A three-stimulus auditory oddball series was presented to experienced Vipassana meditators during meditation and a control thought period to elicit event-related brain potentials (ERPs) in the two different mental states. The stimuli consisted of a frequent standard tone (500 Hz), an infrequent oddball tone (1000 Hz), and an infrequent distracter (white noise), with all stimuli passively presented through headphones and no task imposed. The strongest meditation compared to control state effects occurred for the distracter stimuli: N1 amplitude from the distracter was reduced frontally during meditation; P2 amplitude from both the distracter and oddball stimuli were somewhat reduced during meditation; P3a amplitude from the distracter was reduced during meditation. The meditation-induced reduction in P3a amplitude was strongest in participants reporting more hours of daily meditation practice and was not evident in participants reporting drowsiness during their experimental meditative session. The findings suggest that meditation state can decrease the amplitude of neurophysiologic processes that subserve attentional engagement elicited by unexpected and distracting stimuli. Consistent with the aim of Vipassana meditation to reduce cognitive and emotional reactivity, the state effect of reduced P3a amplitude to distracting stimuli reflects decreased automated reactivity and evaluative processing of task irrelevant attention-demanding stimuli.
The neuroelectric (EEG) effects of meditation on brain activity are as yet not well characterized. There is no consensus as to whether evoked sensory and elicited cognitive event-related potentials (ERPs) are altered systematically from long hours dedicated meditators devote to their practice (Cahn and Polich, 2006). Some meditation effects of increased attention-related activations have been reported for changes in P300 amplitude (Banquet and Lesévre, 1980, Murthy et al., 1997 and Sarang and Telles, 2006), contingent negative variation (CNV) amplitude (Travis et al., 2000 and Travis et al., 2002), and frontal midline theta power (Aftanas and Golocheikine, 2001 and Hebert and Lehmann, 1977). Meditation is most readily conceived as a set of diverse and specific methods of distinct attentional engagement and recent reports have begun to focus specifically on measures of attentional engagement during (state) and from (trait) meditation (Brefczynski-Lewis et al., 2007, Holzel et al., 2007, Jha et al., 2007, Pagnoni and Cekic, 2007, Raz and Buhle, 2006, Slagter et al., 2007 and Srinivasan and Baijal, 2007).
The goal of present study was to assess the state effects of meditation in experienced Vipassana meditators (average 13 years of daily meditation practice) using stimulus conditions indexing neurophysiologic processing underlying perception and attentional engagement. A passive three-stimulus auditory oddball task was employed as it did not require participants to disengage from meditation practice to produce a behavioral response, simultaneously allows for characterization of the sensory aspects of audition via the N1/P2 components, and assays attentional engagement via the P3a potential elicited by the distracter stimulus (Combs and Polich, 2006 and Polich, 2007). As the primary goal was to characterize neurocognitive meditation effects, a within-subject meditation vs. control cognitive task paradigm was employed.
