Transcutaneous vagal nerve stimulation effects on the salience network in patients with amnestic mild cognitive impairment

Abstract

AbstractBackgroundBetter treatments are needed to improve cognition and reduce the disability associated with MCI and Alzheimer’s disease (AD). Transcutaneous vagal nerve stimulation (tVNS) may impact brain networks relevant to AD through multiple mechanisms: the vagus projects to the nucleus tractus solitarius (NTS) which in turn projects to the locus coeruleus (LC), the brain’s primary source of norepinephrine (NE). The NTS also projects directly to the hippocampus, as does the LC. Neuropathological data suggest that the LC may be an early site of AD pathology. Thus, tVNS may modify the activity of several networks that are impaired and that progressively deteriorate in patients with MCI and AD.Method24 patients with mild cognitive impairment (MCI) confirmed via diagnostic consensus conference (sources of info: Montreal Cognitive Assessment Test [MOCA], Clinical Dementia Rating scale (CDR), Functional Activities Questionnaire (FAQ) , Hopkins Verbal Learning Test – Revised [HVLT‐R] and medical record review) were assessed during rest using functional magnetic resonance imaging (fMRI) on a Siemens 3T scanner during tVNS (left tragus, n = 12) or under sham control conditions (ear lobe, n = 12).ResultDuring unilateral left tVNS, patients with MCI showed increased functional connectivity between nodes of the salience network, the anterior cingulate, and the supramarginal gyrus from both the right and left temporal poles.ConclusionIn patients with MCI, tVNS modified cognitively relevant brain networks whose degeneration predicts deterioration in AD. These findings demonstrate afferent target engagement of tVNS which carries implications for noninvasive therapeutic intervention in this population.