Katherine Duncan
Department of Psychology
University of Toronto

The Rhythms of Memory Behaviour

When are you best prepared to learn? Our intuition points to slowly changing factors, like having a good night’s sleep or a cup of coffee. Remarkably, an influential factor may operate so quickly that eludes not only our conscious reflections but also psychological investigation—hippocampal theta rhythm. We know that this rhythm matters for the brain; at different phases of theta, rodent hippocampal neurons receive input from different sources and tend to strengthen vs. weaken their connections. But, do people’s memory abilities also depend on the phase of these rhythms? I will present my lab’s first attempts to answer this question. First, doubling down on behavior, I’ll present our adaptation of the behavioral oscillation paradigm popularly used to study the rhythms of attention. With it, we can reconstruct the time course of how equipped people are to form memories with millisecond precision following an oscillatory resetting stimulus (attention-grabbing cue). Second, I will present our approach to targeting specific hippocampal theta phases with deep-brain stimulation to assess their involvement in memory formation causally. Lastly, I will share surprisingly slow oscillations (~.1Hz) in memory formation that we serendipitously discovered; after making a mistake, people slowly—but rhythmically—alternate between learning task-relevant and irrelevant information for nearly a minute.  Together, this work shows that memory processes aren’t always on, ready to capture or relive an experience. Instead, they paint memory as a rhythmic process with its outcomes at the whim of its beat.