Myelin—More than Insulation

Unusual features of myelin in the mammalian cerebral cortex permit more complex forms of network integration. [Also see Report by Tomassy et al.] Myelin is often compared to electrical insulation on nerve fibers. However, nerve impulses are not transmitted through neuronal axons the way electrons are conducted through a copper wire, and the myelin sheath is far more than an insulator. Myelin fundamentally changes the way neural impulses (information) are generated and transmitted, and its damage causes dysfunction in many nervous system disorders including multiple sclerosis, cerebral palsy, stroke, spinal cord injury, and cognitive impairments. A detailed understanding of myelin structure is therefore imperative, but is lacking. On page 319 of this issue, Tomassy et al. (1) provide a high-resolution global view of myelin structure spanning the six layers of mammalian cerebral cortex. The findings are likely to spark new concepts about how information is transmitted and integrated in the brain.