Some technical issues of vagal nerve stimulation. An approach using a hippocampal formation theta rhythm

Previously, we have demonstrated that hippocampal (HPC) theta rhythm can be produced, depending on current intensity, directly during vagal nerve stimulation (VNS) or with a time delay following stimulation. This suggests that theta EEG pattern can also be used as a bio-indicator of the efficiency of VNS. In the present study, we focused on three specific, technical issues related to the stimulation procedure of the vagal nerve: i/does the type of the electrode used for VNS and the technique of its implantation affect the parameters of the HPC theta rhythm? ii/does the type of electrode used determine the current intensity threshold of VNS-induced HPC theta? iii/is the repeatability of the VNS effect determined by the type of electrode used? We demonstrated that a platinum-iridium cuff electrode offers some important advantages over a tungsten electrode. Firstly, despite some possible mechanical and compression nerve damage related to permanent contact with the vagal nerve, it offers a lower current intensity threshold for inducing theta oscillations. Secondly, and most importantly, the cuff electrode offers repeatability of the VNS effect on the HPC theta rhythm. However, one disadvantage of using this type of an electrode is that the permanent pressure on the vagal nerve by the cuff itself may decrease the amplitude of the investigated field potential.