Research

How does the infant brain manage to function in the moment in the midst of rapid and transformative developmental change? And what is the significance for the developing brain that the majority of the infant’s day is devoted to sleep? Thanks largely to methods that enable recording brain activity in infant rats as they cycle between sleep and wake, the answers to these questions are beginning to emerge. In particular, it is now clear that sleep, especially active (or REM) sleep, activates the infant brain in a way that is unique and profound for the nascent sensorimotor system. The self-generated brain activation that characterizes active sleep in the infant is ideally suited to building and refining somatotopic maps, integrating sensory and motor systems, and laying the foundation for the later-emerging, embodied sense of self. These and other insights are increasingly informing investigations of sleep-related neural activity in human infants.

These and related issues are the primary focus of our lab. Below, some of our present and past research domains are described and links to relevant papers and websites are provided. You can go here to find all our papers.

It should also be stressed that our approach to studying sleep in infants is closely tied to the lab's conceptual affiliation with the Developmental Systems framework. Dr. Blumberg is a strong advocate for this approach, which emphasizes the importance of investigating the moment-to-moment processes of development. He as written and co-edited books and a collection of essays on this topic to communicate its importance to other scientists and the general public.

We hope you enjoy reading about our research. If you'd like to learn more or wish to join the lab, please contact us!

 

Why do infants move so much during active sleep?

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. 

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 sleep is providing valuable insights into the early brain mechanisms that enable the self-other distinction. 

To get a sense of what twitches are and how we relate infant behavior to neural activity, you can watch some videos here. And to appreciate the phenomenon of twitching across the animal kingdom, go here.

Here are some recent empirical papers using rats:

  • Dooley, J. C., Sokoloff, G., & Blumberg, M. S. Developmental onset of a cerebellar-dependent forward model of movement in motor thalamus. bioRxiv

  • Gómez, L. J., Dooley, J. C., Sokoloff, G., & Blumberg, M. S. Parallel and serial processing in developing primary somatosensory and motor cortex. Journal of Neuroscience, 41: 3418-3431, 2021. pdf

  • Dooley, J. C., Glanz, R. M., Sokoloff, G., & Blumberg, M. S. Self-generated whisker movements drive state-dependent sensory input to developing barrel cortex. Current Biology, 30: 2404-2410, 2020. pdf

  • Del Rio-Bermudez, C., Kim, J., Sokoloff, G., & Blumberg, M. S. Active sleep promotes coherent oscillatory activity in the cortico-hippocampal system of infant rats. Cerebral Cortex, 30: 2070-2082, 2020. pdf

In addition to our research with rats, we are also now investigating sleep development in human infants. Although relatively new, this work was highlighted on the recent Netflix documentary series, Babies (Episode 5). You can also watch video introductions to this work here and here. And here are our first two published papers using human infants:

  • Sokoloff, G., Dooley, J. C., Glanz, R. M., Wen, R. Y., Hickerson, M. M., Evans, L. G., Laughlin, H. M. Apfelbaum, K. S., & Blumberg, M. S. Twitches emerge postnatally during quiet sleep in human infants and are synchronized with sleep spindles. Current Biology, 31: 1-7, 2021. pdf 

  • Sokoloff, G., Hickerson, M., Wen, R., Tobias, M., McMurray, B., & Blumberg, M. S. Spatiotemporal organization of myoclonic twitching in sleeping human infants. Developmental Psychobiology, 62: 697-710, 2020. pdf

Here are some reviews on the topic:

  • Blumberg, M. S., Dooley, J. C., & Sokoloff, G. The developing brain revealed during sleep. Current Opinion in Physiology, 15: 14-22, 2020. pdf

  • Del Rio-Bermudez, C., & Blumberg, M. S. Active sleep promotes functional connectivity in developing sensorimotor networks. BioEssays, 40:1700234, 2018. pdf

 

What is 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 are two reviews that explore these issues:

  • Blumberg, M. S., Lesku, J. A., Libourel, P. A., Schmidt, M. H., Rattenborg, N. C. What is REM sleep? Current Biology, 30: R38-49, 2020. pdf

  • Blumberg, M. S., & Rattenborg, N. C. Decomposing the evolution of sleep: Comparative and developmental approaches. In J. H. Kaas (ed.), The Evolution of Nervous Systems 2e, Volume 3, Oxford: Elsevier, 2017, pp. 523-545. pdf

 

The development of ultradian 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 are some papers on this topic:

  • 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

  • Todd, W. D., Gall, A. J., Weiner, J. A., & Blumberg, M. S. Distinct retinohypothalamic innervation patterns predict the developmental emergence of species-typical circadian preference in nocturnal Norway rats and diurnal Nile grass rats. Journal of Comparative Neurology, 520:3277-3292, 2012. pdf

  • Blumberg, M. S., Seelke, A. M. H., Lowen, S. B., & Karlsson, K. Æ. Dynamics of sleep-wake cyclicity in developing rats. Proceedings of the National Academy of Sciences, 102, 14860-14864, 2005. pdf

 

Our methods

In our research, 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. But, in addition to the methods described in our published papers, we are constantly developing and adapting new methods—including, most recently, optogenetics—to answer our research questions. 

This paper describes our approach to recording brain-behavior interactions in preweanling rats:

  • Dooley, J. C., Sokoloff, G., & Blumberg, M. S. Developmental onset of a cerebellar-dependent forward model of movement in motor thalamus. bioRxiv

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