Noninvasive cortical stimulation enhances motor skill acquisition over multiple days through an effect on consolidation

Abstract

Motor skills can take weeks to months to acquire and can diminish over time in the absence of continued practice. Thus, strategies that enhance skill acquisition or retention are of great scientific and practical interest. Here we investigated the effect of noninvasive cortical stimulation on the extended time course of learning a novel and challenging motor skill task. A skill measure was chosen to reflect shifts in the task's speed-accuracy tradeoff function (SAF), which prevented us from falsely interpreting variations in position along an unchanged SAF as a change in skill. Subjects practiced over 5 consecutive days while receiving transcranial direct current stimulation (tDCS) over the primary motor cortex (M1). Using the skill measure, we assessed the impact of anodal (relative to sham) tDCS on both within-day (online) and betweenday (offline) effects and on the rate of forgetting during a 3-month follow-up (long-term retention). There was greater total (online plus offline) skill acquisition with anodal tDCS compared to sham, which was mediated through a selective enhancement of offline effects. Anodal tDCS did not change the rate of forgetting relative to sham across the 3-month follow-up period, and consequently the skill measure remained greater with anodal tDCS at 3 months. This prolonged enhancement may hold promise for the rehabilitation of brain injury. Furthermore, these findings support the existence of a consolidation mechanism, susceptible to anodal tDCS, which contributes to offline effects but not to online effects or long-term retention.long-term retention ͉ motor cortex ͉ motor learning ͉ transcranial direct current stimulation (tDCS) ͉ transcranial magnetic stimulation (TMS) A ccurate motor performance is essential to almost everything we do, from typing, to driving, to playing sports. Having a motor skill implies a level of performance in a given task that is only achievable through practice (1). Evidence indicates that motor skill learning can continue over a prolonged time period (2-5). Within-session performance improvements (online effects) occur in the minutes or hours of a single training session and continue over days and weeks of repeated training sessions until performance nears asymptotic levels. Changes in performance can also occur between training sessions (offline effects), i.e., performance at the beginning of session n ϩ 1 is different from performance at the end of session n (6, 7). We have intentionally chosen to avoid the use of the term ''offline learning'' because it has been used to refer to both a physiological process (consolidation) (6) and a particular measurement result (a positive offline effect) (8). Offline effects could also be negative, presumably because of forgetting processes (7). Skills can be retained to varying degrees over weeks to months after the completion of training (long-term retention) (5). Here we investigated the effect of noninvasive cortical stimulation on measurements of these 3 temporal components of skill learning (online effects, of...

Effects of transcranial direct-current stimulation on laparoscopic surgical skill acquisition

“…It is important to consider that these effects were seen in a single short training session. Multiple days of tDCS‐paired training may lead to larger effects on skill acquisition, particularly on peg transfer, as demonstrated by previous reports of enhanced motor learning22 23. The FLS curriculum suggests a mean number of repetitions required for peg transfer proficiency of 57 (range 26–80).…”

“…The relative lack of skill decay from post‐training is encouraging, and might be further improved with higher doses of training. Reports of tDCS‐enhanced skill retention typically apply stimulation over multiple days of training, possibly facilitating retention through consolidation22 23.…”

“…When paired with motor skill training, stimulation of the motor cortex with anodal tDCS safely enhances skill acquisition of a wide range of tasks, often with large effect sizes22 23 and long‐term skill retention22. Neuroimaging and neurophysiology studies are beginning to elucidate the possible mechanisms behind this enhancement of learning24.…”

Preconditioning tDCS facilitates subsequent tDCS effect on skill acquisition in older adults

“…The FORCE task is a modified version of a task developed by Reis and colleagues (Reis et al 2009). Participants sat in an armchair, positioned 60 cm from a 20 inch screen monitor, with their left forearm placed on a horizontal board at a table situated in front of them.…”

“…Following previous studies (Reis et al 2009, Saucedo Marquez et al 2013), a skill measure (skill index, SI) which reflects a shift in the task's speed-accuracy trade-off function was utilized in the current study. Such a parameter is very useful to quantify skill learning because it enables us to compare performance between trials which involve different speed and accuracy features, e.g., fast movements with many errors and slow movements with few errors.…”