Development and pilot testing of an early childhood somatosensory assessment: Somatosensory test of reaching.

Thirty-two children (50% female, 59.3% White, 7-60 months), from middle to high socioeconomic status families, participated in pilot feasibility and validity testing of the somatosensory test of reaching (STOR). STOR tested the child's accuracy of reach to visual and somatosensory targets. All children were able to complete the assessment. Statistically significant differences were found between age groups (p = .0001), showing developmental trends, and between test conditions (p < .001), showing that the ability to reach to visible targets develops before somatosensory targets. STOR also showed a moderate correlation with the Developmental Assessment of Young Children 2nd edition. STOR appears to be a promising tool for assessing somatosensory processing in very young children, and it warrants additional testing in larger participant samples.

Assessing Proprioception in Children: A Review.

Proprioception is the subconscious and conscious awareness of the spatial and mechanical status of the musculoskeletal framework. When working with children with motor delays and sensory integrative dysfunction, occupational therapists routinely assess the client's proprioceptive system. However, currently available assessments for occupational therapists are primarily observer-based and concerns have been raised about the reliability of observer-based assessments of sensation. The author's purpose was to review measures of proprioception currently available to occupational therapists and explore direct measures of proprioception from neuroscience and rehabilitation that can be adapted for pediatric clinical use. Observer-based and direct measurements of proprioception assessments complement each other in meeting clinical needs. A better understanding of both types of evaluation will improve proprioceptive evaluation.

Two different motor learning mechanisms contribute to learning reaching movements in a rotated visual environment.

Practice of movement in virtual-reality and other artificially altered environments has been proposed as a method for rehabilitation following neurological injury and for training new skills in healthy humans.  For such training to be useful, there must be transfer of learning from the artificial environment to the performance of desired skills in the natural environment.  Therefore an important assumption of such methods is that practice in the altered environment engages the same learning and plasticity mechanisms that are required for skill performance in the natural environment.  We test the hypothesis that transfer of learning may fail because the learning and plasticity mechanism that adapts to the altered environment is different from the learning mechanism required for improvement of motor skill.  In this paper, we propose that a model that separates skill learning and environmental adaptation is necessary to explain the learning and aftereffects that are observed in virtual reality experiments.  In particular, we studied the condition where practice in the altered environment should lead to correct skill performance in the original environment. Our 2-mechanism model predicts that aftereffects will still be observed when returning to the original environment, indicating a lack of skill transfer from the artificial environment to the original environment. To illustrate the model prediction, we tested 10 healthy participants on the interaction between a simple overlearned motor skill (straight hand movements to targets in different directions) and an artificially altered visuomotor environment (rotation of visual feedback of the results of movement).  As predicted by the models, participants show adaptation to the altered environment and after-effects on return to the baseline environment even when practice in the altered environment should have led to correct skill performance.  The presence of aftereffect under all conditions that involved changes in environment demonstrates separation of environmental adaptation and skill learning. Our results support the existence of two distinct learning modules with different adaptation properties.  Therefore we suggest that adaptation to an altered environment may not be useful for training new skills.

Effect of antispastic drugs on motor reflexes and voluntary muscle contraction in incomplete spinal cord injury.

OBJECTIVE: To investigate the effects of antispastic drugs baclofen and tizanidine on reflexes and volitional tasks. DESIGN: Double-blind, placebo-controlled, crossover, before-after trial, pilot study. SETTING: Research laboratory in a rehabilitation hospital. PARTICIPANTS: Men with chronic (>6mo) motor incomplete spinal cord injury (N=10) were recruited for the study. INTERVENTIONS: Tizanidine, baclofen, and placebo were tested in this study. Agents were tested in separate experimental sessions separated by >1 week. MAIN OUTCOME MEASURES: Reflex and strength were measured before and after the administration of a single dose of each intervention agent. Electromyographic and joint torque data were collected during assessments of plantar flexor stretch reflexes, maximum contraction during motor-assisted isokinetic movements, and maximum isometric knee extension and flexion. RESULTS: Reduced stretch reflex activity was observed after the administration of either tizanidine or baclofen. We observed that tizanidine had a stronger inhibitory effect on knee extensors and plantar flexors whereas baclofen had a stronger inhibitory effect on the knee flexors. The effects of these drugs on strength during isometric and isokinetic tasks varied across participants, without a consistent reduction in torque output despite decreased electromyographic activity. CONCLUSIONS: These results suggest that antispastic drugs are effective in reducing stretch reflexes without substantially reducing volitional torque. Differential effects of tizanidine and baclofen on reflexes of flexors and extensors warrant further investigation into patient-specific management of antispastic drugs.

Healthy and dystonic children compensate for changes in motor variability.

Successful reaching requires that we plan movements to compensate for variability in motor output. Previous studies have shown that healthy adults optimally incorporate estimates of motor variability when planning a pointing task. Children with dystonia have increased variability compared with healthy children. It is not known whether they are able to compensate appropriately for the increased variability and whether this compensation leads to changes in reaching behavior. We examined healthy children and those with increased motor variability due to secondary dystonia. Using a simple virtual display, children performed a motor task where the variability of their movements was manipulated. Results showed that both subject groups changed their movement strategies in response to changes in the level of perceived motor variability. Both groups changed their strategy in a way that improved performance relative to the perceived motor variability. Importantly, dystonic children faced with decreased motor variability adapted their movement strategy to perform better and more similarly to healthy children. These findings show that both healthy and dystonic children are able to respond to changes in motor variability and alter their movement strategies.