Active Sleep Promotes Functional Connectivity Among Cortical and Subcortical Sensorimotor Structures in the Infant Brain

• In Event: 3-188 - Sleep, Memory and the Brain During Development

Integrative Statement

During active (REM) sleep, every skeletal muscle in the body twitches, causing jerky movements of the arms and legs, fingers and toes, and even eyes. These spontaneous, discrete, and low-amplitude movements are particularly prominent during the perinatal period when active sleep occupies eight hours of each day (Roffwarg et al., 1966). In part because twitches have traditionally been interpreted as by-products of dreams, there has been little motivation to study them in human infants (Blumberg, 2014). To fill this gap, we recently investigated twitching across the first six postnatal months, documenting its quantity and patterning across the body. The results show that twitching, as in other developing mammals, is abundant in human infants—occurring many thousands of times daily—and is expressed differentially across the body as new motor skills develop. We also observed twitches in the face, including the mouth, cheeks, and brows; rates of facial twitching were at their highest level at 1-2 months of age. Most of the movements were produced unilaterally and occurred during periods of twitching elsewhere in the body. Occasionally, twitches occurred bilaterally, giving the impression of smiles and frowns.

These results in humans complement recent findings in infant rodents that have altered our conception of the neural causes and functional consequences of twitching. Specifically, sensory feedback (i.e., reafference) from twitching limbs is a powerful source of brain activation and a key contributor to functional connectivity among sensorimotor structures (Del Rio-Bermudez et al., 2017). As illustrated in the accompanying figure, twitches are produced by structures in the brainstem, including the red nucleus. Then, after a twitch is triggered, sensory information cascades through the sensorimotor system, resulting in coherent oscillatory activity in such structures as the red nucleus, sensorimotor cortex, and hippocampus. Critically, in newborn rats, these coherently organized oscillations occur predominantly during active sleep; importantly, when pups are awake, oscillatory activity is nearly absent. The widespread activation of sensorimotor circuits in the sleeping infant brain suggests that it helps to bind these areas together in support of developing a body schema—the sense that we own our body (Blumberg and Dooley, 2017).

In light of the functional significance ascribed to brain oscillations for learning and plasticity, these findings indicate that active sleep provides a critical context for the expression of organized brain activity—not only in cerebral cortex but in subcortical structures as well. Moving forward, research in non-human infants will be critical for providing detailed information about brain activity in early development, especially activity in subcortical structures that are largely inaccessible to investigation in human infants. Such a comparative approach has the potential to reveal the significance of healthy sleep for typical development and how sleep disturbances can lead to atypical developmental trajectories. Moreover, increased attention to the quantity and patterning of twitching in individual human infants may ultimately allow us to detect neurodevelopmental disorders much earlier than is currently possible using standard clinical assessments.

Author

• Mark Blumberg, University of Iowa
  Presenting Author