The effect of cerebellar cortical degeneration on adaptive plasticity and movement control.

Clinical and neuroimaging studies provide converging evidence that the cerebellum plays an important role for sensorimotor adaptation by participating in the adaptive process per se, and/or by evaluating motor performance errors as a prerequisite for adaptation. Recent experimental evidence suggests that error signals pertinent to adaptation are related to sensory prediction rather than to online corrections (Tseng et al. in J Neurophysiol 98(1):54-62, 2007).

Motor performance and motor learning in sustained +3 Gz acceleration.

Introduction: Previous studies have shown that increased head-to-foot acceleration (+Gz) like that experienced in maneuvering aircraft impairs motor performance. However, there are few studies of motor performance providing detailed descriptions of specific deficits (e.g.

Transfer of adaptation between ocular saccades and arm movements.

Previous studies found little or no transfer of adaptation from reactive saccades to arm pointing movements, which suggests that the two motor systems rely on distinct adaptive mechanisms. However, this conclusion is based on experiments about the adaptation of response amplitudes, which is known to follow somewhat different principles than the adaptation of response directions. In the present study, we therefore investigate whether adapting the direction of reactive saccades will transfer to arm movements.

Isometric force production during changed-Gz episodes of parabolic flight.

Changes of the normal gravitational acceleration are known to affect sensorimotor performance. For example, subjects exposed to three times the normal terrestrial acceleration (+3 Gz) in a centrifuge will produce exaggerated isometric force. The present study compares the effects of high-Gz to that of micro-Gz on isometric force production.

An fMRI study of brain activation in a visual adaptation task: activation limited to sensory guidance.

Previous neuroimaging studies yielded different patterns of brain areas activated during sensorimotor adaptation, when sensory conflicts are introduced, e.g. by manipulating visual information.

Effects of variable practice and declarative knowledge on sensorimotor adaptation to rotated visual feedback.

It has been shown before that sensorimotor adaptation to rotated vision is more generalized when subjects point at eight, rather than at four or less targets. Here we evaluate whether an even more variable practice has additional benefits. One group of subjects pointed at eight targets, and another group executed unconstrained arm movements throughout the workspace.

Adaptation of grasping responses to distorted object size and orientation.

The present study investigated the adaptive plasticity of the grasp component of prehensile movements. Subjects saw visual objects (V) of various sizes and orientations and were instructed to seize them with the thumb and index finger without manipulating them. The subjects' hand disappeared from view during the response and made contact with a haptic object (H), which could differ with respect to size or orientation from V.

A method to reversibly degrade proprioceptive feedback in research on human motor control.

In research on human motor skills, it is often desirable to manipulate proprioceptive feedback in order to determine its contribution towards subjects' performance. Here we evaluate an easy-to-use, non-invasive method to temporarily reduce proprioceptive responsiveness. Two physiotherapy vibrators contacted the distal end of the subjects' forearm on the flexor and extensor side; they were either turned off, or they vibrated at 80 Hz with an amplitude of 1mm.

Practice ameliorates deficits of isometric force production in +3 Gz.

Background: In our earlier work, we have shown that human subjects produce exaggerated isometric forces when exposed to three times terrestrial gravity (+3 Gz). In the present work, we investigated whether prolonged practice under +3 Gz reduces this deficit, and whether it affects the cognitive costs of force production.

Methods: There were 24 young male student volunteers who produced forces without visual feedback of prescribed directions and magnitudes with their dominant hand, and used their other hand for a four-choice reaction-time task.

The contribution of proprioceptive feedback to sensorimotor adaptation.

It is known that proprioceptive signals from muscles, joints, and skin are involved in the execution of aimed arm movements, but their role in the acquisition of new motor behaviour is largely unknown. Previous research using deafferented patients yielded inconsistent findings: sensorimotor adaptation was found to be less, equal, or even better than in controls. The present study uses a different approach: we degraded proprioceptive signals in healthy subjects by wrist vibration, while leaving them intact in a control group.

Relationship between sensorimotor adaptation and cognitive functions in younger and older subjects.

We investigated whether deficits of adaptive improvement in seniors are related to an age-dependent decay of the brain's executive functions. Younger and older subjects completed a battery of cognitive tests, and preformed aimed arm movements before and during exposure to rotated visual feedback. In accordance with previous work, we found that adaptive improvement during exposure was degraded in seniors, while the transfer of adaptation to a new motor task was not.

Concurrent adaptations of left and right arms to opposite visual distortions.

Previous research has shown that subjects can adapt with either arm to an opposite visual distortion, and the two adaptive states can then be used in sequence to control the respective arm. To extend this finding, we exposed the left and right arms of our subjects to opposite-directed rotations of the visual field alternately for 20 s each, and determined the time-course of adaptation, as well as aftereffects without visual feedback under uni- and bimanual conditions. Our data confirm that two adaptive states can co-exist in the sensorimotor system, one for each arm.

The effect of rest breaks on human sensorimotor adaptation.

We have studied the effect of rest breaks on sensorimotor adaptation to rotated visual feedback in a pointing task. Adaptive improvement was significantly poorer after 1-s breaks than after 5-40-s breaks, with no significant difference among the latter break durations. The benefit of >1-s breaks emerged soon after the onset of adaptation, and then remained steady throughout the adaptation, retention (next day), and persistence (no feedback) phases.