Below is the abstract from a study published in Nature magazine in 1982 by Herbert Benson and others on the Tibetan yogic practice of "inner heat" or Tummo (Tibetan: gtum mo). This was one of the first scientific studies which focused on the physiologic changes which accompany this practice. (Zach Rowinski 2005-01-11)
Author's Abstract: Since meditative practices are associated with changes that are consistent with decreased activity of the sympathetic nervous system, it is conceivable that measurable body temperature changes accompany advanced meditative states. With the help of H.H. the Dalai Lama, we have investigated such a possibility on three practitioners of the advanced Tibetan Buddhist meditational practice known as gTum-mo (heat) yoga living in Upper Dharamsala, India. We report here that in a study performed there in February 1981, we found that these subjects exhibited the capacity to increase the temperature of their fingers and toes by as much as 8.3?C.