Smoking restores impaired LTD-like plasticity in schizophrenia: a transcranial direct current stimulation study

The two-way relationship between nicotine and cortical activity: a systematic review of neurobiological and treatment aspects

Nicotine intake and cortical activity are closely related, as they can influence each other. Nicotine is implicated in the induction and modification of cortical plasticity and excitability, whereas a change on cortical plasticity and excitability can also lead to a modification of the smoking behaviour of an individual. The aim of this systematic review was, on the one hand, to evaluate the effects of nicotinergic modulation on cortical excitability and plasticity, and, on the other hand, to assess if modifying the brain's excitability and plasticity could influence one's smoking behaviour. Two systematic literature searches in the PubMed/MEDLINE and PsycINFO databases were conducted. Studies focusing either on the impact of nicotinergic modulation on cortical activity or the treatment effect of non-invasive brain stimulation techniques (NIBS) on smoking behaviour were included. A total of 22 studies for the first systematic search and 35 studies for the second one were included after full-text screening. Nicotine's effect on cortical activity appeared to depend on smoking status of the individual. While deprived smokers seem to generally profit from nicotine consumption in terms of cortical excitability and plasticity, the contrary was true for non-smokers. Regarding the questions of how changes in cortical excitability can influence smoking behaviour, a trend points towards NIBS being a potential intervention technique for smoking cessation.

Examining bi-anodal transcranial direct current stimulation (tDCS) over bilateral dorsolateral prefrontal cortex coupled with bilateral extracephalic references as a treatment for negative symptoms in non-acute schizophrenia patients: A randomized, double-blind, sham-controlled trial

No studies have examined the efficacy of bi-anodal transcranial direct current stimulation (tDCS) over bilateral dorsolateral prefrontal cortex (DLPFC) coupled with bilateral extracephalic references in treating negative symptoms of non-acute schizophrenia patients. This study aimed to investigate the therapeutic effects of the new approach of tDCS on negative symptoms, other schizophrenia symptoms, cognitive deficits and psychosocial functioning in a double-blind, randomized, sham-controlled trial. Patients with non-acute schizophrenia (N = 60) in randomized order received sham treatment or bilaterally provided tDCS (2 mA, twice-daily sessions for five consecutive days) with the anode over the DLPFC and the reference (cathode) over the ipsilateral forearm. The negative symptoms as measured by a dimensional approach of Positive and Negative Syndrome Scale (PANSS) were rapidly reduced by bimodal tDCS relative to sham stimulation (F = 24.86, Cohen's d = 0.661, p = 6.11 × 10^-6). The beneficial effect on negative symptoms lasted for up to 3 months. The authors also observed improvement with tDCS of psychosocial functioning as measured by the global score of Personal and Social Performance scale (PSP) and psychopathological symptoms especially for disorganization and cognitive symptoms as measured by the PANSS. No effects were observed on other schizophrenia symptom dimensions and the performance on a series of neurocognitive tests. Our results show promise for bi-anodal tDCS over bilateral DLPFC using bilateral extracephalic references in treating negative symptoms and other selected manifestations of schizophrenia. Further studies with electrophysiological or imaging evaluation help unravel the exact mechanism of action of this novel stimulation parameter of tDCS in schizophrenia patients. (ClinicalTrials.gov ID:NCT03701100).

Improving cognitive training for schizophrenia using neuroplasticity enhancers: Lessons from decades of basic and clinical research

Mounting evidence indicates that schizophrenia is a disorder that stems from maladaptive plasticity within neural circuits and produces broad cognitive deficits leading to loss of autonomy. A large number of studies have identified abnormalities spanning many neurotransmitter systems in schizophrenia, and as a result, a variety of drugs have been developed to attempt to treat these abnormalities and enhance cognition. Unfortunately, positive results have been limited so far. This may be in part because the scope of abnormalities in the schizophrenic brain requires a treatment capable of engaging many different neurotransmitter systems. One approach to achieving this kind of treatment has been to use neuroplasticity-based computerized cognitive training programs to stimulate the formation of more adaptive circuits. Although the number of studies implementing this approach has increased exponentially in recent years, effect sizes for cognitive gains have been modest and adherence to treatment remains an important challenge in many studies, as patients are often required to train for 40 h or more. In the present paper, we argue that cognitive training protocols will benefit from the addition of cognitive enhancers to produce more robust and longer lasting targeted neuroplasticity. Indeed, recent data from animal studies have provided support for combining plasticity-enhancing drugs with tailored behavioral training paradigms to restore normal function within dysfunctioning neural circuits. The advantages and challenges of applying this approach to patients with schizophrenia will be discussed.

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.

Elevated mirror neuron system activity in bipolar mania: Evidence from a transcranial magnetic stimulation study

OBJECTIVES

The role of the "mirror neuron system" (MNS) in the pathophysiology of mood disorders is not well studied. Given its posited role in the often-impaired socio-emotional processes like intention detection, empathy, and imitation, we compared putative MNS-activity in patients with bipolar mania and healthy comparison subjects. We also examined the association between putative MNS-activity and hyper-imitative behaviors in patients.

METHODS

We studied 39 medication-free individuals diagnosed with mania and 45 healthy comparison subjects. TMS-evoked motor cortical reactivity was measured via single- and paired-pulse stimuli (assessing SICI-short and LICI-long interval intracortical inhibition) while subjects viewed a static image and goal-directed actions. Manic symptom severity and imitative behaviors were quantified using the Young's Mania Rating Scale and a modification of the Echolalia Questionnaire.

RESULTS

Two-way repeated measures analysis of variance demonstrated a significant group ×time interaction effect indicating greater facilitation of cortical reactivity during action-observation (putative MNS-activity) in the patient group as compared to the healthy group. While LICI-mediated MNS-activity had a significant association with manic symptom severity (r = 0.35, P = 0.038), SICI-mediated MNS-activity was significantly associated with incidental echolalia scores in a subgroup of 17 patients with incidental echolalia (r = 0.75, P < 0.001).

CONCLUSIONS

Our findings demonstrate that putative MNS-activity is heightened in mania, possibly because of disinhibition, and associated with behavioral consequences (incidental echolalia).

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.

Improving working memory in schizophrenia: Effects of 1 mA and 2 mA transcranial direct current stimulation to the left DLPFC

Deficits in various cognitive processes, such as working memory, are characteristic for schizophrenia, lowering patients' functioning and quality of life. Recent research suggests that transcranial direct stimulation (tDCS) applied to the dorsolateral prefrontal cortex (DLPFC) may be a potential therapeutic intervention for cognitive deficits in schizophrenia. Here, we examined the effects of online tDCS to the DLPFC on working memory (WM) performance in 40 schizophrenia patients in two separate experiments with a double blind, sham-controlled, cross-over design. Patients underwent single sessions of active and sham tDCS in a randomized order. Stimulation parameters were anode F3, cathode right deltoid muscle, 21 min tDCS duration, 1 mA tDCS in Experiment 1 (N = 20) and 2 mA tDCS in Experiment 2 (N = 20). Primary outcome was the change in WM performance as measured by a verbal n-back paradigm (1- to 3-back). Irrespective of the stimulation intensity, data analysis showed a significant higher WM accuracy during active tDCS than during sham tDCS (p = 0.019), but no main effect of stimulation intensity (p = 0.392). Subsequent separate analyses revealed a significantly improved WM performance only during 1 mA (p = 0.048). TDCS facilitated WM functioning in schizophrenia, with an advantage of 1 mA over 2 mA. Our results support the notion that tDCS may be a potential treatment for cognitive deficits in schizophrenia and emphasize the need for future research on the specific stimulation parameters.

Modulating Neural Circuits with Transcranial Magnetic Stimulation: Implications for Addiction Treatment Development

Although the last 50 years of clinical and preclinical research have demonstrated that addiction is a brain disease, we still have no neural circuit-based treatments for substance dependence or cue reactivity at large. Now, for the first time, it appears that a noninvasive brain stimulation technique known as transcranial magnetic stimulation (TMS), which is Food and Drug Administration approved to treat depression, may be the first tool available to fill this critical void in addiction treatment development. The goals of this review are to 1) introduce TMS as a tool to induce causal change in behavior, cortical excitability, and frontal-striatal activity; 2) describe repetitive TMS (rTMS) as an interventional tool; 3) provide an overview of the studies that have evaluated rTMS as a therapeutic tool for alcohol and drug use disorders; and 4) outline a conceptual framework for target selection when designing future rTMS clinical trials in substance use disorders. The manuscript concludes with some suggestions for methodological innovation, specifically with regard to combining rTMS with pharmacotherapy as well as cognitive behavioral training paradigms. We have attempted to create a comprehensive manuscript that provides the reader with a basic set of knowledge and an introduction to the primary experimental questions that will likely drive the field of TMS treatment development forward for the next several years.

The effects of medication use in transcranial direct current stimulation: A brief review

BACKGROUND

There has been increased interest in the potential use of transcranial direct current stimulation (tDCS) as treatment for multiple conditions including depression, pain, and cognitive impairment. However, few studies account for the possible influence of comorbid medications when conducting tDCS research.

OBJECTIVE/HYPOTHESIS

This literature review was conducted to examine what is currently known about the impact of medications on tDCS, provide recommendations for future research practices, and highlight areas where more research is needed.

METHODS

Key terms were searched in PubMed and Web of Science to identify studies that examine the impact of medication on tDCS effects in adults. Relevant papers' reference lists were also reviewed for thoroughness. Studies examined the effects of medication on 1 mA tDCS delivered to M1 (motor) and orbit/supraorbital (SO) area. All studies measured the effects of tDCS via MEP TMS paradigm.

RESULTS

Results of the literature review suggest multiple classes of medications, including sodium and calcium channel blockers, and medications that influence various neurotransmitter systems (GABA, dopamine, serotonin, etc.) may all impact tDCS effects on tissue excitability.

CONCLUSIONS

Research to date suggests multiple classes of medications may impact tDCS effects. These results highlight the importance of documenting medication use in research subjects and carefully considering what types of medications should be allowed into tDCS trials. Many questions still remain regarding the exact mechanisms of action for tDCS and how various parameters (medication dosages, tDCS stimulation intensity, etc.) may further impact the effects of medications on tDCS.

Allosteric Modulation of GPCRs: New Insights and Potential Utility for Treatment of Schizophrenia and Other CNS Disorders

G-protein-coupled receptors (GPCRs) play critical roles in regulating brain function. Recent advances have greatly expanded our understanding of these receptors as complex signaling machines that can adopt numerous conformations and modulate multiple downstream signaling pathways. While agonists and antagonists have traditionally been pursued to target GPCRs, allosteric modulators provide several mechanistic advantages, including the ability to distinguish between closely related receptor subtypes. Recently, the discovery of allosteric ligands that confer bias and modulate some, but not all, of a given receptor's downstream signaling pathways can provide pharmacological modulation of brain circuitry with remarkable precision. In addition, allosteric modulators with unprecedented specificity have been developed that can differentiate between subpopulations of a given receptor subtype based on the receptor's dimerization state. These advances are not only providing insight into the biological roles of specific receptor populations, but hold great promise for treating numerous CNS disorders.

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.

Differential effects of cannabis dependence on cortical inhibition in patients with schizophrenia and non-psychiatric controls

BACKGROUND

Cannabis is the most commonly used illicit substance among patients with schizophrenia. Cannabis exacerbates psychotic symptoms and leads to poor functional outcomes. Dysfunctional cortical inhibition has been implicated in the pathophysiology of schizophrenia; however, the effects of cannabis on this mechanism have been relatively unexamined. The goal of this study was to index cortical inhibition from the motor cortex among 4 groups: schizophrenia patients and non-psychiatric controls dependent on cannabis as well as cannabis-free schizophrenia patients and non-psychiatric controls.

METHODS

In this cross-sectional study, GABA-mediated cortical inhibition was index with single- and paired-pulse transcranial magnetic stimulation (TMS) paradigms to the left motor cortex in 12 cannabis dependent and 11 cannabis-free schizophrenia patients, and in 10 cannabis dependent and 13 cannabis-free controls.

RESULTS

Cannabis-dependent patients with schizophrenia displayed greater short-interval cortical inhibition (SICI) compared to cannabis-free schizophrenia patients (p = 0.029), while cannabis-dependent controls displayed reduced SICI compared to cannabis-free controls (p = 0.004). SICI did not differ between cannabis dependent patients and cannabis-free controls, or between dependent schizophrenia patients compared to dependent controls. No significant differences were found for long-interval cortical inhibition (LICI) or intra-cortical facilitation (ICF) receptor function, suggesting a selective effect on SICI.

CONCLUSION

These findings suggest that cannabis dependence may have selective and differing effects on SICI in schizophrenia patients compared to controls, which may provide insight into the pathophysiology of co-morbid cannabis dependence in schizophrenia.

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.

[Non-invasive brain stimulation for treatment of schizophrenic psychoses]

Despite many different available pharmacological and psychosocial treatment options, an optimal control of symptoms is only partly possible for most schizophrenia patients. Especially, persistent auditory hallucinations, negative symptoms and cognitive impairment are difficult to treat symptoms. Several non-invasive brain stimulation techniques are increasingly being considered as new therapeutic add on options for the management of schizophrenia, targeting these symptom domains. The technique which has been available for the longest time and that is best established in clinical care is electroconvulsive therapy (ECT). New stimulation techniques, such as repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) allow a more pathophysiological-based approach. This review article introduces various non-invasive brain stimulation techniques and discusses recent treatment studies on schizophrenia. In total, the novel brain stimulation techniques discussed here can be considered relevant add on therapeutic approaches for schizophrenia. In this context, the best evidence is available for the application of rTMS for the treatment of negative symptoms and persistent auditory hallucinations; however, negative studies have also been published for both indications. Studies using other non-invasive brain stimulation techniques showed promising results but further research is needed to establish the clinical efficacy. Based on a growing pathophysiological knowledge, non-invasive brain stimulation techniques provide new treatment perspectives for patients with schizophrenia.

Consensus paper of the WFSBP Task Force on Biological Markers: Criteria for biomarkers and endophenotypes of schizophrenia part I: Neurophysiology

The neurophysiological components that have been proposed as biomarkers or as endophenotypes for schizophrenia can be measured through electroencephalography (EEG) and magnetoencephalography (MEG), transcranial magnetic stimulation (TMS), polysomnography (PSG), registration of event-related potentials (ERPs), assessment of smooth pursuit eye movements (SPEM) and antisaccade paradigms. Most of them demonstrate deficits in schizophrenia, show at least moderate stability over time and do not depend on clinical status, which means that they fulfil the criteria as valid endophenotypes for genetic studies. Deficits in cortical inhibition and plasticity measured using non-invasive brain stimulation techniques seem promising markers of outcome and prognosis. However the utility of these markers as biomarkers for predicting conversion to psychosis, response to treatments, or for tracking disease progression needs to be further studied.

Potentiation of M1 Muscarinic Receptor Reverses Plasticity Deficits and Negative and Cognitive Symptoms in a Schizophrenia Mouse Model

Schizophrenia patients exhibit deficits in signaling of the M1 subtype of muscarinic acetylcholine receptor (mAChR) in the prefrontal cortex (PFC) and also display impaired cortical long-term depression (LTD). We report that selective activation of the M1 mAChR subtype induces LTD in PFC and that this response is completely lost after repeated administration of phencyclidine (PCP), a mouse model of schizophrenia. Furthermore, discovery of a novel, systemically active M1 positive allosteric modulator (PAM), VU0453595, allowed us to evaluate the impact of selective potentiation of M1 on induction of LTD and behavioral deficits in PCP-treated mice. Interestingly, VU0453595 fully restored impaired LTD as well as deficits in cognitive function and social interaction in these mice. These results provide critical new insights into synaptic changes that may contribute to behavioral deficits in this mouse model and support a role for selective M1 PAMs as a novel approach for the treatment of schizophrenia.

Effects of transcranial direct current stimulation (tDCS) on cognition, symptoms, and smoking in schizophrenia: A randomized controlled study

Schizophrenia is characterized by cognitive deficits which persist after acute symptoms have been treated or resolved. Transcranial direct current stimulation (tDCS) has been reported to improve cognition and reduce smoking craving in healthy subjects but has not been as carefully evaluated in a randomized controlled study for these effects in schizophrenia. We conducted a randomized double-blind, sham-controlled study of the effects of 5 sessions of tDCS (2 milliamps for 20minutes) on cognition, psychiatric symptoms, and smoking and cigarette craving in 37 outpatients with schizophrenia or schizoaffective disorder who were current smokers. Thirty subjects provided evaluable data on the MATRICS Consensus Cognitive Battery (MCCB), with the primary outcome measure, the MCCB Composite score. Active compared to sham tDCS subjects showed significant improvements after the fifth tDCS session in MCCB Composite score (p=0.008) and on the MCCB Working Memory (p=0.002) and Attention-Vigilance (p=0.027) domain scores, with large effect sizes. MCCB Composite and Working Memory domain scores remained significant at Benjamini-Hochberg corrected significance levels (α=0.05). There were no statistically significant effects on secondary outcome measures of psychiatric symptoms (PANSS scores), hallucinations, cigarette craving, or cigarettes smoked. The positive effects of tDCS on cognitive performance suggest a potential efficacious treatment for cognitive deficits in partially recovered chronic schizophrenia outpatients that should be further investigated.