This conversation is with Mark Blumberg, a neuroscientist at the University of Iowa whose work has fundamentally reshaped how we understand infant sleep, movement, and early brain development. Mark’s research reveals that sleep is not a passive state, but an active, self-organizing process essential for building the brain’s earliest sensory and motor circuits.

We begin by asking a basic yet surprisingly difficult question: What is sleep, really? Mark explains why defining sleep across development and across species is far more complex than it seems, and why the brain during sleep—especially during REM sleep—is often more active than during wakefulness. Together, we explore why infants spend so much of their early life in REM sleep, how sleep unfolds in distinct stages, and why the tiny, jerky movements known as sleep twitches are not meaningless byproducts of dreams, but powerful developmental signals that help wire the brain and body. We discuss how these movements contribute to building internal models of the body, how sleep supports plasticity and learning, and what happens when these processes are disrupted early in life.