Hippocampus Generates Deep Sleep Waves

Summary: Scientists discovered a surprising new source for brain waves essential for deep sleep. These waves, traditionally thought to come from a different area, were also found to be generated by the hippocampus, a region crucial for memory.

By studying these waves in single nerve fibers, researchers believe they may be linked to how sleep strengthens memories. This discovery opens doors for a deeper understanding of sleep disorders and paves the way for potentially groundbreaking new treatments.

Key Facts:

  • The hippocampus, known for memory, generates deep sleep brain waves.
  • These waves may be linked to sleep-based memory consolidation.
  • Findings could lead to new treatments for sleep disorders.

Source: UC Irvine

University of California, Irvine biomedical engineering researchers have uncovered a previously unknown source of two key brain waves crucial for deep sleep: slow waves and sleep spindles.

Traditionally believed to originate from one brain circuit linking the thalamus and cortex, the team’s findings, published today in Scientific Reports, suggest that the axons in memory centers of the hippocampus play a role.

For decades, slow waves and sleep spindles have been identified as essential elements of deep sleep, measured through electroencephalography recordings on the scalp. However, the UC Irvine-led team revealed a novel source of these brain waves within the hippocampus and were able to measure them in single axons.

This shows a woman sleeping.
By uncovering the hippocampus’s role in generating slow waves and sleep spindles, this research expands our understanding of the brain’s activity during deep sleep and its impact on memory processing. Credit: Neuroscience News

The study demonstrates that slow waves and sleep spindles can originate from axons within the hippocampus’ cornu ammonis 3 region. These oscillations in voltage occur independently of neuronal spiking activity, challenging existing theories about the generation of these brain waves.

“Our research sheds light on a previously unrecognized aspect of deep sleep brain activity,” said lead author Mengke Wang, former UC Irvine undergraduate student in biomedical engineering who is now a graduate student at Johns Hopkins University (Wang conducted the study while at UC Irvine).

“We’ve discovered that the hippocampus, typically associated with memory formation, plays a crucial role in generating slow waves and sleep spindles, offering new insights into how these brain waves support memory processing during sleep.”

The team utilized innovative techniques – including in vitro reconstructions 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 originate from active ion channels within axons, rather than through volume conduction as previously thought.

“The discovery of spindle oscillations in single hippocampal axons opens new avenues for understanding the mechanisms underlying memory consolidation during sleep,” said co-author Gregory Brewer, adjunct professor of biomedical engineering.

“These findings have significant implications for sleep research, potentially paving the way for new approaches to treating sleep-related disorders.”

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

By uncovering the hippocampus’s role in generating slow waves and sleep spindles, this research expands our understanding of the brain’s activity during deep sleep and its impact on memory processing.

The findings offer a promising foundation for future studies exploring the therapeutic potential of targeting hippocampal activity to improve sleep quality and cognitive function.

Joining Brewer and Wang in this study, which received financial support from the UCI Foundation, were William Tang, professor emeritus of biomedical engineering; Bryce Mander, associate professor of psychiatry & human behavior; and Samuel Lassers, graduate student researcher in biomedical engineering. 

About this sleep and memory research news

Author: Brian Bell
Source: UC Irvine
Contact: Brian Bell – UC Irvine
Image: The image is credited to Neuroscience News

Original Research: Open access.
Spindle oscillations in communicating axons within a reconstituted hippocampal formation are strongest in CA3 without thalamus” by Mengke Wang et al. Scientific Reports


Spindle oscillations in communicating axons within a reconstituted hippocampal formation are strongest in CA3 without thalamus

Spindle-shaped waves of oscillations emerge in EEG scalp recordings during human and rodent non-REM sleep. The association of these 10–16 Hz oscillations with events during prior wakefulness suggests a role in memory consolidation.

Human and rodent depth electrodes in the brain record strong spindles throughout the cortex and hippocampus, with possible origins in the thalamus. However, the source and targets of the spindle oscillations from the hippocampus are unclear.

Here, we employed an in vitro reconstruction of four subregions of the hippocampal formation with separate microfluidic tunnels for single axon communication between subregions assembled on top of a microelectrode array.

We recorded spontaneous 400–1000 ms long spindle waves at 10–16 Hz in single axons passing between subregions as well as from individual neurons in those subregions. Spindles were nested within slow waves.

The highest amplitudes and most frequent occurrence suggest origins in CA3 neurons that send feed-forward axons into CA1 and feedback axons into DG. Spindles had 50–70% slower conduction velocities than spikes and were not phase-locked to spikes suggesting that spindle mechanisms are independent of action potentials.

Therefore, consolidation of declarative-cognitive memories in the hippocampus may be separate from the more easily accessible consolidation of memories related to thalamic motor function.

Join our Newsletter
I agree to have my personal information transferred to AWeber for Neuroscience Newsletter ( more information )
Sign up to receive our recent neuroscience headlines and summaries sent to your email once a day, totally free.
We hate spam and only use your email to contact you about newsletters. You can cancel your subscription any time.