Electrocortical activity prior to unpredictable stimuli in meditators and nonmeditators.

Abstract

Advanced meditators occasionally report experiences of timelessness, or states of awareness that seem to transcend the usual boundaries of the subjective present. This type of experience was investigated in eight experienced meditators and eight matched controls by measuring 32 channels of EEG before, during, and after exposure to unpredictable light and sound stimuli. The experiment postulated that if some aspect of consciousness extends beyond the present moment, then prestimulus electrocortical signals should differ depending on stimuli that were about to be selected by a truly random process, and that if such experiences were catalyzed through meditation practice, then prestimulus differences should be more apparent in meditators than in nonmeditators. Each of the 32 EEG channels was baseline adjusted on each trial by the electrical potential averaged between two- and one-second prestimulus, then for each channel the average potential was determined from one-second prestimulus to stimulus onset. The resulting means across subjects in each group were compared by stimulus type using randomized permutation procedures and corrected for multiple comparisons. Within the control group, no EEG channels showed significant prestimulus differences between light versus sound stimulus conditions, but within the meditator group five of 32 channels resulted in significant differences (P < .05, two tailed). Comparisons between control and meditator groups showed significant prestimulus differences prior to audio tone stimuli in 14 of 32 channels (P < .05, two tailed, of which eight channels were P < .005, two tailed). This outcome successfully replicates effects reported in earlier experiments, suggesting that sometimes the subjective sense of awareness extending into the future may be ontologically accurate.