RESUMO
Meditation is an ancient spiritual practice, which aims to still the fluctuations of the mind. We investigated meditation with fMRI in order to identify and characterise both the "neural switch" mechanism used in the voluntary shift from normal consciousness to meditation and the "threshold regulation mechanism" sustaining the meditative state. Thirty-one individuals with 1.5-25 years experience in meditation were scanned using a blocked on-off design with 45 s alternating epochs during the onset of respectively meditation and normal relaxation. Additionally, 21 subjects were scanned during 14.5 min of sustained meditation. The data were analysed with SPM and ICA. During the onset of meditation, activations were found bilaterally in the putamen and the supplementary motor cortex, while deactivations were found predominately in the right hemisphere, the precuneus, the posterior cingulum and the parieto-temporal area. During sustained meditation, SPM analysis revealed activation in the head of nucleus caudatus. Extensive deactivations were observed in white matter in the right hemisphere, i.e. mainly in the posterior occipito-parieto-temporal area and in the frontal lobes. ICA identified 38 components including known baseline-resting state components, one of which not only overlaps with the activated area revealed in the SPM analysis but extends further into frontal, temporal, parietal and limbic areas, and might presumably constitute a combination of frontoparietal and cinguloopercular task control systems. The identified component processes display varying degrees of correlation. We hypothesise that a proper characterisation of brain processes during meditation will require an operational definition of brain dynamics matching a stable state of mind.
