2 or 5 years. These varied definitions likely result in substantial disparities of patient populations between studies and variable population heterogeneity. Better agreement on the definition of early schizophrenia could aid interpretation and comparison of studies in this patient population and consensus on definitions should allow for better identification and management of schizophrenia patients in the early course of their disease.

Test-retest reliability of short-interval intracortical inhibition and intracortical facilitation in patients with schizophrenia

Impaired short-interval intracortical inhibition (SICI) elicited by paired-pulse TMS (ppTMS) has emerged as one of the most consistent TMS findings in patients with schizophrenia. Reduction of SICI has been reproducibly found, suggesting that SICI may be a new biomarker indexing the inhibitory dysfunction in schizophrenia. This study evaluated whether SICI has the test-retest reliability suitable for clinical trial and research applications. SICIs, intracortical facilitation (ICF), and other ppTMS effects were obtained using inter-stimulus intervals (ISIs) from 1 to 500 ms, on 2 occasions about 3-4 weeks apart in patients with schizophrenia and healthy individuals. Acceptable test-retest reliabilities were found for SICI (at 1 and 3 ms ISIs) in both patients and controls (all intraclass correlation coefficients r > 0.6). However, test-retest reliability in longer ISIs and in ICF were modest or poor. To our knowledge, this is the first study demonstrated the acceptable reliability of SICI measure in patients with schizophrenia. The data support SICI as a reliable biomarker for schizophrenia.

Gene polymorphisms and response to transcranial direct current stimulation for auditory verbal hallucinations in schizophrenia

OBJECTIVE

Recent observations demonstrate a significant ameliorative effect of add-on transcranial direct current stimulation (tDCS) on auditory verbal hallucinations (AVHs) in schizophrenia. Of the many SNPs, NRG1 rs35753505 and catechol-o-methyl transferase (COMT) rs4680 polymorphisms have shown to have a strong association with neuroplasticity effect in schizophrenia.

METHODS

Schizophrenia patients (n=32) with treatment resistant auditory hallucinations were administered with an add-on tDCS. The COMT (rs4680) and NRG1 (rs35753505) genotypes were determined. The COMT genotypes were categorised into Val group (GG; n=15) and Met group (GG/AG; n=17) and NRG1 genotypes were categorised into AA group (n=12) and AG/GG group (n=20).

RESULTS

The reduction in auditory hallucination sub-scale score was significantly affected by COMT-GG genotype [Time×COMT interaction: F(1,28)=10.55, p=0.003, ɳ2=0.27]. Further, COMT-GG effect was epistatically influenced by the co-occurrence of NRG1-AA genotype [Time×COMT×NRG1 interaction: F(1,28)=8.09, p=0.008, ɳ2=0.22]. Irrespective of genotype, females showed better tDCS response than males [Time×Sex interaction: F(1,21)=4.67, p=0.04, ɳ2=0.18].

CONCLUSION

COMT-GG and NRG1-AA genotypes aid the tDCS-induced improvement in AVHs in schizophrenia patients. Our preliminary observations need replication and further systematic research to understand the neuroplastic gene determinants that modulate the effect of tDCS.

Transcranial Direct Current Stimulation, Symptomatology, and Cognition in Psychosis: A Qualitative Review

Schizophrenia is a chronic, debilitating condition that affects approximately 1% of the population. Individuals diagnosed with schizophrenia typically exhibit positive (e.g., hallucinations) and negative symptoms (e.g., anhedonia) and impairments in cognitive function. Given the limitations of antipsychotic medication and psychotherapy in fully treating psychosis symptomatology, there has been increasing interest in other interventions such as transcranial direct current stimulation (tDCS). tDCS is a non-invasive neuromodulation technique, that is safe, cost-effective, and widely accessible. Here, we discuss treatment studies that seek to improve symptoms and cognitive performance in schizophrenia using tDCS. Currently within the literature, there is support for reductions in positive symptoms such as hallucinations after receiving tDCS. Further, studies indicate that tDCS can improve cognitive functioning, which is an area of investigation that is sorely needed, as it is unclear which types of interventions may be useful in ameliorating cognitive deficits among this group. Taken together, the evidence suggests that tDCS holds promise in improving symptoms and cognition. To that end, tDCS has critical clinical implications for this population.

Investigating the neurobiology of schizophrenia and other major psychiatric disorders with Transcranial Magnetic Stimulation

Characterizing the neurobiology of schizophrenia and other major psychiatric disorders is one of the main challenges of the current research in psychiatry. The availability of Transcranial Magnetic Stimulation (TMS) allows to directly probe virtually any cortical areas, thus providing a unique way to assess the neurophysiological properties of cortical neurons. This article presents a review of studies employing TMS in combination with Motor Evoked Potentials (TMS/MEPs) and high density Electroencephalogram (TMS/hd-EEG) in schizophrenia and other major psychiatric disorders. Studies were identified by conducting a PubMed search using the following search item: "transcranial magnetic stimulation and (Schizophrenia or OCD or MDD or ADHD)". Studies that utilized TMS/MEP and/or TMS/hd-EEG measures to characterize cortical excitability, inhibition, oscillatory activity, and/or connectivity in psychiatric patients were selected. Across disorders, patients displayed a pattern of reduced cortical inhibition, and to a lesser extent increased excitability, in the motor cortex, which was most consistently established in Schizophrenia. Furthermore, psychiatric patients showed abnormalities in a number of TMS-evoked EEG oscillations, which was most prominent in the prefrontal cortex of Schizophrenia relative to healthy comparison subjects. Overall, results from this review point to significant impairments in cortical excitability, inhibition, and oscillatory activity, especially in frontal areas, in several major psychiatric disorders. Building on these findings, future studies employing TMS-based experimental paradigms may help elucidating the neurobiology of these psychiatric disorders, and may assess the contribution of TMS-related measures in monitoring and possibly maximizing the effectiveness of treatment interventions in psychiatric populations.

Non-invasive modulation reduces repetitive behavior in a rat model through the sensorimotor cortico-striatal circuit

Involuntary movements as seen in repetitive disorders such as Tourette Syndrome (TS) results from cortical hyperexcitability that arise due to striato-thalamo-cortical circuit (STC) imbalance. Transcranial direct current stimulation (tDCS) is a stimulation procedure that changes cortical excitability, yet its relevance in repetitive disorders such as TS remains largely unexplored. Here, we employed the dopamine transporter-overexpressing (DAT-tg) rat model to investigate behavioral and neurobiological effects of frontal tDCS. The outcome of tDCS was pathology dependent, as anodal tDCS decreased repetitive behavior in the DAT-tg rats yet increased it in wild-type (wt) rats. Extensive deep brain stimulation (DBS) application and computational modeling assigned the response in DAT-tg rats to the sensorimotor pathway. Neurobiological assessment revealed cortical activity changes and increase in striatal inhibitory properties in the DAT-tg rats. Our findings show that tDCS reduces repetitive behavior in the DAT-tg rat through modulation of the sensorimotor STC circuit. This sets the stage for further investigating the usage of tDCS in repetitive disorders such as TS.

Investigating the Interactive Effects of Sex Steroid Hormones and Brain-Derived Neurotrophic Factor during Adolescence on Hippocampal NMDA Receptor Expression

Sex steroid hormones have neuroprotective properties which may be mediated by brain-derived neurotrophic factor (BDNF). This study sought to determine the interactive effects of preadolescent hormone manipulation and BDNF heterozygosity (^+/-) on hippocampal NMDA-R expression. Wild-type and BDNF^+/- mice were gonadectomised, and females received either 17β-estradiol or progesterone treatment, while males received either testosterone or dihydrotestosterone (DHT) treatment. Dorsal (DHP) and ventral hippocampus (VHP) were dissected, and protein expression of GluN1, GluN2A, GluN2B, and PSD-95 was assessed by Western blot analysis. Significant genotype × OVX interactions were found for GluN1 and GluN2 expression within the DHP of female mice, suggesting modulation of select NMDA-R levels by female sex hormones is mediated by BDNF. Furthermore, within the DHP BDNF^+/- mice show a hypersensitive response to hormone treatment on GluN2 expression which may result from upstream alterations in TrkB phosphorylation. In contrast to the DHP, the VHP showed no effects of hormone manipulation but significant effects of genotype on NMDA-R expression. Castration had no effect on NMDA-R expression; however, androgen treatment had selective effects on GluN2B. These data show case distinct, interactive roles for sex steroid hormones and BDNF in the regulation of NMDA-R expression that are dependent on dorsal versus ventral hippocampal region.

Cognitive correlates of visual neural plasticity in schizophrenia

Neuroplasticity may be an important treatment target to improve the cognitive deficits in schizophrenia (SZ). Yet, it is poorly understood and difficult to assess. Recently, a visual high-frequency stimulation (HFS) paradigm that potentiates electroencephalography (EEG)-based visual evoked potentials (VEP) has been developed to assess neural plasticity in the visual cortex. Using this paradigm, we examined visual plasticity in SZ patients (N=64) and its correlations with clinical symptoms, neurocognition, functional capacity, and community functioning. VEPs were assessed prior to (baseline), and 2-, 4-, and 20-min after (Post-1, Post-2, and Post-3, respectively) 2min of visual HFS. Cluster-based permutation tests were conducted to identify time points and electrodes at which VEP amplitudes were significantly different after HFS. Compared to baseline, there was increased negativity between 140 and 227ms for the early post-HFS block (average of Post-1 and Post-2), and increased positivity between 180 and 281ms for the late post-HFS block (Post-3), at parieto-occipital and occipital electrodes. The increased negativity in the early post-HFS block did not correlate with any of the measures, whereas increased positivity in the late post-HFS block correlated with better neurocognitive performance. Results suggest that SZ patients exhibit both short- and long-term plasticity. The long-term plasticity effect, which was present 22min after HFS, was evident relatively late in the VEP, suggesting that neuroplastic changes in higher-order visual association areas, rather than earlier short-term changes in primary and secondary visual cortex, may be particularly important for the maintenance of neurocognitive function in SZ.

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.

The Activity-Induced Long Non-Coding RNA Meg3 Modulates AMPA Receptor Surface Expression in Primary Cortical Neurons

Transcription of new RNA is crucial for maintaining synaptic plasticity, learning and memory. Although the importance of synaptic plasticity-related messenger RNAs (mRNAs) is well established, the role of a large group of long non-coding RNAs (lncRNAs) in long-term potentiation (LTP) is not known. In this study, we demonstrated the expression of a lncRNA cluster, namely maternally expressed gene 3 (Meg3), retrotransposon-like gene 1-anti-sense (Rtl1-AS), Meg8 and Meg9, which is located in the maternally imprinted Dlk1-Dio3 region on mouse chromosome 12qF1, in primary cortical neurons following glycine stimulation in an N-Methyl-D-aspartate receptor (NMDAR)-dependent manner. Importantly, we also validated the expression of Meg3, Meg8 and Meg9 in the hippocampus of mice following cued fear conditioning in vivo. Interestingly, Meg3 is the only lncRNA that is expressed in the nucleus and cytoplasm. Further analysis revealed that Meg3 loss of function blocked the glycine-induced increase of the GluA1 subunit of AMPA receptors on the plasma membrane, a major hallmark of LTP. This aberrant trafficking of AMPA receptors correlated with the dysregulation of the phosphatidylinoside-3-kinase (PI3K)/AKT signaling pathway and the downregulation of the lipid phosphatase and tensin homolog (PTEN). These findings provide the first evidence for a functional role of the lncRNA Meg3 in the intricate regulation of the PTEN/PI3K/AKT signaling cascade during synaptic plasticity in neurons.

Compromised neuroplasticity in cigarette smokers under nicotine withdrawal is restituted by the nicotinic α4β2-receptor partial agonist varenicline

Nicotine modulates neuroplasticity and improves cognitive functions in animals and humans. In the brain of smoking individuals, calcium-dependent plasticity induced by non-invasive brain stimulation methods such as transcranial direct current stimulation (tDCS) and paired associative stimulation (PAS) is impaired by nicotine withdrawal, but partially re-established after nicotine re-administration. In order to investigate the underlying mechanism further, we tested the impact of the α₄β₂-nicotinic receptor partial agonist varenicline on focal and non-focal plasticity in smokers during nicotine withdrawal, induced by PAS and tDCS, respectively. We administered low (0.3 mg) and high (1.0 mg) single doses of varenicline or placebo medication before stimulation over the left motor cortex of 20 healthy smokers under nicotine withdrawal. Motor cortex excitability was monitored by single-pulse transcranial magnetic stimulation-induced motor evoked potential amplitudes for 36 hours after plasticity induction. Stimulation-induced plasticity was absent under placebo medication, whereas it was present in all conditions under high dose. Low dose restituted only tDCS-induced non-focal plasticity, producing no significant impact on focal plasticity. High dose varenicline also prolonged inhibitory plasticity. These results are comparable to the impact of nicotine on withdrawal-related impaired plasticity in smokers and suggest that α₄β₂ nicotinic receptors are relevantly involved in plasticity deficits and restitution in smokers.

Risperidone increases the cortical silent period in drug-naive patients with first-episode schizophrenia: A transcranial magnetic stimulation study

OBJECTIVES

Schizophrenia is accompanied by impaired cortical inhibition, as measured by several markers including the cortical silent period (CSP). It is thought that CSP measures gamma-aminobutyric acid receptors B (GABA_B) mediated inhibitory activity. But the mutual roles of schizophrenia as a disease and the drugs used for the treatment of psychosis on GABA mediated neurotransmission are not clear.

METHODS

We recruited 13 drug-naive patients with first-episode schizophrenia. We used transcranial magnetic stimulation to assess CSP prior to initiating risperidone monotherapy and again four weeks later. At the same time, we rated the severity of psychopathology using the Positive and Negative Syndrome Scale (PANSS).

RESULTS

We obtained data from 12 patients who showed a significant increase in CSP, from 134.20±41.81 ms to 162.95±61.98 ms ( p=0.041; Cohen's d=0.544). After the treatment, the PANSS total score was significantly lower, as were the individual subscores ( p<0.05). However, no correlation was found between ΔCSP and ΔPANSS.

CONCLUSION

Our study in patients with first-episode schizophrenia demonstrated an association between risperidone monotherapy and an increase in GABA_B mediated inhibitory neurotransmission.

The application of tDCS for the treatment of psychiatric diseases

Neuroplasticity represents the dynamic structural and functional reorganization of the central nervous system, including its connectivity, due to environmental and internal demands. It is recognized as a major physiological basis for adaption of cognition and behaviour, and, thus, of utmost importance for normal brain function. Cognitive dysfunctions are major symptoms in psychiatric disorders, which are often associated with pathological alteration of neuroplasticity. Transcranial direct current stimulation (tDCS), a recently developed non-invasive brain stimulation technique, is able to induce and modulate cortical plasticity in humans via the application of relatively weak current through the scalp of the head. It has the potential to alter pathological plasticity and restore dysfunctional cognitions in psychiatric diseases. In the last decades, its efficacy to treat psychiatric disorders has been explored increasingly. This review will give an overview of pathological alterations of plasticity in psychiatric diseases, gather clinical studies involving tDCS to ameliorate symptoms, and discuss future directions of application, with an emphasis on optimizing stimulation effects.

Enhancing Nervous System Recovery through Neurobiologics, Neural Interface Training, and Neurorehabilitation

After an initial period of recovery, human neurological injury has long been thought to be static. In order to improve quality of life for those suffering from stroke, spinal cord injury, or traumatic brain injury, researchers have been working to restore the nervous system and reduce neurological deficits through a number of mechanisms. For example, neurobiologists have been identifying and manipulating components of the intra- and extracellular milieu to alter the regenerative potential of neurons, neuro-engineers have been producing brain-machine and neural interfaces that circumvent lesions to restore functionality, and neurorehabilitation experts have been developing new ways to revitalize the nervous system even in chronic disease. While each of these areas holds promise, their individual paths to clinical relevance remain difficult. Nonetheless, these methods are now able to synergistically enhance recovery of native motor function to levels which were previously believed to be impossible. Furthermore, such recovery can even persist after training, and for the first time there is evidence of functional axonal regrowth and rewiring in the central nervous system of animal models. To attain this type of regeneration, rehabilitation paradigms that pair cortically-based intent with activation of affected circuits and positive neurofeedback appear to be required-a phenomenon which raises new and far reaching questions about the underlying relationship between conscious action and neural repair. For this reason, we argue that multi-modal therapy will be necessary to facilitate a truly robust recovery, and that the success of investigational microscopic techniques may depend on their integration into macroscopic frameworks that include task-based neurorehabilitation. We further identify critical components of future neural repair strategies and explore the most updated knowledge, progress, and challenges in the fields of cellular neuronal repair, neural interfacing, and neurorehabilitation, all with the goal of better understanding neurological injury and how to improve recovery.

Tuning noninvasive brain stimulation with MRI to cope with intersubject variability

PURPOSE OF REVIEW

The review aims at highlighting the additional benefit that can be gained from combining noninvasive brain stimulation as well as repetitive sensory stimulation protocols with MRI techniques to account for the intersubject variability observed in those treatments. Potentially, this should help to identify predictive patterns in the individual receptiveness to the treatment.

RECENT FINDINGS

Knowledge about the underlying physiological principles of excitability changes as induced by noninvasive brain stimulation or repetitive sensory stimulation is accumulating, revealing strong associations with plasticity processes at the synaptic level. In this context, MRI techniques, such as magnetic resonance spectroscopy and functional MRI, emerged as valuable tools for the qualitative assessment of baseline states and induced changes. Those physiological readouts can help explain the interindividual heterogeneity found in behavioural and/or clinical responses to the specific stimulation protocols. This knowledge will eventually translate, first, into the preliminary classification of study participants into treatment groups according to their neurophysiological baseline state and expected responses to a particular stimulation. Subsequently, this should also aid the optimization of stimulation protocols according to the classification outcome, resulting in retuned protocols for particular groups of study participants.

SUMMARY

The consistent MRI-based monitoring of stimulation effects in the neural network promises a considerable gain for the customization of intervention protocols with improved therapeutic potential and rehabilitative predictions.

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.