Tractography-Based Surgical Targeting for Thalamic Deep Brain Stimulation: A Comparison of Probabilistic vs Deterministic Fiber Tracking of the Dentato-Rubro-Thalamic Tract.

BACKGROUND: The ventral intermediate (VIM) thalamic nucleus is the main target for the surgical treatment of refractory tremor. Initial targeting traditionally relies on atlas-based stereotactic targeting formulas, which only minimally account for individual anatomy. Alternative approaches have been proposed, including direct targeting of the dentato-rubro-thalamic tract (DRTT), which, in clinical settings, is generally reconstructed with deterministic tracking. Whether more advanced probabilistic techniques are feasible on clinical-grade magnetic resonance acquisitions and lead to enhanced reconstructions is poorly understood. OBJECTIVE: To compare DRTT reconstructed with deterministic vs probabilistic tracking. METHODS: This is a retrospective study of 19 patients with essential tremor who underwent deep brain stimulation (DBS) with intraoperative neurophysiology and stimulation testing. We assessed the proximity of the DRTT to the DBS lead and to the active contact chosen based on clinical response. RESULTS: In the commissural plane, the deterministic DRTT was anterior (P < 10-4) and lateral (P < 10-4) to the DBS lead. By contrast, although the probabilistic DRTT was also anterior to the lead (P < 10-4), there was no difference in the mediolateral dimension (P = .5). Moreover, the 3-dimensional Euclidean distance from the active contact to the probabilistic DRTT was smaller vs the distance to the deterministic DRTT (3.32 ± 1.70 mm vs 5.01 ± 2.12 mm; P < 10-4). CONCLUSION: DRTT reconstructed with probabilistic fiber tracking was superior in spatial proximity to the physiology-guided DBS lead and to the empirically chosen active contact. These data inform strategies for surgical targeting of the VIM.

Ethical Issues in Intraoperative Neuroscience Research: Assessing Subjects' Recall of Informed Consent and Motivations for Participation.

BackgroundAn increasing number of studies utilize intracranial electrophysiology in human subjects to advance basic neuroscience knowledge. However, the use of neurosurgical patients as human research subjects raises important ethical considerations, particularly regarding informed consent and undue influence, as well as subjects' motivations for participation. Yet a thorough empirical examination of these issues in a participant population has been lacking. The present study therefore aimed to empirically investigate ethical concerns regarding informed consent and voluntariness in Parkinson's disease patients undergoing deep brain stimulator (DBS) placement who participated in an intraoperative neuroscience study.MethodsTwo semi-structured 30-minute interviews were conducted preoperatively and postoperatively via telephone. Interviews assessed participants' motivations for participation in the parent intraoperative study, recall of information presented during the informed consent process, and participants' postoperative reflections on the research study.ResultsTwenty-two participants (mean age = 60.9) completed preoperative interviews at a mean of 7.8 days following informed consent and a mean of 5.2 days prior to DBS surgery. Twenty participants completed postoperative interviews at a mean of 5 weeks following surgery. All participants cited altruism or advancing medical science as "very important" or "important" in their decision to participate in the study. Only 22.7% (n = 5) correctly recalled one of the two risks of the study. Correct recall of other aspects of the informed consent was poor (36.4% for study purpose; 50.0% for study protocol; 36.4% for study benefits). All correctly understood that the study would not confer a direct therapeutic benefit to them.ConclusionEven though research coordinators were properly trained and the informed consent was administered according to protocol, participants demonstrated poor retention of study information. While intraoperative studies that aim to advance neuroscience knowledge represent a unique opportunity to gain fundamental scientific knowledge, improved standards for the informed consent process can help facilitate their ethical implementation.