Mentally Simulated Motor Actions in Neurorehabilitation. a Pilot Study in Multiple Sclerosis

Background: Motor imagery (MI) is defined as the mental movement execution without any actual movement. Mental movement time in healthy adults is similar to actual movement time (isochrony), while temporal discrepancies between actual and mental movements (anisochrony) could be an expression of neurological deficits on action representation. In a previous study, taking into account actions executed as fast and accurate as possible, we showed that in people with Multiple Sclerosis (PwMS) MI is not isochrony as in healthy subjects (HS), with mental movements faster than actual actions.

Objectives: Here, considering mental actions faster than the actual, we investigated if MI could be used to speed ME in PwMS.

Methods: 17 HS and 8 PwMS were recruited. They were seated in front of a table on which a sheet with two identical square targets was placed. They held a pen with the right and were initially positioned on the target on their left. During ME sessions, the subjects were requested to complete five actual cycles of pointing between the two targets as accurately and fast as possible. During MI sessions, the first four cycles were mentally performed, whereas the fifth was really executed. To calculate the differences between MI and ME the time to complete the first four cycles was compared. To evaluate the effect of MI on the ME the fifth cycle in the two conditions was compared. The time was calculated placing on the pen tip a marker recorded by a cameras BTS system. In each session, the size of the target randomly changed: 0.5x0.5, 1x1, 1.5x1.5, and 2x2 cm². 

Results: During ME, HS and PwMS similarly modulated movement duration with the target size, increasing the speed with larger targets, although PwMS were slower. Moreover no differences between ME and MI were found in NS, whereas in PwMS MI were always faster than ME. More importantly, in PwMS, during MI sessions, the fifth cycle was significantly faster than the fifth during ME sessions.

Conclusions: This result seems to indicate that, when an unbalance beetwen mental and actual execution of actions is present with mental movements faster, an effect of speeding on ME occurs. These results agreed with the hypothesis that MI, by recruiting the same motor neural structures involved during ME, could improve the same ME. This result open a new possibility in the field of neurorehabilitation in PwMS, that show mental and motor processes slower than HS and a related general decline of spatiotemporal characteristics.