Vagus nerve and bidirectional gut-brain signalling

Broadcast from KSQD, Santa Cruz on 9-18-2025:

• Dr. Dawn opens by establishing her psychobiology background and introducing the neurohormonal axis connecting mind and body. She describes revolutionary research published in Nature Neuroscience showing that simply seeing sick people in virtual reality triggers actual immune responses. The study used VR avatars displaying infection symptoms approaching participants, measuring brain activity with EEG and fMRI while analyzing blood samples for immune cell changes.
• The research demonstrates that infectious avatars approaching in virtual reality activate the same immune pathways as actual flu vaccination. Brain areas including the salience network and peripersonal space system detect potential threats and communicate with the hypothalamus to trigger white blood cell activation. Proximity matters - threats 20 feet away don't trigger responses, but approaching threats do.
• Dr. Dawn explains the sophisticated methodology, including 128-channel EEG monitoring and flow cytometry analysis of immune markers. Participants showed faster reaction times when infectious avatars approached compared to neutral ones, demonstrating subconscious threat assessment. The study reveals built-in disgust responses that evolved to protect against pathogens. She comments on how her medical training rewire the protective disgust reaction through repeated exposure..
• She transitions to discussing stress effects on gastrointestinal function, explaining how the gut-brain axis operates through the vagus nerve and neurohormonal pathways. The adrenal glands produce both immediate epinephrine responses and longer-term cortisol release, with chronic stress leading to digestive disruption, increased intestinal permeability, and microbiome changes that can trigger food sensitivities and autoimmune conditions.
• Dr. Dawn details the difference between acute and chronic stress responses in the gut. Acute stress redirects energy from digestion for fight-or-flight responses, while chronic stress causes mast cell activation, histamine release, mucus layer thinning, and bacterial overgrowth. These changes can lead to irritable bowel syndrome, increased food allergies, and even celiac disease in genetically susceptible individuals.
• The discussion covers various brain networks including the default mode network active during rest, the central executive network for problem-solving, and the salience network that switches between them when detecting important stimuli like threats, food, or reproductive opportunities. Functional MRI studies show these networks' activity patterns and their connections to immune system regulation through the hypothalamus.
• Dr. Dawn emphasizes practical implications for modern life, warning that constant screen exposure and doom-scrolling activate chronic stress responses unnecessarily. She recommends avoiding phones upon waking, spending time outdoors, wearing amber glasses for evening screen use, and practicing specific breathing techniques - inhaling for 5 counts, holding for 5, exhaling for 5, holding for 5 - to regulate nervous system activation and reduce inflammatory responses.