Sculpting memories during sleep

Our ability to remember past events and experiences lies at the core of cognition and behaviour. But how do fleeting moments get converted into durable memory traces? Recent work has highlighted the pivotal role of post-learning sleep for successful memory consolidation, the process of stabilising new memories over time. However, little is known about the neurophysiological mechanisms through which the sleeping brain consolidates new memories. Not only has this left a gap in our understanding of memory formation as a whole, but also the means to modulate memories during sleep have remained underexplored. SPIN will test the exciting hypothesis that particular electrophysiological signatures of sleep, namely sleep spindles, are the mechanistic vehicle driving memory consolidation. Specifically, I hypothesise that in coordination with hippocampal reactivation events, sleep spindles are deployed to cortical learning sites where they induce lasting structural changes. Using intracranial recordings from the human hippocampus (measuring single neuron firing and associated ‘ripple’ oscillations) and from an array of cortical areas, we will first establish whether spindles are temporally aligned with hippocampal reactivation events. Next, we will use high-density scalp EEG and functional as well as structural MRI in healthy participants to test whether spindle deployment to cortical learning sites predicts structural changes in these regions. To assert causality, we will examine the effects of invasive spindle perturbation in patients on memory consolidation. Finally, we will experimentally enhance local spindles to harness their potential as a tool for boosting human memory. In sum, SPIN will use an unprecedented array of human brain recording and stimulation techniques to provide a mechanistic link between learning, sleep and structural brain changes, culminating in novel tools to enhance human learning and memory.