High Definition Transcranial Direct Current Stimulation Does Not Modulate Implicit Task Sequence Learning and Consolidation

Abstract

The incidental acquisition of a succession of tasks is termed implicit task sequence learning. Patients with dorsolateral prefrontal cortex (DLPFC) lesions are strongly impaired in this ability. However, recent results of conventional transcranial direct current stimulation (tDCS) above the prefrontal cortex showed no modulation of implicit task sequence learning and consolidation. One explanation for these null findings is that conventional tDCS has non-focal effects on the cortex. Thus, the aim of the present study was to use a focal type of tDCS, namely high definition tDCS (HD-tDCS), to influence implicit task sequence learning and consolidation. Participants received stimulation during implicit task sequence learning and, 24 hours later, consolidation was measured. The results showed that sequence learning was present in all conditions and sessions. Furthermore, consolidation was robust. However, both sequence learning and consolidation were not modulated by stimulation. Thus, this study corroborates previous findings by showing that even focal HD-tDCS is not sufficient to modulate implicit task sequence learning and consolidation.

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

“…In some of this research, working memory improvements are selectively observed when cognitive demand is particularly high [29,30]. However, additional work reports null effects of HD-tDCS to the DLPFC on working memory performance [40,66], as well as implicit learning and consolidation [32–35]. In sum, inconsistent results have been observed with DLPFC stimulation, and though the effects observed in the current study are somewhat unexpected, our findings do not completely conflict with the literature more broadly.…”

“…Research using stimulation of the dorsolateral PFC (DLPFC) has demonstrated an influence of tDCS on the cognitive aspects of motor learning [26–31], likely due to the impact on working memory processes that provide essential contributions to skill acquisition. Other work has shown no impact of DLPFC stimulation on sequence learning or consolidation [32–35]; however, these studies specifically evaluated implicit learning. On the contrary, work by Greeley and Seidler [36] presented evidence for improved implicit sequence learning after anodal stimulation to the left DLPFC, while right DLPFC stimulation impeded learning.…”

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

“…In some of this research, working memory improvements are selectively observed when cognitive demand is particularly high [29,30]. However, additional work reports null effects of HD-tDCS to the DLPFC on working memory performance [40,66], as well as implicit learning and consolidation [32][33][34][35]. In sum, inconsistent results have been observed with DLPFC stimulation and, though the effects observed in the current study are somewhat unexpected, our findings do not completely conflict with the literature more broadly and add to the ongoing conversations regarding the effects of prefrontal tDCS on skill acquisition.…”

“…Research using stimulation of the dorsolateral PFC (DLPFC) has demonstrated an influence of tDCS on the cognitive aspects of motor learning [26][27][28][29][30][31], likely due to the impact on working memory processes that provide essential contributions to skill acquisition. Other work has shown no impact of DLPFC stimulation on sequence learning or consolidation [32][33][34][35]; however, these studies specifically evaluated implicit learning. On the contrary, work by Greeley and Seidler [36] presented evidence for improved implicit sequence learning after anodal stimulation to the left DLPFC, while right DLPFC stimulation impeded learning.…”

“…For instance, whether stimulation is applied during task performance or entirely before is an important consideration as some of the excitatory effects of anodal tDCS and null effects of cathodal tDCS have been observed with online protocols [27]. Further, the body of work on the effects of DLPFC stimulation on implicit sequence learning and consolidation is also chiefly reliant on studies that used an online tDCS approach [34][35][36][37]. In the current study, we employed offline stimulation.…”