Acquisition of a Simple Motor Skill: Task-Dependent Adaptation Plus Long-Term Change in the Human Soleus H-Reflex

Abstract

Activity-dependent plasticity occurs throughout the CNS. However, investigations of skill acquisition usually focus on cortex. To expand the focus, we analyzed in humans the development of operantly conditioned H-reflex change, a simple motor skill that develops gradually and involves plasticity in both the brain and the spinal cord. Each person completed 6 baseline and 24 conditioning sessions over 10 weeks. In each conditioning session, the soleus H-reflex was measured while the subject was or was not asked to increase (HRup subjects) or decrease (HRdown subjects) it. When the subject was asked to change H-reflex size, immediate visual feedback indicated whether a size criterion had been satisfied. Over the 24 conditioning sessions, H-reflex size gradually increased in six of eight HRup subjects and decreased in eight of nine HRdown subjects, resulting in final sizes of 140 Ϯ 12 and 69 Ϯ 6% of baseline size, respectively. The final H-reflex change was the sum of within-session (i.e., task-dependent) adaptation and across-session (i.e., long-term) change. Taskdependent adaptation appeared within four to six sessions and persisted thereafter, averaging ϩ13% in HRup subjects and Ϫ15% in HRdown subjects. In contrast, long-term change began after 10 sessions and increased gradually thereafter, reaching ϩ27% in HRup subjects and Ϫ16% in HRdown subjects. Thus, the acquisition of H-reflex conditioning consists of two phenomena, task-dependent adaptation and long-term change, that together constitute the new motor skill. In combination with previous data, this new finding further elucidates the interaction of plasticity in brain and spinal cord that underlies the acquisition and maintenance of motor skills.

Goal-dependent modulation of the long-latency stretch response at the shoulder, elbow, and wrist

“…Indeed, many studies have shown substantial changes in the sensitivity of the short-latency stretch response at the transition between posture and movement (Duysens et al 1993;Komiyama et al 2000;Mortimer et al 1981) and over the course of cyclical movements such as gait (Akazawa et al 1982;Capaday and Stein 1986;Forssberg et al 1975;Zehr and Chua 2000;Zehr and Haridas 2003). In fact, previous work has shown that directly reinforcing the magnitude of the H reflexan electrical analog of the short-latency stretch response-over several days or weeks can yield progressive increases or decreases in its magnitude (Carp et al 2006;Chen et al 2006;Christakos et al 1983;Thompson et al 2009;Wolf and Segal 1996;Wolpaw 1987;Wolpaw et al 1983).…”

A paradigm of galvanic vestibular stimulation diminishes the soleus muscle H-reflex in healthy volunteers

“…Thompson et al 21 demonstrated that the H-reflex size can be decreased or increased voluntarily. However, to accomplish this task, the examinees had biofeedback information on the monitor with H-reflex presentation, and multiple sessions [4][5][6] were needed.…”

The effect of voluntary modulation of the sensory-motor rhythm during different mental tasks on H reflex

“…22 studies (Thompson et al 2009), showing that H reflex was not modulated due to the modulation of the background EMG activity.…”

“…It should be mentioned however, that while there is no published literature on modulation of H reflex using NF, other biofeedback strategies, not directly exploiting the activity of brain, have been successfully applied to modulate the amplitude of the H reflex in a desired direction in humans and animals (Wolpaw 2007, Thompson et al 2009). …”

“…The short 100ms period was based on the requirements of studies looking into the modulation of H reflex during MI (Hale et al 2003). A choice of the 2s period was based on results of biofeedback studies (Thompson et al 2009) which recommended that background EMG should be stable (i.e. within a predetermined range) for at least 2 seconds before stimulation in order to ensure no effect of EMG backgorund on the H reflex.…”