Training-induced adaptive plasticity in human somatosensory reflex pathways

Abstract

This paper reviews evidence supporting adaptive plasticity in muscle and cutaneous afferent reflex pathways induced by training and rehabilitative interventions. The perspective is advanced that the behavioral and functional relevance of any intervention and the reflex pathway under study should be considered when evaluating both adaptation and transfer. A cornerstone of this concept can be found in acute task-dependent reflex modulation. Because the nervous system allows the expression of a given reflex according to the motor task, an attempt to evaluate the training adaptation should also be evoked under the same conditions as training bearing in mind the functional role of the pathway under study. Within this framework, considerable evidence supports extensive adaptive plasticity in human muscle afferent pathways in the form of operant conditioning, strength training, skill training, and locomotor training or retraining. Directly comparable evidence for chronic adaptation in cutaneous reflex pathways is lacking. However, activity-dependent plasticity in cutaneous pathways is documented particularly in approaches to neurological rehabilitation. Overall, the adaptive range for human muscle afferent reflexes appears bidirectional (that is, increased or reduced amplitudes) and on the order of 25-50%. The adaptive range for cutaneous pathways is currently uncertain.

Strength training-induced responses in older adults: attenuation of descending neural drive with age

“…Thus, in addition to motoneuron excitability, the maximal firing frequency, as well as the proportion of motoneurons recruited will determine the size of the V-wave, as they will both affect the probability of antidromic collision. Although pre/postsynaptic inhibition may also affect the amplitude of the V-wave, these factors would influence the amplitude of the Hreflex similarly (Zehr 2006;Vila-Cha et al 2012). Interestingly, the reduction in V/M ratio was more than three times larger than the reduction in H/M ratio.…”

Reflex Inhibition in Human Biceps Brachii Decreases With Practice of a Fatiguing Contraction

“…For example, both healthy and spinal-cord injured subjects were able to decrease the amplitude of the stretch reflex in biceps brachii after 24 training sessions in which subjects were provided with feedback of the response and a reward for producing the desired adaptation (Segal and Wolf 1994;Wolf and Segal 1996). In the present study, however, the adaptation was likely an indirect consequence of the practice (Zehr 2006), as reported for the H reflex in the lower limb (Schneider and Capaday 2003). Presumably changes in reflex responses that parallel improvements in performance indicate a causal association between the transmission of information over the reflex pathway and the ensuing adaptation in motor output.…”

“…Practice-related adaptations in the nervous system can include changes in corticospinal excitability (Jensen et al 2005;Perez et al 2007), somatosensory feedback to the motor neurons (Geertsen et al 2007;Zehr 2006), and the output of the motor neuron pool to muscle (Del Balso and Cafarelli 2007;Duchateau et al 2006). The sites of plasticity in the nervous system are specific to the task performed and can differ, for instance, between motor skill training and strength training (Jensen et al 2005;Semmler and Nordstrom 1998).…”

“…The sites of plasticity in the nervous system are specific to the task performed and can differ, for instance, between motor skill training and strength training (Jensen et al 2005;Semmler and Nordstrom 1998). Furthermore, practice of a task evokes both short-and long-term adaptations in the nervous system that can differ among individuals (Duchateau and Enoka 2002;Zehr 2006).…”

Paresthesias as Reflection of the Lateral Asymmetry of Neural Function in Human

“…Studies incorporating the H-reflex as a neural probe showed changes in excitability of the reflex occur while movement actions and also in the absence of movement what suggests the existence of intrinsic modulating factors in motor control system, connected with the spinal circuit organization and/or with transmission parameters in motor and sensory pathways (Aymard et al, 2000;Kimura, 2001;Misiaszek, 2003;Zehr et. al, 2004;Zehr, 2006;Zehr et.al., 2007). Previous studies with the Hreflex demonstrated clearly that adaptive plasticity could be induced in the spinal cord and that it could be examined by using the H-reflex (Agaard, 2003;Carp & Wolpaw, 1994;Wolpaw & Chen, 2006).…”