Impairment in Motor Imagery Progressively Increases with Multiple Sclerosis Disease Evolution

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 we showed that in patients with Multiple Sclerosis (PwMS) mental states of action are not as accurate as in healthy subjects (HS), with a dilated anisochrony between actual and mental movements.

Objectives: Here, we investigated if accuracy of mental movements could be related to the progression of the disease by evaluating MI in HS, clinically isolated syndrome (CIS) and PwMS at an early stage of the disease (RR). 

Methods: 12 HS, 17 CIS and 15 RR right-handed (Edinburgh Handedness Inventory) subjects were recruited. The following clinical scales were administered: Modified Fatigue Impact Scale (MFIS), Symbol Digit Modality Test (SDMT), 9 Hole peg test (9HPT), Kinesthetic and Visual Imagery Questionnare (KVIQ). Two condition were utilized: (1) Actual task (subjects squeezed a foam ball of 7 cm diameter with the dominant/non-dominant hand); (2) Mental task (subjects imagined with first perspective squeezing the ball with the dominant/non-dominant hand while holding it). Each trial lasted 4 minutes constituted of four consecutive periods of actual (or mental) task (30s) and rest (30s). Subjects were instructed to actually and mentally squeeze the ball at self-pace speed and the number of executed and imagined ball squeezes were recorded as reported by the subject. To examine eventual anisochrony between mental and actual movements, we computed the ratio actual/mental (R) of the number of the ball squeezes.

Results: As expected HS showed very slight anisochrony (R=1.19 for the right hand; R=1.21 for the left). Increasing anisochrony was computed as disease progression function: CIS subjects showed R=1.31 for the right hand and a R=1.37 for the left; RR subjects showed a R=1.48 for the right hand and R=1.60 for the left. 

Conclusions: Disease evolution seems at the origin of a progressive temporal dissociation between actual and imagined movements, more relevant for the non-dominant vs. dominant hand. This study tend to better clarify imagined actions in PwMS in order to possibly identify new rehabilitation strategies towards a better quality of life.