Is transcranial direct current stimulation (tDCS) an effective adjunct to cognitive training for older adults presenting with mild cognitive impairment (MCI)?

Mild cognitive impairment (MCI) is considered a phase between the usual cognitive decline of aging and the marked cognitive decline linked to dementia. Cognitive training (CT) is one strategy used to slow down the cognitive deterioration for persons with MCI. It has been proposed that tDCS could be paired with CT to boost its remedial effects. Targeting neural circuits using tDCS, that are simultaneously engaged in CT exercises may generate better therapeutic outcomes.
33 older adults with MCI were randomly subdivided into three groups: CT only, sham tDCS combined with CT and tDCS combined with CT. The intervention consisted of nine sessions of computerized CT that focused on the working memory and attention domains. 1.5 mA of anodal tDCS was delivered to the left dorsolateral prefrontal cortex with an extra-cephalic cathode electrode. Our novel approach recorded the participant’s performance in every single CT task across all sessions in terms of accuracy and time. Cognitive assessments were carried out at baseline, post-intervention and at six-week follow-up. Immediate and long-term neurophysiological responses were assessed by EEG at baseline, after the first and the last training sessions and at six-week follow-up respectively.
To date, 33 participants have completed the study. Improvement over time in global cognition (MoCA) and everyday memory (RBMT-3) (p<0.016) was noted in all three groups at post-intervention and six-week follow-up. However, only the tDCS+CT group demonstrated a significant increase in processing speed (p<0.05) during the CT. Outcomes of the ongoing EEG experiment will be discussed later by means of EEG power in resting state and in a n-back test paradigm.
These preliminary findings suggest that tDCS paired with CT exercises has a positive impact on the cognitive performance in persons with MCI. Whether tDCS can be used in clinical settings as a useful therapeutic intervention warrants further investigation.