Vagus Nerve Stimulation Improves Severe Depression by 70%, Major US Trial Finds
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On the subject of the vagus nerve and the brain...
There has been a strong correlation between the vagus nerve and Parkinson's. The vagus nerve goes from the gut straight to the brainstem, that has a neural pathway to the substantia nigra which produces dopamine for muscular control. People who have had their vagus nerve cut due to severe stomach ulcers (vagotomy) have been shown to have a significantly lower rate of Parkinson's. One thought is that the nerve acts as a pathway for toxins to travel from the gut straight to the brain (Braak's Hypothesis). There are also studies into dementia and a "silenced" vagus nerve.
Normally, the vagus nerve tells a part of the brainstem (the locus coeruleus) to spray the hippocampus with a chemical called norepinephrine. This chemical acts like a shield, lowering brain inflammation and protecting memory. If the vagus nerve is damaged or quieted by gut toxins, the hippocampus loses this protective shield, leaving it vulnerable to dementia damage.