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Operant conditioning of rat H-reflex affects motoneuron axonal conduction velocity
1Wadsworth Center, New York State Department of Health, Albany 12201, USA. carpj@wadsworth.org
Experimental Brain Research
|February 24, 2001
Summary
Operant conditioning of the soleus H-reflex in rats led to an 8% decrease in motoneuron axonal conduction velocity in successful HRdown conditioning. This suggests neuronal plasticity contributes to learning and motor control.
Area of Science:
- Neuroscience
- Motor Control
- Behavioral Plasticity
Background:
- Operant conditioning can modify reflex activity.
- The H-reflex is a direct measure of motoneuron excitability.
- Previous studies suggested neuronal plasticity underlies operant conditioning of the H-reflex.
Purpose of the Study:
- To assess the impact of H-reflex operant conditioning on motoneuron axonal conduction velocity in rats.
- To investigate the location of neuronal plasticity in operant conditioning.
- To compare conditioning mechanisms across species.
Main Methods:
- Rats underwent operant conditioning (HRup, HRdown) or control (HRcon) for at least 40 days.
- Axonal conduction velocity of triceps surae motor units was measured.
- Stimulation occurred at the ventral root with recording from the tibial nerve.
Main Results:
- Successful HRdown conditioning resulted in an 8% decrease in axonal conduction velocity compared to controls (P=0.02).
- HRup and unsuccessful HRdown rats showed no significant changes.
- The observed changes were localized to the axon, bypassing the spinal cord.
Conclusions:
- HRdown conditioning induces axonal plasticity in motoneurons, decreasing conduction velocity.
- The findings support a mechanism of decreased motoneuron excitability via firing threshold shifts.
- Neuronal plasticity, not solely synaptic plasticity, may underlie operantly conditioned behaviors.