Why does being sick make you so exhausted – and why does that exhaustion sometimes outlast the illness itself? Today, neuroscientist Julia Kaltschmidt returns to the podcast to talk about the body's hidden "sickness reflex," the gut-brain circuitry behind it, and what those things might reveal about chronic fatigue.

Kaltschmidt, a Wu Tsai Neurosciences Institute faculty scholar and professor of neurosurgery at Stanford Medicine, is an expert on the enteric nervous system — the gut's own semi-independent network of 200 to 600 million neurons. She's leading a new Big Ideas in Neuroscience project mapping out exactly how the body tells the brain it's sick, alongside Luis de Lecea, an expert in the brain circuitry of sleep, and Christoph Thaiss, who studies communication between the gut, the immune system, and the brain.

The team believes that understanding the "reflex" of sickness fatigue could eventually lead to something patients with chronic fatigue and long COVID don't currently have: a real biomarker, and a path to treatment, for a condition that's too often been dismissed as "all in your head."

Learn More

• Big Ideas in Neuroscience tackle brain science of everyday life and more (Wu Tsai Neuro, 2026)
• Your gut – the second brain? (Our first conversation with Julia Kaltschmidt)
• The gut's 'second brain' (Stanford Medicine, 2026)
• Discovery sheds light on earliest development of gut motility (Wu Tsai Neuro, 2024)
• Neuroscience sheds light on childhood gut disorders (Wu Tsai Neuro, 2024)
• Could boosting gut–brain communication prevent memory loss? (Podcast episode with Christoph Thaiss)
• Why sleep keeps us young (Podcast episode with Luis De Lecea)
• New Science Shows Immune "Memory" in the Brain (Quanta Magazine, 2021)
• Insular cortex neurons encode and retrieve specific immune responses (Cell, 2021)

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