Search results for "nema"
showing 10 items of 1972 documents
Object size modulates fronto-parietal activity during reaching movements
2014
In both monkeys and humans, reaching-related sensorimotor transformations involve the activation of a wide fronto-parietal network. Recent neurophysiological evidence suggests that some components of this network host not only neurons encoding the direction of arm reaching movements, but also neurons whose involvement is modulated by the intrinsic features of an object (e.g. size and shape). To date, it has yet to be investigated whether a similar modulation is evident in the human reaching-related areas. To fill this gap, we asked participants to reach towards either a small or a large object while kinematic and electroencephalographic signals were recorded. Behavioral results showed that …
Tri-dimensional and triphasic muscle organization of whole-body pointing movements.
2010
Previous kinematic and kinetic studies revealed that, when accomplishing a whole-body pointing task beyond arm's length, a modular and flexible organization could represent a robust solution to control simultaneously target pointing and equilibrium maintenance. Here, we investigated the underlying mechanisms that produce such a coordinative kinematic structure. We monitored the activity of a large number of muscles spread throughout subjects' bodies while they performed pointing movements beyond arm's length, either with or without imposition of postural or pointing constraints. Analyses revealed that muscle signals lied on a tri-dimensional hyper-plane and were temporally organized accordi…
Prevalence of fimA genotypes of Porphyromonas gingivalis and other periodontal bacteria in a Spanish population with chronic periodontitis
2012
Objectives: The aim of this study was to determine the prevalence of the different fimA genotypes of Porphyromonas gingivalis in adult Spanish patients with chronic periodontitis, patients with gingivitis and periodontally healthy subjects, and the relationship between these genotypes and other periodontopathogenic bacteria. Study design: Samples of subgingival plaque were taken from 86 patients (33 with chronic periodontitis, 16 with gingivitis, and 37 periodontally healthy) in the course of a full periodontal examination. PCR was employed to determine the presence of the 6 fimA genotypes of Porphyromonas gingivalis (I-V and Ib) and of Aggregatibacter actinomycetemcomitans, Tannerella fors…
Sensorimotor adaptation of point-to-point arm movements after spaceflight: the role of internal representation of gravity force in trajectory plannin…
2011
International audience; After an exposure to weightlessness, the central nervous system operates under new dynamic and sensory contexts. To find optimal solutions for rapid adaptation, cosmonauts have to decide whether parameters from the world or their body have changed and to estimate their properties. Here, we investigated sensorimotor adaptation after a spaceflight of 10 days. Five cosmonauts performed forward point-to-point arm movements in the sagittal plane 40 days before and 24 and 72 h after the spaceflight. We found that, whereas the shape of hand velocity profiles remained unaffected after the spaceflight, hand path curvature significantly increased 1 day after landing and return…
Effects of movement direction upon kinematic characteristics of vertical arm pointing movements in man
1998
Vertical arm pointing movements in two directions (upwards and downwards), imposing two different loads (unload and 0.5 kg) and speeds (normal and fast) have been studied in six subjects. Movements were recorded using an optoelectronic system. Data analysis concentrated upon finger-tip kinematics. Significant effects of movement direction were recorded upon velocity profiles. The acceleration time, computed relative to total movement time, was greater for downward movements than for upward movements. In contrast however, no effects of load or speed were observed. Movement time was not affected by movement direction or load, for both speeds tested. These results suggest different planning pr…
Human walking along a curved path. I. Body trajectory, segment orientation and the effect of vision.
2003
Task-related characteristics of gait and segment orientation during natural locomotion along a curved path have been described in order to gain insight into the neural organization of walking. The locomotor task implied continuous deviation from straight-ahead, thereby requiring continuous adjustment of body movement to produce and assist turn-related torques. Performance was compared to straight-ahead locomotion. Subjects easily reproduced both trajectories with eyes open (EO). The actual-to-required trajectory difference increased blindfolded (BF), more so during turning. Stride length was unchanged for the outer but decreased for the inner leg. The feet anticipated subsequent body rotati…
Influence of stimulus color on the control of reaching-grasping movements.
2001
This kinematic study aimed to determine whether color is a stimulus property involved in the control of reaching-grasping movements. Subjects reached and grasped a target-object, located either on the right or on the left of the subject's midline. A distractor, placed along the subject's midline, could be randomly presented. The colors, i.e., both chromaticity (red and green stimuli were presented) and lightness, of the target and distractor were varied in experiment 1. Only stimulus lightness and only stimulus chromaticity were varied in experiments 2 and 3, respectively. In experiment 4 subjects matched with their thumb and index finger the size of the target-stimuli presented in experime…
Visual distractors differentially interfere with the reaching and grasping components of prehension movements
1998
In the present study we addressed the issue of how an object is visually isolated from surrounding cues when a reaching-grasping (prehension) movement towards it is planned. Subjects were required to reach and grasp an object presented either alone or with a distractor. In five experiments, different degrees of elaboration of the distractor were induced by varying: (1) the position of the distractor (central or peripheral); (2) the time when the distractor was suppressed (immediately or delayed, with respect to stimulus presentation); and (3) the type of distractor analysis (implicit or explicit). In addition, we tested whether the possible effects of the distractor on reaching-grasping wer…
Modular Control of Pointing beyond Arm's Length
2009
Hand reaching and bipedal equilibrium are two important functions of the human motor behavior. However, how the brain plans goal-oriented actions combining target reaching with equilibrium regulation is not yet clearly understood. An important question is whether postural control and reaching are integrated in one single module or controlled separately. Here, we show that postural control and reaching motor commands are processed by means of a modular and flexible organization. Principal component and correlation analyses between pairs of angles were used to extract global and local coupling during a whole-body pointing beyond arm's length. A low-dimensional organization of the redundant ki…
Language and motor control.
2000
We investigated the possible influence of automatic word reading on processes of visuo-motor transformation. Subjects reached and grasped an object on which the following Italian words were printed: 'VICINO' (near) or 'LONTAN' (far) on an object either near or far from the agent (experiments 1, 2); PICCOLO (small) or 'GRANDE' (large) on either a small or a large object (experiment 4); and 'ALTO' (high) or 'BASSO' (low) on either a high or a low object (experiment 5). The kinematics of the initial phase of reaching-grasping was affected by the meaning of the printed words. Namely, subjects automatically associated the meaning of the word with the corresponding property of the object and acti…