Enhancing spatial memory via auditory entrainment of theta oscillations
Jessica Creery1, Hadley C. Pfalzgraf1, Ken A. Paller1; 1Northwestern University
Memory processing in the brain has been associated with neural oscillations at specific frequencies. To investigate the putative causal roles of these rhythms, they can be manipulated using transcranial direct current stimulation (tDCS) or repetitive transcranial magnetic stimulation (rTMS). Alternatively, oscillatory auditory stimulation can function like oscillatory electromagnetic stimulation. We thus presented pink noise concurrently with pictures of objects, and systematically modulated sound intensity to include frequency-specific signals. We focused on neural entrainment at theta and beta frequencies based on (a) evidence showing neural responses from auditory stimulation at these frequencies and (b) evidence linking theta and beta with memory formation. Participants learned 60 object-location associations on a grid background. For each participant, one-third of the objects were randomly assigned to each of three conditions: 4-Hz theta oscillations, 15-Hz beta oscillations, or static noise. Each association was learned to a criterion and, after a 15-min break, location recall was tested for each object. Scalp electroencephalographic recordings showed that brain activity was altered as expected: theta amplitude was higher during 4-Hz stimulation, whereas beta amplitude was higher during 15-Hz stimulation. To the extent that stimulation enhanced theta, a memory improvement was found for objects presented with 4-Hz stimulation compared to objects with unmodulated noise. That is, this relative memory benefit was correlated with the increase in theta power during stimulation. Sensory entrainment is thus a powerful way to experimentally modify brain oscillations in order to understand their functions, in this case linking theta with effective memory formation.
Topic Area: LONG-TERM MEMORY: Episodic