TIME-DEPENDENT MOTOR MEMORY PROCESSES IN AMNESIC SUBJECTS

The time-dependent nature of memories in humans has also been demonstr ated for certain ''declarative'' memories. When the declarative memory system is damaged, an the time-dependent properties associated with m otor memories intact? To approach this question, we examined five subj ects with global amnesia (AMN), 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 vis uomotor kinematic transformations required in this task, to accurately move the hand in the direction specified by a target. With extensive practice, H.M.'s performance improved significantly. At this point, a force held was imposed on the hand. With practice in field A, H.M. and other AMN subjects developed aftereffects and maintained these aftere ffects for 24 h. To quantify postpractice properties associated with m otor memories, subjects learned field B on day 2 and at 5 min were ret ested in field A. In both subject groups, performance in field A was s ignificantly worse than their own naive performance a day earlier. The aftereffects indicated persistence of the just-learned but now inappr opriate motor memory. After 4 h of rest, subjects were retested in B. Performance was now at naive levels. The aftereffects at 4 h indicated a reduced influence of the memory of field A. The time-dependent patt erns of motor memory perseveration, as measured at 5 min and 4 h, were not different in the AMN and normal control groups.