Subjects
There were 12 volunteers (4 male, 8 female) with normal health as determined by a routine medical examination and ages ranging from 25 to 40 years (Mean 30.1, SD 6.2 years). They had been practising "OM" meditation for 20 days twice a day, 15-min at a time, prior to testing. During a meditation session, subjects would keep their eyes closed and mentally repeat the syllable.

Design of the study
The subjects were assessed in 3 separate sessions conducted on different days, at the same time of the day. Each session lasted for 25 min. The test period was for 15 min, while the 2 periods preceding and following it, were for 5 min each. For all 3 sessions, subjects remained recumbent (supine) with their eyes closed while recording the "pre" and "post" periods. Instructions during the "test" period (15 min) differed among the 3 sessions. In the first 8 min of the "OM" repetition session (MOM) subjects were given instructions using a pre-recorded audiotape, to relax the body from the toes upwards, naming each part of the body. The next 7 min of the 15 min period were spent in mentally repeating "OM". During the test period of the "control" session (COM), the same sequence was followed, i.e. 8 min following the same pre-recorded instructions to relax as for the MOM session, followed by 7 min of mentally repeating "one". During the session with non targeted thinking (NT), subjects spent the first 8 min of the test period following the same pre-recorded instructions as for MOM or COM test periods. The next 7 min were spent in non targeted thinking. These two periods (8 min of guided relaxation and 7 min of specific practice) were decided upon, as subjects reported that they were able to relax while continuously repeating a syllable mentally for a given period, when it was preceded by guided relaxation. The data acquired during the 15 min period as a whole were analyzed. Also, the data obtained during the first 8 min (guided relaxation) and during the next 7 min ("OM"/ "one" repetition /non targeted thinking) were examined separately to note any significant change during either period.

The order of the 3 sessions (MOM, COM, NT) was varied in a random fashion for the subjects. Hence 4 subjects had MOM sessions on day 1, with COM and NT sessions on the next 2 consecutive days. Another 4 subjects had sessions in the order COM, NT, MOM. The 4 remaining subjects followed the order NT, MOM, COM.

Recording conditions and parameters
The sessions were conducted in a dimly lit, sound attenuated cabin. A model 10 polygraph (Recorders and Medicare, Chandigarh, India) was used to record the EKG, respiration, digit pulse volume (DPV) and skin resistance (SR). EKG was recorded using the standard bipolar limb lead I configuration and an AC bioamplifier with 1.5 Hz high pass and 75 Hz low pass settings. Respiration was monitored with a volumetric pressure transducer. The subject was asked to stand erect and the transducer was fixed around the trunk, 5 cm below the lower costal margin. A photoplethysmogram was placed on the volar surface of the distal phalanx of the left index finger to assess the digit pulse volume (DPV). Skin resistance (SR) was recorded using Ag/AgC1 disk electrodes attached to the volar surfaces of the distal phalanges of the right index and middle fingers, with a reference electrode on the volar surface of the right forearm. Electrode gel (Medicon, Madras, India) was used, and a constant current of 10 µA was passed between the electrodes. The signal was processed through a DC preamplifier. The EEG was recorded with Ag/AgC1 disk electrodes placed at F3, F4, 01 and 02 (4), each referenced to the contralateral earlobe. The EOG and EMG were recorded as for standard polysomnography (5). For EEG and EOG the time constant was 0.1 s, for EMG it was 1.0 s). Recordings of EEG. EOG and EMG allowed any sleep episodes to be detected with the purpose of excluding them from analysis.

Data acquisition and analysis
The skin resistance (SR) trace was sampled every 30 s. The amplitude of the digit pulse was sampled from the ascending portion of the wave at 30 s intervals and converted to mV as described elsewhere (6). The heart rate (HR) was calculated by counting the QRS complexes in successive 60 s epochs continuously, to give the HR in beats per min (bpm). The rate of respiration (RR) was similarly calculated by counting the number of respiratory waves also in successive 60 s epochs continuously, and noting the RR as cycles per min (cpm).

Data were analyzed in two ways: (i) a two factor ANOVA using data obtained in the "pre" and "test" periods, but not in the "post" period. The ANOVA was used to examine two factors, viz. a) the two states ("pre" versus "test" - Factor A) and b) the three sessions (MOM, COM, NT Factor B). The multiple comparison Tukey test ("least significant difference" test) was used to make pairwise comparisons, e.g. "pre" (MOM) versus "test" (MOM).
(ii) The "t" test for paired data was used to compare the data of "test" and "post" periods with those of the corresponding "pre" period.