An old friend of mine, who I knew as a guy whose career was just taking off, is now everywhere in Austin. I mean, there are pictures of him on the scrolling advertising screens over the baggage claims at the airport! And he was on Dr Phil not too long ago promoting his book. Now he and another interesting guy have their own little radio program about minds and brains titled “Two Guys on Your Head, which airs on the local public radio station. The episodes on “How Advertising Works” and “Distance” are particularly interesting, I think. The latest episode is about sleep, and I recommend listening to it all, and maybe watching the short, goofy video version:
They first talk about the role of sleep in consolidating memories, which has been one of the most interesting developments in brain science in the last 15 years. While the exact mechanisms involved are still not fully understood, memory consolidation appears to occur in two stages during sleep. First, during slow-wave sleep, or Stage 3 Sleep (formerly Stages 3 and 4), the deepest sleep from which it is most difficult to awake, and which sometimes involves dreaming, memories stored in the hippocampus are reactivated — in a sense, experienced again — and sent off to the areas of the brain where they’ll be stored more permanently. Then, during REM sleep, the brain increases synaptic plasticity, which appears to make it possible to better store the new memories that have been sent there by the hippocampus. In short: the brain first fires up the new memories stored in the hippocampus, then sends them off to the neocortex and other parts of the brain where the brain does its long-term storage, and then in REM sleep the brain stretches its synaptic muscles, so to speak, so that it can build stronger memory connections.
What I find really interesting about this, and what Art touches on at the end of this episode, is the role that memory consolidation during sleep, or rather the lack thereof, may play in mental illness. For example, clinicians have long known that sleep disturbances are a symptom of schizophrenia, and researchers now think that these sleep disturbances may be the cause of some of the cognitive symptoms associated with schizophrenia. In the program, the Two Guys mention the famous study in which finger tapping sequences are remembered better after sleeping than after a period of not practicing while awake. This is not the case for schizophrenics, however (see this study, e.g.). They are able to learn the sequences just fine, but do not show the learning retention associated with the sleep-mediated memory consolidation. Specifically, schizophrenia-related sleep disturbances seem to diminish the ability of the hippocampus to reactivate and send off the memories of the day during slow-wave sleep.
The role of sleep in depression, which they discuss in the program, may be even more important. As with schizophrenia, sleep disturbances are an extremely common and well-known symptom of depression, though exactly what form those disturbances take varies from case to case (and often from day to day): sometimes people suffering from depression sleep too much, sometimes they don’t sleep enough. And to add to the confusion, the effects of sleep disturbances on depression symptoms vary as well. Studies have shown that sleep deprivation can decrease the symptoms of depression in the short term, for example. However, researchers have, over the last decade or so, gathered more and more evidence that memory issues play a big role in depression. Depressed individuals appear to have trouble consolidating newly formed memories, which is precisely what the hippocampus is supposed to be doing during Stage 3 sleep. In the “Two Guys” episode, they discuss the separation of the affective or emotional associations of an experience from the experience itself during sleep, but there’s an even more basic way in which sleep disturbances that interrupt memory consolidation may contribute to depression. One of the most most prominent symptoms of depression is an inability to not think about bad stuff, and in fact to obsess over bad stuff, usually to the exclusion of good stuff. One of the things depressed people tend to do, for example, is think counterfactually about negative experiences — what if I’d done this differently, what if that hadn’t happened, what if I’d never met so-and-so, etc. — over and over and over again, something non-depressed people tend not to do very much. It’s just not a very healthy way of thinking. And it’s possible, perhaps likely, that part of the reason depressed people do this so much is that, because they’re not consolidating new, potentially positive memories during sleep, they are stuck with the older, negative memories on which they can’t help ruminating. Sleep may not, as Art suggests, “heal all wounds,” but it probably gets the healing process started.
Anyway, the show really is worth a listen. You may have heard a lot of the stuff they talk about about before, but they’re two really smart guys who will probably mention an idea or an aspect of the issue that you hadn’t thought about. So, if you’re interested in learning about the mind, I highly recommend checking it out.