Adaptive plasticity in primate spinal stretch reflex: persistence

Area of Science:

• Neuroscience
• Motor Control
• Physiology

Background:

• The spinal stretch reflex (SSR) amplitude in monkeys can be gradually modified through training.
• These modifications develop slowly over months and can reverse at similar rates.

Purpose of the Study:

• To investigate the persistence of SSR amplitude changes during non-performance periods.
• To understand how extended breaks affect learned adjustments in the spinal stretch reflex.

Main Methods:

• Monkeys were trained to modulate biceps SSR amplitude using operant conditioning with reward contingencies.
• Training involved periods of control, SSR increase, and SSR decrease modes, interspersed with nonperformance gaps of up to 38 days.
• Electromyography (EMG) recorded biceps activity to quantify SSR amplitude.

Main Results:

• Animals gradually adapted SSR amplitude according to the training mode (increase or decrease).
• Nonperformance gaps of up to 38 days resulted in transient, nonspecific decreases in SSR amplitude (10-15%) under control conditions.
• These transient decreases resolved within the first week of post-gap performance, with no other significant effects on SSR amplitude.

Conclusions:

• Learned changes in spinal stretch reflex amplitude demonstrate significant persistence even after substantial periods without performance.
• The motor system exhibits robust adaptation and retention of learned motor behaviors, with minor transient effects from performance interruptions.