The primary findings of this study suggest that during this 12-week IY training program, the participants were able to induce mild, but significant, changes in their baseline brain function, and were also able to activate their brain to a greater extent during meditation after training.
These findings are consistent with that of Davidson's study, in which the resting EEG showed changes after an 8-week meditation training program, particularly in the left hemisphere. This is consistent with our finding that changes in symmetry with relatively higher activity in the left-sided structures, particularly the anterior cingulate and the frontal lobe, after training suggest that there are further changes at baseline.
However, the results in the present study are also distinguished in that we found greater overall activations in the right hemisphere rather than the left during the actual act of meditation. This is interesting since it suggests that there are differences in both the baseline brain function and how the brain is activated after an individual goes through a training program.
Our results are also consistent with the study by Lazar et al., who used structural MRI to find that long-term meditators had thicker cerebral cortexes in the right anterior insula, right middle and superior frontal sulci, and left superior temporal gyrus than in controls.13
Thus, the Lazar study suggested more widespread permanent changes.
The baseline changes in the amygdala and sensorimotor cortex in our study are interesting since these areas underlie emotions and the perception of sensory phenomena. Since meditation has been found in some clinical studies to improve emotional responses and depression as well as alter perceptions of sensory stimuli, that these structures appear to be affected as the result of a training program is consistent.
It is particularly interesting to note that the majority of changes associated with the active meditation state were observed in the frontal lobes which is consistent with previous studies of meditation practices.4,5
These studies have typically observed increased activity in the frontal lobes during meditation since this area is also involved with the focus of attention,14
a common component of meditation practice. Thus, the results suggest that the subjects were not able to substantially activate these structures when they were still naïve to the meditation practice. It should be noted that we have not observed significant changes in brain activity in a test–retest paradigm in nonmeditating controls,15
and thus the results appear to reflect more specific changes associated with the yoga program. However, after training, they were able to meditate more effectively and thus activate the brain structures that have been previously reported to be involved in meditation practices. In the yoga tradition, this might be attributable to the dharana
, in which the individual focuses the mind on specific points of the body. This attention focusing may help explain the activation of the frontal lobe structures.
Any differences between our findings and previous imaging studies of meditation may be related to the fact that the focus of the IY program is on yoga postures and not meditation per se, and that it represents a somewhat different approach to meditation. Our studies of different meditation practices have suggested distinct cerebral activity patterns, depending on the type of practice. Thus, the results from this study are related to the entire IY program. One might try to resolve the problem regarding which parts of the IY program are responsible for the brain changes by separating out the different components (i.e., the postures versus the meditation). This may be useful for helping to determine the “active ingredient.” However, separating the components is a challenge in studying different meditation type programs since each component may ultimately have its effect as part of the larger program. This raises important challenges to the future study of such multifaceted programs.
This study is also obviously limited by the small sample size, but these preliminary results suggest the importance of evaluating the long-term effects of meditation and yoga practices in the future, especially when trying to observe clinical changes on a psychiatric or neurologic level. Another limitation is that we maintained the same sequence of baseline followed by yoga for the SPECT scanning sessions. However, we used this method in order to ensure that the baseline would not be influenced by the yoga practice and that whatever sensorimotor changes associated with the yoga would be the same for both the pre- and post-training program scans. Furthermore, the baseline condition should also be carefully regarded since we had the instructor describe IY including its history and basis for the particular exercises and meditations. This was repeated for the postprogram training program, and while it might be argued that the subjects were already used to this description, we felt that this was appropriate since the rest of the session would also be more familiar to the subject. We could have more formally standardized the description, but each IY session is somewhat individualized, depending on what the subject is capable of actually performing. Thus, we tried to make each condition consistent within a range of variability that might be anticipated for any program involving a teacher and student. Any substantial variability would have actually made it more difficult to obtain adequate differentiation between conditions and thus the ability of this study to provide any consistent findings, we feel, suggests that the conditions were relatively stable.
It should also be emphasized that this issue of the appropriate comparison states is always difficult in these studies, since using a state that is similar but does not contain active elements is difficult for studies of yoga and meditation. For example, listening to the instructor provide a description of the IY technique could have a relaxing effect and diminish the ability to detect a difference from the active meditation.
We did not do a correction for multiple comparisons with our statistical analysis, but we felt that by limiting the analysis to those regions previously identified to be affected during meditation practices and thus, presumed to be affected as stated in our hypotheses, we could prevent being overly conservative. However, future studies with a larger number of subjects would help to clarify the significance of the findings. Finally, the effects may have been more from the asanas, or postures, rather than from the ending meditation itself, and future studies will be needed to image the various components of yoga in order to determine the physiologic processes associated with each component.