Biomedical subjects

Rodolphe Gentili

Publications and source records attributed to Rodolphe Gentili.

3 recordsLinked to original sources

PubMed2004

Inertial properties of the arm are accurately predicted during motor imagery.

In the present study, using the mental chronometry paradigm, we examined the hypothesis that during motor imagery the brain uses a forward internal model of arm inertial properties to predict the motion of the arm in different dynamic states. Seven subjects performed overt and covert arm movements with one (motion around the shoulder joint) and two (motion around both the shoulder and elbow joints) degrees of freedom in the horizontal plane. Arm movements were executed under two loading conditions: without and with an added mass (4kg) attached to the subject's right wrist. Additionally, movements were performed in two different directions, condition which implies changes in the arm inertia due to the inertial anisotropy of the arm. Our analysis was focused on the timing features of overt and covert movements measured by means of an electronic stopwatch. Durations of right-direction arm movements (low inertial resistance) were smaller compared to durations of left-direction arm movements (high inertial resistance). Additionally, loading the arm with an added mass of 4kg significantly changed the dynamics of motion: movements were indeed more prolonged under loaded conditions. In both cases, the duration of simulated movements mirrored that of overtly executed movements. Therefore, neither the inertial anisotropy of the arm nor the addition of an external mass affected the timing correspondence between overt and covert movement execution. These findings suggest that the brain internally represents the inertial properties of the arm and makes use of it both for sensorimotor control and for the generation of motor images.

Acceleration↗

PubMed2004

Gait-dependent motor memory facilitation in covert movement execution.

In the current study, we examined whether sensorimotor information stored in short-term memory may influence the temporal features between overt and covert execution of human locomotor movements and, furthermore, to examine to what extent such influence may depend on the ongoing gait activity. The subjects (n=20) who participated in the experiment were separated in two groups and instructed to walk (overt execution) or imagine walking (covert execution) along three locomotor paths: horizontal, uphill and downhill. The subjects of the first group, labeled in block, performed all the covert trials before executing the corresponding overt trials, while the subjects of the second group, labeled in serial, alternated between overt and covert movements. The overt and covert durations were recorded by means of an electronic stopwatch. We found high temporal similarities between overt and covert execution for both groups and for all the locomotor paths. Nevertheless, the execution of imagined movements was more variable compared to their actual counterparts. In addition, timing variability of covert movements was smaller for the group in serial compared to the group in block. This decrease in timing variability was larger for the horizontal walking compared to uphill or downhill locomotion. Furthermore, linear regression analysis performed on the data of the group in serial showed close temporal relationships between each successive overt and covert execution. These relationships were stronger when walking along the horizontal vs. sloped paths. Therefore, our results on timing variability provide evidence for gait-dependent motor memory facilitation in covert movement execution. We propose that gait-dependent contribution of sensory feedback information to movement regulation may account for these findings.

Adult↗

PubMed2002

Imagined and actual arm movements have similar durations when performed under different conditions of direction and mass.

Several experiments have suggested that similar physiological substrates are involved in movement execution and motor imagery, and that the same laws of movement control apply to both processes. Using a mental chronometry paradigm, we examined the effects of movement direction and added mass on the duration of actual and imagined movements. Six subjects executed or imagined arm movements in the sagittal and horizontal plane, in three different loading conditions: without added mass, and with an added mass of 1 and 1.5 kg. The duration of both actual and imagined movements was measured by an electronic stopwatch. The actual movements were significantly increased in duration as a function of mass, for both movement directions. However, direction per se had no effect on duration. The duration of imagined movements was very similar to that of actual movements whatever the subject and mass and direction condition. These results show that both inertial and gravitational constraints are accurately incorporated in the timing of the motor imagery process, which appears therefore to be functionally very close to the process of planning and performing the actual movement.

Adult↗