Signal Over Noise: How Transcutaneous VNS Optimizes Cognition with Dr. Ronan Denyer

Episode SummaryHost Dr. Michael Passmore (Clinical Associate Professor, Department of Psychiatry, University of British Columbia) sits down with Dr. Ronan Denyer, a postdoctoral fellow at the Coactions Lab in Brussels. Dr. Denyer completed his PhD in neuroscience at UBC under Dr. Lara Boyd, and his research sits at the intersection of brain stimulation, neuroimaging, and behavioral neuroscience. In this episode, they take a deep dive into transcutaneous vagus nerve stimulation (tVNS) — what it is, how it works, and what it could mean for the future of cognitive enhancement and neurological treatment.Key Topics CoveredDr. Denyer's background — From Trinity College Dublin to UBC to Brussels, how a final-year undergraduate project set him on the path of brain stimulation researchThe locus coeruleus (LC) — Why this tiny, blue-colored brainstem nucleus with far-reaching noradrenergic projections is one of neuroscience's most intriguing structuresTranscutaneous vagus nerve stimulation (tVNS) — How stimulating specific parts of the outer ear (the cymba conchae and tragus region) can non-invasively activate the vagus nerve → nucleus tractus solitarius → locus coeruleus pathwaytVNS vs. TMS vs. tDCS — Key comparisons between these neuromodulation approaches and why tVNS offers a unique real-time biomarker advantage via pupillometryPerceptual decision-making study (Brain Stimulation journal) — How tVNS boosted accuracy on a random dot motion task without slowing reaction times, supporting the gain hypothesis over the urgency hypothesis of LC function; the "rescue effect" seen after errorsThe drift-diffusion model — How modeling revealed tVNS increases the drift rate (evidence accumulation speed), explaining the accuracy improvementtVNS + TMS combined study — Evidence that tVNS increases corticospinal excitability during stimulation (online effect), with pupillometry confirming LC engagement; intriguing finding that MEP changes and pupil changes were not correlated, hinting at potential sub-nodes within the LCClinical translation potential:Stroke rehabilitation — Pairing tVNS bursts with motor therapy to promote plasticity onlineADHD — The tonic/phasic LC firing model and the explore-vs-exploit hypothesis; why elevated tonic LC firing may underpin attentional difficultiesParkinson's disease — LC degeneration as an early biomarker; tVNS + pupillometry as a potential low-cost screening tool for preclinical Parkinson's; targeting non-motor symptomsAnxiety and PTSD — Emerging hypotheses linking LC dysfunction to these conditionsUpcoming research — The KinArm forced-response reaching task: examining how tVNS shifts the speed-accuracy curve and modulates movement vigor, with implications for stroke rehabKey Concepts ExplainedTermPlain-language meaningtVNSNon-invasive stimulation of the ear to activate the vagus nerve and the brain's noradrenaline systemLocus coeruleusSmall brainstem nucleus; the brain's primary source of noradrenaline; modulates attention, arousal, and decision-makingGain hypothesisLC noradrenaline boosts signal-to-noise ratio, improving perceptual accuracy without speeding up responsesUrgency hypothesisLC increases response speed at the cost of accuracy (not supported by this study)PupillometryMeasuring pupil size as a proxy for LC activityMotor evoked potential (MEP)A muscle twitch elicited by TMS; used to measure corticospinal excitabilityDrift-diffusion modelA mathematical framework for modeling perceptual decision processesTonic vs. phasic LC firingTonic = baseline arousal level; phasic = task-triggered bursts that sharpen perceptionPapers ReferencedXiang et al. — Transcutaneous Vagus Nerve Stimulation Boosts Accuracy During Perceptual Decision Making, Brain Stimulation https://pubmed.ncbi.nlm.nih.gov/40311845/Dr. Denyer's tVNS + TMS corticospinal excitability study (recently published) https://journals.physiology.org/doi/full/10.1152/jn.00008.2026Connect & Learn MoreHost: Dr. Michael Passmore, University of British Columbia, Department of PsychiatryGuest: Dr. Ronan Denyer, Coactions Lab, Brussels (formerly UBC, Lara Boyd Lab)