Shadmehr R, Brandt J, and Corkin S (1998) Time dependent motor
memory processes in amnesic subjects. Journal of Neurophysiology,
Abstract Functional properties of motor memory change with the passage of time. The time-dependent nature of memories in humans has also been demonstrated for certain ``declarative'' memories. When the declarative memory system is damaged, are the time-dependent properties associated with motor memories intact? To approach this question, we examined 5 subjects with global amnesia, including subject H.M., and a group of age-matched control subjects. The task was to make reaching movements to visually presented targets. We found that H.M. (but not the other subjects) was significantly impaired in the ability to perform the visuomotor kinematic transformations required in this task: to accurately move the hand in the direction specified by a target. With extensive pratice, H.M.'s performance improved significantly. At this point, a force field was imposed on the hand. With practice in Field A, H.M. and other amnesic subjects developed aftereffects and maintained these aftereffects for 24 hours. To quantify post practice properties associated with motor memories, subjects learned Field B on Day 2 and at 5 min were retested in Field A. In both subject groups, performance in Field A was significantly worse than their own naive performance a day earlier. The aftereffects indicated persistence of the just learned but now inappropriate motor memory. After 4 hours of rest, subjects were re-tested in B. Performance was now at naive levels. The aftereffects at 4 hours indicated a reduced influence of the memory of Field A. The time-dependent patterns of motor memory perseveration, as measured at 5 min and 4 hours, were not different in the amnesic and normal control groups.