Shailesh S. Kantak

Learning–performance distinction and memory processes for motor skills: A focused review and perspective

Behavioral research in cognitive psychology provides evidence for an important distinction between immediate performance that accompanies practice and long-term performance that reflects the relative permanence in the capability for the practiced skill (i.e. learning). This learning-performance distinction is strikingly evident when challenging practice conditions may impair practice performance, but enhance long-term retention of motor skills. A review of motor learning studies with a specific focus on comparing differences in performance between that at the end of practice and at delayed retention suggests that the delayed retention or transfer performance is a better indicator of motor learning than the performance at (or end of) practice. This provides objective evidence for the learning-performance distinction. This behavioral evidence coupled with an understanding of the motor memory processes of encoding, consolidation and retrieval may provide insight into the putative mechanism that implements the learning-performance distinction. Here, we propose a simplistic empirically-based framework--motor behavior-memory framework--that integrates the temporal evolution of motor memory processes with the time course of practice and delayed retention frequently used in behavioral motor learning paradigms. In the context of the proposed framework, recent research has used noninvasive brain stimulation to decipher the role of each motor memory process, and specific cortical brain regions engaged in motor performance and learning. Such findings provide beginning insights into the relationship between the time course of practice-induced performance changes and motor memory processes. This in turn has promising implications for future research and practical applications.

Neural substrates of motor memory consolidation depend on practice structure

Motor-skill practice drives subsequent offline activity in functionally related resting human brain networks. We investigated the manner in which offline neural networks are modulated by practice structures that affect motor-skill retention. Interference to dorsolateral-prefrontal cortex (DLPFC), but not to primary motor cortex (M1), after variable practice attenuated motor-skill retention, whereas interference to M1, but not to DLPFC, after constant practice attenuated motor-skill retention. We conclude that neural substrates of motor-memory consolidation are modulated by practice structure.

Motor Learning in Children: Feedback Effects on Skill Acquisition

Background and Purpose: Reduced feedback during motor skill practice benefits motor learning. However, it is unknown whether these findings can be applied to motor learning in children, given that children have different information-processing capabilities than adults. The purpose of this study was to determine the effect of different relative frequencies of feedback on skill acquisition in children compared with young adults. Subjects: The participants were 20 young adults and 20 children. Methods: All participants practiced 200 trials of a discrete arm movement with specific spatiotemporal parameters. Participants from each group (adults and children) were randomly assigned to either a 100% feedback group or a reduced (62% faded) feedback group. Learning was inferred from the performance on the delayed (24-hour) retention and reacquisition tests. Results: All participants improved accuracy and consistency across practice trials. During practice, the adults performed with significantly less error than the children. Adults who practiced with reduced feedback performed with increased consistency during the retention test compared with those who practiced with 100% feedback. In contrast, children who received reduced feedback during practice performed with less accuracy and consistency during the retention test than those who received 100% feedback. However, when feedback was reintroduced during the reacquisition test, the children in the reduced feedback group were able to improve their performance comparable to those in the 100% feedback group. Discussion and Conclusions: During motor learning, children use feedback in a manner different from that of adults. To optimize motor learning, children may require longer periods of practice, with feedback reduced more gradually, compared with young adults.

Effect of Task Practice Order on Motor Skill Learning in Adults With Parkinson Disease: A Pilot Study

Background and Purpose: Random practice of motor tasks has been shown to enhance motor learning. The purpose of this study was to investigate the effects of task practice order (random, blocked) on motor learning in adults with Parkinson disease (PD). Subjects: Twenty adults with mild PD and 20 age-matched adults (controls) participated in the study. Methods: Participants in both groups (PD and control) practiced 3 movement tasks with either a blocked or a random practice order. This 2 participant group × 2 practice order design resulted in 4 experimental groups. The Trail Making Test was administered to all participants to determine task-switching capability. Motor performance on the arm movement tasks was quantified on the basis of the root-mean-square error difference between the goal movement task and each participants response. Results: The task-switching capability of the control group was superior to that of the PD group. For acquisition, in general, participants in the control group performed with significantly less error than participants in the PD group. For retention, participants in the control group who practiced with a random order performed more accurately than participants in the control group who practiced with a blocked order. However, for the PD group, the findings were reversed; participants who practiced with a blocked order performed more accurately than participants who practiced with a random order. These findings resulted in a group × practice order interaction. Discussion and Conclusion: These pilot study data suggest that, contrary to the findings for age-matched control learners, for learners with mild PD, a blocked practice order may be better than a random practice order for motor learning.

Low frequency repetitive transcranial magnetic stimulation to the non-lesioned hemisphere improves paretic arm reach-to-grasp performance after chronic stroke

Purpose: To investigate the effect of inhibitory low frequency repetitive Transcranial Magnetic Stimulation (rTMS) applied to the non-lesioned hemisphere on kinematics and coordination of paretic arm reach-to-grasp (RTG) actions in individuals with stroke. Relevance: This study is designed as a phase I trial to determine the feasibility and efficacy of low frequency rTMS applied to the non-lesioned hemisphere for the recovery of reach-to-grasp actions in individuals with hemiparesis secondary to stroke. The results have important implications for the use of rTMS in parallel with complex paretic arm skill practice. Participants: Nine adults, anterior circulation unilateral stroke. Their average age was 59 years, the average time since stroke was 4.8 years. Method and analysis: Two TMS treatments were performed on two separate days: active rTMS and sham rTMS. Cortico-motor excitability (CE) of the non-lesioned hemisphere as well as RTG kinematics of the paretic hand as participants reached for a dowel of 1.2 cm in diameter was assessed before and after the rTMS treatments. In the active condition, rTMS was applied over the “hot spot” of the extensor digitorum communis muscle (EDC) in primary motor cortex (M1) of the non-lesioned hemisphere at 90% resting motor threshold. TMS pulses were delivered at 1 Hz for 20 min. In the sham condition, a sham coil was positioned similar to the active condition; TMS clicking noise was produced but no TMS pulse was delivered. Dependent measures: CE was measured as peak-to-peak amplitude of the motor evoked potential at 120% of resting motor threshold. RTG kinematics included movement time, peak transport velocity, peak aperture, time of peak transport velocity and time of peak aperture. RTG coordination was captured by cross correlation coefficient between transport velocity and grasp aperture size. Results: While 1 Hz rTMS applied over non-lesioned M1 significantly decreased the MEP amplitude of non-paretic EDC, sham TMS did not have a significant effect on MEP amplitude. Active rTMS significantly decreased total movement time and increased peak grasp aperture. There were no changes in peak transport velocity or the time of peak transport velocity or the time of peak aperture after application of active rTMS. Additionally, the participants completed RTG actions with a more coordinated pattern after undergoing active rTMS. Following sham TMS, there were no changes in CE, RTG kinematics or coordination. While there were no significant correlation between changes in cortico-motor excitability and RTG kinematics, the decrease in cortico-motor excitability of the non-lesioned hemisphere showed a strong correlation with an increase in cross-correlation coefficient. Conclusions and implications: The findings demonstrate the feasibility and efficacy of low frequency rTMS applied to the non-lesioned hemisphere for the recovery of reach-to-grasp actions in individuals with hemiparesis secondary to stroke. The inhibitory effect of low frequency rTMS resulted in improved paretic hand reach-to-grasp performance with faster movement time and more coordinated reach-to-grasp pattern. These results have important implications for the use of rTMS for stroke rehabilitation. Implications for Rehabilitation Low frequency repetitive transcranial magnetic stimulation (LF-rTMS) to the non-lesioned hemisphere improves paretic arm reach-to-grasp performance. The preliminary results have important implications for the use of LF-rTMS as conjunctive intervention for stroke rehabilitation.

Movement Pattern and Parameter Learning in Children: Effects of Feedback Frequency.

Reduced feedback during practice has been shown to be detrimental to movement accuracy in children but not in young adults. We hypothesized that the reduced accuracy is attributable to reduced movement parameter learning, but not pattern learning, in children. A rapid arm movement task that required the acquisition of a motor pattern scaled to specific spatial and temporal parameters was used to investigate the effects of feedback (FB) frequency (100% vs. 62% faded) on motor learning differences between 19 school-age children and 19 young adults. Adults and children practiced the task for 200 trials under the 100% or faded FB condition on Day 1 and returned on Day 2 for a no-FB retention test. On the retention test, children who practiced with reduced feedback performed with greater temporal parameter errors, but not pattern error, than children who received frequent feedback. Motor skill learning in children is influenced by feedback frequency during practice that affects parameter learning but not pattern learning.

Transfer of Motor Learning Engages Specific Neural Substrates During Motor Memory Consolidation Dependent on the Practice Structure

ABSTRACT The authors investigated how brain activity during motor-memory consolidation contributes to transfer of learning to novel versions of a motor skill following distinct practice structures. They used 1 Hz repetitive Transcranial Magnetic Stimulation (rTMS) immediately after constant or variable practice of an arm movement skill to interfere with primary motor cortex (M1) or dorsolateral prefrontal cortex (DLPFC). The effect of interference was assessed through skill performance on two transfer targets: one within and one outside the range of practiced movement parameters for the variable practice group. For the control (no rTMS) group, variable practice benefited delayed transfer performance more than constant practice. The rTMS effect on delayed transfer performance differed for the two transfer targets. For the within-range target, rTMS interference had no significant affect on the delayed transfer after either practice structure. However, for the outside-range target, rTMS interference to DLPFC but not M1 attenuated delayed transfer benefit following variable practice. Additionally, for the outside-range target, rTMS interference to M1 but not DLPFC attenuated delayed transfer following constant practice. This suggests that variable practice may promote reliance on DLPFC for memory consolidation associated with outside-range transfer of learning, whereas constant practice may promote reliance on M1 for consolidation and long-term transfer.

Motor learning in children with hemiplegic cerebral palsy: feedback effects on skill acquisition

Motor learning is enhanced with practice and feedback. This cohort control study investigated the effect of different relative feedback frequencies during skill acquisition in children with cerebral palsy (CP) and children with typical development.

Effects of Different Doses of Low Frequency rTMS on Motor Corticospinal Excitability

Low frequency (1Hz) repetitive transcranial magnetic simulation (TMS) is known to reduce motor corticospinal excitability. The purpose of this study was to systematically investigate the effects of different intensities and durations of LF-rTMS on measures of motor cortical excitability and inhibition, while trying to minimize sources of variability that affect corticospinal excitability. 9 non-disabled young adults were recruited and screened for contraindications to TMS. We employed a repeated measures design to investigate the effect of the following four intensity-duration combinations (doses) on motor corticospinal excitability: 1) subthreshold intensity (90%Resting Motor Threshold (RMT)) for 10 minutes, 2) subthreshold intensity (90%RMT) for 20 minutes, 3) suprathreshold intensity (110%RMT) for 10 minutes and 4) suprathreshold intensity (110%RMT) for 20 minutes. Each rTMS dose was administered at 4 different sessions separated by at least 7 days. Changes in the motor corticospinal excitability and inhibition were measured using 1) MEP amplitude evoked by 120% RMT at rest and during active contraction and 2) cortical silent period. 1Hz rTMS applied at suprathreshold intensity (110% RMT) reduced corticospinal excitability at rest, irrespective of the duration of stimulation. In contrast, subthresold 1Hz rTMS signi fi cantly decreased corticospinal excitability at rest only when applied for a longer duration (20 min compared to 10 min).Subthreshold rTMS when applied for 10 min induced cortical inhibition as evidenced by a signi fi cant lengthening of the silent period. Down regulation of corticospinal excitability is dose-dependent with supra-threshold 1Hz rTMS more effective, even with a shorter duration compared with a longer duration of stimulation. Further, our study while not con fi rmatory, suggests that different doses of 1Hz rTMS may affect excitatory and inhibitory circuits differently within the motor cortex.

Improvement in Paretic Arm Reach-to-Grasp following Low Frequency Repetitive Transcranial Magnetic Stimulation Depends on Object Size: A Pilot Study

Introduction. Low frequency repetitive transcranial magnetic stimulation (LF-rTMS) delivered to the nonlesioned hemisphere has been shown to improve limited function of the paretic upper extremity (UE) following stroke. The outcome measures have largely included clinical assessments with little investigation on changes in kinematics and coordination. To date, there is no study investigating how the effects of LF-rTMS are modulated by the sizes of an object to be grasped. Objective. To investigate the effect of LF-rTMS on kinematics and coordination of the paretic hand reach-to-grasp (RTG) for two object sizes in chronic stroke. Methods. Nine participants received two TMS conditions: real rTMS and sham rTMS conditions. Before and after the rTMS conditions, cortico-motor excitability (CE) of the nonlesioned hemisphere, RTG kinematics, and coordination was evaluated. Object sizes were 1.2 and 7.2 cm in diameter. Results. Compared to sham rTMS, real rTMS significantly reduced CE of the non-lesioned M1. While rTMS had no effect on RTG action for the larger object, real rTMS significantly improved movement time, aperture opening, and RTG coordination for the smaller object. Conclusions. LF-rTMS improves RTG action for only the smaller object in chronic stroke. The findings suggest a dissociation between effects of rTMS on M1 and task difficulty for this complex skill.