We quantitatively examined the motor imagery ability using bimanual circle-line coordination task (BCT) in stroke patients and clarified the relationship between motor imagery ability and motor function of hemiplegic upper limbs and amount of the use of paralyzed limbs.

Thirty-one stroke patients participated. Tasks included unimanual-line (UL) which involved drawing a straight line on the non-paralyzed side, and imagery circle-line (ICL) which involved drawing a straight line on the non-paralyzed side, during imagery drawing on the paralyzed side using a tablet PC. Each task was carried out in 3 sets of 12seconds. Drawn linear trajectory was decomposed at every cycle and ovalization was calculated using the formula: Ovalization Index (OI)=Standard deviation of X axis/Standard deviation of Y axis×100(%). The value obtained by subtracting OI of UL from OI of ICL was defined as the ability of motor imagery (ImageOI). Fugl–Meyer motor assessment (FMA), amount of use (AOU), and quality of motion (QOM) of motor activity log (MAL) were the 3 variables used for cluster analysis. The explanation variable was Image OI, parametric variables were AOU and QOM, and the objective variable was FMA, and mediation analysis was performed.

Cluster 1 (FMA<26 points) and Cluster 2 (FMA ≥ 26 points) were formed. In Cluster 2, significant single correlations were found between ImageOI and FMA, AOU, and QOM. When AOU and QOM were mediated between ImageOI and FMA, there was no significant direct correlation between ImageOI and FMA, and a significant indirect effect of AOU and QOM was observed (P<0.01, bootstrap method).

In stroke patients with moderate to mild movement disorder, the motor imagery ability directly affects the amount of use of hemiplegic upper limbs and their quality of motion in daily life. Moreover, it indirectly influences the motor functions via those parameters.