Effects of cerebellar transcranial direct current stimulation on the cognitive stage of sequence learning

Abstract

Though the cerebellum has been previously implicated in explicit sequence learning, the exact role of this structure in the acquisition of motor skills is not completely clear. The cerebellum contributes to both motor and nonmotor behavior. Thus, this structure not only may contribute to the motoric aspects of sequence learning but may also play a role in the cognitive components of these learning paradigms. Therefore, we investigated the consequence of both disrupting and facilitating cerebellar function using high-definition transcranial direct current stimulation (tDCS) before the completion of an explicit motor sequence learning paradigm. Using a mixed within- and between-subjects design, we employed cathodal ( n = 21) and anodal ( n = 23) tDCS (relative to sham), targeting the lateral posterior cerebellum, to temporarily modulate function and investigate the resulting effects on the acquisition of a sequential pattern of finger movements. Results indicate that cathodal stimulation has a positive influence on learning while anodal stimulation has the opposite effect, relative to sham. Though the cerebellum is presumed to be primarily involved in motor function and movement coordination, our results support a cognitive contribution that may come into play during the initial stages of learning. Using tDCS targeting the right posterior cerebellum, which communicates with the prefrontal cortex via closed-loop circuits, we found polarity-specific effects of cathodal and anodal stimulation on sequence learning. Thus, our results substantiate the role of the cerebellum in the cognitive aspect of motor learning and provide important new insights into the polarity-specific effects of tDCS in this area. NEW & NOTEWORTHY The cerebellum contributes to motor and cognitive processes. Investigating the cognitive contributions of the cerebellum in explicit sequence learning stands to provide new insights into this learning domain, and cerebellar function more generally. Using high-definition transcranial direct current stimulation, we demonstrated polarity-specific effects of stimulation on explicit sequence learning. We speculate that this is due to facilitation of working memory processes. This provides new evidence supporting a role for the cerebellum in the cognitive aspects of sequence learning.

Beneficial effects of cerebellar tDCS on motor learning are associated with altered putamen-cerebellar connectivity: a simultaneous tDCS-fMRI study

“…cerebellar tDCS led to better knowledge of the sequence when compared to sham. The findings here are in accordance with previous work showing the beneficial effect of anodal cerebellar tDCS on motor sequence learning (Ferrucci et al, 2013;Shimizu et al, 2017) but in contrast to a recent report showing the opposite effect (Ballard et al, 2019). Note that in the latter study, a multi-channel montage was used with a net current of 2mA compared to our protocol with 1mA.…”

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

“…We used an explicit motor sequence learning paradigm, modeled directly after Kwak et al [49] and used in our past work [15], in order to assess the impact of DLPFC stimulation on the ability to acquire a motor skill and learn a new pattern of events. As research using fMRI has indicated more activation in brain areas associated with cognitive processing during explicit learning, compared to implicit [18,42,50,51], we chose to investigate the influence of stimulation with an explicit sequence learning paradigm to explore its effects on the cognitive, rather than solely motor, aspects of skill acquisition.…”

“…In fact, research suggests that the CBLM impacts cognitive processes through a closed-loop cerebello-thalamo-prefrontal circuit [9–14], which may be particularly important during initial skill acquisition. Notably, we have recently suggested that the PFC is the nexus of this circuit, governing the operations of early sequence learning, while the CBLM may serve more of a supporting role [15]. The PFC coordinates the cooperation of other brain areas involved in sequence learning [16] and is considerably engaged in the early stages of skill acquisition when cognitive and working memory resources are primarily at play [2,5,17,18].…”

The polarity specific nature of single session high-definition transcranial direct current stimulation to the cerebellum and prefrontal cortex on motor and non-motor task performance

“…Grimaldi et al, (2016) suggests that anodal stimulation excites the inhibitory Purkinjie circuit which results in an increase in inhibitory function on the deep cerebellar nuclei (DCN) resulting in a decrease in cerebellar output, ultimately decreasing task performance. This is observed in behavioral work in humans as well (Ballard et al, 2019;Pope & Miall, 2012). Alternatively, it is believed that cathodal stimulation inhibits the inhibitory Purkinjie circuit which results in a decrease in inhibitory function on the DCN, resulting in an increase in cerebellar output, and ultimately increasing task performance.…”

“…Historically, the cerebellum was thought to be primarily involved in motor function (Holmes, 1939) and motor learning (Ballard et al, 2019;Bernard & Seidler, 2013). However, work over the last several decades has also implicated the cerebellum in non-motor cognitive processing (Buckner, 2013;Desmond et al, 1997;E et al, 2014;Leiner et al, 1989Leiner et al, , 1991Rapoport et al, 2000;Schmahmann, 2018;Schmahmann & Sherman, 1998;Stoodley, 2012).…”