In alien hand syndrome, one hand, most often the left, carries out purposeful actions its owner never chose: snatching a cigarette from the mouth, or unbuttoning a shirt as fast as the other hand buttons it. This episode separates the condition, also called Dr. Strangelove syndrome, from twitches and reflexes and explains intermanual conflict, where the hands work against each other. Patients still feel the limb as their own but lose the sense of agency, and many give it a name. One patient described by Rochelle Doody and Joseph Jankovic called hers Baby Joseph and scolded it like a mischievous infant.

The mechanism centers on the efference copy, the internal memo that tells the brain a movement was self-generated. When it fails, the brain reads the hand’s actions as caused by an outside force. The episode covers three variants: the callosal type seen after the corpus callosum is cut to treat epilepsy, the frontal type with compulsive grasping that Derek Denny-Brown described as positive tropism, and the posterior type in which the hand recoils and levitates. It ends with the workarounds patients use and the recovery that neuroplasticity can bring.

• Other names patients have given their hands, from Cheeky to the monster from the moon
• Tonic grasping, where patients must pry the fingers off objects with their other hand
• How approach and withdrawal systems in the brain normally hold each other in check
• Canes, oven mitts, and biofeedback alarms used to keep a rogue hand occupied
• Why one-sided stroke cases often improve significantly within a year