RESULTS & DISCUSSION The Nb wave varied considerably among subjects (with a range of 35 to 65 msec). However, for the group as a whole, the Nb wave peak latency decreased significantly (P<0.05, paired ttest) during meditation (group mean +SD 49.5 + 7.3 msec), as compared to the preceding period (group mean + SD 51.3 + 6.1 msec). This change was consistent for each subject during repeat sessions. There was no significant change during the control period (group mean +SD 51.4 + 7.8 msec) versus its preceding period (group mean + SD, 49.9 + 8.4 msec). Also, the 7 "naive" subjects did not show any change in Nb wave latency between the control period (group mean +SD 54.0+ 5.9 msec) and the preceding period (group mean +SD 53.4 +7.6 msec). There were no significant changes in amplitude or latency of either Na or Pa waves for both meditators and "naive" subjects. An idea of the actual values can be had from the group mean obtained in the period preceding meditation or rest. For meditators, the values for Na wave were 16.4 + 1.5 msec (latency), 0.7 + 0.2 µV (amplitude) and for Pa wave were 31.8 + 3.6 msec (latency), 0.9 + 0.4 µV (amplitude). For naive subjects the Na wave measures were 16.3 + 1.4 msee (Latency), and 0.6 + 0.3 µV (amplitude), and for Pa wave 28.0 + 2.7 msec (latency), and 1.5 + 0.2 µV (amplitude). The small but consistent reduction in Nb wave latency during meditation shows that neural processing at the AEP-MLRs level does change. From the current knowledge of the generators of these waves4, one may hypothesize that meditation on "Om" (a meaningful symbol), leads to changes other than at the prethalamic/thalamic/primary cortical areas. This could be the level of the association cortices. No firm conclusions can be drawn as the actual sample size was small. However, while the subject is awake, there is considerable variability of AEP-MLRs due to large, biphasic wave, viz., the post auricular muscle reflex (PM R), which occurs 10 to 14 msec after the stimulus5. The same study reported that the waveform became more constant during diazepam induced light sleep. The present study shows that the variability persists during eyes closed rest and meditation, as well. Hence a recording of AEP-MLRs may mask changes in neural activity during meditations. AEP-MLRs would therefore not be the method of choice to assess changes at different neural levels during meditation (as anticipated at the start of this study), even though they possibly change during meditation. |