This neurological condition makes people deny their own limbs

Somatoparaphrenia is a rare delusion in which a person denies that one of their limbs, or an entire side of their body, belongs to them — even when shown direct proof. Patients don't just forget the limb is theirs; they invent an explanation for whose it actually is, sometimes elaborate enough that they'll treat the limb as if it belonged to a separate being.

The condition was named in 1942 by the neurologist Josef Gerstmann, combining the Greek para ("against") and phren ("mind") with soma ("body"). It shows up almost always on the left side, and it's usually paired with paralysis of that side plus anosognosia — a total lack of awareness that the paralysis exists at all.

One treatment, mirror therapy, has patients look at the disowned limb reflected in a mirror; while they're looking, they'll often agree the limb belongs to them. The effect doesn't last. Take the mirror away, and the sense of ownership vanishes again, because the delusion is rooted in a first-person body model that reinstating a third-person view can't permanently update.

Previously:

• Exploring the bizarre world of the psychiatric condition called "Glass Delusion"
• Fairytale mushrooms cause "lilliputian hallucinations" of tiny people