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Biomedical subjects

L J Bouyer

Publications and source records attributed to L J Bouyer.

7 recordsLinked to original sources
PubMed2001

Adaptive locomotor plasticity in chronic spinal cats after ankle extensors neurectomy.

After lateral gastrocnemius-soleus (LGS) nerve section in intact cats, a rapid locomotor compensation involving synergistic muscles occurs and is accompanied by spinal reflex changes. Only some of these changes are maintained after acute spinalization, indicating the involvement of descending pathways in functional recovery. Here, we address whether the development of these adaptive changes is dependent on descending pathways. The left LGS nerve was cut in three chronic spinal cats. Combined kinematics and electromyographic (EMG) recordings were obtained before and for 8 d after the neurectomy. An increased yield at the ankle was present early after neurectomy and, as in nonspinal cats, was gradually reduced within 8 d. Compensation involved transient changes in step cycle structure and a longer term increase in postcontact medial gastrocnemius (MG) EMG activity. Precontact MG EMG only increased in one of three cats. In a terminal experiment, the influence of group I afferents from MG and LGS on stance duration was measured in two cats. LGS effectiveness at increasing stance duration was largely decreased in both cats. MG effectiveness was only slightly changed: increased in one cat and decreased in another. In cat 3, the plantaris nerve was cut after LGS recovery. The recovery time courses from both neurectomies were similar (p > 0.8), suggesting that this spinal compensation is likely a generalizable adaptive strategy. From a functional perspective, the spinal cord therefore must be considered capable of adaptive locomotor plasticity after motor nerve lesions. This finding is of prime importance to the understanding of functional plasticity after spinal injury.

Adaptation, Physiological↗
PubMed1999

"Torso Rotation" experiments. 4: the role of vision and the cervico-ocular reflex in compensation for a deficient VOR.

Acute, reversible changes in human vestibular function can be produced by exposure to "Torso Rotation" (TR), a method involving the overuse of certain types of simple, self-generated movements. A single session results in multiple, short-lasting aftereffects, including perceptual illusions, VOR gain reduction, gaze and postural instability, and motion sickness. With repeated exposure, motion sickness susceptibility disappears and gaze stability improves. VOR gain continues to be reduced, however. Therefore, another gaze stabilizing system must come into play. Are visual and/or neck inputs involved in this functional compensation? Six subjects participated in this 7-day experiment. Eye and head movements were measured during 2 tests: 1) voluntary "head only" shaking between 0.3 and 3.0 Hz (lights off) and 2) voluntary "head and torso" shaking, moving the upper body en bloc (neck immobilized). Measurements were obtained before and repeatedly after TR. Velocity gain (eye velocity/head velocity) was determined for each of these tests. Each day, mean velocity gain during "head only" shaking in the dark (averaged over 1.0 to 2.0 Hz) dropped significantly after TR (P < 0.01), with no long-term improvement (P > 0.9). Similar results, although more noisy, were obtained for "head and torso" shaking. As a control, EOG calibration data confirmed that gaze stability in the light did improve over the 7 days of testing. This experiment demonstrates that the reduction in gaze instability following repeated exposure to TR results from an increased use of vision. It excludes the VOR, the COR, and predictive mechanisms (including efference copy) as contributors. In addition, in the 20 minutes following TR completion, gaze stability recovered less than during previous VOR testing in the dark. These results are compatible with the motion that exposure to TR leads to a change in sensorimotor strategy involving a de-emphasis of vestibular inputs.

Adult↗
PubMedDate not supplied

"Torso rotation" experiments; 1: Adaptation to motion sickness does not correlate with changes in VOR gain.

Following a 30-minute exposure to an unusual motor strategy called "Torso Rotation" (TR), the signs and symptoms of motion sickness appear along with perceptual illusions during movement, gaze and postural instability, and a significantly reduced vestibulo-ocular response (VOR) gain. With repeated exposure to TR, the motion sickness disappears and gaze instability seems to be reduced. Is this apparent improvement in gaze stability associated with a reduction of the transient change in VOR gain? Motion sickness (subjective questionnaire) and VOR gain (passive step rotations in darkness) were measured before and repeatedly after TR on 7 consecutive days. Despite a complete loss of symptoms in 3 to 4 days, the transient, daily change in VOR gain remained unaffected. Furthermore, there was no increase in the use of compensatory saccades. It is concluded that adaptation to TR-induced motion sickness is not the result of a change in VOR's sensitivity to TR.

Adaptation, Physiological↗
PubMedDate not supplied

"Torso rotation" experiments; 2: Gaze stability during voluntary head movements improves with adaptation to motion sickness.

Following a 30-minute exposure to an unusual motor strategy called "Torso Rotation" (TR), the signs and symptoms of motion sickness appear along with perceptual illusions during movement, gaze and postural instability, and a significantly reduced vestibulo-ocular response (VOR) gain. With repeated exposure to TR, motion sickness symptoms disappear and gaze instability seems reduced, but without any concomitant change in VOR gain. Is the reduction in gaze instability a perceptual illusion or a real, measurable phenomenon? Velocity gain (eye velocity/ head velocity) was evaluated during voluntary head shaking in the light over the frequency range 0.3 to 3.0 Hz. A significant improvement was seen after 3 days of testing (P < 0.01). Furthermore, the time course of improvement in gaze stability was correlated with the loss of motion sickness symptoms reported in the previous study (1). We suggest that adaptation to motion sickness could be related to an overall change in sensori-motor strategy, perhaps including a de-emphasis of a vestibular reference.

Adaptation, Physiological↗
PubMedDate not supplied

"Torso rotation" experiments; 3: Effects of acute changes in vestibular function on the control of voluntary head movements.

"Torso Rotation" (TR) produces an acute, reversible change in human vestibular function. Experiments were performed to determine if repeated exposure to this technique would result in long-term adaptive modifications. In one experiment, VOR gain was evaluated. Measurements were obtained before and 3 times after 30 minutes of TR, on 7 consecutive days. VOR gain dropped each day after TR, returning to normal within about 20 min. In a separate experiment with different subjects, eyes-open gaze stability was measured during voluntary head shaking between 3.0 and 0.3 Hz. The same test schedule was used. Analysis of gaze stability (limited to frequencies between 1.0 and 2.0 Hz) was complicated by an unexpected finding. Despite careful instructions, head displacement increased each day after TR, also returning to normal within about 20 min. Surprisingly, subjects were unaware of this change. Combining the 2 experiments, VOR gain and head amplitude were averaged across all 7 days, separately for the 4 daily tests. Head amplitude was plotted against VOR gain for these 4 averages. Amplitude was greater when VOR gain was reduced, with a remarkably high correlation (R2 = 0.996). These findings confirm that vestibular feedback plays an important role in the control of voluntary head movement. Furthermore, the data suggest that instability of the visual scene reported by subjects shaking their heads after TR resulted not only from a lower VOR gain, but also from the inadvertent use of higher head velocities.

Female↗