Introduction: Laying Out the Field of Meditation Research

Abstract

Neuroscientifi c evidence interprets both hypnotic trance induction and different medita- tion traditions as modifi ed states of consciousness that emphasize attention, concentra- tion and the letting go of thoughts, but they differ in terms of sensory input, processing, memory, and the sense of time. Furthermore, hypnosis is based on the suggestibility of a person and meditation on mindfulness; therefore it is not surprising to fi nd differential brain plasticity changes. We analysed shared and non-shared neural substrates using electroencephalography (EEG), positron emission tomography (PET), and functional magnetic resonance imaging (fMRI). Most pronounced EEG changes were in deep as compared to light hypnosis (step-by-step induction) and in arm levitation where sug- gested movement was perceived as external. In a within-subject-design changes in brain activity during hypnosis and Tibetan Buddhist meditation were compared. High ampli- tudes in alpha frequency bands were most pronounced with meditation at frontal posi- tions and with hypnosis in central and temporal locations. Signifi cantly greater activity in theta 2 band was observed only with hypnosis in both hemispheres. PET cerebral activation patterns of imagery-mediated learning were analysed in hypnosis in a within- subject-design. Compared with baseline the learning of high-imagery words was associ- ated with (i) more pronounced bilateral activation in the occipital cortex and prefrontal areas and (ii) improved memory performance. Visual illusion in hypnosis was studied with fMRI, analysed with Granger Causality Mapping, showing changes in the effective connectivity relations of fusiform gyrus, anterior cingulate cortex and intraparietal sulcus. Little is known about the neurobiological basis of the process of enhancing cogni- tive and emotional traits in meditation. In a longitudinal fMRI study attention abilities through intensive Soto-Zen meditation were investigated before (baseline), after training (6 months) and at follow-up (9 months). After six months differences were observed in the left inferior and left superior frontal gyrus; after 9 months activations in the left precuneus. Taken together, the fi ndings advance understanding of the neural retrospect leads to a subjective lengthening of past duration. Empirical studies concerning time perception in meditation practitioners would help to understand meditative states and at the same time would foster knowledge on cognitive- emotional as well as neural processes underlying the experience of time. mechanisms that underlie hypnosis and meditation. Further studies with a greater sample size are needed to explore the differences and commonalities of hypnosis and different meditation techniques