Quantitative evaluation of mirror movements in adults with focal brain lesions

Mirror movements (MM), involuntary movements of homologous muscles opposite to unilateral limb activity, decrease in the course of motor development, but may reappear in adults after brain damage. To better characterize this type of acquired MM, grip forces of 36 healthy subjects and 35 patients suffering from focal brain lesions were compared. Holding force transducers in a pinch grip between thumb and index fingers of each hand, subjects had to repeatedly change the grip force in one hand, whilst the other (mirror) hand just had to prevent the manipulandum from dropping. In a second task, force changes had to be produced either in a symmetric or in an antiparallel manner. No significant group differences between patients and controls in the extent of coupling were found. During unimanual squeezing, only six patients had a co-activation in the pathologic range. Whilst performing bimanual asymmetric grip force changes, pathologic coupling was seen only in five patients. No association was found between the presence of pathologic MM and clinical or neuroanatomical features. Brain lesions in adults seem only rarely to be associated with pathologic MM. They might be non-specific and not related to the characteristics of the lesion.