Circadian (5): REM Science
We have arrived at an article where science—and some "out-of-touch" technical but important words—will dominate again. I’m going to try to explain REM sleep, but with a major caveat: science is not privileged to know everything about it as it stands today. It’s much like trying to explain NREM III before 2012, when we knew nothing about the glymphatics.
In the brain, we have identified regions in the brainstem called the pons and the midbrain, wherein lie two switches that determine whether our brain remains in or out of REM. The first switch, which is activated most of the time, keeps us out of REM. This is called the REM-off switch. We keep this switch working because we don’t want to enter REM at any time during our wake period, nor do we want REM to dominate our sleep without limitations. Any amount of noradrenaline will keep this REM-off switch dominant, and serotonin acts as another fuel for it. The second switch is only turned on when we want to go into REM, so this is appropriately called the REM-on switch.
It might help you to consider the neurotransmitter GABA as the body's way of deciding which switch is dominant. Remember, GABA is inhibitory. When we talked about melatonin, we learned that melatonin made GABA more potent, and that potent GABA in turn turns noradrenaline down, allowing for brain shrinkage. At the end of NREM III, our brain sends GABA to the REM-off switch, making it ineffective. This is also the time when noradrenaline and serotonin levels drop to zero, starving the REM-off region of its fuel. Without REM-off influence, we will enter REM. This is fueled by an excitatory (as opposed to inhibitory) neurotransmitter called glutamate acting on the REM-on area. You can either be in REM or NREM; it is a binary world up there.
Under glutamate’s influence, the REM-on switch will start to fire its ammunition to take full advantage of this situation. From the pons—which sits within the brainstem and acts as a physical bridge between the bulk of the brain and the spinal cord—two neurotransmitters are fired in opposing directions. The first, called acetylcholine, goes up to the brain to wake it up. Yes, your brain is technically awake in REM, such that your actual wake brainwaves look similar to REM waves and are hard to tell apart. Your eyes, being part of the brain, move rapidly, giving REM sleep its name: Rapid Eye Movement. But why aren’t you actually awake, you ask? Because the second neurotransmitter, glycine, travels down the spinal cord to ensure total muscle paralysis so you don’t sleep in one county and end up waking up in another after taking instructions from your adventurous REM visions.
The key in this is that during REM sleep, your brain is as active as it is during wake time but with one major difference: your noradrenaline level is near zero or zero. This is the only time in our lives where noradrenaline can reach levels this low. Despite noradrenaline’s important presence in maintaining functions like wakefulness and NREM III, the fact is that it is a stress chemical. When noradrenaline is absent or undetectable, the brain experiences no stress. Guess what a no-stress environment is best for? We all know this: emotional processing. So now you have your simple answer after all of that scientific jargon: REM sleep helps you process emotions.
If you want a simplistic summary of complex neuroscience, it looks like this:
REM-off is fuelled by noradrenaline, serotonin, and histamine.
At the end of NREM III these three are absent; instead, GABA inactivates REM-off.
Glutamate activates REM-on at this point.
REM-on fires acetylcholine up and glycine down = brain active, body paralysed.
We process memory and emotions without stress (noradrenaline).
You can see that in a healthy circadian rhythm, we are equipped with ways to process our experiences from the day prior to ensure that the burden is not carried over to the next day. This way, we become more experienced and mature without being pulled down by the emotional weight that was tagged to the learning environment. REM is not just a tool; it is a necessity for our emotional and mental wellbeing. Is it not then obvious that if we want to look after our mental health, we really need to seriously look at this stage of sleep? Perhaps everyone with a mental health challenge ought to have a specialised polysomnography looking at how well they go in and out of REM?
On that note, I have something quick to tell you about the two most popular drugs for mental health ailments: alcohol (self-medication) and SSRIs (prescribed). Alcohol is a potent GABA agonist—it enhances GABA production. Although GABA helps you "konk out," its overspill goes to the REM-on area and renders the switch inoperable. On top of that, it is an NMDA receptor antagonist. NMDA is the docking station for glutamate, without which it cannot have its excitatory effect. Now your REM-on is turned off, and there is no glutamate to come to the rescue. You may be getting the hours of sleep you need from self-medicating with alcohol, but you will still wake up with the problem you haven’t solved as you would not have spent enough time in REM. And no, the next night’s bottle won’t solve your problem either. This is why alcohol is linked to poor mental health.
SSRIs are not much better when it comes to REM sleep. By definition, Selective Serotonin Reuptake Inhibitors stop serotonin recycling such that your brain continues to have serotonin available. Recall that one of the neurotransmitters which keeps the REM-off switch in the active position is serotonin. If any of these neurotransmitters are around at a detectable level, we cannot go into REM. Effectively, you are trading the body’s intrinsic and most effective emotional therapy for a temporary "level" feeling in the daytime. Some people get really weird and vivid dreams from these drugs and believe they are maintaining a good REM pattern; in reality, this phenomenon is called REM rebound. This is where the body squeezes in as much REM as it can in desperation in the final hours of sleep, as it has finally managed to clear out the last of the serotonin that was in its way. Again, this is not something to be proud of. Rather, it is a red flag—the body can only brush so much under the carpet before things blow out.