Introduction:
Engaging in repetitive performance practice has been associated with the
enhancement of neuro-motor adaptations, functional abilities, and
overall performance improvement, as well as motor learning (Jacksonet al. , 2019; Meek et al. , 2021; Parma et al. ,
2021). Enhancing motor learning to facilitate skill acquisition and
memory consolidation represents a current challenge in both skill
acquisition and functional rehabilitation domains (Debarnot et
al. , 2019).
Serial Reaction Time Tasks (SRTT) are widely utilized for evaluating
implicit sequence motor learning (Trofimova et al. , 2020). This
involves the observation of repeated sequences or random events during
task performance and is recognized as the most commonly used test for
this purpose (Debarnot et al. , 2019). Research has indicated
neuroplastic changes during implicit motor learning across various brain
regions in young, healthy adults (Debarnot et al. , 2019).
Presently, non-invasive brain stimulation (NIBS) techniques are employed
to modulate motor and cognitive functions, aiding the learning process
in both healthy adults and individuals with neurological conditions
(Buch et al. , 2017; Lefebvre et al. , 2017; Cole et
al. , 2018; Santos et al. , 2020)
Research indicates that tDCS has the capacity to impact resting membrane
potential, potentially leading to an increase or decrease in its levels
(Nitsche & Paulus, 2000; Nitsche et al. , 2008). The direction of
this influence depends on whether anodal or cathodal tDCS is
administered (Lefebvre et al. , 2017; Cole et al. , 2018;
Santos et al. , 2020). Notably, research indicates that combining
M1 anodal tDCS with motor training can lead to improved motor
performance and learning compared to cathodal tDCS and sham stimulation
(Stagg et al. , 2009; Ostry & Gribble, 2016; Karok et al. ,
2017; Spampinato & Celnik, 2018; Debarnot et al. , 2019;
Talimkhani et al. , 2019; Iannone et al. , 2022).
Conversely, a study found that applying cerebellar a-tDCS reduced motor
learning during SRTT (Jongkees et al. , 2019). Some studies have
demonstrated that c-tDCS can enhance motor learning in SRTT (Greeleyet al. , 2020; Pollok et al. , 2021). Furthermore, certain
studies have highlighted the positive effects of both a-tDCS and c-tDCS
over M1 compared to sham tDCS on motor learning (Ciechanski & Kirton,
2017; Shilo & Lavidor, 2019).
Evidence suggests that the intensity of tDCS, regardless of polarity,
can significantly impact the outcomes of tDCS (Stagg et al. ,
2011; Ciechanski & Kirton, 2017; Greeley et al. , 2020). Some
studies have shown that both 1 mA and 2 mA tDCS can improve motor
learning compared to sham conditions in healthy adults (Stagg et
al. , 2009; Ciechanski & Kirton, 2017; Shilo & Lavidor, 2019).
Conversely, other studies have indicated that 1 mA or 2 mA tDCS may
interfere with the motor learning process compared to sham stimulation
(Stagg et al. , 2011; Greeley et al. , 2020).
It appears that previous studies have presented conflicting findings
regarding the efficacy of tDCS with different polarities and intensities
on motor learning (Stagg et al. , 2011; Ciechanski & Kirton,
2017; Buchwald et al. , 2019; Shilo & Lavidor, 2019). However, it
is essential to determine the most effective approach to optimize the
use of tDCS for enhancing motor learning. Interestingly, there is a lack
of research comparing the effects of different polarities and
intensities of tDCS on motor learning in healthy young adults. This
study aims to explore the impacts of tDCS on M1 at varying intensities
and polarities on motor learning in healthy young adults using the SRTT.
The hypothesis for this study is:
- Concurrent application of 1 and 2 mA M1 a-tDCS and SRTT would reduce
RT and ER during and after application of interventions compared to
concurrent sham a-tDCS and SRTT.
- Concurrent application of 1 and 2 mA M1 c-tDCS and SRTT would have no
effect on reduction of RT and ER during and after completion of
interventions compared to sham tDCS and SRTT.
- Concurrent application of 1 mA M1 a-tDCS and SRTT would reduce RT and
ER during and after completion of interventions compared to 1 mA M1
c-tDCS and SRTT.
- Concurrent application of 2 mA M1 a-tDCS and SRTT would reduce RT and
ER during and after completion of interventions compared to 2 mA M1
c-tDCS and SRTT.