Psychedelics seem to mess with this system in one of two ways: In some cases, the brain’s predictions about reality go haywire, as when you see faces in the clouds or musical notes leap to life or something happens to convince you you’re being followed. Common on LSD or psilocybin, this kind of magical thinking might occur when top-down predictions generated by the brain are no longer adequately constrained, or corrected, by bottom-up information arriving from the world via the senses.
