Meditation decreases the peak latency of the Na wave, a negative wave between 14-19 msec in middle latency auditory evoked potentials, indicating reduced conduction time at the midbrain-thalamic level. The study measured these evoked potentials in practitioners of Brahmakumaris Raja Yoga meditation and found a decrease in the Na wave latency during meditation, suggesting meditation reduces transmission time in the midbrain and thalamus.

1. Changes in Middle Latency Auditory Evoked Potentials During
Meditation.
Telles S., Naveen K. V.
Psychological Reports: (2004) Volume 94, Issue 2, Pp. 398-400
Summary
In the present study of middle latency auditory evoked potentials
during Brahmakumaris Raja Yoga meditation there was a decrease in
the peak latency of the Na wave (a negative wave between 14 and 19
msec.) during meditation. Since the neural generator of this wave lies
at the midbrain-thalamic level, from the results one can infer that the
meditation reduces conduction time at this level.
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http://www.amsciepub.com/doi/abs/10.2466/pr0.94.2.398-400