Is neural hyperpolarization by cathodal stimulation always detrimental at the behavioral level?

Abstract

Cathodal transcranial direct current stimulation (c-tDCS) is usually considered an inhibitory stimulation. From a physiological perspective, c-tDCS induces hyperpolarization at the neural level. However, from a behavioral perspective, c-tDCS application does not always result in performance deterioration. In this work, we investigated the role of several important stimulation parameters (i.e., timing, presence of pauses, duration, and intensity) in shaping the behavioral effects of c-tDCS over the primary visual cortex. In Experiment 1, we applied c-tDCS at two different times (before or during an orientation discrimination task). We also studied the effects of pauses during the stimulation. In Experiments 2 and 3, we compared different durations (9 vs. 22 min) and intensities (0.75 vs. 1.5 mA) of stimulation. c-tDCS applied before task execution induced an improvement of performance, highlighting the importance of the activation state of the cortex. However, this result depended on the duration and intensity of stimulation. We suggest that the application of c-tDCS induces depression of cortical activity over a specific stimulated area; but to keep reactivity within given limits, the brain react in order to restore the equilibrium and this might result in increased sensitivity in visual performance. This is a further example of how the nervous system dynamically maintains a condition that permits adequate performance in different environments.

Understanding the behavioural consequences of noninvasive brain stimulation

“…By contrast, we know of no account that generates behavioural predictions of the effect of gross polarisation of cortex (Box 3). In support of this, behavioural improvements have also been reported for so-called cathodal stimulation [6,47]. Moreover, suppression of function in one region may even improve behavioural outcomes ('paradoxical facilitation').…”

Modulation of attention functions by anodal tDCS on right PPC

“…Teo et al (2011) found that increasing both stimulation strength and duration was required to reliably enhance working memory: Only during the last 5 min of stimulation (i.e., 15-20 min) at 2 mA, RTs were significantly reduced compared to baseline, while for the 1 mA condition the effect did not reach significance, but was largest during the preceding 5 min (i.e., 10-15 min). Pirulli et al (2014), on the other hand, found that while shortening duration of off-line stimulation of visual cortex from 22 min to 9 min hardly affected performance in a visual orientation task, reducing intensity from 1.5 mA to 0.75 mA abolished the effect on behavioural outcome measures.…”

“…However, in studies of cognition this dichotomy is less frequently observed Jacobson et al, 2012;Sparing et al, 2009;Stone and Tesche, 2009) in particular with respect to cathodal tDCS. While anodal tDCS most consistently shows an improvement (Boggio et al, 2010;Cerruti and Schlaug, 2009;Chi et al, 2010;Flöel et al, 2008;Fregni et al, 2005;Iyer et al, 2005;Kincses et al, 2004;Kraft et al, 2010;Sparing and Mottaghy, 2008) or no change in cognitive tasks Karim et al, 2010;Monti et al, 2008;Rogalewski et al, 2004;Varga et al, 2007), cathodal tDCS may deteriorate Berryhill et al, 2010;Karim et al, 2010;Rogalewski et al, 2004;Varga et al, 2007) as well as enhance (Monti et al, 2008;Moos et al, 2012;Pirulli et al, 2014;Weiss and Lavidor, 2012) performance in healthy participants. It has been suggested that in the latter studies cathodal tDCS might have improved performance by decreasing neuronal competition , acting like a noise filter particularly in highloaded scenes (Weiss and Lavidor, 2012).…”

“…However, the common assumption about these polarity specific effects has been confirmed mostly in motor studies, but rather rarely in cognitive studies (Jacobson et al, 2012;Miniussi et al, 2013). Moreover, these effects seem to depend on the applied tDCS-intensity, duration, and timing (Ball et al, 2013;Batsikadze et al, 2013;Hoy et al, 2013;Pirulli et al, 2013Pirulli et al, , 2014Teo et al, 2011). In particular, the inhibiting effect after cathodal stimulation has been found less frequently, while anodal stimulation more consistently increased cortical excitability (Jacobson et al, 2012;Miniussi et al, 2013).…”

Counteracting Implicit Conflicts by Electrical Inhibition of the Prefrontal Cortex

“…So, if cognitive control in general had been impaired by cathodal stimulation of the pFC , task performance should have suffered in both the Simon and the SNARC task, leading to generally increased conflict effects. Here, in this respect, tDCS was ineffective, possibly undermined by compensatory processes (Pirulli, Fertonani, & Miniussi, 2014) or by the intermediate role of dorsolateral pFC (i.e., as compared with the ACC; Botvinick et al, 2004) during nonemotional conflict processing (i.e., as compared with emotional processing; . Similar behavioral results have been obtained from applying tDCS over medial pFC during an Eriksen flanker conflict task, that is, there was no modulation of executive attention from 2 mA anodal tDCS (Coffman, Trumbo, & Clark, 2012).…”