Brain Effect of Vagal Nerve Stimulation at Rest and Pain

Summary

Participation Requirements

Description

Following informed written consent and screening questionnaires to characterize psychophysiological traits including personality and anxiety/depression inventory, each subject will have a nasogastric tube inserted with the attached distensible balloon positioned in the distal oesophagus. Painful oes...

Following informed written consent and screening questionnaires to characterize psychophysiological traits including personality and anxiety/depression inventory, each subject will have a nasogastric tube inserted with the attached distensible balloon positioned in the distal oesophagus. Painful oesophageal stimulation will be achieved by inflation of the balloon to a pain threshold pre-determined in each subject, defined as the point at which subject describes the transition from sensation to pain. The MR-safe tVNS probe will be attached to the neck for cervical vagal nerve-directed tVNS, and subjects will then be positioned in the MRI scanner. Real-time activity of the ANS will be monitored by heart rate variability as described in the previous study, which has been adapted for use in the MR-environment. All subjects will undergo MRI. For each visit, there will be two scanning periods. High-resolution structural imaging will first be required, and subsequently resting fMRI data will be acquired whilst subjects are asked to relax in the scanner, and their baseline autonomic tone is monitored, using validated methods of acquiring ANS data. This will illustrate a brain signature of real-time brain activity mapped to their parasympathetic tone. Subjects will then be randomised to either the active-tVNS paradigm or sham and a second fMRI data acquisition will then be performed so as to acquire brain activity in conjunction with active and sham-tVNS. Following this, painful oesophageal stimulation will be repeated 20 times while active or sham tVNS continues. Following a two-week washout period, subjects will be crossed over and re-examined to receive the intervention they did not receive in visit 1.

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