University of Iowa researchers have uncovered a brain rhythm in the brain stem of sleeping infant rats that mirrors the rhythm in the cerebral cortex. The discovery reveals the origin of long-distance communication in the developing brain and opens a new path to understanding the connection between a fundamental brain rhythm and breathing, a finding that could inform our understanding of sleep-related breathing disorders in children.

Prior research has shown that sleep can be divided into two general phases: active sleep and quiet sleep. In early development, active sleep predominates. Later, quiet sleep grows in importance and is characterized by a slow cortical rhythm, known as delta. 

This study was conducted by Midha Ahmad, a graduate student in the Department of Psychological and Brain Sciences who works in the laboratory of Professor Mark Blumberg. She used 12-day-old rats to explore the parts of the brain responsible for the developmental emergence of quiet sleep. To their surprise, the researchers found that the rats’ delta rhythm was expressed in a small region of the medulla that, in adult rodents, had earlier been implicated in the regulation of quiet sleep.

The team also discovered that the delta wave in the rats’ medulla was synchronized with the delta wave in the cerebral cortex, and that both rhythms were coordinated with breathing. In other words, the medulla and cortex — at opposite ends of the brain — are already communicating at the age when the delta rhythm is first expressed, and both rhythms are affected by breathing. Because breathing is also regulated in the medulla, these findings suggest that the systems that regulate breathing and sleep act together to influence the expression of the delta rhythm in the infant brain. 

“Understanding sleep and respiratory interactions early in life is relevant for understanding how certain sleep disorders, such central sleep apnea (CSA), arise,” Ahmad says. “CSA is common in young children and premature infants and is often linked to sudden infant death syndrome. We hope to explore further the brain mechanisms that underlie sleep-dependent respiratory control in early development."

The study, “Coincident development and synchronization of sleep-dependent delta in the cortex and medulla,” was published online in the journal Current Biology on May 20.

Study co-authors include Greta Sokoloff and Brett Dwyer from Iowa, and Jangjin Kim from Kyungpook National University in South Korea. 

The research was funded by the National Institutes of Health.