Can Operant Conditioning of EMG-Evoked Responses Help to Target Corticospinal Plasticity for Improving Motor Function in People With Multiple Sclerosis?

Abstract

Corticospinal pathway and its function are essential in motor control and motor rehabilitation. Multiple sclerosis (MS) causes damage to the brain and descending connections, and often diminishes corticospinal function. In people with MS, neural plasticity is available, although it does not necessarily remain stable over the course of disease progress. Thus, inducing plasticity to the corticospinal pathway so as to improve its function may lead to motor control improvements, which impact one's mobility, health, and wellness. In order to harness plasticity in people with MS, over the past two decades, non-invasive brain stimulation techniques have been examined for addressing common symptoms, such as cognitive deficits, fatigue, and spasticity. While these methods appear promising, when it comes to motor rehabilitation, just inducing plasticity or having a capacity for it does not guarantee generation of better motor functions. Targeting plasticity to a key pathway, such as the corticospinal pathway, could change what limits one's motor control and improve function. One of such neural training methods is operant conditioning of the motor-evoked potential that aims to train the behavior of the corticospinal-motoneuron pathway. Through up-conditioning training, the person learns to produce the rewarded neuronal behavior/state of increased corticospinal excitability, and through iterative training, the rewarded behavior/state becomes one's habitual, daily motor behavior. This minireview introduces operant conditioning approach for people with MS. Guiding beneficial CNS plasticity on top of continuous disease progress may help to prolong the duration of maintained motor function and quality of life in people living with MS.

Heksor: the central nervous system substrate of an adaptive behaviour

“…And, because the spinal cord is directly connected to behaviour, these effects on old behaviours are clear, their aetiologies can be discerned, and their mechanisms can be more readily explored. In this body of work, the new behaviour is a larger or smaller soleus H-reflex acquired through operant conditioning (Carp et al, 2006;Chen & Wolpaw, 1995;Thompson et al, 2009;Wolpaw, 1987), or a larger tibialis anterior motor evoked potential (MEP) (evoked by transcranial magnetic stimulation; TMS) also acquired through operant conditioning (Thompson & Sinkjaer, 2020;Thompson et al, 2018aThompson et al, , 2018bThompson et al, , 2019. The old (i.e.…”

“…The studies described so far evaluate the response of one old heksor (the locomotion heksor) to one new heksor (a soleus H-reflex heksor) in people and animals with or without an iSCI that impaired locomotion. More recently, studies in people with or without impaired locomotion have begun to explore the response of the locomotion heksor to a new corticospinal MEP heksor (Thompson & Sinkjaer, 2020;Thompson et al, 2018aThompson et al, , 2018bThompson et al, , 2019. This new work begins to assess the wider applicability of the heksor and negotiated equilibrium concepts.…”

“…In these studies, the corticospinal MEP of the tibialis anterior (TA) muscle in one leg is up-conditioned by a protocol similar to that used to increase or decrease the soleus H-reflex (three 1-h sessions/week over 8-10 weeks) (Thompson & Sinkjaer, 2020;Thompson et al, 2018aThompson et al, , 2018bThompson et al, , 2019. The MEP is produced by TMS.…”

“…B , In a person with locomotion impaired by multiple sclerosis (MS), up‐conditioning gradually increases the TA MEP over three 1‐h sessions/week for 8 weeks. (From Thompson and Sinkjær (2020). ) C , Up‐conditioning of the TA MEP in one leg improves TA and soleus locomotor EMG in both legs.…”

“…Additional beneficial plasticity improves the stance‐phase soleus burst in the contralateral leg. (From Thompson and Sinkjær (2020). ) D , Up‐conditioning of the TA MEP in one leg can improve locomotor kinematics in both legs.…”