Improved Visualization of the Anterior Thalamic Radiation in Bipolar Disorder by Diffusion Tensor Tractography

Abstract

Diffusion tensor imaging (DTI) is a method for noninvasively measuring and imaging the diffusion of water molecules using MRI. Diffusion tensor tractography (DTT) can be used to presume macroscopic nerve fascicle distribution by determining, based on information obtained by DTI, whether the diffusion anisotropy vectors of adjacent voxels are continuous or not. We prepared a DTT map of the cerebral white matter nerve fascicles and investigated its usefulness for differentiation between Alzheimer's disease and bipolar disorder (BD), a major depressive disorder, based on the nerve fiber depiction, in addition to the fractional anisotropy and apparent diffusion coefficient values. We encountered two cases of BD in which the DTT image of the anterior thalamic radiation (ATR) improved following effective treatment with lamotrigine. Lamotrigine increases the synaptic strength due to its effect of promoting the traffic of the α-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor on the neuronal membrane. Downregulation of postsynaptic AMPA receptor expression can reportedly be observed during depressive episodes in BD. We consider that visualization of improvement of the ATR in response to treatment with lamotrigine (related to its pharmacological effect on the AMPA receptor) is valuable, as it suggests reversibility of the damage of the nerve fibers in this disease condition.