Non-invasive measurement of vagus activity in the brainstem – a methodological progress towards earlier diagnosis of dementias?

Abstract

In Alzheimer's disease (AD), mild functional disturbances should precede gross structural damage and even more clinical symptoms, possibly by decades. Moreover, alterations in the brainstem are supposed to occur earlier as cortical affections. Based on these considerations, we developed a new method aiming at the measurement of vagal brainstem functioning by means of evoked potentials after electrical stimulation of the cutaneous representation of the vagus nerve in the external auditory channel. In the current study, a first sample of patients with Alzheimer's disease (n = 7) and mild cognitive impairment (n = 3) were investigated (6m, 4f, range from 57 to 78 y, mean age 68.6 years). Vagus somatosensory evoked potentials (VSEP) were characterized by significantly longer latencies as compared to healthy age- and gender-matched controls (p < 0.05). Future large scale studies - also including preclinical stages of AD - have to assess the value of this non-invasive, fast and cheap method in the early diagnosis of neurodegenerative disorders.

Vagus Somatosensory Evoked Potentials – A Possibility for Diagnostic Improvement in Patients with Mild Cognitive Impairment

“…This finding is in line with previous observations as well as a priori hypotheses: the results of prolonged VSEP in patients with AD in comparison to HC as reported previously [27] could be confirmed by a separate sample of subjects and up-to-date technical equipment. In accordance with previous data, in both bipolar recordings of stimulation on the right side (C4-F4 and FZ-F4) a delay of EP could be shown for patients with AD ( fig.…”

“…In accordance with our previous studies [26,27], the following data refers to the recordings of the right channels during stimulation at the right tragus. An EP with unique and clearly identifiable peaks (P1, N1, and P2) was observed in 20 out of 27 HC with location, shape, latencies, and amplitudes well in line with cited studies.…”

“…This somatosensory potential is characterized by prolonged latencies with increasing age [26]. In addition, neurodegenerative processes such as AD have been found to further increase the latency of the potential, which -in contrast -could not be demonstrated for patients with cerebrovascular diseases [27,28].…”

Vagus nerve somatosensory evoked potentials in Parkinson’s disease

“…Likewise, drug effects cannot be ruled out. Finally, a previous study demonstrated latency prolongation in Alzheimer patients [10]. Thus, lack of formal assessment of cognitive impairment in our study may have led to inclusion of subjects with an Alzheimer comorbidity confounding the results.…”

Vagus somatosensory-evoked potentials are prolonged in patients with multiple sclerosis with brainstem involvement

“…Vagus somatosensory-evoked potentials (VSEP) were proposed for clinical practice as a possible means for the early and differential diagnosis for neurodegenerative diseases and the functional assessment of specific brainstem nuclei in those diseases [1,2]. The principle of VSEP is based on the electrical stimulation of the auricular branch of the vagus nerve (ABVN [3]) showing afferences not only to trigeminal nuclei, but also to the solitary tract nucleus as a central afference of the main vagus trunk [4].…”