“In mirror therapy (MT), a mirror is used to create a reflective illusion of an affected limb in order to trick the brain into thinking movement has occurred without pain, or to create positive visual feedback of a limb movement. It involves placing the affected limb behind a mirror. The mirror is positioned so the reflection of the opposing limb appears in place of the hidden limb.^[1]

Clinicians can create this illusion with a mirror box. This device is simply a box with a mirror in the center allowing the hands to be placed on either side of the mirror. The affected limb is always covered while the unaffected limb is placed on the other side so its reflection can be seen on the mirror.

Mirror therapy was first proposed as a potential therapeutic intervention by Vilayanur S. Ramachandran to help alleviate Phantom limb pain, a condition in which patients feel they still have a pain in the limb after amputation. 

Ramachandran and Rogers-Ramachandran^[2] first devised the technique in an attempt to help those with phantom limb pain resolve what they termed a ‘learned paralysis’ of the painful phantom limb. The visual feedback, from viewing the reflection of the intact limb in place of the phantom limb, made it possible for the patient to perceive movement in the phantom limb. Their hypothesis was that every time the patient attempted to move the paralysed limb, they received sensory feedback (through vision and proprioception) that the limb did not move. This feedback stamped itself into the brain circuitry through a process of Hebbian learning, so that, even when the limb was no longer present, the brain had learned that the limb (and subsequent phantom) was paralysed. To retrain the brain, and thereby eliminate the learned paralysis, Ramachandran and Rogers-Ramachandran created the mirror box.^[3]

You can read more about mirror therapy through Stephen Sumner’s experience who lost his limb some years ago. “

full article here: https://www.physio-pedia.com/Mirror_Therapy