Publication: Hemisphere specific impairments in reach-to-grasp control after stroke: effects of object size
Issued Date
2009-09
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Language
eng
ISSN
0888-4390
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Mahidol University
Rights Holder(s)
SAGE
Bibliographic Citation
Neurorehabilitation and Neural Repair. Vol.23, No.7 (2009), 679-691
Suggested Citation
Jarugool Tretriluxana, Gordon, James, Fisher, Beth E., Winstein, Carolee J. Hemisphere specific impairments in reach-to-grasp control after stroke: effects of object size. Neurorehabilitation and Neural Repair. Vol.23, No.7 (2009), 679-691. doi:10.1177/1545968309332733 Retrieved from: https://repository.li.mahidol.ac.th/handle/20.500.14594/10095
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Title
Hemisphere specific impairments in reach-to-grasp control after stroke: effects of object size
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Abstract
The notion that the left and right hemispheres are asymmetric for the control of skilled movements originally came from careful observations of human behavior.1,2 In a previous study with nondisabled adults, we identified manual asymmetries in grasp preshaping and transport-grasp coordination.3 In particular, each hand performed reach-to-grasp to different sized objects with grasp preshaping that was scaled to object
size. However, the process by which different objects were successfully procured was distinguishable for each hand. For example, the left hand exhibited anticipatory control of grasp aperture preshaping, whereas the right hand exhibited stronger transport-grasp coordination. These hand-specific effects provide support for the existence of manual asymmetries in reachto-grasp actions. However, extrapolation of these findings to
hemispheric specialization can be confounded by hand dominance, such that the stronger transport-grasp coordination found for the right hand may simply reflect more practice or experience4,5 with little relevance to hemispheric specialization. Alternatively, if we assume that manual asymmetries are not solely a reflection of hand dominance, well-designed investigations using patients with unilateral brain damage can be used to provide insight into hemispheric specialization.
Indeed, neuropsychological investigations of aiming movements in individuals with focal hemispheric stroke have provided important data about hemispheric specialization.6,7
Therefore, the purpose of this study was to investigate hemispheric specialization in reach-to-grasp actions with individuals
post focal hemispheric stroke using the same experimental protocol used in our previous study.3 An important consideration in investigations of hemispheric specialization is that it is well known that both hemispheres
participate in the control of unimanual goal-directed movements including reach-to-grasp actions. Imaging studies consistently show bilateral activation during both preparation
and execution of unilateral finger movements.8-10 Ipsilateral contributions to unilateral movements have also been demonstrated using transcranial magnetic stimulation (TMS).11 For example, a recent TMS study demonstrated an inhibitory communication between primary motor areas of the 2 hemispheres prior to movement initiation.12,13 This inhibition is likely mediated
through excitatory transcallosal connections, which terminate onto inhibitory interneurons.13-15 Kobayashi and coworkers provide further evidence for the inhibitory interhemispheric interaction in nondisabled adults with combined functional magnetic resonance imaging (MRI) and TMS.16
With evidence for bilateral activity during unimanual movements, a purely contralateral control model provides little explanatory power for hemisphere-specific contributions previously demonstrated in nondisabled individuals.3 Instead, bilateral control, hereafter referred to as the bilateral model,
provides greater explanatory power for these previous findings in nondisabled individuals.3 The bilateral model includes the unique contributions of each hemisphere and the associated interhemispheric communication.
To test the bilateral model predictions of hemispheric specialization, we employed the same experimental protocol that we used previously but with a stroke-induced unilateral brain damage group. We reasoned that any deficits in the performance of the nonparetic, so-called “ipsilesional” upper extremity would be expected to reflect the unique contributions of each hemisphere, one of which is impaired, and the effects of altered interhemispheric communication known to occur after stroke.17 After hemisphere damage, transcallosal communication effectively downregulates the damaged hemisphere and upregulates the nondamaged hemisphere. This imbalance from
the stroke lesion increases the probability for hemispherespecific effects to emerge, compared to that in the nondisabled case. Because these deficits are apparent for the ipsilesional limb and are not evident in movements of matched nondisabled participants they can provide a unique window into hemispheric specialization.
There is considerable evidence for hemisphere-specific patterns of deficits in goal-directed aiming movements performed
by the ipsilesional hand of individuals with unilateral stroke.18-22 Our previous findings from right-handed nondisabled individuals
showed an earlier aperture preshaping response in the nondominant left hand and more coordinated control of hand
reaching and finger grasping in the dominant right hand.3 If each hemisphere contributes uniquely to the control of reachto-grasp movements, we expect that hemisphere-specific deficits will be observed in the performance of the ipsilesional hand. If the bilateral model is supported, our hypothesis is that participants with a dominant left hemisphere stroke will exhibit deficits in aperture preshaping in the left hand. In contrast, participants with a nondominant right hemisphere stroke will exhibit deficits in the coordination of hand reaching and finger grasping in the right hand.