To investigate changes in regional cerebral blood flow (rCBF) under the prone condition with and without light massage on the back, we measured rCBF quantitatively in healthy human subjects using positron emission tomography with H(2)15O. Biochemical tests showed that the light massage (palm-pressure) reduced levels of stress-related serum cortisol and salivary stress protein chromogranin-A measured after the PET examination. Absolute rCBF significantly increased in the parietal cortex (precuneus) under the prone condition compared with the supine condition, and this rCBF increase was in parallel with comfortable sensation and slowing heart rate during the massage. Correlation analysis in statistical parametric mapping showed that the amygdalar and basal forebrain rCBF correlated with parasympathetic function (heart rate reduction), indicating involvement of the forebrain-amygdala system in mediating activities in the autonomic nervous system in the presence of comfortable sensation. To conclude, prone posture itself can stimulate the precuneus region to raise awareness, and the light massage on the back may help accommodate the brain to comfortable stimulation.