title: D1 and D2 Inhibitions of the Soleus H-Reflex Are Differentially Modulated during Plantarflexion Force and Position Tasks.
abstract: Presynaptic inhibition (PSI) has been shown to modulate several neuronal pathways of functional relevance by selectively gating the connections between sensory inputs and spinal motoneurons, thereby regulating the contribution of the stretch reflex circuitry to the ongoing motor activity. In this study, we investigated whether a differential regulation of Ia afferent inflow by PSI may be associated with the performance of two types of plantarflexion sensoriomotor tasks. The subjects (in a seated position) controlled either: 1) the force level exerted by the foot against a rigid restraint (force task, FT); or 2) the angular position of the ankle when sustaining inertial loads (position task, PT) that required the same level of muscle activation observed in FT. Subjects were instructed to maintain their force/position at target levels set at ~10% of maximum isometric voluntary contraction for FT and 90° for PT, while visual feedback of the corresponding force/position signals were provided. Unconditioned H-reflexes (i.e. control reflexes) and H-reflexes conditioned by electrical pulses applied to the common peroneal nerve with conditioning-to-test intervals of 21 ms and 100 ms (corresponding to D1 and D2 inhibitions, respectively) were evoked in a random fashion. A significant main effect for the type of the motor task (FT vs PT) (p = 0.005, η2p = 0.603) indicated that PTs were undertaken with lower levels of Ia PSI converging onto the soleus motoneuron pool. Additionally, a significant interaction between the type of inhibition (D1 vs D2) and the type of motor task (FT vs PT) (p = 0.038, η2p = 0.395) indicated that D1 inhibition was associated with a significant reduction in PSI levels from TF to TP (p = 0.001, η2p = 0.731), whereas no significant difference between the tasks was observed for D2 inhibition (p = 0.078, η2p = 0.305). These results suggest that D1 and D2 inhibitions of the soleus H-reflex are differentially modulated during the performance of plantarflexion FT and PT. The reduced level of ongoing PSI during PT suggests that, in comparison to FT, there is a larger reliance on inputs from muscle spindles primary afferents when the neuromuscular system is required to maintain position-controlled plantarflexion contractions.
authors.affiliation: School of Arts, Sciences and Humanities, Universidade de São Paulo, EACH-USP, São Paulo, SP, Brazil.|Biomedical Engineering Laboratory, Universidade de São Paulo, EPUSP, Avenida Professor Luciano Gualberto, Travessa 3, n.158, São Paulo, SP, Brazil.|Neuroscience Program, Universidade de São Paulo, São Paulo, SP, Brazil.
authors.forename: Fernando Henrique
authors.initials: FH
authors.lastname: Magalhães
authors.affiliation: Biomedical Engineering Laboratory, Universidade de São Paulo, EPUSP, Avenida Professor Luciano Gualberto, Travessa 3, n.158, São Paulo, SP, Brazil.|Department of Biomedical Engineering, School of Electrical and Computer Engineering, University of Campinas, Campinas, SP, Brazil.
authors.forename: Leonardo Abdala
authors.initials: LA
authors.lastname: Elias
authors.affiliation: Biomedical Engineering Laboratory, Universidade de São Paulo, EPUSP, Avenida Professor Luciano Gualberto, Travessa 3, n.158, São Paulo, SP, Brazil.|Neuroscience Program, Universidade de São Paulo, São Paulo, SP, Brazil.
authors.forename: Cristiano Rocha
authors.initials: CR
authors.lastname: da Silva
authors.affiliation: Biomedical Engineering Laboratory, Universidade de São Paulo, EPUSP, Avenida Professor Luciano Gualberto, Travessa 3, n.158, São Paulo, SP, Brazil.
authors.forename: Felipe Fava
authors.initials: FF
authors.lastname: de Lima
authors.affiliation: Biomedical Engineering Laboratory, Universidade de São Paulo, EPUSP, Avenida Professor Luciano Gualberto, Travessa 3, n.158, São Paulo, SP, Brazil.
authors.forename: Diana Rezende
authors.initials: DR
authors.lastname: de Toledo
authors.affiliation: Biomedical Engineering Laboratory, Universidade de São Paulo, EPUSP, Avenida Professor Luciano Gualberto, Travessa 3, n.158, São Paulo, SP, Brazil.|Neuroscience Program, Universidade de São Paulo, São Paulo, SP, Brazil.
authors.forename: André Fabio
authors.initials: AF
authors.lastname: Kohn
mesh_terms: D000328:Adult; D004576:Electromyography; D005260:Female; D006181:H-Reflex / Q000502:physiology*; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D009046:Motor Neurons / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D012026:Reflex, Stretch / Q000502:physiology; D055815:Young Adult