A rehabilitation chair was a device used in treating mental patients. In 2269, the mental hospital on Elba II had at least one rehabilitation chair which was used to relax the more violent patients. Former Fleet Captain Garth, after taking over the facility, modified the rehabilitation chair into a torture device.
Garth tortured both James T. Kirk and Donald Cory in the rehabilitation chair before Captain Kirk was able to regain control of Elba II. The rehabilitation chair was then converted back to its original use and was part of the treatment used to help cure Garth. (TOS: "Whom Gods Destroy")