Introduction: Several studies have shown an important role for deep brain stimulation of the nucleus accumbens in the treatment of depression and addiction. To date, there have been no noninvasive methods of demonstrating the division of the nucleus accumbens into core and shell subunits. Probabilistic tractography has been used previously to segment subcortical structures such as the thalamus and amygdala into functionally distinct regions. We now apply this technique to segment the nucleus accumbens into putative core and shell subregions.
Methods: T1-weighted MRI images were acquired in 7 healthy volunteers. 20-direction DTI was obtained. Seed masks for the nucleus accumbens were generated using FreeSurfer (http://surfer.nmr.mgh.harvard.edu). Probabilistic tractography and diffusion imaging were performed using FSL (http://www.fmrib.ox.ac.uk/fsl). The probability of connectivity between seed voxels and the whole brain was determined and subjected to k-means clustering analysis.
Results: The nucleus accumbens was amenable to probabilistic tractography and could be segmented into two distinct subregions. These regions were anatomically consistent across subjects and included a dorsomedial area and a more ventrolateral region. There was connectivity between these regions and the orbitofrontal, prefrontal, temporal and parietal cortices, hippocampus, entorhinal cortex, basal forebrain and amygdala. The dorsomedial region had greater connectivity to orbitofrontal and prefrontal cortices while the ventrolateral division was more connected to temporo-parietal cortex.
Conclusions: DTI-based tractography can be used to derive an in-vivo patient-specific connectivity map of the human nucleus accumbens. This map may be used in the future for planning and refinement of DBS within the nucleus accumbens. In addition, this technique provides a novel method to noninvasively study the anatomy and connectivity the nucleus accumbens in humans for the first time. The connectivity seen in this study may reflect the known dichotomy of the nucleus accumbens into core and shell subregions.
Patient Care: This research aims to improve our understanding of the nucleus accumbens, a structure which plays a central role in human behavior and decision making as well in neuropsychiatric disorders such as depression and addiction.
Learning Objectives: By the conclusion of this session, participants should be able to 1) Describe the importance of the nucleus accumbens in behavior 2) Describe the connectivity of the nucleus accumbens 3) Discuss the use of probabilistic tractography to study the connectivity of the nucleus accumbens.