title: Operant conditioning of the soleus H-reflex does not induce long-term changes in the gastrocnemius H-reflexes and does not disturb normal locomotion in humans.
abstract: In normal animals, operant conditioning of the spinal stretch reflex or the H-reflex has lesser effects on synergist muscle reflexes. In rats and people with incomplete spinal cord injury (SCI), soleus H-reflex operant conditioning can improve locomotion. We studied in normal humans the impact of soleus H-reflex down-conditioning on medial (MG) and lateral gastrocnemius (LG) H-reflexes and on locomotion. Subjects completed 6 baseline and 30 conditioning sessions. During conditioning trials, the subject was encouraged to decrease soleus H-reflex size with the aid of visual feedback. Every sixth session, MG and LG H-reflexes were measured. Locomotion was assessed before and after conditioning. In successfully conditioned subjects, the soleus H-reflex decreased 27.2%. This was the sum of within-session (task dependent) adaptation (13.2%) and across-session (long term) change (14%). The MG H-reflex decreased 14.5%, due mainly to task-dependent adaptation (13.4%). The LG H-reflex showed no task-dependent adaptation or long-term change. No consistent changes were detected across subjects in locomotor H-reflexes, EMG activity, joint angles, or step symmetry. Thus, in normal humans, soleus H-reflex down-conditioning does not induce long-term changes in MG/LG H-reflexes and does not change locomotion. In these subjects, task-dependent adaptation of the soleus H-reflex is greater than it is in people with SCI, whereas long-term change is less. This difference from results in people with SCI is consistent with the fact that long-term change is beneficial in people with SCI, since it improves locomotion. In contrast, in normal subjects, long-term change is not beneficial and may necessitate compensatory plasticity to preserve satisfactory locomotion.
authors.affiliation: Helen Hayes Hospital, New York State Department of Health, West Haverstraw, New York; Program in Human Movement Science, Department of Allied Health Sciences, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina;
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Makihara
authors.affiliation: Program in Human Movement Science, Department of Allied Health Sciences, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina; Department of Health Professions, Medical University of South Carolina, Charleston, South Carolina;
authors.forename: Richard L
authors.initials: RL
authors.lastname: Segal
authors.affiliation: Helen Hayes Hospital, New York State Department of Health, West Haverstraw, New York; Wadsworth Center, New York State Department of Health, Albany, New York; Department of Neurology, Neurological Institute, Columbia University, New York, New York; and Department of Biomedical Sciences, State University of New York, Albany, New York.
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Wolpaw
authors.affiliation: Helen Hayes Hospital, New York State Department of Health, West Haverstraw, New York; Wadsworth Center, New York State Department of Health, Albany, New York; Department of Neurology, Neurological Institute, Columbia University, New York, New York; and Department of Biomedical Sciences, State University of New York, Albany, New York a.kido.thompson@gmail.com.
authors.forename: Aiko K
authors.initials: AK
authors.lastname: Thompson
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D003216:Conditioning, Operant; D005260:Female; D006181:H-Reflex; D006801:Humans; D008124:Locomotion; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D013997:Time Factors
keywords: learning; plasticity; rehabilitation; spinal cord; synergists