Investigating the role of peripheral nerve stimulation in mediating noninvasive neuromodulation effects in healthy volunteers

Noninvasive brain stimulation (NIBS) methods hold great promise for treating a wide range of neurological and psychiatric disorders. However, reported effects are often small, difficult to reproduce and the basic mechanisms underpinning them are not clear. It is widely assumed that effects of NIBS are solely caused by the electric field that it generates in the brain. However, NIBS also generate an electric field in the scalp. These fields are strong enough to initiate action potentials in peripheral nerves which could then indirectly modify brain activity. Two nerves that are likely to be stimulated in conventional NIBS electrode montages are the greater occipital nerve and the trigeminal nerve. Afferent fibers from these nerves travel to the brainstem where they project to the nucleus of the solitary tract and the locus coeruleus. These nuclei control the release of neurotransmitters in the cortex which can influence on many basic behavioral processes, including arousal and vigilance. This PhD project will investigate this mechanism in healthy volunteers. Understand the basic NIBS mechanism is the first step towards improving noninvasive neuromodulation methods, leading to improved therapies for neurological and psychiatric disorders.