White matter, composed of neuronal fibers coated with myelin, is increasingly recognized as a significant contributor to psychiatric disorders such as depression and schizophrenia. Myelination, which continues into adulthood, is modifiable by experience and affects information processing by regulating the velocity and synchrony of impulse conduction between distant cortical regions. Recent studies have identified molecular mechanisms that regulate myelination by electrical activity, and myelin also limits the critical period for learning through inhibitory proteins that suppress axon sprouting and synaptogenesis. The article reviews evidence that white matter is involved in learning, information processing, and neurological and psychological disorders, and explores the molecular mechanisms underlying these effects. It highlights the dynamic nature of white matter structure and the potential for white matter plasticity to contribute to cognitive function and learning. The article also discusses the implications of these findings for understanding and treating psychiatric disorders.White matter, composed of neuronal fibers coated with myelin, is increasingly recognized as a significant contributor to psychiatric disorders such as depression and schizophrenia. Myelination, which continues into adulthood, is modifiable by experience and affects information processing by regulating the velocity and synchrony of impulse conduction between distant cortical regions. Recent studies have identified molecular mechanisms that regulate myelination by electrical activity, and myelin also limits the critical period for learning through inhibitory proteins that suppress axon sprouting and synaptogenesis. The article reviews evidence that white matter is involved in learning, information processing, and neurological and psychological disorders, and explores the molecular mechanisms underlying these effects. It highlights the dynamic nature of white matter structure and the potential for white matter plasticity to contribute to cognitive function and learning. The article also discusses the implications of these findings for understanding and treating psychiatric disorders.