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Impairments of reaching movements in patients without proprioception. I. Spatial errors
J Gordon1, M F Ghilardi, C Ghez
1Center for Neurobiology and Behavior, New York State Psychiatric Institute, New York.
Journal of Neurophysiology
|January 1, 1995
Summary
Patients with proprioceptive deficits exhibit significant spatial errors in reaching movements due to impaired movement planning. These errors, particularly in movement extent, are exacerbated by the inability to sense limb position and are linked to altered velocity and acceleration profiles.
Area of Science:
- Neuroscience
- Motor Control
- Human Physiology
Background:
- Proprioception is crucial for accurate motor control, enabling the sense of limb position and movement.
- Large-fiber sensory neuropathy can severely impair proprioception, leading to motor deficits.
- Understanding these deficits is key to characterizing the roles of sensory feedback and motor planning in movement.
Purpose of the Study:
- To analyze spatial errors in a planar reaching task in patients with severe proprioceptive deficits.
- To differentiate errors arising from movement planning and execution versus feedback control impairments.
- To characterize the specific spatial inaccuracies in reaching movements due to proprioceptive loss.
Main Methods:
- Three patients with proprioceptive deficits and normal muscle strength were studied.
- A planar reaching task was employed where subjects moved a hand to targets on a digitizing tablet.
- Visual feedback of hand position during movement was prevented to isolate planning and execution.
- Movement paths were recorded and analyzed for spatial errors, direction, extent, velocity, and acceleration.
Main Results:
- Patients demonstrated significantly larger spatial errors in movement direction and extent compared to controls.
- Directional errors were present from movement onset, indicating planning impairments.
- Hand paths in patients showed increased curvature and secondary movements.
- Systematic, direction-dependent errors in movement extent were prominent in patients, linked to altered velocity and acceleration profiles.
Conclusions:
- Severe proprioceptive deficits lead to substantial impairments in the planning and execution of reaching movements.
- The inability to sense limb position significantly impacts the accuracy of movement extent.
- Patients' motor control strategies show similarities to controls but are less adaptable to directional variations, highlighting the critical role of proprioception in refining motor output.