Scientific Studies Library

Browse clear summaries of published research across VNS, taVNS, sleep, safety, autonomic regulation, heart rate variability, brain pathways, inflammation and gut–brain communication.

Each summary explains the research question, study design, main findings, limitations and source details.

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ABOUT THE SUMMARIES

Clear summaries, with context kept visible.

Each study page separates what was studied, what was found and what the paper cannot establish. Full reference details and links to the original source are included.

The original paper remains the primary scientific source.

STUDY SUMMARIES

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Explore all published study summaries, organised by research area.

taVNS research

SYSTEMATIC REVIEW & META-ANALYSIS2025

Transcutaneous Auricular Vagus Nerve Stimulation in Insomnia: A Systematic Review and Meta-Analysis

Helen Michaela de Oliveira, Mariano Gallo Ruelas, Camilo André Viana Diaz, Guilherme Oliveira de Paula, Pablo Ramon Fruett da Costa, Julie G. Pilitsis

Neuromodulation: Technology at the Neural Interface

A systematic review and meta-analysis of six studies involving 336 participants reported improvements in sleep quality and insomnia severity, while rating the certainty of evidence as low to very low.

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SYSTEMATIC REVIEW & META-ANALYSIS2022

Safety of Transcutaneous Auricular Vagus Nerve Stimulation (taVNS): A Systematic Review and Meta-Analysis

Angela Yun Kim, Anna Marduy, Paulo S. de Melo, Anna Carolyna Gianlorenco, Chi Kyung Kim, Hyuk Choi, Jae-Jun Song, Felipe Fregni

Scientific Reports

A review of 177 studies involving 6,322 participants found no difference in overall adverse-event risk between active taVNS and control conditions, while noting incomplete adverse-event reporting across much of the literature.

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HUMAN NEUROIMAGING / fMRI2015

Non-invasive Access to the Vagus Nerve Central Projections via Electrical Stimulation of the External Ear: fMRI Evidence in Humans

Eleni Frangos, Jens Ellrich, Barry R. Komisaruk

Brain Stimulation

A human fMRI study in 12 healthy adults found that electrical stimulation at the left cymba conchae engaged central pathways associated with the vagus nerve.

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SYSTEMATIC REVIEW2023

A Systematic Review of the Effects of Transcutaneous Auricular Vagus Nerve Stimulation on Baroreflex Sensitivity and Heart Rate Variability in Healthy Subjects

Danesh Soltani, Bayan Azizi, Sepehr Sima, Kiarash Tavakoli, Negin Sadat Hosseini Mohammadi, Abdol-Hossein Vahabie, Kaveh Akbarzadeh-Sherbaf, Ali Vasheghani-Farahani

Clinical Autonomic Research

A systematic review found changes across several HRV measures in taVNS studies, while highlighting substantial variation between stimulation protocols and study designs.

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Foundational models and methods

THEORETICAL PAPER1995

Orienting in a Defensive World: Mammalian Modifications of Our Evolutionary Heritage. A Polyvagal Theory

Stephen W. Porges

Psychophysiology

An influential and debated theoretical paper proposing a polyvagal framework for autonomic state, defensive responses and social engagement.

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CONCEPTUAL MODEL2000

A Model of Neurovisceral Integration in Emotion Regulation and Dysregulation

Julian F. Thayer & Richard D. Lane

Journal of Affective Disorders

A model connecting brain networks, emotional regulation, autonomic flexibility, heart rate variability and vagal activity.

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METHODOLOGICAL STANDARDS1996

Heart Rate Variability: Standards of Measurement, Physiological Interpretation, and Clinical Use

Task Force of the European Society of Cardiology and NASPE

Circulation

A foundational methodological reference for heart rate variability measurement, terminology and interpretation.

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Inflammation and neuroimmune signalling

PRECLINICAL EXPERIMENTAL RESEARCH2000

Vagus Nerve Stimulation Attenuates the Systemic Inflammatory Response to Endotoxin

L. V. Borovikova et al.

Nature

A preclinical experiment using cell and animal models to examine how vagus nerve stimulation influenced systemic inflammatory signalling.

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FOUNDATIONAL REVIEW2002

The Inflammatory Reflex

Kevin J. Tracey

Nature

A foundational paper describing how neural pathways may detect and regulate inflammatory activity through reflex-like mechanisms.

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REVIEW2005

The Cholinergic Anti-Inflammatory Pathway

Valentin A. Pavlov & Kevin J. Tracey

Brain, Behavior, and Immunity

A review of cholinergic signalling and its proposed role in cytokine regulation and immune activity.

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Implanted vagus nerve stimulation

IMPLANTED VNS / RANDOMIZED CONTROLLED TRIAL2005

Vagus Nerve Stimulation for Treatment-Resistant Depression: A Randomized, Controlled Acute Phase Trial

A. John Rush et al.

Biological Psychiatry

A randomized controlled acute-phase trial examining implanted vagus nerve stimulation in treatment-resistant depression.

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Gut–brain communication

REVIEW2011

Gut Feelings: The Emerging Biology of Gut–Brain Communication

Emeran A. Mayer

Nature Reviews Neuroscience

A major review of neural, hormonal, microbial and immune communication between the gut and brain.

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RESEARCH TOPICS

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