Vajrayana and Theravada styles of meditation are based on different neurophysiological mechanisms

[Dreamwalker.]

"Theravada meditation produced enhanced parasympathetic activation (relaxation). In contrast, Vajrayana meditation did not show any evidence of parasympathetic activity but showed an activation of the sympathetic system (arousal)"

http://medicalxpress.com/news/2014-08-reveals-vajrayana-meditation-techniques-tibetan.html

[Auxin]

Interesting.

A bit misleading calling them "Vajrayana and Theravada styles of meditation" tho. There are many common theravada meditations quite a lot like vajrayana visualization exercises. Its not all samatha/vipassana. I expect the reverse is also true.