The human body responds to inflammation, such as psoriatic skin lesions, by activating the cholinergic anti-inflammatory pathway. In patients with plaque psoriasis, this pathway is not sufficient to clear the skin lesions. Importantly, the vagus nerve, that is part of the anti-inflammatory pathway, also innervates the ear where it can be activated through non-invasive transcutaneous auricular vagus nerve stimulation (taVNS). This raises the research question if taVNS - added to standard of care - improves the symptoms of plaque psoriasis by augmenting the function of the cholinergic anti-inflammatory pathway. Thus, the aim of this project is to test the hypothesis that daily taVNS applied for 3 months results in anti-inflammatory actions and improvements in the Psoriasis Area and Severity Index (PASI). Potential anti-inflammatory actions of taVNS compared to a sham-taVNS control group will be assessed by plasma cytokine levels, flow cytometry, and cell culture experiments. This project is potentially significant, because it may demonstrate that taVNS lessens the symptoms of plaque psoriasis and, therefore, improves the quality of life of millions of patients.

An estimated 20% of psoriasis patients experience treatment failure. Afferent vagal nerve fibers that are part of the anti-inflammatory reflex sense inflammation, such as psoriatic skin lesions. The investigators' pilot data show that transcutaneous auricular vagus nerve stimulation (taVNS) activates afferent nerve fibers within the auricular branch of the vagus nerve to trigger anti-inflammatory reflex responses in healthy individuals. However, it is unknown if taVNS improves plaque psoriasis through the anti-inflammatory reflex. The lack of studies on taVNS in plaque psoriasis constitutes a missed opportunity to reduce treatment failures.

The long-term goal of this research is to establish a neuromodulatory approach to activate the anti-inflammatory reflex in patients with plaque psoriasis to lessen treatment failures. The objective of this study is to test the hypothesis that taVNS elicits anti-inflammatory reflex responses and reduces the severity of plaque psoriasis.

In a single-blinded randomized controlled clinical trial, participants will self-administer taVNS or sham-taVNS (control) daily for a duration of 3 months, while continuing their standard-of-care treatment. At baseline, 7 days, and 1, 2, and 3 months, clinical , autonomic, and inflammatory responses will be assessed.

At the conclusion of this study, the investigators expect to demonstrate anti-inflammatory reflex responses to taVNS and reduced severity of plaque psoriasis. These outcomes are expected to have important positive impact, because they are anticipated to reduce treatment failures in patients with plaque psoriasis.

Inclusion Criteria:

• 18 years or older
• Plaque psoriasis diagnosed by a dermatologist

Exclusion Criteria:

• pregnancy
• vestibulocochlear neuronitis or nerve damage
• cardiac arrhythmia
• epilepsy
• anticipated change in medication during the 3-month study period

Patients in both arms will not know in which of the two arms (active treatment or control group) they are randomized. The sham procedure is similar to the transcutaneous auricular vagus nerve stimulation (but does not involve the actual stimulation). Therefore, it is unlikely that patients are able to differentiate whether they are assigned to the control group or to the active treatment group.