Nerve tracts under current -Targeted brain stimulation against obsessive-compulsive disorders

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Berlin, July 3, 2020 – A research group at Charité – Universitätsmedizin Berlin has succeeded in further refining deep brain stimulation as a therapy for obsessive-compulsive disorders. The team determined the exact position of the stimulation electrodes in the brains of patients and was thus able to identify a precise fibre tract that can be optimal clinical results in brain stimulation. Based on these findings, OCD could be treated more reliably and effectively in the future, as now described in the journal Nature Communications*.

In OCD, people with OCD experience an urge to do or think certain things, which they may find difficult or impossible to resist intentionally. Such compulsive acts and thoughts affect more than two percent of the population and are a major hindrance to daily life. One treatment option in severe cases is so-called deep brain stimulation, which is also used for other diseases such as Parkinson’s syndrome. For this purpose, fine electrodes are implanted in deep brain structures, where they send out very weak electrical signals to balance the disturbed brain activity. The stimulation of different areas, such as a fibre tract of the so-called internal capsule or the subthalamic nucleus, can in some cases improve the clinical symptoms. To achieve success, however, it is important that the electrodes are placed with millimetre precision. The optimal target area for brain stimulation in obsessive-compulsive disorders has not been known exactly.

The research group led by Dr. Andreas Horn at the Clinic for Neurology with Experimental Neurology at the Charité has now been able to identify a specific fibre tract as the optimal target area for the first time. To this end, the team examined 50 patients with obsessive-compulsive disorders at various centres worldwide before and after placement of the stimulation electrodes using modern magnetic resonance imaging methodology. This made it possible to visualize surrounding fibre tracts and to check which of them were selectively stimulated by the electrodes. „This analysis shows us that a specific nerve bundle is associated with optimal results. The correlation was reliably shown across the different patient groups from Cologne, Grenoble, London and Madrid,“ explains Dr. Horn, who is also the head of an Emmy Noether junior research group „Towards network-based brain stimulation“.

The researchers initially examined two patient groups in which either the internal capsule or the subthalamic nucleus was stimulated. Although these brain structures have vastly different connections to other areas, in both groups a specific fibre tract between the frontal cortex and the subthalamic core proved to be a suitable target area to contribute to clinical improvements in the patients. The localization of the stimulation electrodes alone enabled the researchers to reliably predict the treatment outcome in the two groups studied and other independent groups. A comparison with other studies also showed that the target areas described therein are also located around the newly identified fibre tract.

„Basically, our study results do not change the target area, but we were able to refine it. You can imagine it like this: In the past, we used to always steer our boat towards an island that was in the fog, but now we can identify the island and perhaps even the jetty and steer more precisely towards it,“ says Ningfei Li, first author of the study, describing the benefits for future implantations. His team has openly published the three-dimensional structures as a data set and thus makes them available to scientists worldwide. At the Charité itself, no patients with obsessive-compulsive disorders are treated by the invasive brain stimulation procedure. However, the research centres are in contact worldwide and are developing protocols to enable the testing of the newly defined target area in future studies.

*Li N et al A unified connectomic target for deep brain stimulation in obsessive-compulsive disorder. Nat Commun (2020), DOI: 10.1038/s41467-020-16734-3.

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