Modulating neural plasticity with non-invasive brain stimulation in schizophrenia

The impact of transcranial direct current stimulation combined with interim testing on spatial route learning in patients with schizophrenia

BACKGROUND

Cognitive deficits in patients with schizophrenia have drawn widespread attention. Transcranial direct current stimulation (tDCS) can modulate cognitive processes by altering neuronal excitability. Previous studies have found that interim testing can enhance spatial route learning and memory in patients with schizophrenia. However, there has been limited research on the combined effects of these two methods on spatial route learning in these patients.

OBJECTIVE

To investigate whether the combination of tDCS and interim testing can effectively contribute to the maintenance of spatial route memory in patients with schizophrenia. The study involved conducting route learning using interim testing after anodal tDCS treatment on the left dorsolateral prefrontal cortex (L-DLPFC).

METHODS

Ninety-two patients with schizophrenia were recruited and divided into groups receiving anodal, sham, or no stimulation. The anodal group received L-DLPFC tDCS treatment 10 times over 5 days (twice daily for 20 min). After treatment, spatial route learning was assessed in interim testing. Correct recall rates of landmark positions and proactive interference from prior learning were compared among the groups.

RESULTS

Regardless of stimulation type, the interim testing group outperformed the relearning group. Additionally, recall scores were higher following anodal stimulation, indicating the efficacy of tDCS.

CONCLUSIONS

Both tDCS and interim testing independently enhance the ability to learn new information in spatial route learning for patients with schizophrenia, indicating that tDCS of the left DLPFC significantly improves memory in these patients.

Noninvasive direct current stimulation for schizophrenia: a review

PURPOSE OF REVIEW

To provide an update of recent studies describing the effects of transcranial direct current stimulation (tDCS) on patients with schizophrenia, with particular focus on auditory verbal hallucinations (AVH), cognitive deficits, and negative symptoms.

RECENT FINDINGS

As a low-cost, easy-to-use neuromodulation technique, tDCS may have clinical implications for those suffering from treatment-persistent AVH, negative symptoms, and cognitive symptoms in schizophrenia. Over the past decade, tDCS has shown no effects for negative symptoms, except when used at a high frequency of sessions, and inconclusive results for AVH and cognitive symptoms. The treatment has little to no adverse effects.

SUMMARY

The studies reviewed here support the need for further investigation and empirical data regarding the use of tDCS. The underlying mechanisms of tDCS as well as the most effective stimulation parameters must be better understood. Findings support the need for increased duration and frequency of tDCS sessions. One of the next steps is the investigation of effects of concomitant nonpharmacological treatments with tDCS.

The integrated model of glutamate and dopamine hypothesis for schizophrenia: Prediction and personalized medicine for prevent potential treatment-resistant patients

Treatment-resistant schizophrenia (TRS) is one of the subgroups of schizophrenia of which little is known with regard to its optimal mechanism. Treatment response, either as full remission of symptoms or prediction by biomarker, is important in psychiatry. We have proposed a model that integrates dopaminergic and glutamatergic systems with the biological interactions of TRS patients. We hypothesize that the subgroups of schizophrenia may be determined by glutamatergic and dopaminergic concentrations prior to medical treatment. This hypothesis implies that higher glutamatergic concentration in the brain with normalized or decreased dopamine synthesis capacity may explain aspects of TRS as observed in clinical medical practice, neuroimaging measurements, and brain stimulations. According to this hypothesis, the ability to prescribe a proper medication combination, to predict the outcome in first-episode psychosis, and personalized medicine for chronic schizophrenia patients can be applied into practice. This represents an initial step in explaining psychosis due to the valence of two neurotransmitters. Future studies are needed to examine the validity of this mechanism.

Development of Electrical Neural Stimulator Generating Periodic and Non-periodic Signals and Supporting Closed-loop Experimental System

It is essential to build a system to generate proper neural stimulus signals with adjusting parameters. We developed a stimulator with up to four channels for separate settings in periodic and non-periodic modes. The device can support a closed-loop experimental system which utilizes neural information in real time as a feedback for controlling stimuli. To confirm whether stimulating signals are properly produced and delivered inside the brain, two experiments with rats were conducted. We observed that the change of firing rates and the cross-power spectral density increased after stimulation which meant that electric signals were transferred well and that they affected the neurons' activities. Thus, it is expected that the stimulator can be utilized to produce appropriate stimulation signals in accordance with various objectives.

Use of Transcranial Direct Stimulation in the Treatment of Negative Symptoms of Schizophrenia

Schizophrenia is a debilitating disease that affects approximately 1% of the population. Negative symptoms are among the major determinants of the functional impairment and a significant proportion of patients with negative symptoms will continue to experience these symptoms despite antipsychotic medications. There are promising results in the application of brain stimulation, particularly transcranial direct current stimulation (tDCS), for the reduction of negative symptoms of schizophrenia. However, findings are still controversial. This is a selective review of the literature published between 2011 and 2017 on use of tDCS in treatment of negative symptoms of schizophrenia. We included only randomized controlled trials where schizophrenia and negative symptoms were assessed using any psychometrically validated scale (eg, Positive and Negative Symptoms Scale or Scale for the Assessment of Negative Symptoms). Studies of participants with neurological conditions were excluded, as were those that did not report any symptom outcome variables. Only 5 studies are included. Three studies showed a decrease of negative symptoms. The other studies did not show any therapeutic effects of tDCS in the severity of positive and negative symptoms compared to controls. Our findings suggest that negative symptoms in schizophrenia can be treated with tDCS over the dorsolateral prefrontal cortex, but results are affected by several factors, such as the electrode montage, the concomitant medication, the homogeneity of the sample, the intensity of the tDCS treatment. Further randomized, double-blinded, sham-controlled studies in large samples are still needed to establish the effectiveness of the tDCS in the treatment of negative symptoms in schizophrenia, but there is the potential for tDCS to become a useful complementary treatment option in this population.

Structural brain changes are associated with response of negative symptoms to prefrontal repetitive transcranial magnetic stimulation in patients with schizophrenia

Impaired neural plasticity may be a core pathophysiological process underlying the symptomatology of schizophrenia. Plasticity-enhancing interventions, including repetitive transcranial magnetic stimulation (rTMS), may improve difficult-to-treat symptoms; however, efficacy in large clinical trials appears limited. The high variability of rTMS-related treatment response may be related to a comparably large variation in the ability to generate plastic neural changes. The aim of the present study was to determine whether negative symptom improvement in schizophrenia patients receiving rTMS to the left dorsolateral prefrontal cortex (DLPFC) was related to rTMS-related brain volume changes. A total of 73 schizophrenia patients with predominant negative symptoms were randomized to an active (n=34) or sham (n=39) 10-Hz rTMS intervention applied 5 days per week for 3 weeks to the left DLPFC. Local brain volume changes measured by deformation-based morphometry were correlated with changes in negative symptom severity using a repeated-measures analysis of covariance design. Volume gains in the left hippocampal, parahippocampal and precuneal cortices predicted negative symptom improvement in the active rTMS group (all r⩽-0.441, all P⩽0.009), but not the sham rTMS group (all r⩽0.211, all P⩾0.198). Further analyses comparing negative symptom responders (⩾20% improvement) and non-responders supported the primary analysis, again only in the active rTMS group (F_{(9, 207)}=2.72, P=0.005, partial η ²=0.106). Heterogeneity in clinical response of negative symptoms in schizophrenia to prefrontal high-frequency rTMS may be related to variability in capacity for structural plasticity, particularly in the left hippocampal region and the precuneus.

Modulation of Brain Activity with Noninvasive Transcranial Direct Current Stimulation (tDCS): Clinical Applications and Safety Concerns

Transcranial direct current stimulation (tDCS) is a widely-used tool to induce neuroplasticity and modulate cortical function by applying weak direct current over the scalp. In this review, we first introduce the underlying mechanism of action, the brief history from discovery to clinical scientific research, electrode positioning and montages, and parameter setup of tDCS. Then, we review tDCS application in clinical samples including people with drug addiction, major depression disorder, Alzheimer's disease, as well as in children. This review covers the typical characteristics and the underlying neural mechanisms of tDCS treatment in such studies. This is followed by a discussion of safety, especially when the current intensity is increased or the stimulation duration is prolonged. Given such concerns, we provide detailed suggestions regarding safety procedures for tDCS operation. Lastly, future research directions are discussed. They include foci on the development of multi-tech combination with tDCS such as with TMS and fMRI; long-term behavioral and morphological changes; possible applications in other research domains, and more animal research to deepen the understanding of the biological and physiological mechanisms of tDCS stimulation.

Parameter-Based Evaluation of Attentional Impairments in Schizophrenia and Their Modulation by Prefrontal Transcranial Direct Current Stimulation

BACKGROUND

Attentional dysfunctions constitute core cognitive symptoms in schizophrenia, but the precise underlying neurocognitive mechanisms remain to be elucidated.

METHODS

In this randomized, double-blind, sham-controlled study, we applied, for the first time, a theoretically grounded modeling approach based on Bundesen's Theory of Visual Attention (TVA) to (i) identify specific visual attentional parameters affected in schizophrenia and (ii) assess, as a proof of concept, the potential of single-dose anodal transcranial direct current stimulation (tDCS; 20 min, 2 mA) to the left dorsolateral prefrontal cortex to modulate these attentional parameters. To that end, attentional parameters were measured before (baseline), immediately after, and 24 h after the tDCS intervention in 20 schizophrenia patients and 20 healthy controls.

RESULTS

At baseline, analyses revealed significantly reduced visual processing speed and visual short-term memory storage capacity in schizophrenia. A significant stimulation condition × time point interaction in the schizophrenia patient group indicated improved processing speed at the follow-up session only in the sham condition (a practice effect), whereas performance remained stable across the three time points in patients receiving verum stimulation. In healthy controls, anodal tDCS did not result in a significant change in attentional performance.

CONCLUSION

With regard to question (i) above, these findings are indicative of a processing speed and short-term memory deficit as primary sources of attentional deficits in schizophrenia. With regard to question (ii), the efficacy of single-dose anodal tDCS for improving (speed aspects of visual) cognition, it appears that prefrontal tDCS (at the settings used in the present study), rather than ameliorating the processing speed deficit in schizophrenia, actually may interfere with practice-dependent improvements in the rate of visual information uptake. Such potentially unexpected effects of tDCS ought to be taken into consideration when discussing its applicability in psychiatric populations. The study was registered at http://apps.who.int/trialsearch/Trial2.aspx?TrialID=DRKS00011665.

[Negative symptoms of schizophrenia: from electrophysiology to electrotherapy]

The aim of this review of the literature is to summarize the state of the knowledge concerning the relationship between negative symptoms in schizophrenia, electrophysiology and electrotherapy. The scientific literature search of international articles was performed during August and September 2015 using the PubMed electronic database. We used the following MeSH terms: "Negative symptoms", "Schizophrenia", "Electrophysiology", "Neurophysiology", "EEG power", "Alpha rhythm", "Transcranial magnetic stimulation", "Transcranial direct current stimulation", "Electroconvulsive therapy", "Neurofeedback", "Vagus Nerve Stimulation", "Deep Brain Stimulation", and "State dependent". Negative symptoms in schizophrenia are associated with altered activity in prefrontal cortex in functional neuroimaging studies. This is in line with electrophysiological measurements that found a change in EEG spectral power in the alpha frequency band over prefrontal brain regions. The notion of functional hypofrontality has led to hypotheses that electrotherapy applied to the prefrontal cortex may be an effective treatment of negative symptoms in schizophrenia. Repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) were used to increase cortical activity in schizophrenia and achieve a clinical effect on negative symptoms. Three meta-analyses confirmed, with a moderate effect size, that rTMS is an effective treatment option for negative symptoms in schizophrenia. The two subsequently published prospective multicenter studies, however, found opposite results from each other. Two randomized controlled studies suggested that tDCS is an effective treatment option for negative symptoms. There is no study on the efficacy of neurofeedback, vagal nerve stimulation or deep brain stimulation on negative symptoms in schizophrenia. Additional studies are needed to confirm the efficacy of rTMS and tDCS on negative symptoms in schizophrenia. Influencing factors, related to clinical and stimulation parameters, of rTMS and tDCS on negative symptoms should be better investigated. Effects related to electrophysiological brain activity of the patient, especially in the alpha band, during the stimulation should also be better investigated. The action of electrotherapy may be state dependent, and a better understanding of electrophysiological effects of electrotherapy techniques could enable their optimization.

A meta-analysis of the effects of aging on motor cortex neurophysiology assessed by transcranial magnetic stimulation

OBJECTIVE

Transcranial magnetic stimulation (TMS) is a non-invasive tool used for studying cortical excitability and plasticity in the human brain. This review aims to quantitatively synthesize the literature on age-related differences in cortical excitability and plasticity, examined by TMS.

METHODS

A literature search was conducted using MEDLINE, Embase, and PsycINFO from 1980 to December 2015. We extracted studies with healthy old (50-89years) versus young (16-49years) individuals that utilized the following TMS measures: resting motor threshold (RMT), short-interval cortical inhibition (SICI), short-latency afferent inhibition (SAI), cortical silent period (CSP), intracortical facilitation (ICF), and paired associative stimulation (PAS).

RESULTS

We found a significant increase in RMT (g=0.414, 95% confidence interval (CI) [0.284, 0.544], p<0.001), a significant decrease in SAI (g=0.778, 95% CI [0.478, 1.078], p<0.001), and a trending decrease in LTP-like plasticity (g=-0.528, 95% CI [-1.157, 0.100] p<0.1) with age.

CONCLUSIONS

Our findings suggest an age-dependent reduction in cortical excitability and sensorimotor integration within the human motor cortex.

SIGNIFICANCE

Alterations in the ability to regulate cortical excitability, sensorimotor integration and plasticity may underlie several age-related motor deficits.

Transcranial direct current stimulation and neuroplasticity genes: implications for psychiatric disorders

BACKGROUND AND AIM

Transcranial direct current stimulation (tDCS) is a non-invasive and well-tolerated brain stimulation technique with promising efficacy as an add-on treatment for schizophrenia and for several other psychiatric disorders. tDCS modulates neuroplasticity; psychiatric disorders are established to be associated with neuroplasticity abnormalities. This review presents the summary of research on potential genetic basis of neuroplasticity-modulation mechanism underlying tDCS and its implications for treating various psychiatric disorders.

METHOD

A systematic review highlighting the genes involved in neuroplasticity and their role in psychiatric disorders was carried out. The focus was on the established genetic findings of tDCS response relationship with BDNF and COMT gene polymorphisms.

RESULT

Synthesis of these preliminary observations suggests the potential influence of neuroplastic genes on tDCS treatment response. These include several animal models, pharmacological studies, mentally ill and healthy human subject trials.

CONCLUSION

Taking into account the rapidly unfolding understanding of tDCS and the role of synaptic plasticity disturbances in neuropsychiatric disorders, in-depth evaluation of the mechanism of action pertinent to neuroplasticity modulation with tDCS needs further systematic research. Genes such as NRG1, DISC1, as well as those linked with the glutamatergic receptor in the context of their direct role in the modulation of neuronal signalling related to neuroplasticity aberrations, are leading candidates for future research in this area. Such research studies might potentially unravel observations that might have potential translational implications in psychiatry.

Impact of antipsychotic medication on transcranial direct current stimulation (tDCS) effects in schizophrenia patients

Transcranial direct current stimulation (tDCS) has generated interest as a treatment modality for schizophrenia. Dopamine, a critical pathogenetic link in schizophrenia, is also known to influence tDCS effects. We evaluated the influence of antipsychotic drug type (as defined by dopamine D2 receptor affinity) on the impact of tDCS in schizophrenia. DSM-IV-TR-diagnosed schizophrenia patients [N=36] with persistent auditory hallucinations despite adequate antipsychotic treatment were administered add-on tDCS. Patients were divided into three groups based on the antipsychotic's affinity to D2 receptors. An auditory hallucinations score (AHS) was measured using the auditory hallucinations subscale of the Psychotic Symptom Rating Scales (PSYRATS). Add-on tDCS resulted in a significant reduction inAHS. Antipsychotic drug type had a significant effect on AHS reduction. Patients treated with high affinity antipsychotics showed significantly lesser improvement compared to patients on low affinity antipsychotics or a mixture of the two. Furthermore, a significant sex-by-group interaction occurred; type of medication had an impact on tDCS effects only in women. Improvement differences could be due to the larger availability of the dopamine receptor system in patients taking antipsychotics with low D2 affinity. Sex-specific differences suggest potential estrogen-mediated effects. This study reports a first-time observation on the clinical utility of antipsychotic drug type in predicting tDCS effects in schizophrenia.

Preserving the Art and Science of Psychotherapy for Advance Practice Psychiatric Mental Health Nurses

Psychiatric Mental Health (PMH) Nurses are challenged to maintain the viability of their roles in today's healthcare climate as advances in research and complexity of mental healthcare needs of society continue to unfold. Today's mental health practice environment includes disciplines with marketable credentials. Roles for PMH nurses in recent decades are less clearly defined than for other disciplines, much of this related to changes in educational and practice settings. This article reviews literature on the topic of psychotherapy and a call for a renewed emphasis on this mode of treatment for psychiatric mental health advance practice nurses.

A Review of Impaired Neuroplasticity in Schizophrenia Investigated with Non-invasive Brain Stimulation

BACKGROUND

Several lines of evidence implicate dysfunctional neuronal plasticity in the pathophysiology of schizophrenia (SCZ). Aberrant glutamatergic and gamma amino--butyric acid neurotransmission are thought to underlie core cognitive deficits and negative symptoms of SCZ. Non-invasive brain stimulation (NIBS) allows for the in vivo study of cortical plasticity and excitability at the systems level of the human motor cortex. This review will focus on summarizing the available neurophysiological evidence for impaired motor cortical plasticity in SCZ assessed by NIBS.

METHODS

A search of MEDLINE, Embase, and PubMed was performed on the use of NIBS techniques to investigate neuroplasticity in the motor cortex of SCZ patients. The relevant articles were summarized.

CONCLUSION

Our review of the literature reveals evidence for disrupted neuroplasticity in SCZ and its close association to alterations in cortical inhibition and dysfunctional intracortical connectivity. Further investigations are required to elucidate the neurobiological mechanisms that underlie dysfunctional plasticity in SCZ in order to develop more targeted therapeutic interventions for SCZ patients.

Left prefrontal high-frequency repetitive transcranial magnetic stimulation for the treatment of schizophrenia with predominant negative symptoms: a sham-controlled, randomized multicenter trial

BACKGROUND

Investigators are urgently searching for options to treat negative symptoms in schizophrenia because these symptoms are disabling and do not respond adequately to antipsychotic or psychosocial treatment. Meta-analyses based on small proof-of-principle trials suggest efficacy of repetitive transcranial magnetic stimulation (rTMS) for the treatment of negative symptoms and call for adequately powered multicenter trials. This study evaluated the efficacy of 10-Hz rTMS applied to the left dorsolateral prefrontal cortex for the treatment of predominant negative symptoms in schizophrenia.

METHODS

A multicenter randomized, sham-controlled, rater-blinded and patient-blinded trial was conducted from 2007-2011. Investigators randomly assigned 175 patients with schizophrenia with predominant negative symptoms and a high-degree of illness severity into two treatment groups. After a 2-week pretreatment phase, 76 patients were treated with 10-Hz rTMS applied 5 days per week for 3 weeks to the left dorsolateral prefrontal cortex (added to the ongoing treatment), and 81 patients were subjected to sham rTMS applied similarly.

RESULTS

There was no statistically significant difference in improvement in negative symptoms between the two groups at day 21 (p = .53, effect size = .09) or subsequently through day 105. Also, symptoms of depression and cognitive function showed no differences in change between groups. There was a small, but statistically significant, improvement in positive symptoms in the active rTMS group (p = .047, effect size = .30), limited to day 21.

CONCLUSIONS

Application of active 10-Hz rTMS to the left dorsolateral prefrontal cortex was well tolerated but was not superior compared with sham rTMS in improving negative symptoms; this is in contrast to findings from three meta-analyses.

Kraepelin revisited: schizophrenia from degeneration to failed regeneration

One hundred years after its conceptual definition as 'Dementia Praecox' by Emil Kraepelin, schizophrenia is still a serious psychiatric illness that affects young adults and leads to disability in at least half of patients. The key treatment issue is partial or non-response, especially of negative symptoms. The illness is also associated with different degrees of cognitive dysfunction, particularly in verbal and working memory; the resulting functional impairment may lead to unemployment and an inability to maintain stable relationships. Patients' cognitive dysfunction led Kraepelin to the assumption that schizophrenia is a form of juvenile dementia caused by a degenerative process of the human brain. Postmortem studies and a plethora of imaging studies do not support the notion of a degenerative process, but such a process is supported by the recently published, largest genome-wide association study on schizophrenia. More than a 100 hits were described, converging on pathways that have a significant role in dopamine metabolism in immune modulation, calcium signalling and synaptic plasticity. This review suggests that research should focus on animal models based on risk genes like transcription factor 4 and study the effects of exposure to environmental stressors relevant for schizophrenia. The use of relevant end points like pre-pulse inhibition or cognitive dysfunction will allow us to gain an understanding of the molecular pathways in schizophrenia and consequently result in improved treatment options, especially for the disabling aspects of this illness.

Dysplasticity, metaplasticity, and schizophrenia: Implications for risk, illness, and novel interventions

In this paper, we review the history of the concept of neuroplasticity as it relates to the understanding of neuropsychiatric disorders, using schizophrenia as a case in point. We briefly review the myriad meanings of the term neuroplasticity, and its neuroscientific basis. We then review the evidence for aberrant neuroplasticity and metaplasticity associated with schizophrenia as well as the risk for developing this illness, and discuss the implications of such understanding for prevention and therapeutic interventions. We argue that the failure and/or altered timing of plasticity of critical brain circuits might underlie cognitive and deficit symptoms, and may also lead to aberrant plastic reorganization in other circuits, leading to affective dysregulation and eventually psychosis. This "dysplastic" model of schizophrenia can suggest testable etiology and treatment-relevant questions for the future.

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

Impaired neuroplastic responses following noninvasive brain stimulation have been reported repeatedly in schizophrenia patients. These findings have been associated with deficits in GABAergic, glutamatergic, and cholinergic neurotransmission. Although various neurophysiological studies have indicated a relationship between nicotine and neuroplasticity in healthy individuals, the present study is the first investigation into the impact of nicotine on LTD-like plasticity in patients with schizophrenia. Cortical excitability and cortical plasticity were explored in 30 schizophrenia patients (17 smoker, 13 nonsmoker) and 45 healthy controls (13 smoker, 32 nonsmoker) by using single-pulse transcranial magnetic stimulation (TMS) before and following cathodal transcranial direct current stimulation (tDCS) applied to the left primary motor cortex. Our analysis revealed abolished LTD-like plasticity in nonsmoking schizophrenia patients. However, these plasticity deficits were not present in smoking schizophrenia patients. In healthy controls, significant MEP reductions following cathodal tDCS were observed in nonsmoking individuals, but only trend-level reductions in smokers. In smoking schizophrenia patients, the severity of negative symptoms correlated positively with reduced neuroplasticity, whereas nonsmoking patients displayed the opposite effect. Taken together, the data of our study support the notion of an association between chronic smoking and the restitution of impaired LTD-like plasticity in schizophrenia patients. Although replication and further research are needed to better understand this relationship, our findings indicate that nicotine intake might stabilize the impaired inhibition-facilitation balance in the schizophrenic brain through a complex interaction between cortical plasticity, and GABAergic and cholinergic neurotransmission, and might explain the reduced prevalence of negative symptoms in this population.

BDNF-Val66Met-polymorphism impact on cortical plasticity in schizophrenia patients: a proof-of-concept study

BACKGROUND

Brain-derived neurotrophic factor (BDNF) has been shown to be a moderator of neuroplasticity. A frequent BDNF-polymorphism (Val66Met) is associated with impairments of cortical plasticity. In patients with schizophrenia, reduced neuroplastic responses following non-invasive brain stimulation have been reported consistently. Various studies have indicated a relationship between the BDNF-Val66Met-polymorphism and motor-cortical plasticity in healthy individuals, but schizophrenia patients have yet to be investigated. The aim of this proof-of-concept study was, therefore, to test the impact of the BDNF-Val66Met-polymorphism on inhibitory and facilitatory cortical plasticity in schizophrenia patients.

METHODS

Cortical plasticity was investigated in 22 schizophrenia patients and 35 healthy controls using anodal and cathodal transcranial direct-current stimulation (tDCS) applied to the left primary motor cortex. Animal and human research indicates that excitability shifts following anodal and cathodal tDCS are related to molecular long-term potentiation and long-term depression. To test motor-cortical excitability before and after tDCS, well-established single- and paired-pulse transcranial magnetic stimulation protocols were applied.

RESULTS

Our analysis revealed increased glutamate-mediated intracortical facilitation in met-heterozygotes compared to val-homozygotes at baseline. Following cathodal tDCS, schizophrenia met-heterozygotes had reduced gamma-amino-butyric-acid-mediated short-interval intracortical inhibition, whereas healthy met-heterozygotes displayed the opposite effect. The BDNF-Val66Met-polymorphism did not influence single-pulse motor-evoked potential amplitudes after tDCS.

CONCLUSIONS

These preliminary findings support the notion of an association of the BDNF-Val66Met-polymorphism with observable alterations in plasticity following cathodal tDCS in schizophrenia patients. This indicates a complex interaction between inhibitory intracortical interneuron-networks, cortical plasticity, and the BDNF-Val66Met-polymorphism. Further replication and validation need to be dedicated to this question to confirm this relationship.

Transcranial direct current stimulation in schizophrenia

Transcranial direct current stimulation (tDCS) is an upcoming treatment modality for patients with schizophrenia. A series of recent observations have demonstrated improvement in clinical status of schizophrenia patients with tDCS. This review summarizes the research work that has examined the effects of tDCS in schizophrenia patients with respect to symptom amelioration, cognitive enhancement and neuroplasticity evaluation. tDCS is emerging as a safe, rapid and effective treatment for various aspects of schizophrenia symptoms ranging from auditory hallucinations-for which the effect is most marked, to negative symptoms and cognitive symptoms as well. An interesting line of investigation involves using tDCS for altering and examining neuroplasticity in patients and healthy subjects and is likely to lead to new insights into the neurological aberrations and pathophysiology of schizophrenia. The mechanistic aspects of the technique are discussed in brief. Future work should focus on establishing the clinical efficacy of this novel technique and on evaluating this modality as an adjunct to cognitive enhancement protocols. Understanding the mechanism of action of tDCS as well as the determinants and neurobiological correlates of clinical response to tDCS remains an important goal, which will help us expand the clinical applications of tDCS for the treatment of patients with schizophrenia.