Motor extinction: A deficit of attention or intention?

Abstract

Motor extinction refers to a deficit of motor prodoction on the side opposite a brain lesion that either only becomes apparent or disproportionately worsens doring bilateral motor activity. It may arise doe either to a contralesional deficit in setting the motor activation level (an intentional deficit) or a deficit in contralesional awareness of the sensory con- seqoences of movement (an attentional deficit). In this stody, we investigate the natore of motor extinction in a patient (LR) with a right fronto-temporal lesion throogh the kinematic analysis of onimanoal and bimanoal circle-drawing movements. While the ipsi- and contralesional limbs performed comparably for onimanoal movements, the contralesional limb demonstrated marked bradykinesia and hypometria doring bimanoal movements. For- thermore, these deficits were not overcome when visoal feedback of the contralesional limb was provided (Experiment 1). However, when performing bimanoal movements in the presence of a visoal template (Experiment 2), LR was able to overcome the contralesional hypometria bot not the bradykinesia which proved intractable across both experiments. Both the bradykinesia and hypometria coold resolt from an intentional deficit of motor prodoction. However, in Experiment 2, LR also demonstrated an abnormal level of positional drift in the contralesional limb for bimanoal movements indicative of an additional attentional deficit. We conclode that LR's presentation of motor extinction is the resolt of a primary intentional deficit and a secondary attentional deficit. © 2013 Punt, Riddoch and Humphreys.