WHO BENEFITS FROM THETA–GAMMA TACS? BEHAVIORAL MARKERS OF EPISODIC MEMORY ENHANCEMENT IN HEALTHY OLDER ADULTS

Theta-gamma transcranial alternating current stimulation (TG-tACS) has shown promising results in enhancing the cognition of healthy adults. However, considering the high degree of variability in outcomes for this type of intervention, there is a need to identify behavioral markers that can predict which participants will benefit. The main aim of this study was therefore to identify pre-treatment behavioral markers in 21 elderly participants (aged 49-81, 14 women) that could predict their response to an 8-session TG-tACS intervention for enhancing episodic memory (EM). Prior to the intervention, participants underwent a comprehensive neuropsychological evaluation and performed a computerized EM task. Based on intervention outcomes, participants were classified as either good or poor responders. Comparisons between groups were then made using independent sample t-tests, and ROC curves were obtained for the variables that differed significantly between groups. Preliminary results showed marginally significant differences between good and poor responders on semantic (p=0.060) and phonological (p=0.062) fluency measures, as well as significant effects on subjective memory complaints (p=0.040), and performance in the EM task, as measured by d′ (p=0.017). The individual ROC curves showed moderate discriminatory ability (AUCs between 0.661 and 0.766). However, the combination of all the identified variables generated a ROC curve with good classification ability (AUC=0.906), achieving a sensitivity of 75% and a specificity of 92%. These findings suggest that a brief assessment (30-45 minutes) prior to intervention may effectively identify elderly subjects who are most likely to respond positively to TG-tACS for EM enhancement.