My previous post on dreaming and sleeping briefly described Revonsuo’s Threat Simulation Theory (TST) and proposed a possible extension. In short, I was struck by the general idea: dreams are useful to rehearse crucial skills, and wondered why Prof. Revonsuo decided to build a theory around “just” threat simulations instead of useful simulations in general.
I am glad to say that Prof. Revonsuo was kind enough to privately comment my ideas and was also happy to allow me to report our conversation in here. Naturally I wish to thank him for taking the time to explain his position and future plans, I highly appreciate it (and do think it’s a rare form of kindness). Getting a chance to briefly discuss with him my own theories, was gratifying for me and a clear act of generosity on his part (time is surely the most scarce commodity nowadays).
As for the content of the discussion it turns out that I’m not the first one to propose an extension (no surprises here!):
In fact, some other commentators have also proposed that the TST, while convincing, may be too narrow in scope. I agree with this idea, that TST may be expanded and that other simulation-rehearsal -based hypothesis on the function of dreaming could (and should) be formulated and tested.
The original focus on threat simulation was justified by the fact that when dealing with dangers, “the costs of not rehearsing (or trying to rehearse only in real life) are potentially very high”, I completely agree with this but are still unconvinced about the narrow scope of simulations. In fact, Revonsuo did mention that they are planning to “formulate and test some other potential simulation functions of dreaming”. This is brilliant news, and I can’t wait to read their results!
I could, and probably should, end this post here, but I do have some more thoughts to share, and I am also planning to use this discussion to illustrate some important points about Evolutionary Psychology, so I will add my own personal considerations below.
- Whatever was the original evolutionary function of dreams, it’s likely that it has been significantly extended. Once the mechanism was in place, and a common ancestor started dedicating a significant amount of time to it (time spent sleeping & dreaming), the usual evolutionary tinkering would have kicked in, and eventually plenty of other useful ways to use both dreams and sleeping-time have probably emerged.
- Since the behaviour is clearly very ancient, lots of things may have changed after the first appearance, so looking for a definitive proof of what was the initial function may prove to be close to impossible. This is also the reason why research should not focus on one species only.
- My hunch is that dreaming is useful to rehearse practical skills, so to create and reinforce complex but automatic reactions. And yes of course, doing so for dangerous activities has a huge (probably the biggest) evolutionary advantage. Any animal that does learn new behaviours (doesn’t rely exclusively on genetically predetermined behaviours) can profit from these “off-line” repetitions.
- Even more: it’s quite possible that dreaming is a required condition to establish such “memories/automatic responses”; all animals that learn new behaviours do dream, so we have a hypothesis that explains the ubiquity of dreams and can be tested on virtually any animal model (or at least any mammal).
- In all cases, I’d look for a conceptually convincing theory and worry about testing it only afterwards: we can’t take it for granted that whatever happens to be true is also easily demonstrable.
In conclusion, I would be very keen to know if someone tried and/or plans to try something like the following:
Using the kind of protocol explained in Martinez-Gonzalez et al. (2004), or some other way to inhibit REM sleep, train rats on some relatively complex task that requires a fast reaction, and see whether the ones trained while suffering REM sleep deprivation (and one could limit this deprivation to 24 or 48 hours) show significant changes in their ability to learn, retain learned information and so on.
It’s a relatively simple (if cruel) set-up that allows for all sorts of interesting controls: for example, what may one conclude if REM deprivation slows down learning and has the same (or very similar) effect of complete sleep deprivation? Does REM deprivation have short- or long-lasting effects on already trained rats? One could keep going for years, I guess.
Martinez-Gonzalez, Dolores, William Obermeyer, Jennifer L. Fahy, Myriam Riboh, Ned H. Kalin, and Ruth M. Benca. “REM sleep deprivation induces changes in coping responses that are not reversed by amphetamine.” Sleep 27.4 (2004): 609-617.