Biomedical subjects

P Ruby

Publications and source records attributed to P Ruby.

5 recordsLinked to original sources

PubMed2004

Regional organisation of brain activity during paradoxical sleep (PS).

Human brain function is regionally organised during paradoxical sleep (PS) in a very different way than during wakefulness or slow wave sleep. The important activity in the pons and in the limbic/paralimbic areas constitutes the key feature of the functional neuroanatomy of PS, together with a relative quiescence of prefrontal and parietal associative cortices. Two questions are still outstanding. What neurocognitive and neurophysiological mechanisms may explain this original organization of brain function during PS? How the pattern of regional brain function may relate to dream content? Although some clues are already available, the experimental answer to both questions is still pending.

Action Potentials↗

PubMed2001

Effect of subjective perspective taking during simulation of action: a PET investigation of agency.

Perspective taking is an essential component in the mechanisms that account for intersubjectivity and agency. Mental simulation of action can be used as a natural protocol to explore the cognitive and neural processing involved in agency. Here we took PET measurements while subjects simulated actions with either a first-person or a third-person perspective. Both conditions were associated with common activation in the SMA, the precentral gyrus, the precuneus and the MT/V5 complex. When compared to the first-person perspective, the third-person perspective recruited right inferior parietal, precuneus, posterior cingulate and frontopolar cortex. The opposite contrast revealed activation in left inferior parietal and somatosensory cortex. We suggest that the right inferior parietal, precuneus and somatosensory cortex are specifically involved in distinguishing self-produced actions from those generated by others.

Acoustic Stimulation↗

PubMed1993

Response of intersegmental knee loads to foot/pedal platform degrees of freedom in cycling.

The hypothesis tested in this article was that the three-dimensional intersegmental knee loads would be reduced in cycling by foot/pedal platforms which permitted relative motion between the foot and pedal. To test this hypothesis, pedal load and lower limb kinematic data were collected from 11 subjects who pedaled with four foot/pedal platforms mounted on a six-load-component dynamometer. One of the four platforms did not allow any relative foot/pedal movement while the other three permitted either medial/lateral translation, adduction/abduction rotation or inversion/eversion rotation. Three-dimensional intersegmental knee loads were computed for each of the four platforms using a previously reported biomechanical model. A number of quantities describing each of the intersegmental knee load components was computed and compared using analysis of variance techniques. The key results were that the medial/lateral translation platform did not cause significant differences in intersegmental knee load quantities relative to those for the fixed platform. However, both of the platforms permitting rotations significantly reduced many but did not significantly increase any intersegmental knee load quantities. Of these two platforms, the abduction/abduction platform significantly reduced both the axial and varus/valgus knee moments while the inversion/eversion platform significantly reduced only varus/valgus moments. These results have application to bicycle pedal design where the goal is to reduce intersegmental knee loads, hence possibly alleviating overuse knee injuries.

Bicycling↗

PubMed1992

The effect of lower-limb anatomy on knee loads during seated cycling.

Overuse knee joint injuries are the primary injuries to cyclists. Overuse injuries have been intuitively linked to the anatomic structure of the foot because external loads are applied to the foot in cycling. Thus, the structure and function of the foot should dictate in part how the loads are transmitted to the knee joint. Therefore, it was hypothesized that patterns in knee loads are related to the anatomic structure of the foot. To test this hypothesis, peak knee loads (dependent variables) were related to anatomical variables (independent variables) through statistical analyses. This required first the detailed evaluation (i.e. measurement) of the anatomical structure of the foot and leg for 23 subjects. Next, three-dimensional knee joint loads were determined for a standardized riding condition. The results of the statistical analyses indicated that a group of cyclists with the most extreme inversion of the forefoot relative to the transverse plane developed significantly greater average posterior knee force and extensive knee moment. In addition, a number of anatomical variables significantly accounted for the variability in peak values of the posterior force, the extensive moment, the varus/valgus moment and the external axial moment. Based on these results, the hypothesis is accepted.

Adult↗

PubMed1992

Three-dimensional knee joint loading during seated cycling.

The hypothesis which motivated the work reported in this article was that neglecting pure moments developed between the foot and pedal during cycling leads to a substantial error in computing axial and varus/valgus moments at the knee. To test this hypothesis, a mathematical procedure was developed for computing the three-dimensional knee loads using three-dimensional pedal forces and moments. In addition to data from a six-load-component pedal dynamometer, the model used pedal position and orientation and knee position in the frontal plane to determine the knee joint loads. Experimental data were collected from the right leg of 11 male subjects during steady-state cycling at 90 rpm and 225 W. The mean peak varus knee moment calculated was 15.3 N m and the mean peak valgus knee moment was 11.2 N m. Neglecting the pedal moment about the anterior/posterior axis resulted in an average absolute error of 2.6 N m and a maximum absolute error of 4.0 N m in the varus/valgus knee moment. The mean peak internal and external axial knee moments were 2.8 N m and 2.3 N m, respectively. The average and maximum absolute errors in the axial knee moment for not including the moment about an axis normal to the pedal were found to be 2.6 N m and 5.0 N m, respectively. The results strongly support the use of three-dimensional pedal loads in the computation of knee joint moments out of the sagittal plane.

Acceleration↗