When the amygdala is activated by threats real or imagined, it triggers the release of adrenaline which, in turn, hinders or even blocks access to the frontal cortex. The amygdala wants us to react, not think. The downside of this necessary mechanism is how quickly irrational threats (especially when powerfully and cleverly packaged) can go viral. With adrenaline pumping, groupthink and confirmation bias quickly can kick in, and presto, the irrational becomes self-evident (think climate change denial, slavery and countless other examples).
Source : https://www.latimes.com/opinion/readersreact/la-ol-le-vaccine-brains-measles-antivax-20190216-story.html