Biomedical subjects

Amy J Bastian

Publications and source records attributed to Amy J Bastian.

At least 19 recordsLinked to original sources

PubMed2006

Learning to predict the future: the cerebellum adapts feedforward movement control.

The role of the cerebellum in motor control and learning has been largely inferred from the effects of cerebellar damage. Recent work shows that cerebellar damage produces greater impairment of movements that require predictive as opposed to reactive control. This dissociation is consistent across many different types of movement. Predictive control is crucial for fast and ballistic movements, but impaired prediction can also affect slow movements, because of increased reliance on time-delayed feedback signals. The new findings are compatible with theories of cerebellar function, but still do not resolve whether the cerebellum operates by predicting the optimal motor commands or future sensory states. Prediction mechanisms must be learned and maintained through comparisons between predicted and observed outcomes. New results show that not all such error information is equivalent in driving cerebellar learning.

Adaptation, Physiological↗

PubMed2006

Cerebellar contributions to locomotor adaptations during splitbelt treadmill walking.

Locomotor adaptability ranges from the simple and fast-acting to the complex and long-lasting and is a requirement for successful mobility in an unpredictable environment. Several neural structures, including the spinal cord, brainstem, cerebellum, and motor cortex, have been implicated in the control of various types of locomotor adaptation. However, it is not known which structures control which types of adaptation and the specific mechanisms by which the appropriate adjustments are made. Here, we used a splitbelt treadmill to test cerebellar contributions to two different forms of locomotor adaptation in humans. We found that cerebellar damage does not impair the ability to make reactive feedback-driven motor adaptations, but significantly disrupts predictive feedforward motor adaptations during splitbelt treadmill locomotion. Our results speak to two important aspects of locomotor control. First, we have demonstrated that different levels of locomotor adaptability are clearly dissociable. Second, the cerebellum seems to play an essential role in predictive but not reactive locomotor adjustments. We postulate that reactive adjustments may instead be predominantly controlled by lower neural centers, such as the spinal cord or brainstem.

Adaptation, Physiological↗

PubMed2006

Sensorimotor function and axonal integrity in adrenomyeloneuropathy.

BACKGROUND: Gait abnormalities and sensorimotor disturbances are principal defects in adrenomyeloneuropathy (AMN). However, to our knowledge, their association with overall impairment and neuroanatomical changes has not been defined. OBJECTIVES: To understand how sensorimotor impairments create mobility deficits and to analyze how these impairments are related to specific metrics of axonal integrity. DESIGN: Cross-sectional study assessing impairments, including vibration sensation, strength, spasticity, and global measures of walking and balance. Fractional anisotropy was measured to evaluate the integrity of the corresponding brainstem tracts. PARTICIPANTS: Men with AMN and healthy control subjects. RESULTS: Individuals with sensory loss only showed minimal walking deficits. Concomitant strength and sensory loss resulted in slower walking, with abnormal knee control; increased spasticity led to an exaggerated trunk motion and a knee-flexed (crouched) posture. Hip strength was an independent predictor of walking velocity in subjects with AMN. Subjects with sensory loss only had greater sway amplitudes during standing balance testing, which did not worsen with additional impairments. There were significant associations among sway amplitude, great toe vibration sense, and dorsal column fractional anisotropy. Brainstem fractional anisotropy in AMN was significantly negatively correlated with impairment, indicating that overall tract integrity is associated with sensorimotor abnormalities in AMN. CONCLUSIONS: Impairment measures capture specific abnormalities in walking and balance that can be used to direct rehabilitation therapy in AMN. Tract-specific magnetic resonance imaging metrics, such as fractional anisotropy (used herein to evaluate structure-function relationships), significantly reflect disease severity in AMN.

Adrenoleukodystrophy↗

PubMed2006

Can spasticity and dystonia be independently measured in cerebral palsy?

Selecting and evaluating appropriate treatments for children with cerebral palsy has been challenging. One difficulty is in the ability to quantify the presence and importance of coexisting motor signs. This study presents quantitative measures developed to assess spasticity and dystonia. Children diagnosed with extrapyramidal or spastic cerebral palsy and matched control children were studied. Spasticity was measured as the slope of the force-velocity relationship from a test where we measured the forces required to passively extend the elbow at different velocities. Dystonia was assessed by measuring "overflow" movements of arm during active movement of the other arm. Measures of dystonia and spasticity did not correlate with one another, but did correlate with their respective clinical measurement tools, the Modified Ashworth scale and the Barry-Albright Dystonia scale. Most children had a combination of both spasticity and dystonia, despite diagnosis. Our measures also related to different aspects of reaching: children with increased dystonia made more curved paths, and children with increased spasticity hit higher peak velocities. These measurements allow us to distinguish between different motor disorders and the degree to which each contributes to reaching performance. Use of quantitative measures should improve selection and evaluation of treatments for childhood motor disorders.

Adolescent↗

PubMed2006

Relationships between sensorimotor impairments and reaching deficits in acute hemiparesis.

OBJECTIVE: To determine the relationships between sensorimotor impairments and upper extremity reaching performance during the acute phase of stroke and to determine which, if any, measures of sensorimotor impairment can predict variance in reaching performance during this phase. METHODS: Sensorimotor impairments of upper extremity (UE) strength, active range of motion, isolated movement control, light touch sensation, joint position sense, spasticity, and shoulder pain were evaluated in a group of 46 individuals with acute hemiparesis (mean time since insult = 9.2 days). Subjects performed a reaching task to a target placed on their affected side. Three-dimensional kinematic analyses were used to assess reaching speed, accuracy, and efficiency. Forward stepwise multiple linear regression analyses were used to determine which impairment was the best predictor of variance in reaching performance. RESULTS: Measures of UE strength predicted the largest proportion of variance in the speed, accuracy, and efficiency of forward reaching. Isolated movement control, somatosensory deficits, and elbow spasticity predicted smaller amounts of variance in reaching performance. CONCLUSIONS: The authors' data show that deficits in strength appear to be the most influential sensorimotor impairment associated with limited reaching performance in subjects with acute hemiparesis.

Adult↗

PubMed2005

Deficits in grasp versus reach during acute hemiparesis.

We studied how acute hemiparesis affects the ability to perform purposeful movements of proximal versus distal upper extremity segments. Given the gradient of corticospinal input to the spinal motoneuron pools, we postulated that movement performance requiring distal segment control (grasping) should be more impaired than movement performance requiring proximal segment control (reaching) in people with hemiparesis. We tested subjects with acute hemiparesis and control subjects performing reach and reach-to-grasp movements. Three characteristics of movement performance were quantified for each movement: speed, accuracy, and efficiency. For the reach, we calculated peak wrist velocity, endpoint error, and reach path ratio. For the grasp, we calculated peak aperture rate, aperture at touch, and aperture path ratio. To evaluate the relative deficits in reaching versus grasping, performance measures were converted to z-scores using control group means and standard deviations. For both the movements, movement times were longer and performance was more variable in the hemiparetic group compared to the control group. Hemiparetic z-scores indicated that relative deficits in movement speed were small in the two movements, with deficits in grasp being slightly greater than deficits in reach. Relative deficits in accuracy showed a trend for being larger in the reach compared to the grasp, but this difference did not reach statistical significance. In contrast, relative deficits in efficiency were larger in the grasp compared to the reach, with reaching efficiency near the range of normal performance. When considering data across all three movement characteristics, the ability to perform a purposeful movement with the distal segments was not clearly more disrupted than the ability to perform a purposeful movement with the proximal segments in people with acute hemiparesis.

Acute Disease↗

PubMed2005

Interlimb coordination during locomotion: what can be adapted and stored?

Interlimb coordination is critically important during bipedal locomotion and often must be adapted to account for varying environmental circumstances. Here we studied adaptation of human interlimb coordination using a split-belt treadmill, where the legs can be made to move at different speeds. Human adults, infants, and spinal cats can alter walking patterns on a split-belt treadmill by prolonging stance and shortening swing on the slower limb and vice versa on the faster limb. It is not known whether other locomotor parameters change or if there is a capacity for storage of a new motor pattern after training. We asked whether adults adapt both intra- and interlimb gait parameters during split-belt walking and show aftereffects from training. Healthy subjects were tested walking with belts tied (baseline), then belts split (adaptation), and again tied (postadaptation). Walking parameters that directly relate to the interlimb relationship changed slowly during adaptation and showed robust aftereffects during postadaptation. These changes paralleled subjective impressions of limping versus no limping. In contrast, parameters calculated from an individual leg changed rapidly to accommodate split-belts and showed no aftereffects. These results suggest some independence of neural control of intra- versus interlimb parameters during walking. They also show that the adult nervous system can adapt and store new interlimb patterns after short bouts of training. The differences in intra- versus interlimb control may be related to the varying complexity of the parameters, task demands, and/or the level of neural control necessary for their adaptation.

Adaptation, Physiological↗

PubMed2005

Antiparkinson medications improve agonist activation but not antagonist inhibition during sequential reaching movements.

The execution of sequential arm movements is critical to activities of daily living such as eating and grooming. It is known that movement sequences are bradykinetic in people with Parkinson's disease (PD) and that antiparkinson medications improve the speed of movement sequences. However, it is unclear how muscle activity is modulated during sequential movements and what effect antiparkinson medications have on muscle modulation. We studied subjects with PD and age- and gender-matched control subjects making sequential reaching movements. Subjects with PD were tested before and after their morning dose of antiparkinson medications (levodopa and/or dopamine agonists). We examined the effect of antiparkinson medications on the modulation of muscle activity (i.e., the ability to activate and inhibit each muscle throughout the course of a sequence). Results showed that the group with PD, before medication, moved more slowly and modulated muscle activity poorly compared to the control group. Antiparkinson medications improved movement speed as expected, although sequential movements remained slower than normal even after medication. Medication improved the ability to activate agonist muscle activity but did not improve the ability to inhibit antagonist activity. Instead, antagonist activity was also increased, resulting in minimal improvements in muscle modulation during sequential reaching movements.

Adult↗

PubMed2004

Prism adaptation during walking generalizes to reaching and requires the cerebellum.

Adaptation of arm movements to laterally displacing prism glasses is usually highly specific to body part and movement type and is known to require the cerebellum. Here, we show that prism adaptation of walking trajectory generalizes to reaching (a different behavior involving a different body part) and that this adaptation requires the cerebellum. In experiment 1, healthy control subjects adapted to prisms during either reaching or walking and were tested for generalization to the other movement type. We recorded lateral deviations in finger endpoint position and walking direction to measure negative aftereffects and generalization. Results showed that generalization of prism adaptation is asymmetric: walking generalizes extensively to reaching, but reaching does not generalize to walking. In experiment 2, we compared the performance of cerebellar subjects versus healthy controls during the prism walking adaptation. We measured rates of adaptation, aftereffects, and generalization. Cerebellar subjects had reduced adaptation magnitudes, slowed adaptation rates, decreased negative aftereffects, and poor generalization. Based on these experiments, we propose that prism adaptation during whole body movements through space invokes a more general system for visuomotor remapping, involving recalibration of higher-order, effector-independent brain regions. In contrast, prism adaptation during isolated movements of the limbs is probably recalibrated by effector-specific mechanisms. The cerebellum is an essential component in the network for both types of prism adaptation.

Adaptation, Physiological↗

PubMed2004

Cerebellar damage produces context-dependent deficits in control of leg dynamics during obstacle avoidance.

It has been suggested that the cerebellum is an important contributor to CNS prediction and control of intersegmental dynamics during voluntary multijoint reaching movements. Leg movements subserve different behavioral goals, e.g., locomotion versus voluntary stepping, which may or may not be under similar dynamic control. The objective was to determine whether cerebellar leg hypermetria (excessive foot elevation) during obstacle avoidance in locomotion and voluntary stepping could be attributed to a particular deficit in appropriately controlling intersegmental dynamics. We compared the performance of eight individuals with cerebellar damage to eight healthy controls as they walked or voluntarily stepped in place over a small obstacle. Joint kinematics and dynamics were calculated during swing phase for both movement contexts. The kinematic analysis showed that hypermetria occurred during both walking and stepping and was associated with excessive knee flexion. When present, the amplitude of hypermetria was greater during stepping compared to walking. During stepping, subjects with cerebellar damage produced excessive knee flexor muscle torques and consequently overcompensated for interaction and gravitational torques normally used to decelerate the limb. During walking, the torque pattern was very similar to that of control subjects walking over a taller obstacle, and therefore might be a voluntary compensatory strategy to avoid tripping. Our results show that the extent of kinematic and dynamic abnormalities associated with cerebellar leg hypermetria is context-specific, with more fundamental abnormalities of leg dynamics being apparent during stepping as opposed to walking.

Adult↗

PubMed2004

Role of the cerebellum in the control and adaptation of gait in health and disease.

In humans, inability to stand and walk is the most limiting of motor disabilities. In humans, upright stance and gait is the most sensitive indicator of cerebellar disease. From animal and human studies, much has been learned about how the cerebellum coordinates normal movement, and how it may play roles in normal motor adaptation and learning. Much of this work suggests that different parts of the cerebellum control stance and gait in different ways, and differently located lesions cause different deficits. What is not known is whether the cerebellum can compensate for stance and gait disorders caused by lesions in other parts of the nervous system, or whether one part of the cerebellum can compensate for deficits caused by lesion of another part. These issues have become increasingly important in rehabilitation research and practice.

Adaptation, Physiological↗

PubMed2004

Children with autism adapt normally during a catching task requiring the cerebellum.

The cerebellum, which has been found to be abnormal in histopathological studies of autism, is important for motor adaptation. We studied controls and children with high functioning autism (HFA) performing a catching adaptation test that is known to be impaired following cerebellar damage. Results showed no differences in adaptation rates or after-effects for HFA subjects versus controls. The findings indicate normal motor adaptation in HFA, suggesting normal or compensated cerebellar function for this task.

Adaptation, Physiological↗

PubMed2004

Cerebellar control of balance and locomotion.

The cerebellum is important for movement control and plays a particularly crucial role in balance and locomotion. As such, one of the most characteristic signs of cerebellar damage is walking ataxia. It is not known how the cerebellum normally contributes to walking, although recent work suggests that it plays a role in the generation of appropriate patterns of limb movements, dynamic regulation of balance, and adaptation of posture and locomotion through practice. The purpose of this review is to examine mechanisms of cerebellar control of balance and locomotion, emphasizing studies of humans and other animals. Implications for rehabilitation are also considered.

Animals↗

PubMed2003

Different effects of unilateral versus bilateral subthalamic nucleus stimulation on walking and reaching in Parkinson's disease.

The purpose of this study was to determine the effects of unilateral versus bilateral subthalamic nucleus (STN) stimulation on quantitative measures of walking and reaching in Parkinson's disease (PD). We used kinematic measures and the Unified Parkinson's Disease Rating Scale (UPDRS) motor subscale (subscale III) to evaluate the movement of 6 people with PD who had bilateral STN stimulators implanted for at least 6 months and withheld their anti-parkinson medication for at least 8 hours. Subjects were studied with both stimulators off, one on, and both on. Kinematic data were collected as subjects walked, reached to a target, and were rated using the UPDRS motor subscale. STN stimulation improved walking speed and stride length, with the greatest benefit from bilateral stimulation. Reaching speed was improved by unilateral STN stimulation alone, with no additive effect of bilateral stimulation. UPDRS motor subscale ratings paralleled the kinematic findings. STN stimulation did not restore PD subjects' movements to the level of age-matched controls. Overall, these results provide further evidence that the basal ganglia pathways involved in control of walking and reaching may be distinct. We speculate that basal ganglia may influence walking through bilateral pedunculopontine projections and reaching through ipsilateral thalamocortical projections. Our findings also suggest that maximal improvement of walking requires bilateral rather than unilateral STN stimulation.

Adult↗

PubMed2003

Effects of pallidotomy and levodopa on walking and reaching movements in Parkinson's disease.

We examined the effects of levodopa and unilateral pallidotomy on quantitative measures of walking and reaching in Parkinson's disease (PD). We also compared quantitative measures of movement with standard clinical rating scales. We used kinematic measures and the Unified Parkinson's Disease Rating Scale (UPDRS) motor subscale (subscale III) to evaluate the movement of 10 people with PD. Subjects were tested after withholding PD medications for at least 8 hours and again 30 to 45 minutes after taking the first morning dose of levodopa. They were studied in this manner before unilateral pallidotomy and then 3.5 to 10 months after surgery. The UPDRS motor subscale was performed in each state. Kinematic data were collected as subjects reached to a target and walked. The UPDRS motor subscale ratings were similar to those reported in the literature: pallidotomy improved the overall motor score and the contralateral bradykinesia + rigidity score, but not the gait + posture score. In contrast, kinematic measures demonstrated that levodopa and pallidotomy had different effects on walking and reaching speed. Both treatments improved walking speed, and the effect was additive. Levodopa improved reaching speed before pallidotomy but did not improve it as much after pallidotomy. Additionally, pallidotomy had inconsistent effects on reaching; some subjects were faster and others were slower. The subjects who initially reached more slowly improved after pallidotomy; the subjects who initially reached more normally (faster) worsened after pallidotomy. On the basis of our results, we speculate that basal ganglia output pathways that control walking and reaching may be distinct, such that bilateral projections to the pedunculopontine area influence walking, whereas ipsilateral thalamocortical projections influence reaching.

Aged↗

PubMed2002

Relative contributions of balance and voluntary leg-coordination deficits to cerebellar gait ataxia.

Different cerebellar regions participate in balance control and voluntary limb coordination, both of which might be important for normal bipedal walking. We wanted to determine the relative contributions of balance versus leg-coordination deficits to cerebellar gait ataxia in humans. We studied 20 subjects with cerebellar damage and 20 control subjects performing three tasks: a lateral weight-shifting task to measure balance, a visually guided stepping task to measure leg- coordination, and walking. We recorded three-dimensional joint position data during all tasks and center of pressure coordinates during weight-shifting. Each cerebellar subject was categorized as having no detectable deficits, a balance deficit only, a leg-placement deficit only, or both deficits. We then determined the walking abnormalities associated with each of these categories. Five of 10 measures of gait ataxia were abnormal in cerebellar subjects with a balance deficit, but only 1 was abnormal in cerebellar subjects with a leg-placement deficit. Furthermore, subjects with a balance deficit performed worse than subjects with a leg-placement deficit on 9 of the 10 gait measures. Finally, performance on the balance task, but not the leg-placement task, explained a significant proportion of the variance in walking speed for the entire cerebellar group. We conclude that balance deficits are more closely related to cerebellar gait ataxia than leg-placement deficits. Our findings are consistent with animal literature, which has suggested that cerebellar control of balance and gait are interrelated, and dissociable from cerebellar control of voluntary, visually guided limb movements.

Adult↗

PubMed2002

Interaction of levodopa and cues on voluntary reaching in Parkinson's disease.

The bradykinesia associated with Parkinson's disease (PD) can be improved by both levodopa and the use of external cues. We examined the combined effect of levodopa and external cueing on the voluntary reaching movements of individuals with PD. Nine subjects with PD and nine matched controls were studied reaching to a ball target. Subjects with PD were studied after being off levodopa overnight and again on their morning dose. Kinematic data were collected as all subjects made both accurate and fast reaches under two different cue conditions: noncued (self-initiated) and cued (triggered by a light). Subjects with PD reached more slowly than controls under all conditions. PD subjects increased their reach velocity and decreased movement time after taking levodopa and also when moving to a cue. However, the effects of levodopa and cueing were not additive. Instead, levodopa improved reach velocity to a greater extent in the noncued vs. cued condition. We also found that levodopa improved accurate (self-paced) reaches more than fast reaches. These data suggest that levodopa may preferentially improve voluntary reaches that are more internally generated.

Antiparkinson Agents↗

PubMed2002

Cerebellar limb ataxia: abnormal control of self-generated and external forces.

Our work has been focused on understanding the mechanism of movement abnormalities associated with cerebellar ataxia. The hypothesis tested is that the cerebellum acts to modulate muscle activity across multiple joints in anticipation of the mechanical interaction torques generated by one's own movement and by external forces. Individuals with cerebellar damage were studied in two sets of experiments. In the first experiment, we studied how cerebellar subjects' movement changed when interaction torques were present, and then reduced via mechanically constraining movement to a single joint. Consistent with the hypothesis, it was found that cerebellar endpoint errors were greatly improved when interaction torques were reduced. We also found that cerebellar deficits in the unconstrained condition were not explained by a general failure of torque timing or magnitude scaling. This supports the idea that the cerebellum plays a specific and important role in adjusting for the dynamics of one's own body movements. In the second experiment, we studied how well cerebellar subjects could adapt arm movements to external loads. Cerebellar subjects were tested as they adapted a catching movement to balls of different weight. It was found that they were slow or unable to adapt through practice and did not show evidence of storage of the adaptation. This suggests that the cerebellum is needed for rapid adaptations for loads in movement. Given these findings, we think that the cerebellum is important in anticipating and adjusting for the mechanical demands of movement though trial-and-error practice.

Analysis of Variance↗