11/7/25 Ayman Aljishi: Dentate spikes in the hippocampus of sleeping macaques
Neuroscience brown bag
Ayman Aljishi
PhD Student
Date: Friday, November 7, 2025
Time: 1:25-2:15pm
Location: 316 Wilson Hall
Dentate spikes in the hippocampus of sleeping macaques
The sleeping brain exhibits distinctive electrophysiological events that are linked to memory consolidation across neocortical and hippocampal regions. Slow waves (0.5–2 Hz) and spindles (10–16 Hz) are the key neocortical oscillatory events during non-rapid eye movement sleep. In the hippocampus, sharp wave ripples (SWRs) and dentate spikes (DSs) are prominent local field potential events that mark brief epochs of highly synchronous neuronal firing during offline states. Both phenomena (SWRs and DSs) signal local and long-range changes to network states and accompany the reactivations of waking neuronal activity patterns during sleep (replay), though in distinct temporal windows, and potentially recruiting distinct neuronal ensembles. Furthermore, whereas SWRs have been described across mammalian species, DSs have only been reported in rodents, leaving open the question of whether they exist in primates and how they may interact with other established sleep oscillations. We implanted adult female macaques with indwelling, movable, high-density linear probes targeting hippocampal (CA1 and dentate gyrus) and neocortical (ventromedial prefrontal and posteromedial) regions. We recorded 512 channels wirelessly during a task in which monkeys learned to infer object category membership using spatial context rules, and we continued recording during subsequent post-task sleep. Using established detection methods, we identified hippocampal DS and SWR events and neocortical slow waves across multiple nights of sleep recordings. Dentate spikes had their highest incidence during the epochs of sleep that coincided with high slow-wave rate and exhibited a fine temporal relationship with SWRs. I will describe the detection of dentate spikes and preliminary results on their prevalence, state dependence, and interactions with other key sleep oscillations. Given the extensive theoretical emphasis on coordinated hippocamo–neocortical activity during slow-wave sleep as a mechanism for memory consolidation, I will discuss how dentate spikes may contribute to this cross-regional interaction.