Cognitive prostheses interact with human cognitive abilities to extend an individual's capacity. They have application both with healthy functioning individuals and those who have suffered brain injury. In Alzheimer's disease (AD) patients experience progressive, but inconsistent deterioration across cognitive domains over the course of the illness. Some abilities are relatively well retained in AD and offer the clear potential for developing cognitive prostheses. Here we report the successful development of CIRCA, a system designed for people with AD based on maximizing their retained abilities and working round impaired ones to enable their participation in social interactions with caregivers. Specifically we demonstrate that it is possible to circumvent the working memory problems characteristic of AD and enable people to once more make choices and initiate topics of conversation. Benefits of the current system are temporally linked to contemporaneous use but highlight the potential for future development of prostheses with rehabilitative functions.