The impact of unilateral brain damage on anticipatory force scaling when lifting everyday objects

Introduction: The ability to predict and anticipate the weight of everyday objects promotes smooth and skillful motor actions and affords economical force adaptation. An ongoing question is how unilateral brain damage influences this knowledge and, in particular, if there is a correlation with apraxia.

Methods: In the present study 27 subjects with unilateral brain damage (11 right-brain damage RBD, 16 left brain damage LBD) and corresponding control subjects were investigated. Subjects lifted 12 everyday objects (e.g. a tea cup, a cigarette box or a book) with a wide range of weights. Special finger sensors enabled the measurement of the grip forces exerted during grasping and lifting the objects. The grip force rate was calculated from the time course of the grip force. The maximum grip fore rate (GFRmax) that occurred shortly after contact of the object was considered a measure of the ability to predict the physical properties of the objects.

Results: In the control groups GFRmax was linearly related to the weight of the 12 objects. ANOVA for the LBD patients and corresponding control subjects revealed significantly lower slope (F=8.0, p=0.009) and R² (F=7.0, p=0.014) of the linear regression for the patients. The RBD patient exhibited only a trend for decreased weight anticipation compared to their control subjects (slope: F=4.3, p=0.053), R²: F<1, P>0.1). In the LBD patients the variables of the linear regression correlated strongly with an apraxia score of imitation (slope: R=0.63, p>0.009; versus R²: R=0.76, p=0.001) but less with a pantomime score (slope: R=0.21, p>0.1; versus R²: R=0.50, p=0.047;). Lesion analysis revealed a high frequency of lesions in the left inferior frontal (IFG) cortex and premotor cortex (PM) in those patients with impaired anticipation.

Discussion: Our results suggest that the left brain has a particular role in the ability to anticipate the physical properties of everyday objects during manipulation. Possibly left brain damage impairs the recall or the integration of memory for object properties into the action plan. Part of this process may also be of relevance for symptoms of apraxia as suggested by the significant correlation with apraxia scores. Structures in the IFG and PM may play a particular role in these processes.

Supported by the Deutsche Forschungsgemeinschaft DFG (HE 3592/6–1).