Sleep VIII

Even though I'm trying my best to pick out the key points of the chapters and i'm sticking to the notes I made - often times directly quoting the book, the real magic is reading the whole book itself and I find myself stopping the writing just to re-read the whole chapter all over again because the notes just don't do enough justice. If you have the time and the can get yourself a copy of this gorgeous book - please read it! 

This one is a short chapter on learning and sleep. We've spoken before about how sleep helps consolidate learning. But in this chapter Matthew talks about an experiment he did with his own students at Harvard University. In the survey he shares with his students at the start of the course he tries to understand what their sleeping habits are. And he answer he usually finds is that more than 85% of them pull all-nighters - especially to study for an upcoming exam. 

So he decided to conduct an experiment. He divided his students into two groups: sleep and sleep deprivation. After a regular day, the sleep group was sent to sleep a full 8 hours and the sleep deprivation group was kept awake in his lab. The following morning, at midday, the participants were placed inside an MRI scanner and asked to learn a few facts one at a time while their brain activity was being monitored. 

After this, both groups were given two nights of recovery sleep and were then tested on the facts they had learnt. Sleep deprivation was only in effect during the act of learning and not during the later act of recall.

The result: there was a 40% deficit on the ability of the sleep deprived group to cram new facts into the brain relative to the group that obtained a full night of sleep. The hippocampus showed a lot of learning related activity in the students who had slept and none in the students who hadn't. It was as though sleep deprivation had shut down their memory in-box, and any new information was simply being bounced. Also interesting is that memory formed without sleep are weaker memories, evaporating quickly.

Sleep deprivation even impacts the DNA and the learning-related genes in the brain cells of the hippocampus itself. A lack of sleep is a deeply penetrating and corrosive force that enfeebles the memory-making apparatus within your brain, preventing you from constructing lasting memory traces.

Another really great experiment that furthers the bond between sleep and learning is below. 

Dr. Robert Stickgold had 133 undergraduates learn a memory task through repetition.Participants returned to his lab and were tested on how much they had retained. Some returned after a day's sleep, some after two days and some after three. A night's sleep strengthened the newly learned memories, boosting their retention. Additionally, the more nights of sleep participants had before they were tested, the better their memory was.

 One additional twist gives us a new result. One more group was tested after three nights - the first night without any sleep and the next two nights with a full 8 hour sleep. They showed no evidence of a memory consolidation improvement. If you do not sleep after the very first night of learning, you lose the chance to consolidate memories even if you get lots of "catch-up sleep" thereafter.

In Matthew's words "Sleep is not like a bank. You can not accumulate a debt and hope to pay it off at a later point in time"