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Biomedical subjects

P Archambault

Publications and source records attributed to P Archambault.

9 recordsLinked to original sources
PubMed2000

Multi-muscle control of head movements in monkeys: the referent configuration hypothesis.

It is suggested that the nervous system may specify a referent configuration (R) of the body determined by the set of the threshold joint angles at which all skeletal muscles may be silent. At the same time, electromyographic (EMG) activity and forces are generated to resist deflections of the body from this configuration. The R configuration may thus be considered an internal geometric image with which the actual body configuration (Q) is compared. Thereby the difference between the R and Q is a major factor determining the recruitment and gradation of the activity of each skeletal muscle. Control systems may produce movements by changing the R configuration according to task demands. The referent hypothesis predicts that when the R and Q configurations match each other, a global minimum in the EMG activity of all muscles involved should occur, an event most likely observed in movements with reversal in direction. To test the validity of the R hypothesis for head movements, three-dimensional kinematics and EMG activity of 14 functionally diverse neck muscles were analysed in monkeys during head rotations to and from fruit targets placed beyond the oculomotor range. Despite the functional and anatomical diversity of the neck muscles, the activity of all muscles was minimised at a reversal point of the movement trajectory, as predicted by the R hypothesis. This study thus illustrates the notion that a change in the internal geometric image of a biomechanical system may underlie movement production.

Animals↗
PubMed1999

Recruitment and sequencing of different degrees of freedom during pointing movements involving the trunk in healthy and hemiparetic subjects.

Previous studies have shown that in neurologically normal subjects the addition of trunk motion during a reaching task does not affect the trajectory of the arm endpoint. Typically, the trunk begins to move before the onset and continues to move after the offset of the arm endpoint displacement. This observation shows that the potential contribution of the trunk to the motion of the arm endpoint toward a target is neutralized by appropriate compensatory movements of the shoulder and elbow. We tested the hypothesis that cortical and subcortical brain lesions may disrupt the timing of trunk and arm endpoint motion in hemiparetic subjects. Eight hemiparetic and six age-matched healthy subjects were seated on a stool with the right (dominant) arm in front of them on a table. The tip of the index finger (the arm endpoint) was initially at a distance of 20 cm from the midline of the chest. Wrist, elbow, and upper body positions as well as the coordinates of the arm endpoint were recorded with a three-dimensional motion analysis system (Optotrak) by infrared light-emitting diodes placed on the tip of the finger, the styloid process of the ulna, the lateral epicondyle of the humerus, the acromion processes bilaterally, and the sternal notch. In response to a preparatory signal, subjects lifted their arm 1-2 cm above the table and in response to a "go" signal moved their endpoint as fast as possible from a near to a far target located at a distance of 35 cm and at a 45 degrees angle to the right or left of the sagittal midline of the trunk. After a pause (200-500 ms) they moved the endpoint back to the near target. Pointing movements were made without trunk motion (control trials) or with a sagittal motion of the trunk produced by means of a hip flexion or extension (test trials). In one set of test trials, subjects were required to move the trunk forward while moving the arm to the target ("in-phase movements"). In the other set, subjects were required to move the trunk backward when the arm moved to the far target ("out-of-phase movements"). Compared with healthy subjects, movements in hemiparetic subjects were segmented, slower, and characterized by a greater variability and by deflection of the trajectory from a straight line. In addition, there was a moderate increase in the errors in movement direction and extent. These deficits were similar in magnitude whether or not the trunk was involved. Although hemiparetic subjects were able to compensate the influence of the trunk motion on the movement of the arm endpoint, they accomplished this by making more segmented movements than healthy subjects. In addition, they were unable to stabilize the sequence of trunk and arm endpoint movements in a set of trials. It is concluded that recruitment and sequencing of different degrees of freedom may be impaired in this population of patients. This inability may partly be responsible for other deficits observed in hemiparetic subjects, including an increase in movement segmentation and duration. The lack of stereotypic movement sequencing may imply that these subjects had deficits in learning associated with short-term memory.

Adult↗
PubMed1998

1998 ISEK Congress Keynote Lecture: Multi-muscle control in human movements. International Society of Electrophysiology and Kinesiology.

It has been suggested that the coordination of the activity of multiple muscles results from the comparison of the actual configuration of the body with a referent configuration specified by the nervous system so that the recruitment and gradation of the activity of each skeletal muscle depend on the difference between these two configurations. Active movements may be produced by the modification of the referent configuration. The hypothesis predicts the existence of a global minimum in electromyographic (EMG) activity of multiple muscles during movements involving reversals in direction. This prediction was tested in five subjects by analysing movements resembling the act of reaching for an object placed beyond one's reach from a sitting position. In such movements, initially sitting subjects raise their body to a semi-standing position and then return to sitting. Consistent with the hypothesis is the observation of a global minimum in the surface EMG activity of 16 muscles of the arm, trunk and leg at a specific phase of the movement. When the minimum occurred, EMG activity of each muscle did not exceed 2-7% of its maximal activity during the movement. As predicted, global EMG minima occurred at the phase corresponding to the reversal in movement direction, that is, during the transition from raising to lowering of the body. The global EMG minimum may represent the point at which temporal matching occurs between the actual and the referent body configurations. This study implies a specific link between motor behavior and the geometric shape of the body modified by the brain according to the desired action.

Abdominal Muscles↗
PubMed1992

Level of disrupted peer relations and poor self-esteem in children with behavior problems and the effectiveness of day treatment.

Children with disruptive behavior disorders often show deficits in peer relations and self-esteem, putting them at risk for later life psychiatric disorders. The prevalence of poor peer relations and low self-esteem in behavior-problem children, as well as the efficacy of an intensive day treatment program in addressing these deficits, was evaluated. Twenty-five normal-population (NP) children were matched sequentially by age and sex to 25 behavior-problem (BP) children who received day treatment. Groups were compared on measures of self-esteem and peer relations. Pre-/posttreatment comparisons were made for the BP group on the same variables. Mann-Withney U tests showed that the BP group had significantly more problems in self-esteem and peer relations than the NP group. Their scores significantly improved with day treatment and were no longer different from those of the control group. The study indicates that children with behavior disorders present with more problems in peer relations and self-esteem. Intensive multimodal day treatment is an efficient approach for treating these difficulties.

Analysis of Variance↗
PubMed1989

[Acceptability of the Hemoccult test in general medical practice. Results of a pilot study].

In view of preparing a controlled trial to assess the efficacy of screening for colorectal cancer by fecal occult blood testing in reducing cancer mortality, a pilot study was performed to evaluate the acceptability rate of the Hemoccult test in non selected subjects consulting in a general practice. 566 subjects aged 45 to 74 years from two small towns, Neuville-aux-Bois (Loiret) and Vicherey (Vosges) were included in the study. The screening test was proposed by GPs to 89.2% of their patients; of these, 5.6% refused the test and 9.4% did not return it. Of the tests carried out, 80.8% were performed spontaneously, and 19.2% after a recall letter. Acceptability depended neither on age or on sex. The patients' confidence in his GP was the most important acceptability factor (60%), followed by explanations the GP had provided, and ease of application. The results suggest that after receiving the correct information, a GP will succeed in prescribing the Hemoccult test to most high-risk subjects and that acceptability then proves excellent. Experience drawn from the pilot study has been very useful in conceiving the on-going controlled trial in Burgundy.

Aged↗
PubMed1988

Herpes zoster ophthalmoplegia. Report of six cases.

Ophthalmoplegia occurs infrequently in herpes zoster ophthalmicus. The third nerve appears to be the most commonly affected and the fourth nerve the least. We describe herein the clinical course of six patients with herpes zoster ophthalmoplegia. Spontaneous recovery occurred in four patients. The pathogenesis and clinical features of this syndrome are described.

Abducens Nerve↗
PubMed1987

Incidence of retinopathy of prematurity among infants weighing 2000 g or less at birth.

A retrospective study was carried out to determine the incidence of retinopathy of prematurity (ROP) among 157 neonates who weighed 2000 g or less at birth and who were examined at a referral centre for critically ill newborns between January 1983 and December 1985. Overall, 24 cases (15%) of ROP were detected, 18 (75%) among neonates with a birth weight of 1000 g or less. The incidence of ROP was more than eight times higher among neonates in this birth weight category than among those who weighed between 1001 and 2000 g. Grade I ROP accounted for 16 cases (67%), grade II for 7 cases (29%). Only one case (4%) of grade IV ROP was diagnosed, in an infant who weighed 1020 g at birth.

Canada↗