Mentally represented motor actions in normal aging: III. Electromyographic features of imagined arm movements

Motor imagery is a cognitive process during which subjects mentally simulate movements without actually performing them. Here, we investigated the temporal and electromyographic (EMG) features of imagined arm movements in healthy elderly adults. Twelve young (mean age: 24.0+/-1.3 years) and 12 elderly (mean age: 67.0+/-4.5 years) participants executed and mentally simulated, with their right and left arms and as fast and as accurately as possible, arm pointing movements between three targets located in the frontal plane. We used the mental chronometry paradigm as an indicator of the accuracy of the motor imagery process (i.e. isochrony between executed and imagined movements) and the EMG activity of four arm muscles (anterior deltoid, posterior deltoid, biceps brachii, triceps brachii) during imagined actions as an indicator of the ability to generate purely mental actions. Our findings indicated that young and elderly participants mentally simulated arm movements without activating (i.e. above the baseline level) the muscles of the right or the left arm which are involved in the execution of the same movements. This finding suggests that young and, notably, elderly adults are able to generate covert actions without any overt component. However, we found that motor imagery accuracy (i.e. the temporal correspondence between executed and imagined movements) was significantly deteriorated in elderly adults. We suggest that elderly adults use efferent copies of motor commands to generate motor representations; however, this ability is progressively deteriorated in the aging brain. Therefore, we propose using motor imagery cautiously for motor rehabilitation in the elderly.