gms | German Medical Science

Objective: Because of its central position within the neural systems underlying mental disorders, the n. accumbens (NAc) is a promising target for Deep Brain Stimulation (DBS) of psychiatric patients. The aim of this study was to outline pathways connecting the NAc with different areas of the human brain using diffusion (MR)-imaging (dMRI) based probabilistic fiber tracking and an anatomical data driven approach.

Method: After a comprehensive pubmed search we identified 198 publications describing the NAc afferent and efferent connectivity basing upon in vivo tracer studies in rodents and primates. Specific NAc-projection areas were registered and frequencies of their verification were counted. Using T1-weighted (MPRAGE) and FLAIR-images from 11 subjects, we created an averaged MRI-template, defined bilaterally the NAc (seed region) and the 10 most frequently described projection areas (target regions) and transformed these regions into individual diffusion data space (1.6mm resolution, 60 gradient directions) of the subjects for fiber tracking . After inverse replication of the tracking with the NAc as target region, we reconstructed an averaged template of all tracked fibers from overlay-maps of the individual tracts and this was finally taken for statistical comparisons.

Results: Using MRI-data sets from volunteers, we were able to visualize anticipated projections to the NAc for each brain area of interest with high reliability. Moreover, the course and connectivity patterns of the displayed fibers were in accordance with the literature, which we used as a base for our data driven evaluation. Inter-subject (relation of tracked fibers between left and right hemisphere) and intra-subject comparison (relation of tracked fibers between two different time points) displayed significantly high correlations for the outlined connectivity patterns indicating high a reproducibility of our approach.

Conclusions: To the best of our knowledge, this analysis is the first transfer of NAc fiber connectivity elaborated in vivo into the human brain. Probabilistic dMRI fiber tracking basing upon data driven definition of target regions provides reliable maps of NAc connectivity. Transferred into patients, these maps may render possible selective electrical stimulation of individual fiber bundles instead of non-directed neuromodulation of the entire NAc. This approach combined with targeted current steering could improve the efficacy of DBS for the treatment of mental disorders.