Research

model head fix

Recent Research

Why Twitch?

Neural Control of Sleep

Sleep and
Circadian Rhythms

Our Methods

 

 

Recent Research

One of the fundamental distinctions that animals must make is that between "self" and "other." It is still a mystery where in the brain this distinction comes from (it likely has many sources), but failure to make it can be devastating (e.g., as with auditory hallucinations in schizophrenia). As odd as it may seem, our work on the twitches that we and other animals produce while in active (or REM) sleep is providing some useful insights into the early brain mechanisms that subserve the self-other distinction. Currently, we are focusing much of our attention on the cerebellar system, which includes the cerebellum itself and its associated input (e.g., external cuneate nucleus, lateral reticular nucleus, inferior olive) and output (e.g., red nucleus) structures.

One of the key mechanisms to distinguishing between self and other involves the production of a corollary discharge (or motor copy) in association with motor commands. Specifically, nervous systems distinguish between self- and other-generated movements by monitoring discrepancies between planned and performed actions. To do so, corollary discharges are conveyed to sensory areas and gate expected reafference. Such gating is observed in neonatal rats during wake-related movements. In contrast, twitches, which are self-generated movements produced during active sleep, differ from wake movements in that they reliably trigger robust neural activity. Accordingly, we hypothesized that the gating actions of corollary discharge are absent during twitching. In a recent study (see Tiriac & Blumberg, eLife, 2016, below), we found support for this hypothesis by recording from the external cuneate nucleus (ECN), which processes sensory input from the forelimbs. We found that whereas pharmacological disinhibition of the ECN unmasked wake-related sensory feedback from the forelimbs, twitch-related feedback was unaffected. This is the first demonstration of a neural comparator that is differentially engaged depending on the kind of movement produced (i.e., wake-related vs. twitch). And the mechanism that we identified explains how twitches, though self-generated, can trigger such abundant activation of sensorimotor circuits in the developing brain. 

To get a feel for what twitches look like and how we relate infant behavior to neural activity, you can watch some videos here.

To appreciate the phenomenon of twitching across the animal kingdom, go here.

Some recent papers:
Del Rio-Bermudez, C., Kim, J., Sokoloff, G., and Blumberg, M. S. Theta oscillations during active sleep synchronize the developing rubro-hippocampal sensorimotor network. Current Biology, 27: 1413-1424, 2017. pdf
Tiriac, A., & Blumberg, M. S. Gating of reafference in the external cuneate nucleus during self-generated movements in wake but not sleep. eLife, 5, p. e18749, 2016. pdf
Sokoloff, G., Plumeau, A. M., Mukherjee, D., & Blumberg, M. S. Twitch-related and rhythmic activation of the developing cerebellar cortex. Journal of Neurophysiology, 114, 1746-1756, 2015. pdf
Tiriac, A., Del Rio-Bermudez, C., & Blumberg, M. S. Self-generated movements with "unexpected" sensory consequences. Current Biology, 24, 2136-2141, 2014. pdf

 

 

 

 

 

Why Twitch?

Every animal must learn how to use its limbs within the developmental context of an ever-changing body. Typically, investigations of sensorimotor development focus on waking movements. We consider another class of behavior: Twitching movements that occur exclusively during active (REM) sleep. Twitches are particularly abundant in early infancy when critical sensorimotor networks are established. Based on behavioral, electrophysiological, neurophysiological, and computational investigations of this unique behavior, we argue that twitches are critical for the development and maintenance of the sensorimotor system, as well as its repair after injury or disease. 

In addition to our work in rodents, we are translating our work to human infants. You can watch a video introduction to this work here and can also learn more about our project by visiting our Facebook page

To get a feel for what twitches look like and how we relate infant behavior to neural activity, you can watch some videos here.

Here are some recent reviews of this work:
Blumberg, M. S., & Dooley, J. C. Phantom limbs, neuroprosthetics, and the developmental origins of embodiment. Trends in Neurosciences, 40: 603-612, 2017. pdf
Blumberg, M. S. Developing sensorimotor systems in our sleep. Current Directions in Psychological Science, 24, 32-37, 2015. pdf
Blumberg, M. S., Marques, H. G., & Iida, F. Twitching in sensorimotor development from sleeping rats to robots. Current Biology, 23, R532-R537, 2013. pdf

 

 

 

Neural Control of Sleep

Sleep, like waking, is a complex phenomenon comprising fluctuations in many neural and physiological systems. When we fall asleep, our skeletal muscle loses tone, the electrical activity in our cerebral cortex (i.e., the EEG) changes, and, during active sleep, our eyes dart around and our limbs twitch. The challenge of studying infant sleep is that these various components, which have been studied extensively in adults, do not always present themselves clearly in infants. For example, the EEG of infant rats before eleven days of age does not exhibit the clearly differentiable activity upon which researchers rely so heaviliy when judging adult sleep. These and other factors mean that we must assess infant sleep on its own terms rather than judge it against an adult standard.

Here is a paper that reviews some of this work:
Blumberg, M. S., & Seelke, A. M. H. The form and function of infant sleep: From muscle to neocortex. In: The Oxford Handbook of Developmental Behavioral Neuroscience, edited by M. S. Blumberg, J. H. Freeman, and S. R. Robinson. New York: Oxford University Press, 2010, pp. 391-423. pdf 

 

 

 

Sleep and Circadian Rhythms

Perhaps the most interesting developmental changes in sleep and wakefulness relate to the temporal organization of these states. For example, we have documented seminal developmental changes in the temporal organization of sleep-wake bouts and are seeking to identify the neural mechanisms that underlie these developmental changes in Norway rats. Developmental analyses can also be helpful for exploring evolutionary issues pertaining to sleep-wake organization. For example, we recently adopted a developmental comparative approach to explore circadian rhythmicity using nocturnal (i.e., night-active) Norway rats and diurnal (i.e., day-active) Nile grass rats. 

Here is a paper that reviews some of this work:
Blumberg, M. S., Gall, A. J., & Todd, W. D. (2014). The development of sleep–wake rhythms and the search for elemental circuits in the infant brain. Behavioral Neuroscience, 128, 2014. pdf

 

 

 

 

Our Methods

In our research with infant rats and mice, we employ a wide range of behavioral, neurophysiological, and neuroanatomical methods. The best way to learn about these methods and what they afford is to read the papers themselves. Of particular importance for much of our work has been the development of a method for recording neural activity in infant rats as they cycle between sleep and wake (see paper below). For performing advanced analyses of behavior, we also use high-speed videography (see paper below). 

This paper describes our head-fix method in infant rats:
Blumberg, M. S., Sokoloff, G., Tiriac, A., & Del Rio-Bermudez, C. A valuable and promising method for recording brain activity in behaving newborn rodents. Developmental Psychobiology, 57, 506-517, 2015. pdf

This paper describes the use of high-speed video for analyzing twitches in developing rats:
Blumberg, M. S., Coleman, C. M., Gerth, A. I., & McMurray, B. Spatiotemporal structure of REM sleep twitching reveals developmental origins of motor synergies. Current Biology, 23, 2100-2109, 2013. pdf