In attempting to memorize a sentence about an action, such as "Pick up the glass," performing the action (motor encoding) results in better memory performance than simply memorizing the words (verbal encoding). Such enhancement of memory is known as the enactment effect. Several theories have been proposed to explain this phenomenon using concepts such as physical motor information associated with speed, form, amplitude of movement and/or movement representations involved in movement imaging, knowledge on manipulating tools, and spatial relationships in the enactment effect. However, there have been no cognitive neuropsychological studies investigating whether the enactment effect is crucially influenced by physical motor information or movement representations. To clarify this issue, we compared healthy adult control participants with two different types of apraxia patients. One patient with left hemisphere lesions caused by cerebral infarction had a disability involving multiple movement representations. The other patient showed symptoms of corticobasal syndrome and was not able to benefit from feedback on the accuracy of her motor movements during enactment. Participants memorized action sentences via either verbal or motor encoding and responded to recall and recognition tests. Results indicated that the patient with the movement representation deficits exhibited worse memory performance than the other patient or control participants following both verbal and motor encoding. Although the enactment effect was present during recall in both patients, the effect was not observed for recognition in the patient with severe movement representation deficits. These results suggest that movement representations are involved in encoding episodic memories of action. Moreover, the role of movement representations appears to depend on the form of retrieval that is being used.
Keywords: Apraxia; Enactment effect; Memory of actions; Movement representation; Subject-performed task.