Enhancing episodic memory in older adults through modulating oscillatory activities in the fronto-posterior network using transcranial alternating current stimulation (MEMTACS)

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Theta oscillatory activity in the fronto-posterior network plays a crucial role in successful implementation of episodic memory processes. Aging-related changes in frontal theta power and fronto-posterior phase synchronization have been linked to cognitive deficits in older adults. Over the past few years, first promising evidence indicates that transcranial alternating current stimulation (tACS) in the theta frequency range applied to frontal and posterior sites may increase inter-regional theta-phase synchronization and augment cognitive processes in younger adults. This opens up the possibility of using tACS to modulate aging-related declines in oscillatory activity and consequently improve cognitive function in older adults. So far, tACS-induced effects on cognitive functions and associated brain oscillations have been shown for younger adults, whereas studies in older adults as well as knowledge about potential age-dependent variations in stimulation effects are still missing. Furthermore, the neural mechanisms underlying tACS-induced effects, and its potential to modulate oscillatory activity and enhance episodic memory functions in older adults, have not been explored. To this end, we will characterize electrophysiological correlates of sequential episodic memory processes in older adults and examine determinants of successful performance. Additional analyses of functional and structural networks and biophysical modeling of current flow will help to elucidate relationships of memory processes with neural integrity and explore individual distribution of induced electric currents in older brains. Subsequently, we will test tACS-induced modulation of memory functions and fronto-posterior theta oscillations in older adults. The project will provide novel insights into the mechanisms of tACS-induced effects on hippocampus-dependent memory processes in the course of healthy aging. Outcomes of the project will help to develop age-appropriate stimulation protocols to successfully counteract cognitive decline in older adults.