Ask neurologists or psychiatrists to name a white matter (WM) brain disease and they are very likely to say multiple sclerosis (MS), a demyelinating brain disorder caused by immune-mediated destruction of oligodendrocytes, the glial cells that manufacture myelin without which brain communications would come to a standstill.
MS is often associated with mood or psychotic disorders, yet it is regarded as a neurologic illness, not a psychiatric disorder.
Many neurologists and psychiatrists may not be aware that during the past few years, multiple diffusion tensor imaging (DTI) studies have revealed that many psychiatric disorders are associated with WM pathology.1
Most people think that the brain is composed mostly of neurons, but in fact the bulk of brain volume (60%) is comprised of WM and only 40% is gray matter, which includes both neurons and glial cells (astroglia, microglia, and oligodendroglia). WM includes >137,000 km of myelinated fibers, an extensive network that connects all brain regions and integrates its complex, multifaceted functions, culminating in a unified sense of self and agency.
The role of the corpus callosum
Early in my research career, I became interested in the corpus callosum, the largest interhemispheric WM commissure connecting homologous areas across the 2 cerebral hemispheres. It is comprised of 200 million fibers of various diameters. Reasons for my fascination with the corpus callosum were:
The studies of Roger Sperry, the 1981 Nobel Laureate who led the team that was awarded the prize for split-brain research, which involved patients whose corpus callosum was cut to prevent the transfer of intractable epilepsy from 1 hemisphere to the other. Using a tachistoscope that he designed, Sperry discovered that the right and left hemispheres are 2 independent spheres of consciousness (ie, 2 individuals) with different skills.2 Cerebral dominance (laterality) fully integrates the 2 hemispheres via the corpus callosum, with a verbal hemisphere (the left, in 90% of people) dominating the other hemisphere and serving as the “spokesman self.” Thus, we all have 2 persons in our brain completely integrated into 1 “self.”2 This led me to wonder about the effects of an impaired corpus callosum on the “unified self.”
Postmortem and MRI studies conducted by our research group showed a significant difference in the thickness of the corpus callosum in a group of patients with schizophrenia vs healthy controls, which implied abnormal connectivity across the left and right hemispheres.3
Continue to: I then conducted a clinical study