[Functional magnetic resonance imaging before motor cortex stimulation for phantom limb pain]. / fMRT vor Motorkortexstimulation beim Phantomschmerz.

This study deals with the diagnostic value of functional magnetic resonance imaging (fMRI) in a patient with phantom limb pain following traumatic amputation of the right arm. After failure with medication, resection of stump neurinoma, and spinal cord stimulation, fMRI with evidence of cortical reorganization was performed. Tactile stimulation of the perioral region and motor imagery with cranial, tactile stimulation of the stump led to a caudal shift in fMRI activity. Subsequent motor cortex stimulation brought relief from the pain. By detecting cortical reorganization, fMRI contributes to the indication for motor cortex stimulation for phantom pain and aids in electrode positioning.

The influence of microgravity on memorized arm movements.

To investigate sensory and motor functions in microgravity, goal-oriented arm movements were performed by 9 cosmonauts in weightlessness. The ability to reproduce predefined motor patterns was examined pre-, in-, and post-flight under two different paradigms: In a first test, the cosmonaut had to reproduce passively learned movements with eyes closed, while in the second test, the cosmonaut learned the pattern with eyes open. The different learning paradigms effected the metric parameters of the memorized stimulus pattern while the influence of the different gravity levels resulted in significant offsets and torsions of the reproduced figures. In comparing the inflight condition with preflight, intact proprioceptive afference seemed to play an important role for reproducing movements from motor short-time memory correctly.

Slowing of human arm movements during weightlessness: the role of vision.

The human motor system responds to weightlessness by the slowing of movement. It has been suggested that deficits in visuo-motor co-ordination cause this effect. We studied the mechanisms of the slowing of movement in three long-term missions to the Russian space station Mir. In particular, the role of vision in the control of movement in microgravity has been studied in these experiments on seven cosmonauts, pre-, in-, and post-flight. The cosmonauts made arm movements to visual targets under the following conditions of visual control: no visual control, interrupted visual control, and undisturbed visual control. The results showed that the slowing of movement during weightlessness was manifested by decreases of peak velocity and peak acceleration, was not associated with a prolongation of the movement phase of deceleration, and was not affected by manipulation of the conditions of visual control. The slowing of movement tended to subside after the months of the flight and completely disappeared within days after the landing. Accuracy of the movements strictly depended on the constraints imposed on the vision and remained unaffected in-flight. The data presented demonstrate that the slowing of movement in microgravity is not directly related to deficits in sensori-motor co-ordination and is not associated with a reduction of the accuracy of movement. The strategy for motor control in microgravity seems to be directed towards the generation of smooth movements and the maintenance of their accuracy.

The effect of head-to-trunk position on the direction of arm movements before, during, and after space flight.

This contribution deals with the examination of the consequences of different head-to-trunk positions on arm movements under normal gravity and during prolonged space flight. One of the objectives of this study was to investigate the influence of weightlessness on the condition of the spatial analysis system. Aimed arm movements in the horizontal plane (pointings towards two visual targets) were recorded, first with eyes open, head straight (learning part), then with eyes closed, head straight and during yaw or roll position of the head (performance part). Measurements related to these different head-to-trunk-positions were taken in one short-term and nine long-term cosmonauts preflight, inflight, and postflight. Terrestrial control experiments were carried out with an extended experimental design in 14 healthy volunteers. The analysis of these experiments revealed that, with eyes closed and the head in yaw position, cosmonauts before flight and control subjects exhibit significant slants of the movement plane of the arm. Contrary to terrestrial measurements, in space experiments roll tilt of the head to the right is correlated with considerable counterclockwise slant of the movement plane. This slant of the movement plane of the arm was interpreted as tilt of the internal representation of the horizontal coordinate. The effect is larger with greater distortion induced by the changed head position and with larger muscular involvement to keep this position. This effect is also increased by the reduction of information (for example, in microgravity). The amount and the direction of the horizontal offset of the arm movements are shown to be dependent on the head-to-trunk position, too. Additionally, we have found changes in the amplitude and in the duration of the arm movement, in the vertical offset, and in the curvature of the movement paths, depending on the experimental conditions.

[Discrimination between pain-induced head movement disturbances after whiplash injuries and their simulation]. / Diagnose schmerzbedingter und simulierter zervikaler Bewegungsstörungen nach Akzelerations-Dezelerations-Trauma der Halswirbelsäule.

Neck pain after whiplash injury of the cervical spine often induces typical changes in head motion patterns (amplitude, velocity). These changes of kinematics may help to recognize malingerers. We investigated the hypothesis that malingerers are not able to reproduce their simulated head movement disturbances three times. The kinematics of head movements of 23 patients with neck pain after whiplash injury and of 22 healthy subjects trying to act as malingerers were compared. The healthy subjects were informed about the symptomatology of whiplash injury and were asked to simulate painful head movements. Two different kinds of head movements were registered and analyzed by Cervicomotography: (1) the slow free axial head rotation (yaw) and (2) the axial head rotation (yaw) tracking a moving visual target. Each experimental condition was presented three times, expecting the malingerers not to be able to produce as well as to reproduce the same head movement disturbances again and again. In patients, as a consequence of their distinct pain patterns, we expected less variance between the test repetitions. The statistical analysis showed significant differences of the calculated kinematic parameters between both groups and the inability of healthy subjects to simulate and to reproduce convincingly distinct pain patterns.

Pointing arm movements in short- and long-term spaceflights.

Accuracy and kinematics of horizontal arm pointing movements to visual targets were studied on three cosmonauts in 10-, 140-, and 172-d spaceflights in order to investigate mechanisms of the sensorimotor adaptation to microgravity. The Austrian equipment MONIMIR was mounted on board the Russian space station MIR and used for three-dimensional recording of the arm position and presentation of the targets. It was found that movement accuracy remained constant whereby movement durations significantly increased in all inflight sessions compared to the preflight baseline values. Inflight, movement peak velocities as well as acceleration and deceleration peak values decreased significantly. Analysis of the velocity-time profiles showed that the ratio between acceleration and deceleration phases decreased slightly for one cosmonaut and increased insignificantly for the other two cosmonauts. All phases of the acceleration-time profiles increased inflight by the same factor. These data fail to support the assumption of an increased role of the direct visual guidance in movement execution in microgravity. This suggests that the movement slowing in microgravity may be caused by a control strategy employed by the CNS to avoid the specific disadvantage of the absence of gravity. It is hypothesized that intra-movement control mechanisms play an important role in the movement coordination in the altered gravity environment.

The auditory subjective vertical as a function of body tilt.

A loudspeaker is moved from a position beside the subject to a position vertically above the subject's head. The subject's head is either in the normal upright position (= 0 degrees) or the head (and body) is tilted 30 degrees or 60 degrees to the left. The subject estimates the sound as vertical (=auditory subjective vertical, ASV) before it reaches the true above-head position. This results in differences between the ASV obtained from clockwise or counterclockwise movement (Fig. 1). The ASV changes with experimental time (Fig. 2). The data are discussed with respect to findings about the visually perceived SV.

The effect of preceding tilt on the perceived vertical. Hysteresis in perception of the vertical.

The subjective vertical (SV) was measured at various positions of roll-tilt (R). Positions R90-right, R 45-right, R0, R45-left, R90-left were reached either in clockwise sequence (i.e. starting with R 90-left) or in counterclockwise sequence (starting with R90-right); position R135-right was attained from R 110-right or R 160-right. The SV was affected by the preceding tilt (hysteresis). Clockwise position sequence produced, for example, a counterclockwise SV deviation (from the medium value at the obtained position) as though indicating a more advanced tilt position (Fig. 5). It is concluded that the aftereffects and hysteresis differences in perception of position and of SV depend on adaptational processes in the somatoreception system which interacts with the labyrinth posture-receptors.