Patricio Riva Posse

O17. Connectomics in Subcallosal Cingulate Deep Brain Stimulation: Effective Connectivity as a Biomarker for Target Engagement

Background: Responders to deep brain stimulation (DBS) in the subcallosal cingulate (SCC) share stimulation on a stereotypic connectome of converging white matter bundles. A tractography-based target selection using a “connectome blueprint” of past DBS responders shows improved results. While this structural pattern is a necessary requirement for antidepressant efficacy, there has been no functional evidence describing the distinction between effective and non-effective contacts. Methods: Four subjects were implanted with DBS in the SCC using a tractography-based approach. Stimulation from effective and non-effective contacts was performed (2 Hz, 6 V), and the cortical evoked response (ER) was captured with 256channel EEG. Results: Magnitude of the ER to unilateral left stimulation is greater following stimulation from effective versus non-effective contacts, with a different signal emerging in dorsolateral prefrontal cortex (DLPFC). Source analysis shows greater ER magnitude from the effective target in left DLPFC between 60ms and 100 ms from the initiation of the propagation pattern. Coincident scalp topography appears as a positive focus over dorsal anterior midline that migrates in the posterior direction and is reliable across individuals. Conclusions: Absence of objective biomarkers to guide target selection and stimulation parameter setting is a barrier to adequate implementation of SCC DBS. A non-invasive metric of effective connectivity from a white matter target in the subcallosal cingulate has the requisite properties of a biomarker of the effective contacts. This putative biomarker showing involvement of DLPFC in effective stimulation may be informative and relevant to the mechanism of treatment efficacy. Supported By: Hope for Depression Research Foundation

Residents benefit from insights into the role and challenges of psychiatry departments.

To the Editor: We would like that thank the authors of the articles in the March issue of Academic Psychiatry, which focused on the functioning and roles of academic psychiatry departments. As a group of psychiatry residents, comprising interns, education committee representatives, and upcoming chief residents, we benefited immensely from the insights into departmental functioning that were discussed in this issue. As residents in a program with an interim chairman and with changes to our residency leadership structure, the authors found the discussions regarding succession-planning and the role of interim chairmen to be particularly informative. The article by Magen et al., “Funding the Educational Mission: Challenges to Departments of Psychiatry” has really helped to broaden our understanding of both the financial challenges and wide-ranging mission that an academic department of psychiatry faces. We believe that having better-informed residents, who are aware of these challenges, but also watchful for opportunities, may allow more constructive and fruitful resident involvement in departmental roles such as education and research. Certainly the authors feel better educated to participate in discussions within the program, such as our monthly residency-education committee meeting. The authors encourage residency programs and departments to keep residents informed and to be active participants in departmental roles. Thank you,