Why Variability Facilitates Spinal Learning

Abstract

Spinal Wistar Hannover rats trained to step bipedally on a treadmill with manual assistance of the hindlimbs have been shown to improve their stepping ability. Given the improvement in motor performance with practice and the ability of the spinal cord circuitry to learn to step more effectively when the mode of training allows variability, we examined why this intrinsic variability is an important factor. Intramuscular EMG electrodes were implanted to monitor and compare the patterns of activation of flexor (tibialis anterior) and extensor (soleus) muscles associated with a fixed-trajectory and assist-as-needed (AAN) step training paradigms in rats after a complete midthoracic (T8 -T9) spinal cord transection. Both methods involved a robotic arm attached to each ankle of the rat to provide guidance during stepping. The fixed trajectory allowed little variance between steps, and the AAN provided guidance only when the ankle deviated a specified distance from the programmed trajectory. We hypothesized that an AAN paradigm would impose fewer disruptions of the control strategies intrinsic to the spinal locomotor circuitry compared with a fixed trajectory. Intrathecal injections of quipazine were given to each rat to facilitate stepping. Analysis confirmed that there were more corrections within a fixed-trajectory step cycle and consequently there was less coactivation of agonist and antagonist muscles during the AAN paradigm. These data suggest that some critical level of variation in the specific circuitry activated and the resulting kinematics reflect a fundamental feature of the neural control mechanisms even in a highly repetitive motor task.

Training with robot-applied resistance in people with motor-incomplete spinal cord injury: Pilot study

“…There is increasing evidence that providing more variable practice conditions during training enhances motor performance [56,[61][62][63]. This is also implied from clinical research showing that overground gait training or therapist-assisted BWSTT enables better ambulatory outcomes in people with SCI or stroke than with robotguided training [16,61].…”

“…This is also implied from clinical research showing that overground gait training or therapist-assisted BWSTT enables better ambulatory outcomes in people with SCI or stroke than with robotguided training [16,61]. The rigid imposition of movement trajectories by robot-assisted training limits the variability with which the lower limbs are moved and consequently could interfere with the nervous system's ability to effectively relearn gait patterns [61][62]. Indeed, variability during practice is seen as a key feature for facilitating learning because the nervous system is presented with repeated (and varied) opportunities to experience errors and solve motor problems [55], as opposed to simply learning how to reproduce an imposed trajectory [63].…”

“…Indeed, variability during practice is seen as a key feature for facilitating learning because the nervous system is presented with repeated (and varied) opportunities to experience errors and solve motor problems [55], as opposed to simply learning how to reproduce an imposed trajectory [63]. Others have also suggested that variability or "noise" during training provides a stochastic resonance to help reinforce convergent synaptic connections from central and sensory inputs to the locomotor circuitry [62].…”

Effect of robotic gait training on cardiorespiratory system in incomplete spinal cord injury

“…These new controllers allow active participation of patients in the kinematics of locomotion, which may be more effective for motor learning [26][27]. However, the effects on the cardiorespiratory system have not yet been studied.…”

Robot aided gait training and assessment : development of support strategies and assessment methods for LOPES

“…In other words, effective practice requires more than just movement repetitions. Animal studies have shown that training with a variable stepping pattern results in higher levels of recovery than walking with a fixed stepping pattren [128,129]. Although recovery mechanisms in mice and rats may not be representative for humans, similar benefits of movement variability are seen in neurological patients, suggesting that training with kinematic variability is advantageous.…”