Closed-loop auditory stimulation in phase with slow waves during sleep enhances cerebrospinal fluid flow in humans

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closed-loop auditory stimulation (CLAS)

Recurrent neural networks (RNNs)

"... In a new study, ... researchers have shown that they can strengthen these CSF waves through exposure to short bursts of a gentle, staticky sound known as “pink noise” during sleep. These bursts increase the amplitude of slow electrical waves in the brain, which then enlarges the CSF waves. ...

Their fMRI studies also revealed that the slow waves stimulate blood vessels to constrict and dilate, allowing them to act as a pump that drives CSF out of the brain. Slow waves are seen only during non-REM sleep, and they become more prominent in deeper stages of sleep. ..."

From the abstract:

"Cerebrospinal fluid (CSF) is a key component of healthy brain function, constantly circulating to maintain brain homeostasis.

Large waves of CSF flow appear in nonrapid eye movement (NREM) sleep, and these CSF flow waves are associated with neural slow waves in the electroencephalogram (EEG).

Whether neural slow waves are causally linked to CSF flow, and whether this flow can be enhanced, is not yet established.

We developed a technique for performing closed-loop auditory stimulation of sleep slow waves with simultaneous magnetic resonance imaging (MRI) using real-time denoising and a neural network–based strategy for stimulus targeting.

We first established that our technique could increase EEG slow waves during sleep inside the MRI scanner in healthy adults.

We then found that closed-loop auditory stimulation during sleep caused increased CSF flow waves.

Furthermore, this CSF flow effect was phase dependent and only apparent when auditory stimuli were aligned with slow-wave peaks. Widespread hemodynamic waves were also elicited by the stimulus, suggesting a brain-wide modulation contributing to this CSF flow effect.

This work demonstrates that closed-loop slow-wave neurofeedback causes waves of CSF flow and provides a technique for simultaneous modulation and imaging of CSF flow during sleep that can next be explored as a potential translational tool in clinical populations."

A burst of “pink noise” may lead to more restorative sleep | MIT News | Massachusetts Institute of Technology "Delivered at just the right time, this type of auditory stimulus can strengthen the flow of cerebrospinal fluid, which clears debris from the brain and keeps it healthy."

Closed-loop auditory stimulation in phase with slow waves during sleep enhances cerebrospinal fluid flow in humans | Science Translational Medicine

Fig. 1. An integrated RNN and real-time EEG-fMRI algorithm enables closed-loop slow-wave enhancement inside the MRI scanner.

Fig. 2. CLAS causes a CSF flow wave in the fourth ventricle.