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Long latency postural reflexes are under supraspinal dopaminergic control
B R Bloem1, D J Beckley, J P van Vugt
1Department of Neurology, University Hospital Leiden, The Netherlands.
Movement Disorders : Official Journal of the Movement Disorder Society
|September 1, 1995
Summary
Parkinson's disease disrupts postural reflexes. Dopamine pathways are crucial for adapting long latency (LL) reflexes to predictable and unpredictable balance challenges, with deficits observed in various parkinsonian syndromes.
Area of Science:
- Neuroscience
- Motor Control
- Systems Neuroscience
Background:
- Postural stability relies on long latency (LL) reflexes.
- Abnormal LL reflex scaling is observed in Parkinson's disease (PD).
- The role of dopaminergic pathways in this abnormality is unclear.
Purpose of the Study:
- To investigate the contribution of dopaminergic pathways to abnormal LL reflex scaling in PD.
- To examine LL reflex responses to predictable and unpredictable balance perturbations.
Main Methods:
- Studied LL reflexes in 22 patients with hypodopaminergic syndromes (neuroleptic-induced parkinsonism, young-onset PD, MPTP-induced parkinsonism) and 10 healthy controls.
- Applied predictable and unpredictable "toe-up" rotational perturbations of varying amplitudes (4 and 10 degrees).
- Measured tibialis anterior muscle LL reflex amplitudes.
Main Results:
- Healthy controls adapted LL reflex amplitude to predictable perturbation sizes and showed a large "default" response to unpredictable ones.
- Patients with neuroleptic-induced parkinsonism and young-onset PD had intact scaling for predictable stimuli but lacked the large default response to unpredictable stimuli.
- Patients with MPTP-induced parkinsonism showed absent LL reflex scaling in both predictable and unpredictable conditions.
Conclusions:
- Abnormal LL reflex scaling in PD is linked to reduced supraspinal dopaminergic influence.
- Dopaminergic pathways are critical for adaptive LL reflex responses to varying sensory input.
- Specific aspects of LL reflex control are differentially affected by dopaminergic deficits.