Researchers from the Department of Biomedical Engineering at the University of California, Irvine, have discovered a new origin of two important brain waves—slow waves and sleep spindles—that are critical for deep sleep. Although these brain waves were traditionally thought to arise solely from a circuit connecting the thalamus and cerebral cortex, the team’s findings were published as follows: Scientific Reportssuggests that axons in the memory centers of the hippocampus play a role.

For decades, slow waves and sleep spindles were considered key elements of deep sleep as measured by scalp electroencephalography recordings. But a team led by the University of California, Irvine, discovered a new source of these brain waves in the hippocampus and was able to measure them in individual axons.

The study shows that slow waves and sleep spindles may arise from axons in cornu ammonis region 3 of the hippocampus. These voltage fluctuations occur independently of the impulse activity of neurons, challenging current theories regarding the generation of these brain waves.

Research methodology and results

“Our study sheds light on a previously unknown aspect of brain activity during deep sleep,” said lead author Mengke Wang, a former undergraduate biomedical engineering student at UC Irvine and now a graduate student at Johns Hopkins University in Irvine.

“We found that the hippocampus, normally associated with memory formation, plays a critical role in the formation of slow waves and sleep spindles, offering new insights into how these brain waves support memory processing during sleep.”

The team used innovative techniques, including in vitro reconstruction of hippocampal subregions and microfluidic tunnels for single axon communication, to observe spontaneous spindle waves in isolated hippocampal neurons. These findings suggest that spindle oscillations arise from active ion channels in axons rather than volume conduction as previously thought.

Implications and future research

“The discovery of spindle oscillations in individual hippocampal axons opens new avenues for understanding the mechanisms underlying memory consolidation during sleep,” said co-author Gregory Brewer, associate professor of biomedical engineering. “These findings have important implications for sleep research and potentially pave the way for new approaches to treating sleep-related disorders.”

Brewer’s other research organizations include the Memory Impairment and Neurological Disorders Institute and the Center for the Neurobiology of Learning and Memory.

By revealing the role of the hippocampus in the formation of slow waves and sleep spindles, this study expands our understanding of brain activity during deep sleep and its impact on memory processing. Our results provide a promising basis for future studies that will examine the therapeutic potential of influencing hippocampal activity to improve sleep quality and cognitive function.