Temporal gamma tACS and auditory stimulation affect verbal memory in
healthy adults
Abstract
Research suggests a potential of gamma oscillation entrainment for
enhancing memory in Alzheimer’s disease and healthy subjects. Gamma
entrainment can be accomplished with oscillatory electrical, but also
sensory stimulation. However, comparative studies between sensory
stimulation and transcranial alternating current stimulation (tACS)
effects on memory processes are lacking. This study examined the effects
of rhythmic gamma auditory stimulation (rAS) and temporal gamma-tACS on
verbal long-term memory (LTM) and working memory (WM) in 74 healthy
individuals. Participants were assigned to two groups according to the
stimulation techniques (rAS or tACS). Memory was assessed in three
experimental blocks, in which each participant was administered with
control, 40 Hz, and 60 Hz stimulation in counterbalanced order. All
interventions were well-tolerated, and participants reported mostly
comparable side effects between real stimulation (40 Hz and 60 Hz) and
the control condition. LTM immediate and delayed recall remained
unaffected by stimulations, while immediate recall intrusions decreased
during 60 Hz stimulation. Notably, 40 Hz interventions improved WM
compared to control stimulations. These results highlight the potential
of 60 Hz and 40 Hz temporal cortex stimulation for reducing immediate
LTM recall intrusions and improving WM performance, respectively,
probably due to the entrainment of specific gamma oscillations in the
auditory cortex. The results also shed light on the comparative effects
of these neuromodulation tools on memory functions, and their potential
applications for cognitive enhancement and in clinical trials.