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J C Lepecq

Publications and source records attributed to J C Lepecq.

11 recordsLinked to original sources
PubMed2001

Vestibular projections in the human cortex.

There is considerable evidence from studies on cats and monkeys that several cortical areas such as area 2v at the tip of the intraparietal sulcus, area 3av in the sulcus centralis, the parietoinsular vestibular cortex adjacent to the posterior insula (PIVC) and area 7 in the inferior parietal lobule are involved in the processing of vestibular information. Microelectrode recordings from these areas have shown that: (1) most of these cortical neurons are connected trisynaptically to the labyrinthine endorgans and (2) they receive converging vestibular, visual and somatosensory inputs. These data suggest that a multimodal cortical system is involved in postural and gaze control. In humans, recent positron emission tomography (PET) scans and functional magnetic resonance imaging (fMRI) studies have largely confirmed these data. However, because of the limited temporal resolution of these two methods, the minimum time of arrival of labyrinthine inputs from the vestibular hair cells to these cortical areas has not yet been determined. In this study, we used the evoked potential method to attempt to answer this question. Due to its excellent temporal resolution, this method is ideal for the investigation of the tri- or polysynaptic nature of the vestibulocortical pathways. Eleven volunteer patients, who underwent a vestibular neurectomy due to intractable Meniere's disease (MD) or acoustic neurinoma resection, were included in this experiment. Patients were anesthetized and the vestibular nerve was electrically stimulated. The evoked potentials were recorded by 30 subcutaneous active electrodes located on the scalp. The brain electrical source imaging (BESA) program (version 2.0, 1995) was used to calculate dipole sources. The latency period for the activation of five distinct cortical zones, including the prefrontal and/or the frontal lobe, the ipsilateral temporoparietal cortex, the anterior portion of the supplementary motor area (SMA) and the contralateral parietal cortex, was 6 ms. The short latency period recorded for each of these areas indicates that several trisynaptic pathways, passing through the vestibular nuclei and the thalamic neurons, link the primary vestibular afferents to the cortex. We suggest that all these areas, including the prefrontal area, process egomotion information and may be involved in planning motor synergies to counteract loss of equilibrium.

Brain Mapping↗
PubMed2001

Imagined body orientation and perception of the visual vertical.

The existence of body orientation mental imagery was tested by examining whether self roll tilt imagery affects the subjective visual vertical (SVV). Twenty healthy subjects judged the orientation of a dim luminous bar with respect to gravitational vertical, while normally seated in complete darkness with their head firmly restrained earth vertically. SVV was measured in three conditions: a reference condition with no imagery, and a left and a right imagery condition, during which the bar orientation was to be judged while the subjects imagine themselves roll-tilted towards left or right, respectively. The imagined roll tilts were of the same magnitude as roll tilts which generally induce an E-effect, i.e., an SVV lean toward the side opposite to those of body tilt. If imagery and perception of self roll tilt share common processes, self roll tilt imagery should induce an E-like effect. Results show an imagery-induced E-like effect, which strongly supports the idea that humans can perform mental imagery of body orientation about gravity.

Adult↗
PubMed2000

Evidence of imagined passive self-motion through imagery-perception interaction.

The existence of whole-body passive self-motion mental imagery was investigated by examining whether the perception of passive body accelerations can be affected by passive self-motion imagery. Twenty healthy subjects recognised target passive body acceleration. This recognition task was performed under three conditions: (1) a baseline condition without imagery; (2) a compatible imagery condition during which subjects imagined themselves passively moving in the same direction as the target acceleration; (3) a non-compatible imagery condition during which subjects imagined themselves passively moving in the direction opposite to that of the target acceleration. The recognition of the target acceleration was improved under compatible and degraded under non-compatible imagery. This interaction implies that perception and imaginary share common representations, and supports the existence of passive self-motion imagery.

Acceleration↗
PubMed1999

Vestibular sensitivity and vection chronometry along the spinal axis in erect man.

A study is reported of the relations between vestibular sensitivity and vection chronometry in healthy human adults. Twenty-three subjects were examined. For both vestibular and vection investigations, the subjects were seated in an armchair with the spinal axis aligned with the earth vertical and the head normally erect. The subjects' vestibular thresholds for detection of vertical upward accelerations were assessed by a double-staircase psychophysical method. The subjects' vection onset latencies were measured for both upward and downward directions. Since the vection onset latencies are presumed to be shortened by the decrease of the conflict between visual and vestibular afferents, the less-vestibular-sensitive subjects were hypothesised to have shorter vection onset latencies than the more-vestibular-sensitive ones. As expected, the results indicate a negative correlation between vestibular thresholds and vection onset latencies: the higher the vestibular thresholds, the lower the vection onset latencies.

Adult↗
PubMed1998

Linear-vection chronometry along spinal and sagittal axes in erect man.

The present study investigates the onset latencies for linear vection along both the spinal and the sagittal axis in erect human adults. For each axis, both directions have been investigated (upward vs downward, forward vs backward). The vection-onset latency is thought to be shortened by the decrease of the conflict between visual and vestibular afferents. Since this sensory conflict can be presumed to be more important in the horizontal sagittal axis than in the vertical spinal one, the vection-onset latencies have been hypothesised to be longer in the former case than in the latter. Additionally, since the magnitude of this sensory conflict can be presumed to be the same between the two opposite directions within each axis, the vection-onset latencies have been expected not to vary between directions within each axis. The results confirm both these hypotheses.

Adult↗
PubMed1995

Cognitive effects on visually induced body motion in children.

Cognitive effects on linear sagittal vection in children were investigated. Forty children (7 and 11 years old) were exposed to a bilateral backward optical flow in a single physical condition (seated in a stationary armchair) but in two contrasted cognitive conditions. In one cognitive condition, the children were precisely informed that the armchair could move. In the other, they were informed that the armchair could not move. In each age group, half the children were assigned to one cognitive condition, the other half to the other condition. The results indicate that knowledge about the plausibility of a physical displacement does not affect the probability of obtaining vection. However, at both ages, the latencies for reporting vection were shorter when the physical displacement was known to be possible than when it was known to be impossible. The present results indicate that exclusively cognitive factors do not affect vection occurrence but can modulate latencies for reporting vection.

Adult↗
PubMed1993

The effect of linear vection on manual aiming at memorized directions of stationary targets.

Stationary observers were required to aim manually at either a straight-ahead, or a lateral, immobile target (0 degrees and 20 degrees of eccentricity, respectively). First, they aimed at a perceptually present target. Second, they aimed at the memorized direction of the target. Third, they aimed at the memorized direction of the target after a 4 s period of forward sagittal vection. The comparisons of the post-vection versus ante-vection aimings at the memorized direction of the targets reflect an illusory increase in the eccentricity of the lateral target, and no change in the direction of the straight-ahead target. These results objectivate the idea that forward sagittal vection (a particular case of linear vection) corresponds to an illusion of self-displacement, ie an illusory change of body place through space.

Adult↗
PubMed1985

Spontaneous non-nutritive sucking in continuously fed infants.

In order to investigate the effects of a deprivation of the nutritive sucking (NS) on the activity of non-nutritive sucking (NNS), we examined 8 infants (ages 1-13 months) continuously fed by intracaval catheter. They had no NS experience at all from birth. Eight age-matched normally fed infants served as controls. The infants were examined for a full 24-h period by polygraphic recordings and behavioural observation. The amount of NNS was computed for the whole 24-h period and separately for each behavioural state (waking, quiet sleep, paradoxical sleep and ambiguous sleep). All the continuously fed infants showed a typical pattern of NNS. There were no differences in amount of NNS between continuously fed and control infants in any behavioural state. These results suggest that NS does not contribute to the long term maintenance of the NNS activity.

Child Behavior↗