Getting more sleep helps the brain clear out junk.

There's now even more justification for getting at least eight hours of sleep, as if we needed any more. While you sleep, neurons are still firing. Unbeknownst to us, the brain uses this time for replenishment to clear out unnecessary items that have accumulated during our awake states.

Sleep is similar to a gentle reboot. We already knew that slow brainwaves were associated with peaceful sleep, and now scientists from St. Louis' Washington University School of Medicine have discovered why. Our neurons need energy to perform complicated functions like solving puzzles and storing information in our memories when we are awake. The issue arises from the debris that is left over after they eat these nutrients. The neurons in our sleep use these rhythmic waves to aid in the removal of metabolic waste from brain tissue as cerebrospinal fluid passes through it.

Put differently, neurons must clear the clutter to prevent it from building up and possibly causing neurodegenerative illnesses. In a study that was just published in Nature, the WUSTL research team stated that neurons "serve as master organizers for brain clearance."

Integrated garbage disposal

The brain's parenchyma, or functional tissue, is shielded from external influences by the blood-brain barrier and contains billions of neurons, a feature shared by the brains of humans and other higher organisms.

Metabolic waste is produced by these neurons in every action, frequently in the form of broken proteins. According to findings from other research, these pieces might be a factor in neurodegenerative illnesses like Alzheimer's.

The brain must find a way to get rid of its waste, and it does so by means of the glymphatic system (no, that's not a typo). This system transports cerebrospinal fluid, which pushes waste out of the parenchyma through channels that are close to blood vessels. That did not, however, address the remaining questions: What and how exactly powers the glymphatic system to accomplish this? The WUSTL group was curious to learn more.

Scientists used mice in their experiments, implanting electrodes in the spaces between neurons and probing their brains to see what signaled the glymphatic system to empty the trash. The mice were then given ketamine anesthesia to put them to sleep.

Upon slumber, neurons discharged potent electrical currents. Even though the majority of brain waves during anesthesia were long and slow, the cerebrospinal fluid experienced corresponding waves of current. The debris would then be carried away by the fluid as it passed through the dura mater, the outer layer of tissue that lies between the brain and the skull.

Simply flush it.

The researchers aimed to confirm that neurons were, in fact, the driving force behind the activation of the glymphatic system. In order to achieve that, they had to genetically modify the brains of some mice so that, while they slept, their neurons almost completely stopped firing (but not to the point of brain death). The remaining mice's brains were left intact for purposes of comparison.

The long, slow brain waves that were previously observed in these genetically altered mice were absent. The fluid was consequently no longer forced to remove metabolic waste from the brain. This could only indicate that the brain's self-cleaning cycle was dependent on active neurons.

In addition, the researchers discovered that the brain waves of the unmodified mice fluctuated, with somewhat faster waves presumably directed towards the debris that was more difficult to eliminate (at least, this was their theory). It's similar to washing a plate and then having to scrub a little bit harder in areas where the residue is particularly tenacious.

The reason behind the disparate outcomes of earlier experiments was also discovered by the researchers. Neural activity plays a critical role in the flushing out of waste-carrying cerebrospinal fluid, so the type of anesthetic used was important because anesthetics that block neural activity can affect the outcome. Due to damage brought on by more traditional and invasive techniques for inserting the monitoring hardware into brain tissues, other earlier trials did not function as well. This damaged neurons as well.

In the same study, the team stated, "The experimental methodologies we used here largely avoid acute damage to the brain parenchyma, thereby providing valuable strategies for further investigations into neural dynamics and brain clearance."

Now that the glymphatic system is understood to be activated by neurons, greater focus can be placed on the details of that procedure. Learning more about the accumulation and removal of metabolic waste products could help us better understand neurodegenerative illnesses. It's definitely something to consider before turning in for the night.