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Sunday, July 19 • 9:00pm - 10:00pm
P93: Investigation of Stimulation Protocols in Transcutaneous Vagus Nerve Stimulation (tVNS)

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ckeatch@swin.edu.au

Zoom Link: https://swinburne.zoom.us/j/97069565624?pwd=dm1nQWYyYUcwVkdyNkJQaEwwa2RiQT09
Password: 575701

Charlotte Keatch
, Paul Stoddart, Elisabeth Lambert, Will Woods, Tatiana Kameneva

Transcutaneous vagus nerve stimulation (tVNS) is a type of non-invasive brain stimulation that is used increasingly in the treatment of a number of different health conditions such as epilepsy and depression. Although there is a great deal of research into different medical conditions that can be improved by tVNS there is little conclusive evidence into the optimal stimulation parameters, such as stimulation frequency, pulse type or amplitude. Understanding whether variation of these stimulation parameters can directly influence the brain response could improve treatment delivery and lead to a customised approach to therapy.

The aim of this project is to use MEG imaging to determine whether tVNS leads to a direct brain response, and whether varying the stimulation parameters of tVNS can influence the induced brain response. 

Twenty healthy participants were selected based on their suitability for both magnetoencephalography (MEG) and magnetic resonance imaging (MRI) based on predetermined exclusion criteria. The experimental sessions were carried out at the Swinburne Imaging Facility, Swinburne University of Technology. Four different stimulation protocols were delivered via electrical stimulation to the left ear; active stimulation to the cymba concha at stimulation frequency of 24 Hz regular pulses, sham stimulation to the ear lobe at stimulation frequency of 24 Hz regular pulses, stimulation to the cymba concha at stimulation frequency of 1 Hz regular pulses, and stimulation to the cymba concha at stimulation frequency of 24 Hz pulse frequency modulated (PFM) pulses (modulated at 6 Hz).

Participant brain dynamics were analysed in response to stimulation through different signal processing techniques. First the raw data was passed through the software MaxFilter which uses Signal Space Separation (SSS) of Maxwell’s equations to remove major sources of noise and artifacts. The stimulation artifact was then removed from the data by spline interpolation, which removed part of the data from the onset of the stimulation pulse and then interpolated to reconstruct the signal. The data was then downsampled and filtered before applying Fast Fourier Transforms (FFT) to obtain power spectrums at sensor level. The response to different protocols could be contrasted by taking ratios for all participants and was then averaged to see group response at sensor level.

Preliminary results suggest that the brain does respond differently to different stimulation frequencies of tVNS. Comparison of the sham and active site 24 Hz stimulation shows that tVNS does elicit a brain response, but the presence of a stimulation artifact on the left side of the brain (at the site of stimulation) suggests that both our method and placement of the sham stimulation electrode could be improved. Futhermore, comparison of the 1 Hz and 24 Hz stimulation proves that the brain does respond differently to different stimulation frequencies, with the negative activity suggesting either an stronger response to the 24 Hz, possibly due to the larger amount of energy in the 24 Hz stimulation or that the 1 Hz stimulation elicits an inhibitory brain response. Similarly, comparisons between the PFM and 24 Hz regular pulses shows that the brain responds strongly to the PFM in the 10 - 14 Hz frequency band, which suggests that the brain is responding to harmonics of modulated carrier frequency. This gives evidence to the idea that the brain can be directly driven by different stimulation frequencies which could lead to customised treament approaches being developed in the application of tVNS for different medical conditions.

Speakers
CK

Charlotte Keatch

Biomedical Engineering, Swinburne University of Technology



Sunday July 19, 2020 9:00pm - 10:00pm CEST
Slot 06