Anodal Transcranial Direct Current Stimulation Over Prefrontal Cortex Slows Sequence Learning in Older Adults

Area of Science:

• Neuroscience
• Gerontology
• Motor Control

Background:

• Aging leads to sensorimotor function decline.
• Transcranial direct current stimulation (tDCS) combined with training can potentially mitigate age-related declines.
• However, tDCS can sometimes impair performance and learning.

Purpose of the Study:

• To investigate the effects of anodal tDCS on motor learning in older adults.
• To determine if tDCS over specific brain regions (prefrontal cortex, supplementary motor complex, M1) enhances motor sequence learning.
• To test the hypothesis that prefrontal cortex stimulation would improve motor learning in aging individuals.

Main Methods:

• Sixty-three older adults practiced a Discrete Sequence Production (DSP) task over 3 days.
• Anodal tDCS was applied over the left prefrontal cortex (PFC), right PFC, supplementary motor complex (SMC), or left M1, alongside a sham condition.
• Motor learning was assessed by changes in reaction time and sequence chunking.

Main Results:

• Contrary to hypotheses, tDCS over the right and left PFC slowed motor learning.
• Specifically, slowed reaction time reduction was observed in session one, and slower chunking in session two, compared to sham.
• These results indicate potential detrimental effects of PFC stimulation on motor learning in older adults.

Conclusions:

• The right PFC may play an early role in sequence learning, while the left PFC is involved in chunking in older adults.
• Anodal tDCS over the PFC appears to impede rather than enhance motor learning in this population.
• Findings highlight the complexities and potential difficulties of applying tDCS to aging populations for sensorimotor enhancement.