INTRODUCTION
Vagal nerve stimulation (VNS) is used as treatment in depression and epilepsy.[1,2] A positron emission tomography (PET) study[3] has shown decreased blood flow to limbic brain regions during direct (cervical) VNS. Another functional magnetic resonance imaging (fMRI) study[4] has shown significant deactivation of limbic brain regions during transcutaneous VNS. In this procedure electrical stimulus is applied over the inner part of the left tragus and hence the auricular branch of the vagus.
The use of ‘OM’ chanting for meditation is well known.[5] Effective ‘OM’ chanting is associated with the experience of vibration sensation around the ears. It is expected that such a sensation is also transmitted through the auricular branch of the vagus nerve. We therefore hypothesized that like transcutaneous VNS, ‘OM’ chanting too produces limbic deactivation. Specifically, we predicted that ‘OM’ chanting would evoke similar neurohemodynamic correlates, deactivation of the limbic brain regions, amygdala, hippocampus, parahippocampal gyrus, insula, orbitofrontal and anterior cingulate cortices and thalamus) as were found in the previous study.[4]
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