The Interaction of a New Motor Skill and an Old One: H-Reflex Conditioning and Locomotion in Rats

Abstract

New and old motor skills can interfere with each other or interact in other ways. Because each skill entails a distributed pattern of activity-dependent plasticity, investigation of their interactions is facilitated by simple models. In a well characterized model of simple learning, rats and monkeys gradually change the size of the H-reflex, the electrical analog of the spinal stretch reflex. This study evaluates in normal rats the interactions of this new skill of H-reflex conditioning with the old well established skill of overground locomotion.In rats in which the soleus H-reflex elicited in the conditioning protocol (i.e., the conditioning H-reflex) had been decreased by down-conditioning, the H-reflexes elicited during the stance and swing phases of locomotion (i.e., the locomotor H-reflexes) were also smaller. Similarly, in rats in which the conditioning H-reflex had been increased by up-conditioning, the locomotor H-reflexes were also larger.Soleus H-reflex conditioning did not affect the duration, length, or right/left symmetry of the step cycle. However, the conditioned change in the stance H-reflex was positively correlated with change in the amplitude of the soleus locomotor burst, and the correlation was consistent with current estimates of the contribution of primary afferent input to the burst.Although H-reflex conditioning and locomotion did not interfere with each other, H-reflex conditioning did affect how locomotion was produced: it changed soleus burst amplitude and may have induced compensatory changes in the activity of other muscles. These results illustrate and clarify the subtlety and complexity of skill interactions. They also suggest that H-reflex conditioning might be used to improve the abnormal locomotion produced by spinal cord injury or other disorders of supraspinal control.Key words: H-reflex conditioning; spinal cord plasticity; motor control; learning; memory consolidation; locomotion; rehabilitation IntroductionThe nervous system maintains a broad repertoire of adaptive behaviors acquired through practice, commonly referred to as skills (Compact Oxford English Dictionary, 1993). New skills may interfere, or interact in other ways, with old ones. These interactions are often addressed in terms of unitary concepts of memory consolidation, reactivation, and interference (Shadmehr and Holcomb, 1997;Krakauer et al., 1999;Goedert and Willingham, 2002;Wigmore et al., 2002;Walker et al., 2003;Caithness et al., 2004). However, it is now clear that even the simplest skills involve complex distributed patterns of activitydependent plasticity (Wolpaw and Lee, 1989;Carrier et al., 1997;Cohen et al., 1997;Lieb and Frost, 1997;Thompson et al., 1997;Whelan and Pearson, 1997;Lisberger, 1998;Garcia et al., 1999;Medina et al., 2000Medina et al., , 2002Hansel et al., 2001;King et al., 2001;Wolpaw and Tennissen, 2001;Carey and Lisberger, 2002;van Alphen and De Zeeuw, 2002;Wolpaw, 2002;Blazquez et al., 2003). A new skill may involve different kinds of plasticity that occur at different sites at dif...

Operant Conditioning of H-Reflex Can Correct a Locomotor Abnormality after Spinal Cord Injury in Rats

“…After treadmill locomotion and locomotor H-reflexes were assessed, the rat was (eight HRup rats) or was not (five control rats) exposed to the H-reflex up-conditioning (HRup) protocol, and then treadmill locomotion and locomotor H-reflexes were assessed again. The procedures for LC transection, electrode implantation, treadmill locomotion, H-reflex conditioning, histological evaluation, and data analysis are described have been described in detail previously (Chen and Wolpaw, 1995, 1997Chen et al, , 1999Chen et al, , 2001aChen et al, , 2002aChen et al, , 2005 and are summarized here. Figure 1 A shows the experimental sequence.…”

“…Before implantation surgery, each rat learned to walk quadripedally on a motor-driven treadmill at 9 -10 m/min (Burghardt et al, 2004;Chen et al, 2005). After implantation and LC transection, locomotor data were collected in one treadmill session after the Basso, Beattie, and Bresnahan (BBB) score (Basso et al, 1995) had returned to 20 -21 and in a second session 49 -72 d after the first.…”

“…As previously described and supported by video recording, the times of soleus burst onset and offset were used to define the stance phase (Chen et al, 2005). By these criteria, stance-phase H-reflexes were elicited just past the middle of the stance phase, and the swing-phase H-reflexes were elicited late in the swing phase.…”

“…By these criteria, stance-phase H-reflexes were elicited just past the middle of the stance phase, and the swing-phase H-reflexes were elicited late in the swing phase. From the rectified EMG, these locomotor H-reflexes were measured as average EMG amplitude in the H-reflex interval minus average background EMG amplitude at the time of stimulation and were expressed in units of average background EMG amplitude (Chen and Wolpaw, 1995, 1997Chen et al, 2005). We measure H-reflex size in this manner because the typically high variability in the form of the rat H-reflex makes a simple peak-to-peak measure inappropriate.…”

“…In normal animals and humans, operant conditioning of the spinal stretch reflex (SSR) (i.e., the tendon jerk) or its electrical analog the H-reflex can modify descending activity and thereby induce spinal cord plasticity that can affect motor function (Wolpaw et al, 1983;Wolpaw, 1987Wolpaw, , 2001Evatt et al, 1989;Chen and Wolpaw, 1995;Segal, 1997;Chen et al, 2005). This suggests that such conditioning might be used to improve defective motor function.…”