https://www.npr.org/2004/04/23/1848385/ravels-bolero-a-product-of-dementia
"But in recent years, psychiatric researchers have offered another possible explanation. They suggest that the repetition in Boléro could reflect a manifestation of Alzheimer's disease, or some other serious mental deterioration.
Perseveration, an Alzheimer's symptom, is the obsession of repeating words or actions, and could have been the mastermind behind Ravel's infamous masterpiece."