A Review of Studies on the Role of Diffusion Tensor Magnetic Resonance Imaging Tractography in the Evaluation of the Fronto-Subcortical Circuit in Patients with Akinetic Mutism

Akinetic mutism (AM) is characterized by the complete absence of spontaneous behavior (akinesia) and speech (mutism) with the preservation of executive functions for movements and speaking. Elucidation of the pathophysiological mechanisms or neural correlates for AM is clinically important because patients can recover from AM after medication and neuromodulation. The fronto-subcortical circuit is a critically important neural structure in the pathophysiology of AM. Using diffusion tensor tractography, a few neural tracts in the fronto-subcortical circuit can be reconstructed. This mini-review article evaluated 6 DTT-based studies on the fronto-subcortical circuit injury in patients with AM. According to these results, the neural tracts among the fronto-subcortical circuit, which are related to AM, were as follows (in decreasing order of importance): 1) the prefronto-caudate tract, 2) the prefronto-thalamic tract, and 3) the cingulum. In particular, the medial prefrontal cortex is an important brain area related to recovery from AM. However, only 6 studies on this topic have been published, and most were case reports. In addition, these studies analyzed only a few neural tracts in the fronto-subcortical circuit. Because AM is a rare disorder, studies involving a large number of subjects might be impossible. Nevertheless, an analysis of various neural tracts in the fronto-subcortical circuit is necessary. For this, reconstruction of the other neural tracts in the fronto-subcortical circuit should be performed first. This review aims to present the findings from recent studies on the role of DTT in evaluation of fronto-subcortical circuit injury in patients with AK.