Auditory Information Processing During Meditation Based on Evoked Potential Studies

Background: Auditory evoked potentials (AEPs) were recorded to examine the neurophysiological correlates of four mental states described in ancient yoga texts. These are (i) focused attention (dharana), (ii) contemplation (dhyana) (iii) random thinking (cancalata) and (iv) non meditative focused thinking (ekagrata). The auditory evoked potentials allowed changes from the periphery (cochlear nucleus) to the center (auditory association cortex) were measured. Method: There were sixty male participants with ages ranging from 18 to 45 years (group mean age ± SD, 27.0 ± 8.3 years) who were assessed in four sessions. These four sessions were i) random thinking (cancalata), ii) non meditative focusing (ekagrata), (iii) meditative focusing (dharana), and (iv) contemplation (dhyana). The order of the sessions was randomly assigned. The data were analysed with repeated measure ANOVA followed by a post hoc analysis. Results: The BAEPs results showed that the wave V peak latency significantly increased in random thinking (p<0.05), non-meditative focused thinking (p<0.01) and meditative focused thinking (p<0.05) sessions which suggest that during meditation there was no change in processing time of information at the inferior colliculus. MLAEPs results showed that there were significantly increased latencies of the Na and Pa waves during meditation (p<0.05) which suggest reduced auditory information transmission at the medial geniculate and primary auditory cortices. The LLAEPs result showed that there was a significant decrease in the amplitude of P1, P2 and N2 waves during random thinking (p<0.01; p<0.001; p<0.01, respectively) and non-meditative focused thinking (p<0.01; p<0.01; p<0.05, respectively) sessions and a decrease in the latency of P2 wave during and after meditation (p<0.001) session which suggest facilitated auditory transmission at the auditory association cortex. The changes in P300 event related potentials suggested that meditation improved the interaction between the frontal lobe; hippocampus and temporal-parietal parts of the brain during the P300 auditory oddball task. Hence, through brainstem, midlatency, long latency and event related potentials changes in the auditory sensory pathway were assessed in different mental states. Conclusion: Meditation showed no changes in auditory information transmission at the collicular level, but decreases it at the geniculate, primary and association auditory cortices.