Every brain sends signals back down its sensory hierarchies, and multisensory hubs feed all senses. Disinhibited feedback proposes that synesthesia happens when that returning traffic runs louder than usual, pushing what is normally subliminal into experience.
The theory’s strength is what it explains without new anatomy: psychedelics can induce synesthesia-like effects within an hour, far too fast to grow connections, and everyone shows weak cross-modal correspondences that look like the same channels whispering.
It competes with cross-activation as the standard account, and the field increasingly treats them as complementary rather than exclusive.