TDCS increases cortical excitability: Direct evidence from TMS–EEG

Background Transcranial direct current stimulation (tDCS) is increasingly used in research and clinical settings, and the dorsolateral prefrontal cortex (DLPFC) is often chosen as a target for stimulation. While numerous studies report modulation of cognitive abilities following DLPFC stimulation, the wide array of cognitive functions that can be modulated makes it difficult to predict its precise outcome. Objective The present review aims at identifying and characterizing the various cognitive domains affected by tDCS over DLPFC. Methods Articles using tDCS over DLPFC indexed in PubMed and published between 2000 and January 2014 were included in the present review. Results tDCS over DLPFC affects a wide array of cognitive functions, with sometimes apparent conflicting results. Conclusion Prefrontal tDCS has the potential to modulate numerous cognitive functions simultaneously, but to properly interpret the results, a clear a priori hypothesis is necessary, careful technical consideration are mandatory, further insights into the neurobiological impact of tDCS are needed, and consideration should be given to the possibility that some behavioral effects may be partly explained by parallel modulation of related functions.

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“…[85]), TMS-EEG (e.g. [86]), magnetic resonance spectroscopy (e.g. [87]), functional magnetic resonance imaging (e.g.…”

Section: Resultsmentioning

confidence: 99%

The Uncertain Outcome of Prefrontal tDCS

et al. 2014

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“…By this account, anodal (excitatory) stimulation induces an increase in the background spontaneous firing rate by depolarizing cell membranes. In contrast, cathodal (inhibitory) stimulation attenuates cortical excitability by hyperpolarizing cell membranes (Romero Lauro et al, 2014). When coupled to the findings from those prone to visual aura/hallucination, the implication is that transient paroxysmal neural firing becomes more likely and may ride on the back of these more gradual changes in membrane potential.…”

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confidence: 93%

“…The stimulatory effects of tDCS are thought to occur not only in the regions directly beneath or immediately proximal to the electrodes, but they also permeate through brain tissue e suggesting both localised and more general stimulatory effects (Miranda, Mekonnen, Salvador, & Ruffini, 2013;Romero Lauro et al, 2014). Therefore, although one may place an electrode over primary visual cortex, the diffuse effects of tDCS may also propagate into spatially distant visual association cortex and the regions defined by both electrodes (Keeser et al, 2011;Peña-G omez et al, 2012).…”

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confidence: 96%

Stimulating the aberrant brain: Evidence for increased cortical hyperexcitability from a transcranial direct current stimulation (tDCS) study of individuals predisposed to anomalous perceptions

Braithwaite

Mevorach

Takahashi

2015

Cortex

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Findings from neurological and clinical groups have shown that increased predisposition to anomalous experience/aura reflects an elevation in aberrant neural processes in the brain. However, studies of anomalous experiences in non-clinical/non-neurological groups are less clear on this matter and are more typically confined to subjective questionnaire measures alone. The current investigation, the first to our knowledge, carried out a transcranial Direct Current Stimulation (tDCS) study of cortical hyperexcitability, and its association with anomalous experience in non-clinical/non-neurological groups. Sixty participants completed; (i) both excitatory (anodal) and inhibitory (cathodal) brain stimulation conditions of the visual cortex; (ii) a computerised pattern-glare task, where observers reported phantom visual distortions from viewing highly irritable visual patterns (a metric of cortical hyperexcitability), and; (iii) questionnaire measures of predisposition to anomalous perceptions. There were no reliable signs of cortical hyperexcitability (via pattern-glare tasks) when collapsed across the whole sample. However, a significant positive correlation between predisposition to anomalous experience and elevated signs of cortical hyperexcitability was observed. Crucially, there was a significant negative correlation between tDCS stimulatory conditions. A visual cortex that reacted more strongly to excitatory stimulation, responded less well to inhibitory suppression, and this pattern was related to predisposition to anomalous perceptions. Both findings are consistent with the presence of a hyperexcitable cortex. Collectively the present findings provide objective evidence that the brains of individuals predisposed to anomalous experiences/hallucinations can be hyperexcitable - even in the non-clinical/non-neurological population. These data are consistent with continuum models of anomalous experience and have important implications for contemporary theories of aberrations in self-consciousness.

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“…tDCS relies on the application of a weak electrical current through the scalp that is able to modulate both long-term and short-term cortical excitability (Nitsche and Paulus, 2001;Romero Lauro et al, 2014). The stimulation outcome depends on the electrode placed over the target area, with the anode increasing cortical excitability and the cathode decreasing it (although the effects of cathodal stimulation on non-motor areas are debated, see Jacobson et al, 2012).…”

Section: Introductionmentioning

confidence: 99%