***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Transcranial direct current stimulation ( tDCS ) of the human motor cortex results in polarity-specific shifts of cortical excitability during and after stimulation . Anodal tDCS enhances and cathodal stimulation reduces excitability . Animal experiments have demonstrated that the effect of anodal tDCS is caused by neuronal depolarisation , while cathodal tDCS hyperpolarises cortical neurones . However , not much is known about the ion channels and receptors involved in these effects . Thus , the impact of the sodium channel blocker carbamazepine , the calcium channel blocker flunarizine and the NMDA receptor antagonist dextromethorphane on tDCS-elicited motor cortical excitability changes of healthy human subjects were tested . tDCS- protocol s inducing excitability alterations ( 1 ) only during tDCS and ( 2 ) eliciting long-lasting after-effects were applied after drug administration . Carbamazepine selectively eliminated the excitability enhancement induced by anodal stimulation during and after tDCS . Flunarizine result ed in similar changes . Antagonising NMDA receptors did not alter current-generated excitability changes during a short stimulation , which elicits no after-effects , but prevented the induction of long-lasting after-effects independent of their direction . These results suggest that , like in other animals , cortical excitability shifts induced during tDCS in humans also depend on membrane polarisation , thus modulating the conductance of sodium and calcium channels . Moreover , they suggest that the after-effects may be NMDA receptor dependent . Since NMDA receptors are involved in neuroplastic changes , the results suggest a possible application of tDCS in the modulation or induction of these processes in a clinical setting . The selective elimination of tDCS-driven excitability enhancements by carbamazepine proposes a role for this drug in focussing the effects of cathodal tDCS , which may have important future clinical applications Weak transcranial direct current stimulation ( tDCS ) induces persisting excitability changes in the human motor cortex . These plastic excitability changes are selectively controlled by the polarity , duration and current strength of stimulation . To reveal the underlying mechanisms of direct current (DC)-induced neuroplasticity , we combined tDCS of the motor cortex with the application of Na(+)-channel-blocking carbamazepine ( CBZ ) and the N-methyl-D-aspartate (NMDA)-receptor antagonist dextromethorphan ( DMO ) . Monitored by transcranial magnetic stimulation ( TMS ) , motor cortical excitability changes of up to 40 % were achieved in the drug-free condition . Increase of cortical excitability could be selected by anodal stimulation , and decrease by cathodal stimulation . Both types of excitability change lasted several minutes after cessation of current stimulation . DMO suppressed the post-stimulation effects of both anodal and cathodal DC stimulation , strongly suggesting the involvement of NMDA receptors in both types of DC-induced neuroplasticity . In contrast , CBZ selectively eliminated anodal effects . Since CBZ stabilizes the membrane potential voltage-dependently , the results reveal that after-effects of anodal tDCS require a depolarization of membrane potentials . Similar to the induction of established types of short- or long-term neuroplasticity , a combination of glutamatergic and membrane mechanisms is necessary to induce the after-effects of tDCS . On the basis of these results , we suggest that polarity-driven alterations of resting membrane potentials represent the crucial mechanisms of the DC-induced after-effects , leading to both an alteration of spontaneous discharge rates and to a change in NMDA-receptor activation The aim of our study was to test if the electrical stimulation of the prefrontal cortex ( PFC ) could modify probabilistic classification learning ( PCL ) .  Transcranial direct current stimulation ( tDCS ) was administered to the left prefrontal and to the primary visual cortex of 22 healthy subjects while they performed a PCL task .  In this task subjects learned which of two outcomes would occur on each trial after presentation of a particular combination of cues . Ten minutes of anodal , but not cathodal , stimulation improved implicit learning only when the left PFC was stimulated . Our results show that implicit PLC can be modified by weak anodal tDCS , which probably increases neural excitability , as has been shown in the motor and visual cortices previously . Our results suggest that further studies on the facilitation of learning and memory processes by tDCS are warranted OBJECTIVE To evaluate the importance of the distance between stimulation electrodes , in various montages , on the ability to induce sustained cortical excitability changes using transcranial direct and r and om noise stimulation . METHODS Twelve healthy subjects participated in four different experimental conditions . The stimulation electrode was always placed over the primary motor cortex ; the reference electrode was placed at the contralateral orbit or at the ipsilateral/contralateral arm . MEPs were recorded in order to measure changes in cortical excitability over time . RESULTS The distance between the two electrodes correlates negatively with the duration and magnitude of induced after-effects . CONCLUSIONS In particular when using extracephalic reference electrodes with transcranial electric stimulation techniques , the stimulation intensity has to be adapted to account for interelectrode distance . SIGNIFICANCE Electrode distance plays a critical role in the induction for stimulation after-effects in tDCS and tRNS studies , and must be taken into account in future studies and also when making comparisons with the published literature Somatosensory integration is a critical cognitive function for human social interaction . Though somatosensory integration has been highly explored in cognitive studies ; only a few studies have explored focal modulation of cortical excitability using a speech perception paradigm . In the current study , we aim ed to investigate the effects of tDCS applied over the temporal cortex of healthy subjects during a go-no-go task in which stimuli were shapes and non-words . Twenty-eight subjects were r and omized to receive cathodal , anodal or sham tDCS bilaterally over the superior temporal cortex ( the reference electrode was on deltoid ) in a counterbalanced order . The effects on judgment of congruency between shapes and non-words in healthy volunteers were measured by a go-no-go task . Our findings show a significant modification of performance according to the polarity of stimulation , task and subject gender . We found that men  performed worse on the no-go condition for congruent stimuli during cathodal tDCS . For reaction time , on the other h and , there was a similar effect for anodal and cathodal stimulation . There were significantly faster responses on incongruent trials during both anodal and cathodal tDCS . Along with previous literature showing gender differences in tasks associated with speech perception , the findings of this study provide additional evidence suggesting that men may have a more focal and restricted neural processing in this multisensory integration task In this paper we demonstrate in the intact human the possibility of a non-invasive modulation of motor cortex excitability by the application of weak direct current through the scalp .  Excitability changes of up to 40 % , revealed by transcranial magnetic stimulation , were accomplished and lasted for several minutes after the end of current stimulation . Excitation could be achieved selectively by anodal stimulation , and inhibition by cathodal stimulation . By varying the current intensity and duration , the strength and duration of the after-effects could be controlled . The effects were probably induced by modification of membrane polarisation . Functional alterations related to post-tetanic potentiation , short-term potentiation and processes similar to postexcitatory central inhibition are the likely c and i date s for the excitability changes after the end of stimulation . Transcranial electrical stimulation using weak current may thus be a promising tool to modulate cerebral excitability in a non-invasive , painless , reversible , selective and focal way OBJECTIVE Some 25%–30 % of patients with schizophrenia have auditory verbal hallucinations that are refractory to antipsychotic drugs . Outcomes in studies of repetitive transcranial magnetic stimulation suggest the possibility that application of transcranial direct-current stimulation ( tDCS ) with inhibitory stimulation over the left temporo-parietal cortex and excitatory stimulation over the left dorsolateral prefrontal cortex could affect hallucinations and negative symptoms , respectively . The authors investigated the efficacy of tDCS in reducing the severity of auditory verbal hallucinations as well as negative symptoms . METHOD Thirty patients with schizophrenia and medication-refractory auditory verbal hallucinations were r and omly allocated to receive 20 minutes of active 2-mA tDCS or sham stimulation twice a day on 5 consecutive weekdays . The anode was placed over the left dorsolateral prefrontal cortex and the cathode over the left temporo-parietal cortex . RESULTS Auditory verbal hallucinations were robustly reduced by tDCS relative to sham stimulation , with a mean diminution of 31 % ( SD=14 ; d=1.58 , 95 % CI=0.76–2.40 ) . The beneficial effect on hallucinations lasted for up to 3 months . The authors also observed an amelioration with tDCS of other symptoms as measured by the Positive and Negative Syndrome Scale ( d=0.98 , 95 % CI=0.22–1.73 ) , especially for the negative and positive dimensions . No effect was observed on the dimensions of disorganization or gr and iosity/excitement . CONCLUSIONS Although this study is limited by the small sample size , the results show promise for treating refractory auditory verbal hallucinations and other selected manifestations of schizophrenia 
    Output:
    
First , different montages that are used to target a specific brain area such as dorsolateral prefrontal cortex ( DLPFC ) could have different effects ; therefore providing a unified classification enables us to take these differences into account .