Everybody knows abut Rapid Eye Movement sleep (REM sleep) now. It wasn’t always that way. I found out about it in med school when my wife pointed me to a fascinating article in the New Yorker, concerning the work of Dement and Kleitman. Briefly, if you wake someone up during REM, they’ll tell you they’re dreaming. As a budding Neurologist, I actually got an afternoon off from my internship to hear Dement talk. I’d been up most of the previous night, and after a nice lunch they turned the lights off as Dement began showing slides and I promptly feel asleep. After it was over and the lights came back on, the guy next to me asked what I’d been dreaming.
There’s been a huge amount of progress on sleep in the past year.
1. At long last, we may actually have a clue as to why we spend a third of our lives asleep. The short answer is that it is to flush out the brain. For details please see https://luysii.wordpress.com/2013/10/21/is-sleep-deprivation-like-alzheimers-and-why-we-need-sleep-in-the-first-place/
2. A recent paper found an area in the brain, which, when stimulated, takes a sleeping mouse into REM sleep. The technique is yet another use of optogenetics (which is almost sure to win Karl Diesseroth a Nobel). For details please see https://luysii.wordpress.com/2013/05/19/a-certain-nobel-prize/.
Optogenetics gives you the ability (after a lot of molecular biological work) to turn specific sets of neurons on (or off). It was known that a very old area of the brain was involved in consciousness, wake and sleep. Just which areas were crucial for REM was controversial. Prior to optogenetics, lesions were made in various place and the animals studied. Neurologic diagnosis of what part of the brain did what was essentially done this way using the various natural disasters which befall the brain. A stroke here cause language problems, a tumor there, caused visual disturbance etc. etc. It worked well, but always contained an essential ambiguity. If you turn of a switch, a light bulb stops shining. But the switch doesn’t really produce the light although it is necessary.
However, stimulating a given nucleus and shifting an animal from regular sleep to REM sleep is far less ambiguous.
The details are quite technical and probably not comprehensible to most of the readership, but here they are for the neurophysiologists in the audience.
[ Proc. Natl. Acad. Sci. vol. 112 pp. 584 – 589 ’15 ] Cholinergic neurons in the mesopontine tegmentum have been implicated in REM sleep, but lesions of the area have had varying effects on REM. This work shows that selective optogenetic activation of cholinergic neurons in the pedunculopotine tegmentum (PPT) or the laterodorsal tegmentum (LDT) increases the number of REM sleep episodes without changing REM sleep duration. Activating them in either nucleus during NREM induces REM. The work was done in transgenic mice which have extra copies of the vesicular AcCh transporter with increased cholinergic tone.
Monamines (particularly norepinephrine) are alerting, and it has been shown that neurons in LDT are inhibited by seronin in rat and guinea pig.