This study will compare the acute effects of respiratory-gated transcutaneous vagus nerve stimulation (tVNS) at different stimulation frequencies and sham stimulation during five sessions within a 2 week period. Heart rate variability (HRV) point process adaptive filtering estimation algorithms will be used to evaluate changes in cardiac autonomic physiology in subjects with major depression in response to tVNS. The effects of tVNS on cardiovagal regulation will be evaluated at rest and in response to an emotion reactivity task. Depression rating scales (Beck's Depression Inventory) will be used to evaluate short term effects of tVNS on depressive symptoms in these subjects. In addition, the study will evaluate the acute effects of the stimulation on serum levels of pro-inflammatory cytokines. The stimulation frequency that produces the greatest regulatory effects on depressive symptoms and physiological variables in this population will be used in a second longitudinal phase of the study.
This study will evaluate the short term effects of respiratory-gated transcutaneous vagus nerve stimulation on the regulation of cardiovagal activity, depressive symptomatology and immune function in subjects with major depression and determine the optimal stimulation frequency for this population.