Adaptive plasticity in the primate spinal stretch reflex: reversal and re-development

Area of Science:

• Neuroscience
• Motor Control
• Neuroplasticity

Background:

• The spinal stretch reflex (SSR) amplitude in monkeys can be modulated voluntarily.
• Previous research indicates that changes in SSR amplitude occur slowly over weeks.
• The underlying mechanisms for sustained SSR modulation remain unclear.

Purpose of the Study:

• To investigate the reversibility and re-development of SSR amplitude changes.
• To explore the time course of SSR modulation, reversal, and re-development.
• To test the hypothesis that persistent segmental alterations in the spinal cord underlie SSR plasticity.

Main Methods:

• Monkeys were trained to either increase or decrease their SSR amplitude.
• Following initial modulation, the direction of modulation was reversed.
• Subsequently, the original modulation direction was re-established.
• Control data were collected throughout the study period.

Main Results:

• Monkeys successfully modulated SSR amplitude in both increase and decrease modes.
• The development, reversal, and re-development of SSR amplitude changes all occurred over weeks.
• The time courses for development, reversal, and re-development were remarkably similar.
• No changes in initial muscle length or background EMG activity accompanied SSR amplitude modulation.

Conclusions:

• The findings support the hypothesis of persistent segmental alterations in the spinal cord.
• These persistent alterations are proposed as a potential substrate for memory.
• The study demonstrates the dynamic and reversible nature of spinal reflex plasticity.