Just as our bodies produce waste every day – which is why we need to shower and use the toilet – our brains produce harmful waste proteins. But how can our brains “shower” themselves?
正如我们的身体每天都会产生废物 —— 这也是我们需要洗澡、上厕所的原因 —— 我们的大脑也会产生有害的废弃蛋白质。但是我们的大脑又是如何“清洁”自己的呢？
A 2013 study found the answer. Researchers at the US University of Rochester studied the brains of mice and discovered that they cleaned themselves while the mice slept. A kind of fluid in the brain, called cerebral spinal fluid, was found to increase dramatically during sleep, washing away waste proteins that had been building up between brain cells in waking hours.
“This study shows that the brain has different functional states when asleep and when awake,” Maiken Nedergaard, the lead researcher, told NBC News. It also explains why we can’t seem to think clearly after a sleepless night while a good night’s sleep leaves us feeling sharp and refreshed.
Now a new study, published on Oct 31 in Science, digs a little deeper into our brains’ self-cleaning procedure. Instead of mice, this time humans were the test subjects.
Researchers at Boston University, US, monitored the brain waves of 13 healthy adults who were sleeping, using accelerated fMRI, which is capable of recording faster changes inside the brain than a regular fMRI machine. They found that every 20 seconds, blood flowed out of the brain, making room for a large amount of CSF to come in and “clean”. This cycle coincided with the rhythm of the brain’s slow waves – an electrical activity that happens when we’re in deep sleep.
美国波士顿大学的研究人员通过增强性磁共振成像监测了13名健康成年人睡眠时的脑电波，和普通的功能性磁共振成像仪器相比，这种技术能够捕捉到脑内更快的变化。他们发现，每隔20秒血液会流出大脑，从而让脑脊液流入，进行“清洁”。这一循环与大脑慢波频率一致 —— 这是种我们进入深度睡眠才会发生的脑电活动。
It’s still unknown how these brain activities are connected. But the mere fact that they are connected is exciting enough, since it allows researchers to piece together possible new explanations for misunderstood diseases.
For example, slow-wave sleep has been proven to play a role in strengthening our memories. This may explain why people with Alzheimer’s often have fewer and weaker slow brainwaves. Based on this new study, there could be one more explanation for diseased brains: They are not clean.
Nedergaard, leader of the 2013 study, is also excited about the new findings. “Maybe the most important take-home message is that sleep is a serious thing,” she told Scientific American. “You really need to sleep to keep a healthy brain because it links electrical activity to a practical ‘housekeeping’ function.”