Sleep sorts the day
- Monday eveningsharpA night's sleepTuesday morningduller
Picture the same silence, remembered on Monday evening and then on Tuesday morning. On Monday evening it is sharp. On Tuesday morning it is the same fact, and duller. Nothing happened in between except sleep. Sleep is where the day's memories are sorted, and the sorting takes some of the sting out.
- The day's memory, with its chargeDream sleep replays itThe fact is keptThe charge is turned down
During the part of sleep when the eyes move and dreams come, the brain replays the day. It keeps the facts and turns down the alarm attached to them. That is what some sleep researchers find: a night's sleep keeps what happened and softens how it felt. The memory stays. The charge comes off.
- Sharp memoryA night's sleepNext morning?
What does a night's sleep do to a sharp memory from the day?
Makes it sharper by going over it.
Not yet. Replaying in sleep is not the same as replaying awake. The sleeping replay runs with the alarm chemicals low, and that is what turns the charge down rather than up.Deletes it.
Not yet. The fact is kept; on Tuesday the silence is still remembered. What is smaller is the alarm attached to it, which is why it is duller and not gone.Keeps the fact and turns the charge down.
Right. On Tuesday the silence is still remembered, and it is duller. The replay in sleep runs with the alarm chemicals low, which is what takes the charge off. - Slept100 alarm responseAwake 35 hours160 alarm response
The same upsetting pictures, 2007 study. Slept = 100. The other direction is measured too. In a 2007 study, people who had been awake for about thirty-five hours were shown upsetting pictures in a brain scanner. The alarm part of their brain responded about sixty per cent more strongly than in people who had slept. Short of sleep, the alarm fires harder at the same picture.
Move the control to set the night before. The alarm's strength is made up and round, scaled from the 2007 result: a full night 100, no sleep 160.
Alarm strength100After a full night1008 hoursA full night. The alarm fires at its usual strength: 100.
Alarm strength115After a full night1006 hoursSix hours. The thinking part's hand on the alarm is a little weaker. The same picture lands at about 115.
Alarm strength135After a full night1004 hoursFour hours. The alarm fires harder at the same picture: about 135.
Alarm strength160After a full night100NoneNo sleep. The 2007 study's number: the alarm fires about 60 per cent harder at the same picture. 160.
The same silence, read after a night with no sleep. What is different?
The alarm fires about half as hard again, at the same silence.
Right. The silence is the same. The alarm reading it is not: short of sleep it fires harder, by about sixty per cent in the study, so the same fact lands as a bigger threat.Nothing; the silence is the silence.
Not yet. The silence is the same, and the alarm reading it is not. Short of sleep it fires harder at the same fact, which is what the scanner measured.The alarm is tired too, so it fires less.
Not yet. The thinking part is tired and slower. The alarm is not; it is the thinking part's hand on the alarm that has weakened, so the alarm runs louder.Move the control.
- 0561126 amMidnight
Cortisol through a day. The shape is real; the scale is made up, with the morning peak at 100. Cortisol, the slow messenger, also has a daily tide. It is highest in the half hour after waking, when it rises by about half, and lowest in the first hours of sleep. A hurt read at nine in the morning is read on a high tide. The same hurt at ten at night is read on a low one.
Here is a day in three parts. Tap the part when the slow messenger is naturally at its lowest.
Tap the part of the picture that answers it.
Just after wakingMid-afternoonAround midnightAround midnight
Right. Midnight is the bottom of the tide. A worry at midnight can still feel huge, and that is the replay at work, with the tired thinking part keeping little hold on it.Just after waking
Not yet. The half hour after waking is the top of the tide, when cortisol rises by about half. A silence read with the first coffee is read on the highest tide of the day.Mid-afternoon
Not yet. Mid-afternoon is on the way down, well below the morning and well above midnight. The tide falls through the day and reaches its lowest in the small hours.- alarm at 100Restedalarm at 160Short of sleep
So sleep touches the hurt twice. The night after takes some of the charge off the memory. The night before sets how hard the alarm fires at it. A silence read after a bad night, on the morning tide, lands harder than the same silence read rested. Same message, different body reading it.
- Slept eight hoursUp at four
Two players get the same harsh comment from a coach. One slept eight hours; one was up at four for a flight. By this lesson, what is the difference?
The tired one's alarm fires harder at the same words, and tonight's sleep is what takes the charge off for both.
Right. The words are the same; the alarm reading them is louder in the tired player. Tonight, dream sleep will replay the comment for both with the alarm chemicals low.No difference; the comment is the same.
Not yet. The comment is the same. The alarm reading it is not: short of sleep it responds harder, by about sixty per cent in the study, so the words land as a bigger threat.The tired one will forget it faster.
Not yet. Sleep is what sorts a memory and turns its charge down. The tired one has had less of that, not more, and is starting with a louder alarm.
Lesson complete
A night's sleep takes the charge off a memory, and a night without sleep makes the alarm fire harder.