White matter in learning, cognition and psychiatric disorders

Abstract

White matter is the brain region underlying the gray matter cortex, composed of neuronal fibers coated with electrical insulation called myelin. Previously of interest in demyelinating diseases such as multiple sclerosis, myelin is attracting new interest as an unexpected contributor to a wide range of psychiatric disorders, including depression and schizophrenia. This is stimulating research into myelin involvement in normal cognitive function, learning and IQ. Myelination continues for decades in the human brain; it is modifiable by experience, and it affects information processing by regulating the velocity and synchrony of impulse conduction between distant cortical regions. Cell-culture studies have identified molecular mechanisms regulating myelination by electrical activity, and myelin also limits the critical period for learning through inhibitory proteins that suppress axon sprouting and synaptogenesis.

Brain oscillatory complexity across the life span

“…Is WM involved in synchronisation? The excellent review by Fields (2008) might answer this question. Fields (2008) points out that WM has been traditionally considered a passive insulation substance that ensures the transmission of neural impulses.…”

“…The excellent review by Fields (2008) might answer this question. Fields (2008) points out that WM has been traditionally considered a passive insulation substance that ensures the transmission of neural impulses. The author proposes that emerging evidence indicates this is a too simplistic perspective, and WM also participates in the speed control of impulse conduction and consequently in the synchronisation among cortical regions.…”

Child Psychiatry Branch of the National Institute of Mental Health Longitudinal Structural Magnetic Resonance Imaging Study of Human Brain Development

“…Myelination does not simply maximize speed of transmission, it fine-tunes the timing and synchrony of neuronal firing patterns (Fields and Stevens-Graham, 2002). Myelin also influences neuronal plasticity by releasing molecular factors that inhibit axon sprouting and the creation of new synapses (Fields, 2008). These non-subtle impacts of myelin on the brain's ability to process information and adapt to the environment may underlie many of the cognitive abilities associated with our species.…”

Literacy effects on language and vision: Emergent effects from an amodal shared resource (ASR) computational model

“…Measures of myelination and white matter integrity have been shown to be reflected in the efficiency (Deary et al, 2006;Engel, Fries, & Singer, 2001;Li et al, 2009) and the speed (Gutiérrez, Boison, Heinemann, & Stoffel, 1995;Madden, Bennett, & Song, 2009;Penke et al, 2010;Tolhurst & Lewis, 1992;Waxman, 1980) of information processing, with such factors shown to modulate performance on a range of cognitive tasks (Deary et al, 2006;Li et al, 2009;Turken et al, 2008). Critically, myelination has been shown to be modifiable by experience (see Fields, 2008) and to increase as a result of learning (Bengtsson et al, 2005) and therefore has the potential for modulation by environmental variables such as exposure to literacy training. Studies have indeed shown that myelination of brain regions associated with language processing coincides with vocabulary acquisition (Pujol et al, 2006).…”