Gut-First or Brain-First?¶
Run the Gut-First or Brain-First? MicroSim Fullscreen
About This MicroSim¶
This is a model of competing ideas, not a proven map of Parkinson's disease. In Parkinson's, a protein called alpha-synuclein misfolds and clumps inside neurons, and the clumping may spread from one neuron to connected neurons (prion-like spread). Scientists disagree about where the first clumps form.
- The gut-first (body-first) idea says the process can start in the gut wall, climb the vagus nerve to the brainstem, and reach the dopamine neurons of the substantia nigra later. It predicts constipation and acting out dreams years before movement symptoms.
- The brain-first idea says the process starts inside the brain and reaches the dopamine neurons early. It predicts movement symptoms first, with gut problems later.
The body diagram colors each region as pathology builds up there, and red lines show the path the spread takes. The timeline below shows when each symptom appears. The dashed red line marks diagnosis, when movement symptoms begin. All years are made-up "model years" chosen to show the order of events.
How to Use¶
- Leave the starting point on Gut-first and press Start. Watch the spread climb the vagus nerve.
- When the run ends, read the status line: how many model years before diagnosis did constipation begin?
- Switch to Brain-first and run it again. Which symptom comes first now? When does constipation appear?
- Check Cut the vagus nerve and run both routes. In which route does cutting the nerve change what happens in the brain?
- Use Speed to slow the run down, and Reset to return to the starting settings.
Learning Objective¶
Bloom level: Analyze and Evaluate. The learner will compare the gut-first and brain-first hypotheses of Parkinson's disease by the order of early symptoms each predicts, and explain why cutting the vagus nerve matters only in the gut-first route.
Iframe Embed Code¶
<iframe src="https://aaryavvatts-lab.github.io/gut-brain-textbook/sims/ch14-two-routes/main.html" height="672px" width="100%" scrolling="no"></iframe>
Lesson Plan¶
Grade level: 9 to 12 (biology, anatomy and physiology, health science, or psychology)
Duration: 25 to 30 minutes
Activity:
- Warm-up (3 minutes). Ask: "Could a brain disease start somewhere other than the brain?" Students write one reason it might and one reason it might not.
- Explore (8 minutes). In pairs, students run both routes and record the model year when constipation, acting out dreams, smell loss, and movement symptoms begin.
- Test a prediction (6 minutes). Before checking "Cut the vagus nerve," each pair predicts what will happen in each route. Then they test it and compare with the 2019 mouse study and the mixed human vagotomy studies in Chapter 14.
- Debate (6 minutes). Half the class argues for gut-first and half for brain-first, using only evidence from the chapter. Then everyone names one piece of evidence that would settle the question.
- Limits (3 minutes). Read the "What this model leaves out" box and name one way the model oversimplifies real Parkinson's.
Assessment questions:
- Which early symptoms does the gut-first hypothesis predict before diagnosis, and why?
- Why does cutting the vagus nerve block the spread in the gut-first route but not change the brain-first route?
- A person had constipation for 12 years before a Parkinson's diagnosis. Does that prove their disease started in the gut? Explain.
- Name one kind of human study that could help decide between the two hypotheses.