Does Transcutaneous Vagal Nerve Stimulation Improves Fear Extinction in Humans

A recent study with rats showed that electrical stimulation of the vagus nerve (VNS) facilitates extinction of fear (Pena, Engineer, \& McIntyre, Biological Psychiatry, 2013). The hypothesized mechanism is that VNS both enhances memory consolidation (by increasing noradrenergic neurotransmission) and reduces anxiety (thus: preventing fear responses to the CS which may re-consolidate the fear memory). The effect was only apparent when VNS occurred during exposure of the fear conditioned stimulus (CS), and not when stimulation was given immediately following exposure. These results may have implications for the treatment of anxiety disorders in humans. However, until recently, the only means to investigate the effects of VNS on human fear learning would have required the invasive implantation of vagus nerve stimulators. This has fortunately changed, as a non-invasive transcutaneous VNS device has been approved for use in the E.U. for the treatment of psychological disorders. This study proposes to use a t-VNS to investigate its effects on fear learning and extinction in (healthy) humans. Previous research has only investigated the effects it has on human mood and memory. The results obtained suggest that it reduces negative affect and enhances memory, findings which are consistent with those reported for rats. It is thus reasonable to expect that t-VNS will facilitate the extinction of fear in humans. The present study aims to answer the following research questions: Does t-VNS during extinction training: 1. accelerates extinction curves 2. reduces spontaneous recovery of previously extinguished fear 3. reduce re-acquisition of fear 4. reduce generalization of fear to other stimuli that resemble the CS+? 5. facilitates the generalization of inhibitory learning to stimuli that resemble the CS-?