Subjects
Subjects: There were 25 normal healthy volunteers, all males with ages between 20.0 and 32.0 years (mean ± SD, 26.2 ± 3.4 years). 

Design of the study : Each subject was assessed with different filter (low frequency or LF and high frequency or HF) settings, viz.I: LF 0.1 HF 15, LF 0.3 HF 15, LF 5.0 HF 15; II: LF 0.1 HF 35, LF 0.3 HF 35, LF 5.0 HF 35; and III: LF 0.1 HF 75, LF 0.3 HF 75. LF 5.0 HF 75. With each filter setting recordings were made in the baseline state (1 minute), during slow and deep breathing (1 minute), and while receiving 4 auditory stimuli, spaced 15 seconds apart (1 minute), making a total of 9 minutes.

Recording procedure: The sympathetic skin response was recorded using two Ag/AgCl disc electrodes filled with conducting paste, and placed on palmar and dorsal surfaces, over the hypothenar eminence. A ground electrode was placed on the right ankle above the medial malleolus. The electrodes were connected to an AC bioamplifier.