In the first study on novice meditators, participants included 7 males and 3 females - paid volunteers 19 to 23 years old (5 Caucasian, 3 Asian and 2 Hispanic). Average age was 21.5 years. Subjects were recruited by campus advertisements at the University of Kentucky or word of mouth. All ten accepted subjects appeared in excellent health, and underwent general screening using a detailed questionnaire to eliminate those with medical or psychiatric illness or sleep disorders, and limited use of caffeine, alcohol, and other drugs. Two subjects were screened out and did not participate based on this information. Subjects were instructed to abstain from caffeine, nicotine, alcohol, and all other drugs on each study day. They were also instructed to keep a regular sleep-wake schedule, for a week prior to each testing day. The sleep-wake behavior was monitored in all subjects prior to each experimental day using an activity monitor watch (IM Systems, ACTITRAC) to ensure conformity. Average sleep time was 7.48 ± 0.40 hours/day on the nights prior to each experimental session (based on actigraphy data), which was also generally consistent throughout the experimental period. Subjects typically had late bed-times (around 1:00 am) and late wake-times (around 8:30 am), as is common in a young university community.

Subjects were tested under four treatments: Control (C), Nap (N), Meditation (M) and Sleep Deprivation plus Meditation (SD+M). For the first three treatment conditions, C, N and M, each subject was tested twice (a total of 6 different days), and once for the SD+M treatment. The testing was done on non-consecutive days, and the activity for each day was randomly assigned (without the subjects' prior knowledge), with the one night of total SD completed over a weekend. Each subject refrained from caffeine and other stimulants or depressants throughout each experiment. Each subject was given 2 practice runs on the PVT, ahead of the experimental days. None of the subjects had prior experience with meditative techniques. Each subject was given instructions in simple eyes-closed concentrative meditation techniques (with focus on breathing) for 2 days in pairs (one hour per day), ahead of the experimental schedule. All training was done by the same individual who practices such meditation and had recently completed a twelve-week course in order to provide more uniform instruction. Subjects were taught in the kneeling position with the aid of a kneeling meditation bench (Samadhi Cushions, Barnet, Vermont, USA) that is especially helpful for beginners in optimizing spinal alignment and reducing weight and stress on the knees, hips, ankles, and back. The bench was covered with the optional cushion, along with a floor cushion, for further comfort. Subjects were taught uniform abdominal breathing, with focus on abdominal movements throughout the 40 minute meditation period. On control days, subjects sat in a standard desk chair, listened to soft music and engaged in either light reading or conversation to ensure a constant period of eyes open wakefulness. On nap days, the subjects were asked to lie down in bed and attempt to sleep for the entire 40 minutes. All conditions were completed in a quiet room of the subjects' choosing.

PVT-192 (Ambulatory Monitoring Inc.) was used to test for vigilance and reaction time. Three 10 min tests were done at 3:00 pm, 4:00 pm and 4:50 pm respectively. The treatments(C, N, and M) took place between 3:10 pm and 3:50 pm. Between 4:10 pm and 4:50 pm, each subject was involved in control activities the same as the control condition above (sitting, with light music background, reading or conversation, eyes open).

In the second study with long-term meditators, 7 subjects (3 females and 4 males, from India) with at least 3 years of regular meditation practice (2 hrs or more per day for most days of the year) were used. Age range 24-48 years (all citizens of India in the Delhi region) and average age 38.1 years. All were healthy with no history of major medical, psychiatric or sleep problems. All practiced traditional yogic styles of meditation with focus on the breathing, and all would probably be classified as "concentrative" meditation as opposed to "mindfulness" meditation, although these distinctions are not always clear. Sleep journals were kept on a pre-supplied format for a minimum of 15 days (a maximum of 30 days). Activity monitors (ACTITRAC) were used for Actigraphy records for a minimum of 15 days to a maximum of 22 days. A marker button (read digitally) was pressed by the subjects every time they would commence to meditate. EEGs were done on a subset of subjects (n = 3) using a Neurocare Wingraph Digital EEG system (Biotech). A standard 10 lead placement system was used. MSLT and PVT tests were also conducted on a subset of subjects (n = 4) using standard methods. EEGs were scored by hand with the assistance of a trained and certified polysomnographic technician. Twenty-three control subjects in India were also selected for total sleep time comparisons relative to the seven meditators. These control subjects were sex and age matched.

All data were analyzed with analysis of variance (ANOVA) by using the General Linear Model (GLM) within SYSTAT 12 (SYSTAT Software, Inc., 1735, Technology Drive, Ste 430, San Jose, CA 95110, USA), or nonparametric alternatives when the assumptions of ANOVA were not met. We used the Kolmogorov-Smirnov, Shapiro-Wilk and Anderson-Darling tests for normality, and Levene's test for homogeneity of variances.

The first experiment was analyzed as a repeated measures design. The response variable was change in PVT reaction time, post- minus pre-. Each of 10 subjects was tested in each of 4 experimental treatments (Control, Nap, Meditation, Sleep Deprivation plus Meditation) in a two-way mixed model without replication, where Treatment was a fixed effect and Subject, the blocking variable, was a random effect. We were interested primarily in the treatment effects. The 4 treatments were compared with each other with a series of post hoc contrasts, and the resulting probabilities were Bonferonni adjusted. These 4 treatments were explored further with a repeated measures analysis of covariance (ANCOVA), where post- was our response variable, and pre- was our covariate.

We intended to analyze this response variable with a repeated measures analysis of variance (ANOVA), which is a two-way, randomized-block design, without replication. The two factors in the ANOVA are Treatment (fixed effect) and Subject (random effect, the blocking variable). Although our response variable satisfied the assumption of normality, it did not satisfy the assumption of homogeneity of variances (Levene's test statistic = 5.890, p < 0.005), and standard data transformations did not correct this problem. Variance heterogeneity presents problems for ANOVA. We rank-transformed the data, and found that the variances of the ranks among treatment groups were homogeneous (Levene's test statistic = 1.769, p > 0.176) and these ranks also satisfied the assumption of normality. We analyzed these ranks with the nonparametric alternative to a randomized block ANOVA, Friedman's Randomized Blocks. We found significant treatment effects on change in PVT reaction time (Friedman Test Statistic = 23.4, df = 3, p << 0.0005; Figure 1, Table 1). The M and SD+M treatments showed faster post-treatment reaction times, whereas the N and C treatments showed slower post-treatment reaction times (Figure 1, Table 1). We performed three post-hoc comparisons, the two treatments that had faster reaction times (M versus SD+M), the two treatments that had slower post-treatment reaction times (C versus N), and the treatments with meditation against those without meditation ([M plus SD+M] versus [C plus N]). Although these contrasts are orthogonal, they were unplanned. To preserve an experiment-wise error rate of 0.05, we applied the Bonferroni correction for these three contrasts, and compared their test statistics against p < 0.0167. These post hoc contrasts revealed that M and SD+M are one nonsignificant subset of the data (Friedman Test Statistic = 1.6, df = 1, p > 0.20), that C and N are another nonsignificant subset of the data (Friedman Test Statistic = 3.6, df = 1, p > 0.05), and that these two groups significantly differ from each other (Friedman Test Statistic = 20.0, df = 1, P < 0.0005). Note that doing a parametric ANOVA on the rank transformed data gives qualitatively the same results as the nonparametric Friedman's Randomized Blocks (Overall ANOVA: F 3,27 = 25.799, p << 0.0001; M versus SD+M: F 1,27 = 0.893, p > 0.893; C versus N: F 1,27 = 3.338, p > 0.078; [M plus SD+M] versus [C plus N]: F 1,27 = 73.164, p << 0.0001).

Table 1 The data on which Figures 1 and 2 are based. For the Nap, Control, and Meditation Treatments, the data are the averages for the 2 days of measurement. Full size table

Figure 1 Mean change in PVT reaction time for our four experimental treatments: Control (C), Nap (N), Meditation (M), Sleep Deprivation Plus Meditation (SD+M). Performance improves following meditation (M, SD+M) and declines following a nap and in controls (N, C); Friedman Test Statistic = 23.4, df = 3, p << 0.0005. Treatments noted with the same letter (a or b) denote nonsignificant subsets of the overall analysis. Values represent the mean PVT reaction times before treatment minus the post-treatment. Error bars denote one standard error. Full size image

Unlike change in PVT reaction time, we found that pre- and post-treatment PVT reaction times do satisfy the assumptions of normality and homogeneity of variances. Therefore, we also performed a repeated measures analysis of covariance (ANCOVA) without replication, where post-treatment PVT reaction time was our response variable, our two factors were Treatment (fixed variable) and Subject (random blocking variable), and our covariate was pre-treatment reaction time. Although neither main factor was significant (Treatment: F 3,23 = 1.798, p = 0.176; Subject: F 9,23 = 0.535; P = 0.834), both the Covariate (Pre-: F 1,23 = 23.315. p <<0.0001) and the Treatment By Covariate interaction term were significant (Treatment × Pre: F 3,23 = 3.13, p < 0.05; the Subject by Covariate interaction term was not significant, F 9,14 = 0.318. p = 0.955, and dropped from the model). The very strong covariate effect indicates that post-treatment and pre-treatment reaction times are highly correlated among Subjects and Treatments; whereas, the Treatment by Covariate interaction term indicates heterogeneity among treatments in the slopes of these relationships. A post hoc examination of these trends revealed that the two treatments that include meditation, M and SD+M, have shorter Post-Treatment PVT Reaction Times (F 1,27 = 7.152, p < 0.02) and a shallower regression slope (F 1,27 = 12.610, p < 0.002) than the two treatments that do not include meditation, C and N (Figure 2). Separate Analysis of Covariance for C versus N treatments, and for the M versus SD+M treatments indicates no significant effects of Treatment, Subject, Treatment by Covariate interaction, or Treatment by Subject interaction for either grouping.

Figure 2 A plot of Post-Treatment PVT Reaction Time versus Pre-Treatment PVT Reaction Time for our four treatments. The treatments that included meditation, M and SD+M, showed faster post- than pre-treatment reaction times; whereas, the reverse was true for the C and N treatments. The M and SD+M treatments have a shallower regression slope than the two treatments that do not include meditation, C and N (F 1,27 = 12.610, p < 0.002). Full size image

In our second experiment, our response variable was average sleep duration, which was analyzed with a one-way ANOVA with two treatments: Meditators versus Non-meditators.

All research protocols were reviewed and approved by the University of Kentucky's - Institutional Review Board. All protocols and ethical directives were strictly adhered to including informed consent from all study participants.