Using high-definition transcranial direct current stimulation to investigate the role of the dorsolateral prefrontal cortex in explicit sequence learning

Abstract

Though we have a general understanding of the brain areas involved in motor sequence learning, there is more to discover about the neural mechanisms behind which a new skill is learned. Initial skill acquisition may be subserved, in part, by interactions between the cerebellum (CBLM) and prefrontal cortex (PFC) through a cerebello-thalamo-prefrontal network. We investigated the consequence of stimulating the PFC using high-definition transcranial direct current stimulation (HD-tDCS) before administering an explicit motor sequence learning paradigm. Using a mixed within-and betweensubjects design, we employed anodal (n = 24) and cathodal (n = 25) tDCS (relative to sham) to temporarily alter brain function and examine the effects on skill acquisition. In order to gain a comprehensive perspective on the role of this network in sequence learning, we compared the current findings to our recent research investigating the CBLM using the same experimental design. The PFC results indicate that anodal stimulation negatively impacts explicit motor sequence learning, relative to sham, while the effects of cathodal stimulation are minimal, though indicative of either a stabilizing or facilitatory influence. This is consistent with past CBLM results. Our findings, therefore, suggest polarityspecific effects of tDCS on the acquisition of a sequential pattern of finger movements, both when applied to the PFC and CBLM. Collectively, this supports the involvement of a cerebello-thalamo-prefrontal network in initial skill acquisition when cognitive processes, such as working memory, are utilized. Exploring methods that may improve motor learning is important in developing therapeutic strategies for motor-related diseases and rehabilitation.

Comparing the effects of focal and conventional tDCS on motor skill learning: A proof of principle study

“…While this focal montage can induce greater changes in cortical excitability and facilitate movement response times when compared to the conventional montage ( Masina et al, 2021 ; Kuo et al, 2013 ), it remains unclear whether a more-targeted approach is beneficial for motor learning. Indeed, utilizing the 4 × 1 ring configuration in the context of motor learning has led to some mixed results ( Doppelmayr et al, 2016 ; Cole et al, 2018 ; Ballard et al, 2021 ), which likely depend on the target-site ( Lefebvre et al, 2019 ) and stimulation intensity ( Lerner et al, 2021 ). Of these studies, only Cole and colleagues have compared the effects of focal and conventional tDCS on fine motor skill performance in children and found that both montages similarly improved manual dexterity compared to sham.…”

Targeting the fronto-parietal network using multifocal personalized transcranial alternating current stimulation to enhance motor sequence learning in healthy older adults

“…Although this has been the first time that both the DLPFC and the PPC have been targeted with the use of bifocal stimulation during a sequence learning task, studies have targeted the two areas separately. Stimulation of the DLPFC with the use of transcranial direct current stimulation (tDCS) has found heterogenous results for motor learning tasks [74–76]. A recent study using high-definition tDCS (HD-tDCS) to the DLPFC before the practice of an explicit MSL task found a decrease in performance after both anodal and cathodal HD-tDCS [74].…”

“…Stimulation of the DLPFC with the use of transcranial direct current stimulation (tDCS) has found heterogenous results for motor learning tasks [74–76]. A recent study using high-definition tDCS (HD-tDCS) to the DLPFC before the practice of an explicit MSL task found a decrease in performance after both anodal and cathodal HD-tDCS [74]. Hashemirad and colleagues applied anodal tDCS to the DLPFC and the PPC separately during an MSL task.…”