Why are persons with Bipolar affected so much more if they do not receive direct light everyday?
How Light Affects the Brain
“You know about rods and cones, right? Those are the two kinds of receptors in your eyeball, on your retina, for light. But you didn’t know that there is another receptor for light in the eye (I’m guessing you don’t know, because until I came across this research, I didn’t know either).”
“Whereas the rods and cones send information to the visual cortex (the “occipital cortex”, at the back of your head), this other light receptor sends its information to your internal clock. The nerve cables from these receptors don’t even go to the vision center at all. They go straight to the middle of your brain, to a region of the hypothalamus called the suprachiasmatic nucleus, which is well known to be the location of the biological clock for us humans.”
“You know about this clock, right? Everybody has one: it’s the gizmo that is setting your biological rhythms every day — when you feel like eating, when you feel like sleeping, when you feel like getting up in the morning. It’s the gizmo that gets confused by east-west travel, causing “jet lag”. It regulates hundreds of chemical reactions all timed to match the natural cycle of days and nights in our environment.”
‘Or what used to be our environment. Nowadays we’ve altered that environment in many ways, of course (Nature is getting ready to get back at us, big time; but hey, that’s our kids’ worry, right?). One of the most significant changes in our environment is our ability to have LIGHT when we used to have DARKNESS.’
“But our brains were not built for this. There were built for a regular period of darkness within every 24 hours (by whom or what doesn’t matter right now; don’t stop, read my page on evolution later. I keep interrupting you with these big-picture ideas like God and global warming. I must be worried about something). Some people are not very strongly affected by our artificially lit environment. But some people, perhaps especially those with bipolar disorder, may suffer when they get too little, or too much. Right now most such people just have to learn this the hard way.”
“Your biological clock resets itself every day by the appearance of morning light. That’s why you can, over a few days, adjust your clock if you fly to some other continent, or even across one. As you may know, our biological clocks are not perfect 24-hour machines. They drift a little bit every day. Most people drift toward a longer day (their clock takes more than 24 hours to complete a cycle). This is probably why most people find it easier to stay up late than to wake up early. For some people, that drift toward later hours can be very dramatic. They may be the ones who most need to learn about what I’m presenting here. They don’t stay glued to “real time” very well. They need to avoid getting “unglued” any further. And light at night may be one of the most important ungluing fact.”
So, how does the clock reset itself?
“Here’s the short answer. The long answer is a beautiful example of brain science; I’ll send you there in a minute if you’re interested. Briefly then: every morning light turns off a chemical process and allows the clock process, which is a very interesting string of chemical reactions, to start all over again. Clock researchers have identified all the important molecules in this process. Lo and behold: lithium directly affects one of the key enzymes in the resetting of the clock. Here we find “ground zero” of our biological rhythms, the very center of the clock process, and there’s lithium right in the middle of it. Very interesting. If that’s enough to get you interested, have a look at the long story about how the clock works, including how lithium affects it.”
Light is central to biological rhythms — and so is DARKNESS
“If light starts the clock every day, is it possible that darkness is a necessary ingredient as well? Look at the question this way: sleep deprivation can cause manic episodes. In part that’s too little sleep itself — but might part of the story be “too much light?” Generally when people are sleeping less and heading toward mania, they’re not hanging out in the dark. They’re up late at night in very well lit places, like casinos, roadways with bright car lights in their eyes, their office preparing the big talk that will secure their future millions, and so forth. They’re not sitting in some dark room. Is there any chance that being forced to stay in the dark during an emerging manic episode could actually turn them in the other direction? We’ll look at some evidence for that in just a moment.”
“Here’s another angle on light and dark: suppose that the appearance of light every morning can reset your clock only when you’ve had enough darkness. Maybe the brain needs to be able to see the contrast? What would happen if you didn’t get enough darkness? Maybe you’d lose your biological rhythm entirely; your body wouldn’t know when to make you sleep and when to wake you up. You’d be up in the middle of the night sometimes, for days in a row, backwards to real time. Then you might be so asleep during the real day you could hardly get out of bed; getting up in the morning would feel like getting up from sleep in the middle of the night does for the rest of us, ugh.”
“And finally, imagine that if your clock cuts loose from real time, you lose even the 24-hour connection. Remember, the clock is not really a 24 hour machine in most people. Maybe you would lose your rhythm entirely so that you body could do the sleep thing, or the really awake thing, at any time, on any day. You’d have no idea where you were, in terms of body cycling, totally erratic. Extreme forms of “rapid cycling bipolar disorder” look just like this: no rhythm at all.”
“All of these lines of thought led a research team at the National Institute of Mental Health to wonder: maybe some people with rapid-cycling bipolar disorder have lost the connection between their internal clock and external light/dark reality. Maybe one way to treat that would be to simply “enforce darkness”! The results of their test of this idea will be described in a moment.’