Why variability facilitates spinal learning.

Area of Science:

• Neuroscience
• Motor Control
• Spinal Cord Injury Research

Background:

• Spinal cord injury (SCI) impairs locomotor function.
• Locomotor training with assistance can improve stepping ability in SCI models.
• Spinal cord circuitry exhibits plasticity and learning capabilities.

Purpose of the Study:

• To investigate the role of training variability in motor learning after spinal cord transection.
• To compare the effects of fixed-trajectory versus assist-as-needed (AAN) stepping paradigms on spinal locomotor control.
• To determine if AAN training imposes fewer disruptions on intrinsic spinal cord control strategies.

Main Methods:

• Wistar Hannover rats with T8-T9 spinal cord transection were trained to step bipedally.
• Intramuscular EMG electrodes monitored flexor (tibialis anterior) and extensor (soleus) muscle activation.
• Robotic assistance provided either fixed-trajectory or AAN guidance during stepping.
• Quipazine was administered intrathecally to facilitate stepping.

Main Results:

• The AAN paradigm resulted in fewer corrections per step cycle compared to fixed-trajectory training.
• Less coactivation of agonist and antagonist muscles was observed during AAN stepping.
• The fixed-trajectory method led to more disruptions in muscle activation patterns.

Conclusions:

• Training variability, as provided by the AAN paradigm, is crucial for effective motor learning in spinal circuits.
• The spinal cord's intrinsic control strategies are better preserved with AAN training.
• Variability in neural activation and kinematics is a fundamental aspect of spinal locomotor control.