What Is Brain Waste?
In the past few years, you may have seen alluring headlines like "Healthy lifestyle choices boost brain waste disposal" and "How to optimise your brain's waste disposal system." Enticed, you click to learn that frequent exercise, a proper amount of sleep, and even resting on your side can help your brain clear out waste products, keeping your cognitive functions in tip-top shape. But wait, what is this brain "waste"? And why does your brain produce it in the first place?
Just like you produce and excrete waste products every day, so do your cells. The process of cellular respiration, which extracts energy from sugar, amino acids and fatty acids, creates byproducts like carbon dioxide, water, ammonia, as well as various types of proteins.
Neurons (brain cells) are notorious energy hogs, and thus produce waste in even greater quantities than other bodily cells. Of the refuse they produce, the most concerning are two proteins: amyloid beta and tau. Amyloid beta is infamous for forming the plaques found in the brains of Alzheimer's patients. When misfolded, tau can create tangles that lead cell microtubules to dissassemble, alter neuronal signaling, and cause mitochondrial dysfunction. Tangles of tau are the hallmark of many neurodegenerative diseases.
Luckily, as Maiken Nedergaard of the University of Rochester Medical Center and her colleagues discovered back in 2012, the brain has a mechanism to clear out tau and amyloid waste. It's called the glymphatic system, which Nedergaard endearingly dubbed the "Garbage Truck of the Brain."
The signature action of the glymphatic system is flushing out neuronal waste products by flooding the brain with cerebrospinal fluid. Using sophisticated imaging techniques, Nedergaard and her team witnessed the process in mice brains. Tanya Lewis described it for Wired:
"Cerebrospinal fluid flowed along the outside of blood vessels, carried through a network of pipe-like protein structures. The fluid picked up waste that accumulated between cells, then drained out through major veins."
Follow-up studies demonstrated that intercellular spaces within the brain expand by as much as 60% when mice are sleeping, facilitating the cleaning process. Deeper, uninterrupted sleep makes the system run even more efficiently. Sleeping on your side can also help.
Tau and amyloid are waste products you don't want gumming up your neurons, so lend your brain a hand!