This study has a number of strengths that assert progress in the field of meditation research. First, the use of a large sample, and rigorous methodology, particularly the efforts taken to exclude the effects of nonspecific factors is a notable methodological strength. This is one of the largest RCTs to make an earnest attempt to control for nonspecific effects and one of the only independent RCTs to compare two different conceptual understandings of meditation. Second, in this study there was no evidence of adverse effects associated with either intervention since both intervention groups generated significantly fewer negative responders than the untreated group. This is an important though often neglected consideration. Third, this study provides evidence to suggest that a “mental silence” definition of meditation is more likely to be associated with specific benefit. The implications of this third point are particularly fascinating, and we discuss some of them below.
A differential effect across the two intervention groups compared to nontreatment was found in this study. Our findings indicate that the mental silence-orientated approach is specifically effective in reducing work-related stress and depressive feelings. This is the first RCT of this approach to meditation for occupational stress to clearly demonstrate a specific effect in comparison to credible controls (waitlist nontreatment and relaxation). Similar findings were observed in an RCT comparing the same approach to meditation to a standardized stress management intervention for sufferers of moderate to severe asthma (on prestabilized treatment but who remained symptomatic). It demonstrated significantly greater improvements in a number of important subjective and objective outcome measures associated with meditation [36
A field study in which 293 medical practitioners were taught a meditation skill based on Sahaja yoga for the enhancement of psychological well-being made a number of important observations with regard to the relationship between mental silence and the study outcomes [27
]. The relationship between participants' self-reported experience of “mental activity/silence” and their self-reported experience of “calm/peaceful” and “tension/anxiety/stress” was strong and highly significant, such that the more that participants' mental activity moved toward the silent state, the more calm/peaceful (r
= 0.78, P
< .001) and the less tense/anxious/stressed they felt (r
= 0.70, P
< .001). In the diary card data, a significant relationship between self-rated mental silence and K10 score such that a higher self-rated score of mental silence was associated with a lower level of psychological distress (i.e., a lower K10 score). Among those GPs who regarded the intervention as highly effective, there was a significant positive relationship between the change in mental silence rating and change in K10 score. Taken together, (this study and Manocha's field study) suggest an effect not simply attributable to relaxation or placebo, indicating that “reduction of thought activity” has particular effectiveness for the reduction of stress and stress-related illness.
A fundamental challenge for those who design RCTs of meditation is how to develop the behavioral equivalent of a “sugar pill”. In this study, we explore an innovative strategy to address this challenge. Since reviews such as Ospina's and other thorough examinations of meditation published in the literature suggest that the “relaxation” model of meditation generates a predominantly nonspecific effect then, rather than using it as an intervention, we have in this study used “relaxation” as a control. In the context of this study, by comparing the “relaxation” model of meditation to a more classical Eastern “mental silence” model this study might not only be understood as a trial that controls for the important nonspecific effects (placebo, credibility, activity, and physiological dearousal associated with relaxation) but also as a head to head comparison of two differing conceptualizations of meditation. In this scenario, despite both approaches being “meditative”, the approach that emphasized the experience of mental silence demonstrated an effect greater than the one that emphasizes relaxation.
Conventionally, the stress reducing effects of meditation have been ascribed to meditation's ability to reduce physiological arousal. Following this line of thinking, the effects observed in this study may have occurred because mental silence-orientated forms of meditation simply reduce physiological arousal more effectively than relaxation-orientated approaches to meditation. Alternatively, current theories of stress might explain the observed changes as arising from the possibility that mental silence may more effectively facilitate greater awareness by reducing distracting and unnecessary mental activity thereby facilitating better veridical perception, reduced negative affect, and improved vitality. This contrasts with methods of meditation that emphasize relaxation, or other models of meditation that do not involve mental silence.
There is some experimental data suggesting that mental silence-orientated approaches to meditation might act via pathways that are different to simple relaxation. For example, Aftanas has conducted neurophysiological trials of the same mental silence-orientated meditation, assessing EEG changes in advanced meditators. The research revealed that the practice was associated with reproducible brain electrical changes, and that these patterns correlated strongly with the specifically defined, self-reported experience [37
]. A small study in which the same approach to meditation was compared to rest demonstrated that while those who “rested” manifested skin temperature increases consistent with the “relaxation response” paradigm, those who meditated in “mental silence” manifested skin temperature reduction. Yet the heart rate changes in both groups were not significantly different. Interestingly, the degree of skin temperature reduction in the meditation group correlated highly with meditator's self-reported experience of mental silence [39
]. The skin temperature changes suggest that a potentially unique fractionation of the relaxation response occurs in association with the mental silence experience. This implies that the mental silence-orientated conceptualization of meditation may be associated with specific physiological changes. Perhaps these changes are responsible for the specific effects observed in this study. Future studies of this approach to meditation should therefore correlate clinical and behavioral changes with convention measures of arousal.
Until 2006, the U.S. National Center for Complementary and Alternative Medicine (NCCAM) defined meditation as “a conscious mental process that induces a set of integrated physiological changes termed the relaxation response” [40
]. Remarkably, however, in 2006 the NCCAM reviewed its definition of meditation, describing a new central feature: “In meditation, a person learns to focus his attention and suspend the stream of thoughts that normally occupy the mind
] The fundamental change in emphasis from the physiology of rest (a Westernized understanding of meditation) to the experience of “suspension of thought activity” (a more classical eastern idea of meditation) raises an important question about whether or not this shift in conceptualization has practical and clinical significance. Our study throws some important empirical light on these theoretical and philosophical shifts. On a more theoretical level, meditation is popularly perceived as having specific effects. In fact historical tradition, especially Eastern tradition, asserts that meditation has a unique effect and yet the scientific evidence, based mainly on studies of Westernized models of meditation, does not agree with these perceptions. The outcomes of this trial suggest that one way to resolve this conundrum may be to propose a definition of meditation based on the “experience of mental silence”.
We do acknowledge limitations to this study. Our primary research question was whether or not mental silence meditation had a specific effect on work stress and this is best assessed at the postintervention point; therefore, this trial did not incorporate a follow-up assessment. In light of the outcomes of this study, future studies warrant a follow-up assessment strategy to assess whether participants continue using the intervention and the degree to which the benefits are maintained. The use of instruments such as the PSQ, DD, and STATE in our study may be considered by some as not adequately objective, but it should be noted that the use of such measures is currently considered to be both a reliable and standard approach to studying the effects of interventions for work stress. There is good evidence that these measures are clinically useful and reliable and in fact, although more objective measures might be more desirable in studies like this, there is currently no agreement amongst work stress researchers about which objective measures are both reliable and feasible for use in field studies.
The use of intention to treat analysis in this study is likely to give a very conservative understanding of the independent variable's impact. The dropout rates in our trial were similar to other trials of meditation for work stress and meditation trials in general. The dropout rates in the two groups were not significantly different, and there were no significant differences between the dropouts and finishers in baseline and demographic data suggesting that their exit did not introduce any major selection bias. Compliance measures would be theoretically useful as a covariate in the analysis of the outcome data. We did not, however, assess home compliance directly because our experience in pilot studies was that assessments such as daily practice diaries were not sufficiently reliable. We did not assess credibility of the two active interventions. This is a potential drawback however as both were legitimate interventions in their own right. Moreover, the fact that dropout rates in both groups were not different strongly suggests that both interventions were sufficiently and similarly credible. This trial required subjects to attend after normal working hours at a site separate from their workplace, however, future trials that are well integrated into daily activities within an organization may generate significantly lower dropout rates. Finally, the recruitment of participants working in the CBD of Sydney in the study through newspapers and other media means that inferences from the study can only be made to the population defined as responding to the media of an industrialized area with a mainly Caucasian population.