If you’ve ever watched a sleeping baby, you’ve probably noticed the twitching movements they make in their sleep. Because these movements have typically been thought of as remnants of dreams, few have thought that they might serve a function. However, a research team at the University of Iowa has provided compelling evidence that these involuntary movements are important to the developing brain.
Mark Blumberg, F. Wendell Miller Professor in the Departments of Psychology and Biology in the UI College of Liberal Arts and Sciences, studies the role that sleep plays in the development of the nervous system. In a recent study published in Current Biology, Blumberg and his co-authors reported the discovery that the whiskers of newborn rats twitch as they sleep, the equivalent of rapid eye movements (REM) in humans. Those whisker twitches are tied to bursts of activity in the brain, which typically aren’t seen when the rats are awake.
Blumberg and his research team on this project recently sat down with Iowa Now to talk about the study. In addition to Blumberg (MB), the team includes: Greta Sokoloff (GS), Ph.D., Research Associate; Alex Tiriac (AT), third-year graduate student in psychology and first author on the research paper; Brandt Uitermarkt (BU), second-year graduate student in psychology and second author on the research paper; and Alex Fanning(AF), senior psychology major.
Tell me about your research. What do whisker twitches in sleeping infant rats tell us about ourselves?
AT – This lab has long been interested in twitching during sleep and during early development. Rats rely heavily on their whiskers for scanning their environment. We hypothesized that if limb twitches are important for the development of the limbs, we might see similar twitches of the whiskers.
GS – At the beginning of life for all animals, including ourselves, we spend most of our time asleep. Most of that time is in REM sleep, which is also known as active sleep. That’s what changes as you age—you have less REM sleep. During infancy, the nervous system is developing and forming lots of connections. That’s when twitching is most prevalent.
BU – People think of sleep as being devoid of behavior, whereas we’re seeing all these types of behaviors during sleep. We think they are integral for development.
MB – Twitching is a very predominant behavior in infants and we do it throughout our lives. If you’ve ever watched a sleeping dog or human infant you’ve seen these jerky movements. Traditionally, they’ve been thought of as functionless by-products of a dreaming brain (think dogs “chasing rabbits” in their dreams). It turns out that this popular idea can’t be correct—certainly can’t be completely correct—because if you take out parts of the brain that are critical for dreaming, the animals still twitch.
So, if we know they’re not functionless by-products, what are they for? Might they play a role in the development of the nervous system? We know from work in other systems about so-called spontaneous activity that plays a role in driving brain activity early in development and helping the system learn about itself.
You’ve estimated that the muscles are each twitching at least 40,000 times a day. How do you record that activity?
MB – The whole project started with measuring the twitches of whiskers. But how do you do that? Tiriac and I sort of fumbled around a bit trying to figure out how to do that and one way we came up with was to apply fluorescent paint on the tips of the whiskers and then shine blacklight on them to make them glow. Next, using high-speed video, we recorded the twitching whiskers while the pups were sleeping and sure enough, as we expected, there were these beautiful and diverse movement patterns happening.
The twitches of the whiskers seemed to be driving activity in certain parts of the brain, is that correct?
MB - That is correct. So the question was, ‘do these movements matter?’ To find that out, you have to record neural activity in very young animals, which is something we’ve been doing for awhile now. Tiriac, working with Fanning, spearheaded a project looking at one part of the brain, the thalamus, that receives information from the whiskers. Uitermarkt and Sokoloff spearheaded another project that involved imaging cortical activity. In both cases it was clear that whisker twitching during sleep drives brain activity, similar to what has been seen with twitching of the limbs. This tells us that not only are the whiskers twitching, but the brain is paying attention to it.
Why rats?
MB – Rats and mice are the two most popular lab animals for a variety of reasons. They’re very useful for what we do. The pups are born in a very immature state; they’re about the size of your thumb, they have no fur, they’re blind, they’re deaf, and you can watch development happen in these animals because so much of it happens after they’re born. Almost all the things we see in humans that we see as critical for our work, we can basically see as analogs in rats.
AT – And the whisker system is one of their most used sensory systems. That also makes it appealing.
Alex, tell me about this experience, from an undergraduate perspective.
AF – I think I got the most out of this. As an undergraduate you don’t have a lot of experience with science. To go through the whole process and see every aspect of it, it can be a bit overwhelming, but it’s very compelling.
My role in this project was to record neural activity in the thalamus and to help analyze the data.
Is this your first experience with this type of research?
AF – Yes, this is my first experience being involved in a project like this. I’ve worked in a lab prior to this, but it wasn’t this advanced.
The research that we’ve done and this project has given me a great idea of whether or not I want to do this in the future. I feel like I now know what to expect and it will be helpful as I think about graduate school. I hope it will help me hit the ground running, or at least not stumbling quite so much.
Where do you go from here? What’s next?
MB – This sort of a project becomes a springboard for different people going in different directions. In the case of Tiriac, he’s going to try to pursue functional questions about the twitches—what are they actually doing for the developing animal? This paper opened up avenues for asking those questions. Brandt will continue exploring brain activity using several imaging techniques.
GS - I think we have interesting ideas for the future using the behavioral activity that you see during REM sleep as kind of a measure of ordered or disordered states. In certain diseases, like Parkinson’s disease, they actually can have a REM sleep disorder where they don’t have muscle atonia and they appear to “act out their dreams.” We’re playing around with lots of interesting ideas around the phenomenon of twitching, not only during development when it’s very important, but also across the lifespan.