Electrifying the motor engram: effects of tDCS on motor learning and control

Abstract

Learning to control our movements accompanies neuroplasticity of motor areas of the brain. The mechanisms of neuroplasticity are diverse and produce what is referred to as the motor engram, i.e. the neural trace of the motor memory. Transcranial direct current stimulation (tDCS) alters the neural and behavioral correlates of motor learning, but its precise influence on the motor engram is unknown. In this review, we summarize the effects of tDCS on neural activity and suggest a few key principles: 1) firing rates are increased by anodal polarization and decreased by cathodal polarization, 2) anodal polarization strengthens newly formed associations, and 3) polarization modulates the memory of new/preferred firing patterns. With these principles in mind, we review the effects of tDCS on motor control, motor learning, and clinical applications. The increased spontaneous and evoked firing rates may account for the modulation of dexterity in non-learning tasks by tDCS. The facilitation of new association may account for the effect of tDCS on learning in sequence tasks while the ability of tDCS to strengthen memories of new firing patterns may underlie the effect of tDCS on consolidation of skills. We then describe the mechanisms of neuroplasticity of motor cortical areas and how they might be influenced by tDCS. We end with current challenges for the fields of brain stimulation and motor learning.

Differential effects of primary motor cortex and cerebellar transcranial direct current stimulation on motor learning in healthy individuals: A randomized double-blind sham-controlled study

“…In addition, the current study also confirmed the findings of previous studies which tDCS enhancement of the motor learning is polarity dependent Stagg et al, 2011). Anodal tDCS could increase the rate of motor sequence learning, while cathodal tDCS induces opposite effects Stagg et al, 2011;Orban de Xivry and Shadmehr, 2014).…”

“…In line with this finding, Hess et al (1996) also reported that a decrease in activity of GABAergic system is required for long-term potentiation in the motor cortex (Hess et al, 1996). In addition, it seems that a-tDCS over both M1 and cerebellum increases firing rate of neurons and strengthen the newly formed associations among neurons which can affect neural networks and consolidation of sequence learning task (Nitsche et al, 2003;Orban de Xivry and Shadmehr, 2014). Bindman et al (1962) also indicated that excitability of neurons was increased during and for several hours after anodal polarization.…”

“…Moreover, the findings of the current study indicated that M1 atDCS induces more short-term offline learning effect (evidenced by reduction of RT) as compared to sham/no tDCS, while this significant short-term effect was not observed between cerebellar and sham/no tDCS groups. Most of the previous studies investigating efficiency of M1 a-tDCS on motor skill acquisition indicated lasting effect of M1 a-tDCS on improvement of motor function (Boggio et al, 2006;Hummel et al, 2005;Reis et al, 2009;Orban de Xivry and Shadmehr, 2014). In addition, Galea et al (2011) study also indicated that reduction of error numbers following application of M1 a-tDCS was significantly increased 10-min after training.…”

Transcranial direct current stimulation (tDCS) reverts behavioral alterations and brainstem BDNF level increase induced by neuropathic pain model: Long-lasting effect

“…Additionally, previous studies from our group using chronic inflammation and hyperalgesia induced by chronic restraint stress models (Spezia Adachi et al, 2012) showed an antinociceptive effect of cortical stimulation by tDCS. Beyond the analgesic effect, human studies with tDCS have shown effects on motor control, stress, and depression, which could justify our results (Gonçalves, 2012;Nitsche et al, 2009a;Orban de Xivry and Shadmehr, 2014).…”

Effects of tDCS on motor learning and memory formation: A consensus and critical position paper

“…Adaptation of highly-learned, target-directed pointing or shooting movements to environment perturbations has been regularly investigated (Orban de Xivry & Shadmehr, 2014).…”