This paper identifies a new existential risk factor that has not been recognised in prior literature: Brain-Computer Interfaces (BCIs). We illustrate how BCI technology could significantly raise the existential risk from global totalitarianism in the near future. In particular this is achieved not just by expansion of surveillance, but the expansion of brain stimulation. At present, this risk factor has been entirely unnoticed. We suggest that given the high likelihood of its impact, and the possible magnitude of such an impact, it deserves more attention, more research, and more discussion.