Subjects
Forty-two male volunteers with ages ranging from 18 to 48 years (group mean± S.D., 27.1 ± 6.3 years) participated in the study. They were residing at a yoga center. Male subjects alone were studied as auditory evoked responses have been shown to vary with the phases of the menstrual cycle (Yadav et al., 2002) and the P300 evoked by stimuli of the visual modality also varied with sex (Polich & Conroy, 2003). All of them were in normal health based on a routine clinical examination and none of the volunteers were taking any medication. The subjects had experience of the practice of cyclic meditation for more than 3 months (mean experience ± SD, 15.3 ± 13.3 months). The aims and methods of the study were explained to them and all the subjects gave their informed consent.

Design of the Study
Subjects were assessed in two separate sessions, namely, cyclic meditation (CM) and supine rest (SR). For half the subjects the CM session took place on the one day, with SR the next day. The remaining subjects had the order of the sessions reversed. Subjects were alternately allocated to either schedule to prevent the order of the sessions influencing the outcome. The subjects were unaware about the hypothesis of the study. The assessments were done before and after each session, which lasted for 22 min 30 s.

Recording Conditions
The peak latencies and peak amplitudes of P300 were recorded using Nicolet Bravo System (USA). The P300 component was elicited with a simple discrimination task known as the “oddball” paradigm because two stimuli are presented in a random series so that one of them occurred infrequently that is, the oddball (Polich, 1999). For assessments subjects were seated in a sound attenuated and dimly lit cabin and were monitored on a closed circuit television with instructions being given through an intercom, so that subjects could remain undisturbed during a session.

Electrode Positions

Ag/AgCl disk electrodes were affixed with electrode gel (Ten 20 conductive EEG paste, D.O. Weaver, USA) at the Fz, Cz, and Pz scalp sites, referred to linked earlobes (A1–A2) with the ground electrode on the forehead (FPz); according to the International 10–20 system (Jasper, 1958). The electroocular
activity (EOG) was recorded with a bipolar derivation from electrodes placed 1 cm above and 1 cm below the outer canthus of the right eye. The electrode
impendence was kept below 5 k
at all scalp sites.

Amplifier Settings

The electroencephalographic (EEG) activity was amplified with a sensitivity of 100 µV. The low pass filter was kept at 0.01 Hz and the high pass filter was kept at 30 Hz. The P300 ERPs were computer averaged in 300 trial sweeps, in the 75–750 ms range. The pre-stimulus delay was kept at 75 ms and the level of artifact rejection was set at 90%.

Stimulus Characteristics

Binaural tone stimuli of alternating polarity delivered at 0.9mswith a frequency of 1 KHz (50 cycles for the plateau, 10 cycles for the ramp) for the standard
stimuli and 2 KHz (10 cycles for the plateau, 20 cycles for the ramp) for the target stimuli were used to trigger online averaging of the EEG. The percentage
of standard stimuli was set at 80 and for the target stimuli at 20. The stimulus intensity was kept at 70 dB SPL.

Recording Procedure

Subjects were asked to avoid substances that influence cognitive performance (e.g., coffee for the caffeine content) for the day preceding and the day of the
recording. Where this was unavoidable the session was taken on another day. The P300 evoked potentials were recorded in the eyes-closed supine position.
The “standard” and “target” auditory stimuli were delivered through close- fitting earphones (TDH-39, Amplivox, UK). Subjects were asked to distinguish
between the two tones by mentally counting the “target” stimuli. The P300 responses were recorded before and immediately after the intervention.

Interventions

Cyclic Meditation. Throughout the practice subjects kept their eyes closed, and followed pre-recorded instructions. The instructions emphasized carrying out the practice slowly, with awareness and relaxation. The practice began by repeating a verse (40 s) from the yoga text, the Mandukya Upanisad (Chinmayananda, 1984); followed by isometric contraction of the muscles of the body ending with supine rest (1 min); slowly coming up from the left side and standing at ease (called tadasana) and ‘balancing’ the weight on both feet (called centering) (2 min); then the first actual posture, bending to the right (ardhakaticakrasana, 1 min 20 s); a gap of 1 min 10 s in tadasana with instructions about relaxation and awareness; bending to the left (ardhakaticakrasana, 1 min 20 s); a gap as before (1 min 10 s); forward bending (padahastasana, 1 min 20 s); another gap (1 min 10s); backward bending (ardhacakrasana, 1 min 20 s); and slowly coming down in the supine posture with instructions to relax different parts of the body in sequence (10 min). The postures were practiced slowly, with awareness of all the sensations that are felt. The total duration of the practice was 22 min 30 s (Telles et al., 2000). Supine rest. During the supine rest session, the subjects lay supine with their legs apart and arms away from the sides of the body in corpse posture (shavasana), with their eyes closed. This practice lasted 22 min 30 s, so that the duration was the same as for CM.

Data Extraction

The peak amplitude and peak latency of the P300 was measured at the three electrode sites; that is, Fz, Cz and Pz. The peak amplitude (inµV)was defined as
the voltage difference between a pre-stimulus baseline and the largest positivegoing peak of the ERP waveform within 250–500 ms latency (Polich, 1999). The peak latency (ms) was defined as the time from stimulus onset to the point of maximum positive amplitude within the latency window. The peak latency and the peak amplitude were selected using the cursors.

Data Analysis
Statistical analysis was done using SPSS (Version 10.0). Data were analyzed using the repeated measures analysis of variance (ANOVA). There were two “Within subjects” factors, that is, Factor 1: Sessions, that is, CM and SR and Factor 2: States, that is, Pre and Post. Paired t-test analyses were performed to compare the data of the “post” periods with those of the respective “pre” periods.