U.S.A. For years, scientists have been investigating why we sleep. Thus far, a number of hypotheses have been proposed, such as the idea that we need sleep in order to store memory.

However, a new study out of the University of Rochester Medical Center, run by Dr. Nedergaard, shows that we might actually need to sleep in order to clean our brain, and possibly, to prevent diseases.

In 2012, the University of Rochester’s Center of Translational Neuromedicine first published a study that revealed the existence of the glymphatic system. A clearance system in the brain, the glymphatic system could be seen to eliminiate a number of toxic wastes, including amyloid beta, a product believed to be involved in Alzheimer’s.

Now, a second study has shown that the rate of flow of the glymphatic system increases with sleep, and thus, we might need to sleep in order to fully clean our brain. As expected with a finding of this magnitude, there has been a lot of interest generated both in the scientific community and within the general population. ROOSTERGNN had the opportunity to speak with Michael Chen, a graduate student at the University of Rochester, about the work his lab has done.

The lab you work in recently made the discovery that that the brain may flush out toxins during sleep. How does this happen?

This was discovered via a tracer [a dye injected to the brain] study that involved analyzing the influx and efflux of tracers. We would inject tracers into the cisterna magna [opening into the brain] and analyze the degree of tracer influx and efflux.

In the study, the researchers believe the glymphatic system is responsible for clearing out these toxins. In general, how does this system work and is it responsible for other functions in the brain?

The general mechanism of the system is the generation of a convective flow of interstitial fluid. CSF [cerebral spinal fluid] would flow down penetrating arteries to go deep into the brain. Through astrocytic AQP4 channels [water channels specific to astrocytes as opposed to neurons], CSF would flow into the parenchyma [functional parts of the brain]. As the fluid flows the parenchyma, the convective flow is able to pick up metabolites and toxins on it way out to large draining veins.

Does this study have any implications for neurodegenerative diseases like Alzheimer’s?

Yes it does. Such a clearance method could be used to clear out metabolites and toxic compounds that have been linked to Alzheimer. One example is that in our recent Science paper, we injected Beta amyloid into the brain and showed that a more efficient clearance system was able to remove more beta amyloid.

What types of experiments are involved in order to make this kind of discovery?

Several experiments and techniques are required. First the tracer injections experiments are crucial. However, 2 photon microscopy [fluorescence imaging technique] is also crucial to image and follow the movement of tracers. Another crucial experiment is the TMA [an ammonium cation, a positively charged ion] experiments. TMA is a charged ion and through TMA measurements we are able to determine the volume and tortuosity of a space.

The Nedergaard lab is also known as the Center of Translational Neuromedicine. Is a translational lab different from a regular research lab?

I wouldn’t say we are “different.” Dr. Nedergaard’s lab has a focus on determining how our research is able to translate to clinical findings.

Regarding research in general, the lab is known for having a glial focus, as opposed to neuronal. What are glial cells and why is it important to study these cells?

The lab has a specific focus on the astrocytes. Traditionally, astrocytes were seen as supportive cells. However in recent years they have been shown to do much more. As a result it is very important to study these cells to specifically determine their roles.

What kind of functions have been thus far been attributed to glial cells?

Several functions have been attributed to astrocytes. In this paper, we argue that astrocytes via AQP4 channels are able to control a clearance system that is important to clear brain metabolites.


Michael Chen graduated in 2010 with a bachelor of science from the University of Rochester. Upon graduating, he served full time as a lab technician in Dr. Maiken’s Nedergaard lab at the Center for translational Medicine at the Strong Hospital. He is currently pursuing a Neuroscience PhD at the University of Rochester and is in the process in transitioning into a MD/PhD dual degree program.