Mirror movements of the left arm following peripheral damage to the preferred right arm.

Cerebral damage which renders the preferred arm useless may lead patients to use their non-preferred arm for everyday tasks including writing. In these circumstances, mirror writing and other mirror movements may occur. The present study on 10 formerly right-handed patients was carried out to determine whether similar phenomena occurred when serious damage to the right arm itself had occurred, cerebral function remaining intact or any damage being coincidental and non-focal. The patients were asked to describe the events that had occurred when they started using their left hand, to carry out a number of writing tests, and to undertake two graphic tasks to assess directional motor preferences. Seven patients had executed mirror reversal of letters, and eight had experienced mirror phenomena when carrying out everyday tasks with their left hand; brief case histories are cited. No patient exhibited mirror writing on formal testing, and there was no evidence of alteration in the expected preference of direction in which graphic tasks were undertaken. The practical and theoretical implications of these observations are discussed.