During the 1980s, thousands of infants in Romanian orphanages spent up to 20 hours a day lying untouched in their cribs, deprived of human contact. As they grew up, neurological and psychological tests confirmed a haunting phenomenon observed in other species, such as mice and rhesus monkeys: Early isolation and neglect can produce lasting cognitive damage, ranging from severe emotional instability to mental retardation. Now, researchers say they have discovered a possible explanation for why early neglect wreaks such havoc—isolation may stunt the growth of the brain cells that insulate neurons, resulting in slower communication between different areas of the brain.
Scientists have known for 50 years that the strength and arrangement of connections between neurons changes as we learn and experience new things, says Gabriel Corfas, senior author of the paper published online today in Science and a neuroscientist at Harvard Medical School in Boston and Boston Children’s Hospital. But the role of the brain’s non-neuronal cells in creating, strengthening, and shaping these neural circuits is more mysterious. The brain’s “white matter”—as opposed to its gray matter, which is composed of neurons—consists mostly of glial cells, which produce the fat and protein myelin sheaths that insulate a neuron’s branching axons, the slender fibers that conduct electrical impulses to other cells. One purpose of myelin, scientists think, is to reduce “leakage” of electric current as electrochemical signals zip to and fro. When the myelin is thin or damaged, the signals can’t travel as fast; that slowdown can impair many different brain functions, including motor control, language, and memory.