This study was conducted in the Department of Physiology, JIPMER, Pondicherry India, during May 2011 to December 2011. Yoga training was given at the Advanced Centre for Yoga Therapy Education and Research (ACYTER), JIPMER, Pondicherry. The study was commenced after obtaining approval from the institute’s scientific advisory committee and human ethics committee.

We considered volunteers who were in the age group of [18–25] years, who were in self-reported good health, who were undergoing various healthcare courses (medical, nursing and allied medical sciences). We excluded volunteers who had practised yoga in the past one-year and those with current or previous mental or neurological diseases. We explained the study design to the volunteers and made them aware that their participation would remain anonymous and that they had the freedom to withdraw from the study at any time.We included only those who gave their written informed consents to participate in the study (n=84).

Parameters Measured

Reaction time for the detection of auditory (ART) and visual signals (red and green lights) (VRT—R and VRT—G respectively) was recorded on apparatus supplied by Ananda agencies (Pune, India). RT is an indirect index of the processing capacity of the central nervous system, and it is a simple and inexpensive method of determining sensorimotor performance [20].

The persons involved in the recording of the parameters and the analysis of data were blind to the experimental conditions (i.e., the group that the participants belonged to).

We familiarized the participants with the test batteries and gave them adequate practice on the reaction time apparatus on two separate occasions, to produce results that were more consistent. On the day of assessment, participants reported to the Department of Physiology, JIPMER, between 9 and 10 AM, at least two hours after eating a light breakfast. Then, the above-mentioned parameters were recorded. We administered these tests in the same order as are given here, to all the participants.

Then, the participants (n=84) were randomly assigned into three groups:

We trained the participants in their respective pranayama technique for one week, before the start of the intervention period. Pranayama intervention was carried out for about thirty-five minutes a day, three times per week, for a duration of 12 weeks. A certified yoga trainer at ACYTER gave the Pranayama training and intervention. Participants practised the pranayama in a quiet room which was maintained at a comfortable temperature (25 ± 2°C). We followed pranayama techniques followed in ACYTER, JIPMER [21]. Typical sessions of fast and slow pranayamas were as follows:

Fast Pranayama: Each cycle (six minutes) consisted of practising one minute of Kapalabhati, one minute of Bhastrika and one minute of Kukkriya pranayamas, interspersed with one minute of rest between each pranayama. Participants were asked to complete four cycles in each session (24 minutes).

Slow Pranayama: Each cycle (nine minutes) consisted of practising two minutes of Nadishodhana, two minutes of Pranava and two minutes of Savitri pranayamas which were interspersed with one minute of rest between each pranayama. While they were sitting in a comfortable posture (sukhasana), participants were asked to perform three rounds per session (27 minutes).

Power and sample size software, version 3.0 was used to calculate the adequate sample size (at assumed power of 90%) which was required for the study and to analyze the post–test power of the study. Analysis of the data was done by using IBM SPSS, version 19. The normality of the data was tested by Kolmogorov–Smirnov test. Intergroup comparison was done using one way ANOVA, followed by Tukey Krammer post–hoc test for pair wise comparisons. Intragroup comparisons were done by using paired t-test for parametric measures and Wilcoxon signed rank test was used for non-parametric measures. Chi-square test was used to compare intergroup gender distributions. The Mann Whitney U-test was used to compare the percentage change between groups. A p value less than 0.05 was considered to be statistically significant.

A post-test analysis, revealed that the lowest power of the study with a mean RDS difference of 0.36 (SD=1.13) between fast and slow pranayama groups was 85%, which showed that the sample size was adequate and that the strength of the study was good.

There were no significant differences in age, height or weight between the three groups [Table/Fig-1]. There was no significant difference in gender distribution between the groups. The three groups were comparable in executive functions and attention span before the intervention [Table/Fig-2]. There was a significant decrease in LCT (time) (p<0.001), number of omissions in LCT (p<0.001), total time taken for TTA (p<0.001), total time taken for TTB (p<0.001), ART (p<0.001) and VRT (both green and red light) (p<0.005) in both the study groups but not in the control group after the study period (12 weeks). We have also observed that practice of fast and slow pranayama lead to siginificant decrease in PSS scores [18] which we have published earlier. In addition, a significant improvement was seen among participants of both fast pranayama group and slow pranayama group in FDS (p<0.001), whereas a change in RDS was seen only in fast pranayama group participants.

There were no significant differences in the percentage of change from pre- to post-test between fast and slow pranayama groups in stress scores and in all of the executive function parameters. However, the fast pranayama group showed a significantly improved performance as compared to the slow pranayama group in ART, VRT-R (P<0.05) and VRT-G (P<0.01) [Table/Fig-3,4].

According to the traditional wisdom of yoga, pranayama is the key to bringing about psychosomatic integration and harmony.

Specifically, we observed a significant reduction in perceived stress and improvement in the following cognitive domains: attention, visuo-motor speed and memory retention capacity in both fast and slow pranayama groups. Prefrontal cortex regulates physiological functions by integrating information from ongoing cognitive processes, emotional processes and current stress level [14,22]. Chronic (perceived) stress alters normal patterns of prefrontal cortex activation during cognitive tasks, resulting in enhanced autonomic arousal [14,22]. The reduced stress in both pranayama groups could have enabled their improved cognitive functions. Our results were consistent with those of previous studies, which found significant improvement in various cognitive domains with the practice of different yoga breathing techniques [10,23–25].

In the present study, it was not possible to determine the mechanism of action of pranayama techniques, but we hypothesized that the improvements in cognitive functions in pranayama groups may have occurred due to reduced stress and improved parasympathetic tone.

The particular contribution of pranayama to stress reduction might be mediated by the bidirectional vagal system. Vagal afferents from peripheral receptors are connected with the nucleus tractus solitarius from which fibres ascend to the thalamus, limbic areas and anterior cortical areas. The descending projections then modulate autonomic, visceral, and stress arousal mechanisms at the different levels of the neuraxis [26]. The bottom-up mechanisms of pranayama practice may be induced through the stretch of respiratory muscles, specifically the diaphragm [14,26]. During above tidal inhalation (as was seen in Hering Breuer’s reflex), stretch of lung tissue produces inhibitory signals in the vagus nerve, which ultimately shifts the autonomic nervous sytem into parasympatho-dominance, that results in a calm and alert state of mind [27].

During both fast and slow types of pranayama practice, when participants intentionally focus on breathing at different frequencies of respiration and intend to relax, attention is drawn away from extraneous distracting stimuli. With continuous pranayama practice, the participants’ ability to concentrate is enhanced and the changes in mental processing (e.g., focused attention and reduced stress) are rapidly expressed in the body via the autonomic and neuro endocrine systems. This reorganizes neural representation within the CNS and improves bidirectional communication between the cerebral cortex and the limbic, autonomic, neuro endocrine, emotional, and behavioural activation [22]. Also, generalized alteration in information processing at thalamo-cortical level induces modification in neural mechanisms which regulate the respiratory system [28].

The shortening of auditory and visual RT in our pranayama groups represents greater arousal, better concentration and faster responsiveness [12]. The improvement was significantly greater in the fast pranayama group as compared to that in slow pranayama group. One previous study found insignificant decreases in ART and VRT, with a shorter (three weeks) training period of Savitri (slow breathing) and Bhastrika (fast breathing) pranayamas [12]. Our study, on the other hand, demonstrated that a prolonged practice (12 weeks) of pranayama could be beneficial in reducing RT.

There was a difference in training times between the fast and slow pranayama groups (24 vs. 27 minutes), since the participants in the fast pranayama group found it difficult to do more than four rounds in a session. Also, there was a difference in the number of male and female participants in the study. Nevertheless, the male and female participants were equally distributed between the groups, i.e. the gender ratio was almost similar. Since this study was conducted only on healthy participants, future studies should broaden the current research and include clinical populations such as patients with psychiatric disorders, whose cognitive functions are adversely compromised.

Slow and rapid types of pranayama are beneficial for stress reduction and for improving cognitive functions, but fast pranayama has additional effects on sensori-motor performance (i.e. faster auditory and visual RT).

The findings discussed in this research article are a part of the bigger study to evaluate the effect of fast and slow pranayama on various physiological parameters in adolescents. Part of the study has earlier been published in International Journal of Yoga 2013; 6: 104–10 [29].