The Effects of Temporal and Spatial Predictions on Stretch Reflexes of Ankle Flexor and Extensor Muscles While Standing

Abstract

The purpose of the present study was to investigate how stretch reflex (SR) responses in the ankle extensor (soleus: SOL) and flexor (tibialis anterior: TA) muscles would be modulated with temporal and/or spatial predictions of external perturbations and whether their effects are specific to the standing posture. SR responses in the SOL/TA were elicited by imposing quick ankle toes-up/toes-down rotations while standing upright and in the supine position. We designed four experimental conditions based on pre-information about perturbations: no information (No Cue), the timing of the perturbation onset (TIM), the direction of the perturbation (DIR), and both the timing and direction of the perturbation (TIM/DIR). Each condition was separated and its order was counterbalanced. In the SR of TA evoked by toes-down rotation, integrated electromyography activities of the late component were significantly reduced in the TIM and TIM/DIR conditions as compared with those in the No Cue and DIR conditions. The occurrence rate of late SR components that reflects how often the reflex response was observed was also lower in the TIM and TIM/DIR conditions as compared with that in the No Cue and DIR conditions. On the other hand, no significant changes were seen among the four conditions in the early SR component in the TA and both SR components in the SOL. The same results in the occurrence rate were found in the supine position. The present results suggest (1) only temporal predictions have a remarkable effect on the SR excitability of the TA, and (2) this effect is independent of posture.

Corticospinal Excitability Is Modulated as a Function of Postural Perturbation Predictability

“…Our present analyses demonstrated that the corticospinal excitability in the TA was enhanced when the timing cue was given. This result is inconsistent with previous studies of the stretch reflex that reported the reduced amplitude of the long-latency response ( Nakazawa et al, 2009 ; Fujio et al, 2016 ). We suspect that this discrepancy is due to the difference in perturbation types.…”

“…The long-latency EMG responses of the ankle plantar muscle and dorsiflexor muscle were reported to be enhanced when the posture was unstable ( Christensen et al, 2001 ; Nakazawa et al, 2003 ). It was also demonstrated that the amplitude of these EMG responses was markedly reduced when an advance notification about the timing of perturbation onset was given to the subjects ( Nakazawa et al, 2009 ; Fujio et al, 2016 ). It is thus plausible that the excitability of a corticospinal pathway would be enhanced when a subject can predict that a postural perturbation is to occur, and the enhanced excitability could be reduced when the subject can predict the timing of the perturbation.…”

Influência de processos cognitivos em respostas posturais automáticas a perturbações extrínsecas

“…Há evidências de que as respostas posturais podem ser moduladas por processamento cognitivo (Fujio, Obata, Kawashima, & Nakazawa, 2016;Mierau, Hulsdunker, & Struder, 2015;Smith, Jacobs, & Horak, 2012, 2014Varghese et al, 2014). Essas evidências sugerem que várias regiões corticais e subcorticais, tais como as áreas frontais, o córtex cingulado anterior, área pré-motora, cerebelo e gânglios da base estão relacionados com processos atencionais e de preparação motora envolvidos com o controle postural.…”

“…Uma questão advinda dessa definição é quais informações de contexto podem ser utilizadas pelo central set para melhorar as respostas posturais automáticas. Essa participação do central set em respostas posturais automáticas tem sido generalizada para diferentes informações do contexto, tais como dicas prévias sobre as características da perturbação postural (Chong, Horak, & Woollacott, 2000;Fujio et al, 2016;Jacobs et al, 2008;Mochizuki et al, 2010;Mochizuki, Sibley, Esposito, Camilleri, & McIlroy, 2008;Silva et al, 2015;Smith et al, 2012Smith et al, , 2014, experiência prévia com a perturbação postural (Horak et al, 1989;Mierau et al, 2015;Papegaaij et al, 2012), restrição imposta por uma tarefa manual realizada concomitantemente à manutenção do equilíbrio postural (de Lima-Pardini et al, 2014;de Lima-Pardini et al, 2012;de Lima, de Azevedo Neto, & Teixeira, 2010), condições posturais iniciais , instrução (Smith et al, 2014) e estado emocional (Maki & McIlroy, 2005).…”

“…Especificamente para as características da perturbação postural, a influência do central set em respostas posturais automáticas tem sido investigada em estudos que avaliaram o efeito da dica sobre o momento (Adkin et al, 2008;Fujio et al, 2016;McChesney, Sveistrup, & Woollacott, 1996;Mochizuki et al, 2008;Silva et al, 2015), direção (Badke, Duncan, & Di Fabio, 1987;Diener, Horak, Stelmach, Guschlbauer, & Dichgans, 1991;Silva et al, 2015) e magnitude (Diener et al, 1991;Horak et al, 1989;Maki & Whitelaw, 1993;Smith et al, 2012) da perturbação. Ao oferecer dicas sobre amplitude e direção da perturbação, Diener et al (1991)…”