Most neural responses like this use baroreceptors, special nerve endings found in the carotid arteries, the aorta, and other larger arteries in the neck.
Either forming in the brain artery itself or forming closer to the heart in the heart or in the carotid artery and dislodging and blocking blood flow to the brain.
An examination of his online activity revealed searches on how to locate the carotid artery, how to incapacitate a person, and how to inflict fatal wounds.