I've only heard the burnt toast thing in relation to a patient Dr. Wilder Penfield treated for recurrent seizures, where she would smell burnt toast before an episode. This led to developing the Montreal Procedure for epilepsy treatment.

Obligatory Heritage Minute link: https://youtu.be/pUOG2g4hj8s?si=KcjNhMEwIL4ywkkY

Brief info article: https://www.sciencedirect.com/science/article/abs/pii/S1525505018301677