Researchers at Aarhus University in Denmark used the country's national health registries to find everyone who had undergone a vagotomy for ulcer disease decades earlier, then tracked how many of them went on to develop Parkinson's, compared with the general population.
People who had a truncal vagotomy, which severs the full trunk of the nerve, had a 15 percent lower risk of Parkinson's overall, not statistically significant, and a 47 percent lower risk when more than 20 years had passed, while a selective version that spared most of the nerve showed no such pattern.
Since the vagus nerve runs directly between the gut and the brainstem, the result backed the idea that Parkinson's, in some people, begins outside the brain, matching autopsy work finding the same misfolded protein in gut nerves. The study is observational and the numbers were small, so it shows an imprecise pattern, not a proven mechanism.
Read the original study
Svensson et al., Annals of Neurology, 2015 · doi.org/10.1002/ana.24448
One cut nerve, one clue about origin.
Source
- Svensson, E., Horváth-Puhó, E., Thomsen, R. W., Djurhuus, J. C., Pedersen, L., Borghammer, P., & Sørensen, H. T. (2015). Vagotomy and subsequent risk of Parkinson's disease. Annals of Neurology, 78(4), 522–9. https://doi.org/10.1002/ana.24448