Reducing negative affect with anodal transcranial direct current stimulation increases memory performance in young - but not in elderly - individuals

Affect can have a direct impact on memory processing, which offers the opportunity to shape memory performance by modulating affective responses. The left dorsolateral prefrontal cortex (dlPFC) is functionally involved in both affect and memory, with an increased activity being associated with more positive affect and better memory performance. This study explores if transcranial direct current stimulation (tDCS), which modulates region specific brain activity, is able to change affect and thereby improve memory. We randomly assigned 94 healthy individuals (n=43 young, n=51 elderly) to either sham or real tDCS over their left dlPFC during encoding of a verbal episodic memory task. We applied anodal tDCS (1mA) for 20 minutes with the cathodal reference electrode placed on the contralateral supraorbital region. We presented the Profile of Mood States (POMS) as well as the Positive and Negative Affect Schedule (PANAS) pre- and post-stimulation. Participants had to recall items unexpectedly 20 minutes after learning and to name which feelings were associated with this free recall. We used mediation analysis to test if tDCS significantly influenced memory via affective modulation. In young, but not in elderly participants, tDCS significantly modulated negative affective responses in both questionnaires (i.e., POMS, PANAS). Younger participants in the real stimulation group also reported significantly less negative feelings associated with the unexpected free recall. Furthermore, a stronger reduction of negative affect through tDCS significantly enhanced verbal delayed recall. In healthy young individuals, tDCS reduces negative affect while in the healthy elderly other stimulation protocols might be more suitable. The reduction of negative affect via tDCS directly influences episodic memory – at least in healthy young individuals -, lending further support for the close relation between affect and memory