Every night, you get brainwashed.
As you’re sleeping, slow brain waves trigger gentle pulses of cerebrospinal fluid (CSF) that bathe your brain, flushing out the waste that’s accumulated during the day. It’s an important process, and one that’s been linked to cognitive health, neuroprotection, and memory consolidation. Of course, as we age, we also tend to sleep less. Now, a new study published in Nature Aging is taking a look at what happens to these revitalizing waves as we get older.
A team of neuroscientists led by imaging specialists at the Massachusetts Institute of Technology recruited some young (ages 18-39) and older (ages 60-84) volunteers to spend a night getting their brains scanned. While they dozed, the participants had their noggins imaged by both fMRI and a modified MRI technique to measure CSF flow. Their brain activity was also recorded by an EEG machine. As the younger group drifted off, their slow EEG waves intensified—and the CSF pulses followed suit. Among the older participants, however, these CSF waves were markedly weaker.
Read more: “Is Sleeping in on the Weekends Bad for Your Heart?”
To find out what was behind the differences, the researchers observed their brain activity while they were awake. First they tested their neurovascular coupling, or the relationship between brain activity and blood flow, by using an image of a flickering checkerboard. This usually cranks up neural activity which in turn increases blood flow. It did, for both groups, but the older cohort again showed an attenuated response.
The same pattern showed up in tests of the brain’s vascular system. The researchers asked the participants to hold their breath in order to trigger a carbon dioxide build-up to dilate the brain’s blood vessels. On average, older participants showed a weaker vasodilation.
Still, the attenuated neurovascular coupling and decreased blood flow didn’t account for the full gap between the young and old. In other words, there’s more to this story. “Aging is so complex, and so many different things change, that it’s really hard to disentangle the individual factors,” study author Sydney Bailes of MIT explained in a statement. “We try to account for some of the mechanisms, but there definitely are a lot of other factors related to vascular health and lifestyle. If you were able to measure all of them, you might be able to break it apart into different explanations for why an individual’s CSF flow might be more or less impaired.”
Importantly, not all of the older participants experienced a drop-off in CSF pulses. Some of them were indistinguishable from their younger counterparts. “It’s really intriguing that for some of these older adults, their CSF fell right in the range of the healthy young adults,” senior author Laura Lewis of MIT said. “We are really interested in what’s different in those people and how that might be related to future health outcomes.”
While we wait for someone to find out, remember to get a good night’s sleep—weak waves or not.
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