Invisible Grasps: Grip Interference in Anosognosia for Hemiplegia

Objectives: Previous findings suggest that, in anosognosic patients, their illusory motor experience is based on a “normal” motor intention and planning for the paralyzed limbs. However, these studies involved proximal muscles (shoulder) that can be mediated by the ipsilateral (intact) cortex more than distal muscles (fingers). In the present study, we asked whether, in anosognosic patients, the spared motor intention for the paralyzed limb can go as far as to influence kinematic parameters of distal movements. Method: Six hemiplegic patients (1 with and 5 without anosognosia) were required to reach and grasp with both hands targets of the same or different size, attached to a plinth. Maximum grip aperture of the right (intact) hand was recorded using an infrared motion capture system. All patients were evaluated with a specific battery for anosognosia and different neurpsychological test. Results: In the patient affected by anosognosia for hemiplegia, the grip aperture of the healthy hand was influenced by the intended (but not executed) movement of the plegic hand when the patient was trying to reach to grasp targets of different size, F(2, 14) = 11.87, p < .001. Patients affected by hemiplegia (without anosognosia) didn’t show any interference effect between the plegic and healthy hand even when they were asked to reach to grasp targets of different size. Conclusions: Our results confirm the hypothesis that a spared intention-programming system within the contralateral (damaged) cortex can go as far as to influence distal kinematic parameters of the healthy hand of patients affected by anosognosia for hemiplegia