Altering stimulus timing via fast rhythmic sensory stimulation induces STDP-like recall performance in human episodic memory

Abstract

Animal studies suggest that the strength of synaptic modification depends on spike timing between pre- and post-synaptic neurons on the order of tens of milliseconds, which is termed spike-timing-dependent plasticity (STDP). However, evidence for STDP in human episodic memory is lacking. We investigated this using rhythmic sensory stimulation to drive visual and auditory cortices at 37.5 Hz with four phase offsets. Visual relative to auditory cued recall accuracy was significantly enhanced in the 90{degrees} condition since the visual stimulus led at the shortest delay (6.67 ms). This pattern was reversed in the 270{degrees} condition when the auditory stimulus led the shortest delay. Within cue modality, recall was enhanced when a stimulus of the corresponding modality led the shortest delay as compared to the longest delay (20 ms). Our findings provide novel evidence for STDP in human memory, which builds an important bridge from in-vitro studies in animals to human behaviour.