Boosting Cognition: Effects of Multiple-Session Transcranial Direct Current Stimulation on Working Memory.

Area of Science:

• Neuroscience
• Cognitive Science
• Neuromodulation

Background:

• Transcranial direct current stimulation (tDCS) over the left dorsolateral prefrontal cortex (lDLPFC) can improve working memory (WM) in healthy adults after a single session.
• Previous studies combining multiple tDCS sessions with WM training showed limited additional benefits or transfer effects.
• The current study investigated the impact of repeated tDCS sessions on WM using an enhanced protocol and daily baseline measures.

Purpose of the Study:

• To investigate the effects of three consecutive days of anodal tDCS over the lDLPFC on verbal WM performance.
• To assess whether tDCS-induced WM benefits transfer to other WM tasks.
• To explore individual differences in response to repeated lDLPFC tDCS.

Main Methods:

• Participants received anodal (20 min, 1 mA) or sham tDCS over the lDLPFC for three consecutive days, paired with a challenging verbal WM task.
• WM performance was assessed using a verbal WM updating task (letter n-back) during stimulation sessions.
• Transfer tasks included different letter set n-back, spatial n-back, and operation span, measured before and after the stimulation period.

Main Results:

• Anodal tDCS over lDLPFC enhanced WM performance during the first session, with effects persisting for 24 hours.
• No additional WM gains were observed in the second and third stimulation sessions at the group level.
• Individual difference analyses revealed that initial WM improvement predicted transfer task performance in the anodal group, while some participants showed worsened performance.

Conclusions:

• Repeated anodal tDCS over lDLPFC may enhance WM in some individuals, but not universally, and can potentially impair performance.
• The findings highlight the importance of investigating individual differences in tDCS response.
• Further research is needed to develop optimal multisession tDCS protocols for widespread cognitive enhancement.