A human newborn's brain is uniquely impressionable, allowing social interactions and the environment to shape its development. But this malleability may come with a price, a new study finds. A comparison of juvenile chimpanzee and human brains suggests that differences in the development of myelin—the fatty sheath that surrounds nerve fibers—may contribute not only to our unusual adaptability, but also to our vulnerability to psychiatric diseases that start in early adulthood.
Research increasingly suggests that psychiatric illnesses like depression and schizophrenia may involve problems with the timing of neural signals, says Douglas Fields, a neuroscientist at the National Institutes of Health in Bethesda, Maryland, who was not involved in the study. The nerve fibers, or axons, that connect neurons are usually protected by myelin, which enhances the neural relay of information throughout the brain. "Myelin speeds transmission of information [by] at least 50 times," Fields says, "so it matters a great deal whether or not an axon becomes myelinated."
Humans start out with comparatively few myelinated axons as newborns. We experience a burst of myelin development during infancy that is followed by a long, slow growth of myelin that can last into our thirties, says Chet Sherwood, a neuroscientist at George Washington University in Washington, D.C., and a co-author of the new study. In contrast, other primates, such as macaques, start out with significantly more myelin at birth, but stop producing it by the time they reach sexual maturity. However, Sherwood says, "extraordinarily little data exists" on brain growth and the development of myelin in our closest genetic relatives, chimpanzees.
Read the rest here.