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Published on: October 16, 2019
Disentangling acute motor deficits and adaptive responses evoked by the loss of cerebellar output
Nirvik Sinha1,2,3, Sharon Israely1, Ora Ben Harosh1
1Edmond and Lily Safra Center for Brain Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel.
Abstract:
Patients with cerebellar damage experience various motor impairments, but the specific sequence of primary and compensatory processes that contribute to these deficits remains unclear. To clarify this, we reversibly blocked cerebellar outflow in monkeys engaged in planar reaching tasks. This intervention led to a spatially selective reduction in hand velocity, primarily due to decreased muscle torque, especially in movements requiring high inter-joint torque coupling. When examining repeated reaches to the same target, we found that the reduced velocity resulted from both an immediate deficit and a gradually developing compensatory slowing to reduce passive inter-joint interactions. However, the slowed hand velocity did not account for the fragmented and variable movement trajectories observed during the cerebellar block. Our findings indicate that cerebellar impairment results in motor deficits due to both inadequate muscle torque and an altered motor control strategy for managing impaired limb dynamics. Additionally, impaired motor control elevates noise, which cannot be entirely mitigated through compensatory strategies.
Insights
Cerebellar damage impairs motor control by reducing muscle torque and altering movement strategies. The brain attempts to compensate, but this leads to slower, fragmented movements and increased motor noise.
Area of Science:
- Neuroscience
- Motor Control
- Cerebellar Function
Background:
- Cerebellar damage causes motor deficits, but the underlying mechanisms involving primary and compensatory processes are not fully understood.
- Understanding these processes is crucial for developing effective rehabilitation strategies for individuals with cerebellar disorders.
Purpose of the Study:
- To elucidate the sequence of primary and compensatory mechanisms contributing to motor impairments following cerebellar damage.
- To investigate how reversible cerebellar outflow blockade affects motor control during reaching tasks.
Main Methods:
- Reversible blockade of cerebellar outflow in monkeys performing planar reaching movements.
- Analysis of hand velocity, muscle torque, and movement trajectories during reaching tasks.
Main Results:
- Cerebellar blockade caused a spatially selective decrease in hand velocity, mainly due to reduced muscle torque, particularly in movements with high inter-joint coupling.
- Compensatory slowing was observed over repeated reaches, aimed at minimizing passive inter-joint interactions, but did not fully explain fragmented trajectories.
- Impaired motor control led to increased motor noise that could not be entirely compensated for.
Conclusions:
- Cerebellar impairment results in motor deficits from both insufficient muscle torque and altered motor control strategies for limb dynamics.
- Compensatory mechanisms are insufficient to fully mitigate motor deficits and increased noise caused by cerebellar damage.
- These findings provide critical insights into the neural basis of motor control and cerebellar dysfunction.
