Recently, the vagus nuclei in the brainstem have come into the focus of interest in psychiatric and neurological research mainly for two reasons: Firstly, their function is altered early in the course of Alzheimer's disease (AD; Parvizi et al., 2001). Secondly, in a small pilot study the electrical stimulation of the left vagus nerve in the neck by means of an implanted stimulator has shown to improve cognitive impairments in patients with AD (Sjogren et al., 2002).

Based on these findings a method for the non-ionvasive measurement of far-field potentials from the vagus nuclei evoked by means of an electrical stimulation via a peripheral branch of the nerve in the outer ear is a potentially interesting diagnostic procedure.

Vagus Sensory Evoked Potentials (VSEP) can be elicited in a reliable manner in younger and elderly healthy subjects. VSEP-latencies have been found to increase with age in healthy subjects. In a first clinical application, VSEP-latencies in patients with mild to moderate AD were found to be prolonged as compared to age-matched healthy participants.

This new, none-invasive measure is very easy to apply and may be a disease marker for AD, possibly also in preclinical stages. Further studies are necessary which systematically investigate changes in VSEP measures in patients with neurodegenerative disorders in order to elucidate their diagnostic specifity and validity.