The Journal of Neurophysiology Vol. 80 No. 3 September 1998, pp. 1590-1597
Copyright ©1998 The American Physiological Society

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Time-Dependent Motor Memory Processes in Amnesic Subjects

Reza Shadmehr¹, Jason Brandt², and Suzanne Corkin³

¹ Department of Biomedical Engineering and ² Department of Psychiatry and Behavioral Sciences, Johns Hopkins University, Baltimore, Maryland 21205-2195; and ³ Department of Brain and Cognitive Sciences, and the Clinical Research Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

Shadmehr, Reza, Jason Brandt, and Suzanne Corkin. Time-dependent motor memory processes in amnesic subjects. J. Neurophysiol. 80: 1590-1597, 1998. 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 five subjects 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 visuomotor 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 field was imposed on the hand. With practice in field A, H.M. and other AMN subjects developed aftereffects and maintained these aftereffects for 24 h. To quantify postpractice 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 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 patterns of motor memory perseveration, as measured at 5 min and 4 h, were not different in the AMN and normal control groups.

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