Project Summary During sleep, our brains remain active and exhibit a range of characteristic electrical signals not observed during awake periods. These characteristic signals are assumed to be fundamental events in the sleeping brain’s organization of information into our memories. The research described in this proposal will utilize intracranial depth electrode data to further our understanding of memory consolidation in humans. Despite the fundamental role sleep and memory play in our lives, little is definitively known about how memories are formed and maintained. The availability of intracranial data presents a rare opportunity for fresh insight. The research described in this proposal will determine the role local spindles play in memory consolidation. Spindles are transient bursts of 11-16 Hz oscillations in the electroencephalogram, and their activity could serve as a unique biomarker for mental health conditions and memory-related pathology and performance. Spindles were once considered relatively uniform electrical events, globally distributed throughout the neocortex. This understanding is complicated by recent findings of local spindles restricted to specific brain regions. The role of local spindles in memory consolidation remains a mystery. Aim 1 will determine if local spindle activity (like global spindle activity) is sensitive to the acquisition of new information related to a procedural memory task. Task-related sounds played during sleep are known to reactivate the associated memories and lead to improved recall of those memories after awakening. The replay of select auditory cues during sleep, which is known to bias memory formation, will allow us to hone in on and examine the neural dynamics associated with those particular moments in time. We will examine how the local spindle neural dynamics that immediately follow cue presentation relate to improvement on the task. The use of intracranial data will allow us not only to detect local spindles, but also to relate them to activity in deep brain structures like the hippocampus, which is thought to play a critical role in sleep-mediated memory consolidation. Aim 2 will employ the same procedure as in Aim 1, but using a declarative memory task in which subjects are asked to recall the locations of various objects presented on a computer screen. Success in our aims will provide a detailed understanding of how local spindle dynamics contribute to both declarative and procedural memory consolidation and inform the broader effort to understand how oscillatory activity during sleep consolidates memories. This work will also support the identification of effective sleep interventions for memory improvement in health and disease.