Individualized, connectome-based, non-invasive stimulation of OCD deep-brain targets: A proof-of-concept

Treatment-resistant obsessive-compulsive disorder (OCD) generally improves with deep-brain stimulation (DBS), thought to modulate neural activity at both the implantation site and in connected brain regions. However, its invasive nature, side-effects, and lack of customization, make non-invasive treatments preferable. Harnessing the established remote effects of cortical transcranial magnetic stimulation (TMS), connectivity-based approaches have emerged for depression that aim at influencing distant regions connected to the stimulation site. We here investigated whether effective OCD DBS targets (here subthalamic nucleus [STN] and nucleus accumbens [NAc]) could be modulated non-invasively with TMS. In a proof-of-concept study with nine healthy individuals, we used 7T magnetic resonance imaging (MRI) and probabilistic tractography to reconstruct the fiber tracts traversing manually segmented STN/NAc. Two TMS targets were individually selected based on the strength of their structural connectivity to either the STN, or both the STN and NAc. In a sham-controlled, within-subject cross-over design, TMS was administered over the personalized targets, located around the precentral and middle frontal gyrus. Resting-state functional 3T MRI was acquired before, and at 5 and 25 min after stimulation to investigate TMS-induced changes in the functional connectivity of the STN and NAc with other regions of the brain. Static and dynamic seed-to-voxel correlation analyses were conducted. TMS over both targets was able to modulate the functional connectivity of the STN and NAc, engaging both overlapping and distinct regions, and unfolding following different temporal dynamics. Given the relevance of the engaged connected regions to OCD pathology, we argue that a personalized, connectivity-based procedure is worth investigating as potential treatment for refractory OCD.

[Experimental and therapeutic neuromodulation of emotion and social cognition with non-invasive brain stimulation]

Transcranial magnetic stimulation (TMS) is not only a highly elegant method for basic neuroscientific research that employs transient lesions to explore the relationship between brain structure and function but in a clinical context it is also a very promising approach to augmentation therapy in middle to severe grade depressive episodes. This overview illustrates the methodological basis of TMS and illuminates its neuromodulatory potential with reference to findings from recent studies on emotion regulation and social cognition. Against this empirical background, it becomes clear that preclinical studies on healthy participants are extremely important to develop innovative stimulation protocols and define functionally relevant target regions to be tested in clinical studies for therapeutic efficacy. Finally, the perspectives and limitations of functionally guided, individualized TMS neuronavigation will be explored based on task-independent connectivity and task-dependent activity measurements.