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Biomedical subjects

F Lacquaniti

Publications and source records attributed to F Lacquaniti.

At least 73 records · Page 4Linked to original sources
PubMed1986

EMG responses to load perturbations of the upper limb: effect of dynamic coupling between shoulder and elbow motion.

Load perturbations were applied to the arm of human subjects under conditions where both limb segments (upper arm and forearm) were free to move. The perturbations consisted of pulses of torque 50 ms in duration and of pseudo-random sequences of such pulses. They were applied to either the forearm or the upper arm. Under all conditions, the perturbations resulted in angular motion at the shoulder and elbow joints and evoked consistent responses in muscles acting about these joints (biceps, triceps, anterior and posterior deltoid). Activity in biceps and triceps was not related simply to angular motion at the elbow joint. For example, activation of biceps could be evoked during elbow flexion (by applying a torque perturbation at the shoulder) as well as during elbow extension (by applying a torque perturbation at the elbow). The effect of varying degrees of dynamic coupling between upper arm and forearm on EMG responses was investigated by applying torque perturbations to the upper arm over a wide range of elbow angles. When the forearm is extended, such a perturbation induces a greater amount of elbow flexion than when the forearm is in a flexed position. The results of these experiments showed that the larger was the amount of flexion of the forearm induced by the perturbation, the larger was the activation of biceps. The results are incompatible with the notion of a negative feedback of total muscle length as being responsible for the EMG activity following the load perturbations. It is suggested that the EMG responses can best be interpreted functionally in terms of parameters more global than muscle length. Among such global parameters, changes in net torque at a joint resulting from the perturbation gave the best correlation with the pattern of EMG activities observed.

Arm↗
PubMed1986

Responses of mono- and bi-articular muscles to load perturbations of the human arm.

We studied the behavior of muscles acting synergistically in elbow flexion in response to load perturbations. The perturbations were applied either proximally or distally to the elbow joint and consisted of single pulses or steps of torque and of pseudo-random sequences of torque pulses. They produced changes in angular position and torque at both the shoulder and elbow joints. The electromyographic (EMG) responses evoked in biceps, brachio-radialis and brachialis muscles were different when elbow and shoulder motion was in the same direction and when the two angular motions were oppositely directed. For example, elbow extension resulted both when a downward force perturbation was applied to the forearm as well as when a posteriorly directed force applied to the upper arm was released. Elbow flexors were activated at a short latency only in the former case and not in the latter. The modulation of EMG activity in elbow flexors evoked by the perturbations was related to the global motion of the limb, including the angular motions at both the shoulder and elbow joints. The time course of the EMG responses in biceps, which acts on both joints, differed from that of brachio-radialis and brachialis muscles, which act only at the elbow. The results are discussed in the context of the possible mechanisms responsible for the muscle responses to the perturbations.

Arm↗
PubMed1986

Simulation studies on the control of posture and movement in a multi-jointed limb.

Simulation studies were performed to evaluate the effectiveness of different control schemes in stabilizing a multi-jointed limb (human arm) in response to force perturbations. The mechanical properties of the arm were modeled as a linear visco-elastic system and the effectiveness of negative feedback of angular position and torque was evaluated. The effectiveness of a given amount of position feedback depended strongly on the initial position of the arm and on the perturbation, while torque feedback was much more consistently effective in damping the motion of the limb.

Animals↗
PubMed1986

Coordination of arm movements in three-dimensional space. Sensorimotor mapping during drawing movement.

In this paper data are presented concerning the motion of limb segments during drawing movements executed in different planes in free space. The technique used allows the determination of the wrist and elbow positions in space as well as the measurement of the elbow angle of extension. Other kinematic variables are determined trigonometrically. Elbow and shoulder torque is also calculated. For circles and ellipses, it was found that the motion at the wrist is sinusoidal in two orthogonal directions in the plane of motion. Angular motion, when described by a set of angles previously identified psychophysically as constituting an appropriate coordinate system, is also sinusoidal. Although the number of degrees of freedom of the arm affords many possible ways of performing the task, there is a fixed phase relation between the angles of elevation of the upper arm and forearm for naturally executed movements in all planes of space. Also, the phase of the yaw angles of the upper arm and forearm relative to the angles of elevation are related to the plane of motion and to the slant of ellipses in a fixed manner. There is a simple mapping between angular motion and intended wrist trajectory. Because this mapping is not valid for all planes of space, the actual trajectory can deviate from the intended one. However, the subject has no cognizance of the distortion. The calculated torque deviates substantially from sinusoidal and does change significantly when the same movement is executed in different planes. Results of simulations and mathematical analysis indicate that the fixed phase relationship between angles of elevation leads to a minimal distortion from sinusoidal motion at the wrist in an average sense and that the characteristic distortions observed in the sagittal plane result inevitably from this constraint on the phase relations. The results support the assumption that the topology of the sensorimotor map used for the production of the movement and for its perception is the same. The problem of invariant relationships between kinematic parameters is discussed and the suggestion is made that they represent a general constraint, leading through learning and practice to an optimal solution in an average sense.

Arm↗
PubMed1986

Path constraints on point-to-point arm movements in three-dimensional space.

In this paper data are presented concerning the kinematic and dynamic characteristics of point-to-point arm movements which are inwardly or outwardly directed in three-dimensional space. Elbow and wrist position as well as elbow angle of extension were measured. From these data, other angles were computed trigonometrically and elbow and shoulder torques were calculated. Some of the angles describing arm and forearm motion were found to be linearly related for any given movement. Changes in shoulder and elbow torque were found to be similar to those described for movements restricted to one degree of freedom. Shoulder and elbow motions were not affected when it was required that the orientation of the hand in space remain constant. These observations were taken to indicate that shoulder and elbow motions are tightly coupled for movements in three-dimensional space and that wrist motion has no influence on this coupling. Linear relations between angles express such coupling. They are taken to result from functional constraints and may facilitate the mapping between extrinsic and intrinsic coordinate systems. Some of the observations pertaining to the torque lead to the hypothesis of a further constraint limiting the number of possible trajectories in a point-to-point movement.

Arm↗
PubMed1984

Behavior of the stretch reflex in a multi-jointed limb.

When an external perturbation acts on a segment of a multi-jointed limb, angular motion results in all limb segments which are inertially linked to the one which is perturbed. In such a situation, different hypotheses on the functional role of the stretch reflex lead to different predictions on reflex responses by the stretched muscles. These predictions were examined experimentally and it was found that the EMG responses of elbow muscles evoked by forces applied to either the upper arm or the forearm were not uniquely related to changes in elbow angular position. They were instead correlated with the direction of changes in the net elbow torque resulting from the perturbation.

Arm↗
PubMed1984

Cat posture on a tilted platform.

The posture of cats trained to stand freely on a platform was studied during static tilts (up to +/- 30 degrees). Vertical projection of the center of mass on the support surface, as well as limb orientation in space and degree of limb flexion, varied minimally with platform tilt angle. The limbs' main axes were kept almost lined up with the vertical. This data indicates that postural control is simplified by strong internal constraints which limit the number of possible postural configurations. The mechanical advantages of this postural strategy are also considered. Finally, the data are discussed in the context of previously held views on the role of vestibular and neck reflex control of posture in intact animals.

Adaptation, Physiological↗
PubMed1983

Modification of trajectory of a pointing movement in response to a change in target location.

1. Arm movements toward a target involving motion at the shoulder and elbow joints and restricted to the sagittal plane were investigated. During some movements, target location changed suddenly, thus requiring an intentional correction of the trajectory by the human subject. 2. The reaction time to correct the trajectory was comparable to the reaction time to initiate the movement. 3. Coordination of arm and shoulder movements in this task was achieved by means of a reduction of the number of degrees of freedom of the movement. Such a simplification of the task took two forms. 4. Angular acceleration at the elbow and shoulder were linearly related to each other in the deceleratory phase of the movement, when the trajectory had to be corrected as well as when no such correction was required. 5. When the correction required an increase or decrease in flexor torque at the shoulder and elbow, electromyographic (EMG) activity in anterior deltoid and biceps increased or decreased simultaneously. When the correction demanded more activity in triceps and deltoid, these muscles were activated sequentially instead. It is concluded that rapid corrections of a movement involve the production of stereotyped patterns of activity in shoulder and elbow muscles.

Adult↗
PubMed1982

Some factors pertinent to the organization and control of arm movements.

Trajectories of arm movement during a pointing task were shown to be unaffected by large loads. Moreover, when the effective arm length was changed, the target was still approached along a direct trajectory. It is concluded that: (1) compensation for load occurs automatically without affecting those constraints on the basis of which movements are organized; (2) that the effective lengths of body segments as well as joint angles constitute variables utilized in the organization of trajectories.

Arm↗
PubMed1982

The mechanical behavior of the human forearm in response to transient perturbations.

Static and dynamic components of mechanical impedance of human forearm were evaluated by applying two kinds of perturbations: 1) large viscoelastic loads, and 2) small pseudo-random perturbations. When the task involved the active resistance of the perturbations, both stiffness and viscosity increased relatively to their values in the passive task, the increment in stiffness being larger than that in viscosity. The time course of such changes was investigated during the transition between the two operating points defined by the instructions "do not resist" and "resist" the applied perturbations. The changes in stiffness and viscosity were relatively slow, those in the latter lagging behind those in the former.

Biomechanical Phenomena↗
PubMed1982

Coordination of arm and wrist motion during a reaching task.

An analysis of arm movements involving forward projection of the hand in order to reach for and grasp a target at different orientations is presented. The reaching movements required shoulder flexion, elbow extension, and wrist pronation or supination. The relation between elbow and shoulder instantaneous angular position proved to be consistent from trial to trial of each task, independent of movement speed. Further, this relation was not influenced by the presence or absence of a concomitant wrist rotation. During the deceleratory phase of the movement, the slope of elbow angular velocity to shoulder angular velocity was constant and independent of target orientation. Wrist motion was instead highly variable in timing, course, and duration. Supinatory movements tended to be fractionated. On average, the duration of wrist movements was shorter than that of shoulder and elbow motions. The pattern of biceps EMG activity during supinatory and pronatory movements was different. Since motion at the shoulder and elbow was virtually identical in the two cases, net flexor torque at the elbow was also little different. It is concluded that other elbow flexors and extensors also exhibit a task-dependent patterning of activity so as to produce the same net torque. The results are discussed in the context of the internal constraints present during the movements that we examined. These constraints are the inertial coupling between shoulder and elbow motion and those which derive from the bifunctional nature of many of the muscles participating in the movement.

Arm↗
PubMed1981

Acute neurologic complications of hemodialysis. Study of 14,000 hemodialyses in 103 patients with chronic renal failure.

We have examined and subjected to statistical analysis the transient acute neurological complications arising in the course of hemodialysis in 103 patients with chronic renal failure (13,969 hemodialysis sessions). Our data show that such complications are multiform. Some of the symptoms are aspecific: headache, nausea and/or vomiting, muscle cramps. We have found these symptoms in over 96% of patients, often combined with extraneurological symptoms and phenomena, such as cardiocirculatory shock or increased blood pressure. The other symptoms denote real cerebral impairment: convulsions, consciousness disturbances, psychomotor agitation. They are present in 36% of the patients, but only 10.5% of the patients show a combination of at least two symptoms. In these patients the so-called "Disequilibrium syndrome" is present: its percentage in our case-series is similar to that reported in literature.

Adolescent↗
PubMed1981

Invariant characteristics of a pointing movement in man.

Simple arm movements involving forward projection of the hand toward a target were studied by measuring simultaneous wrist position in three-dimensional space and changes in elbow angle. An attempt was made to identify those features of the movement which exhibit invariant characteristics under the hypothesis that such invariances may reflect the operations by which central processes participate in the organization of the movement. The first such invariance to be identified was that the trajectory in space is independent of movement speed. Secondly, the movement can be viewed as consisting of two phases, an acceleratory phase and a deceleratory one, with the movement during the acceleratory phase being so organized as to maintain the ratio of elbow angular velocity to shoulder angular velocity invariant with respect to target location in the deceleratory phase. It is suggested that proprioceptive information is used to control the movement and that the latter invariance may result from a negative feedback of force involving tendon organ afferents.

Arm↗
PubMed1979

Brain stem auditory evoked potentials and blink reflexes in quiescent multiple sclerosis.

Brain stem auditory evoked potentials (BAEP) and blink reflexes (BR) were studied in 25 patients with multiple sclerosis (MS), the diagnosis being definite according to McAlpine's criteria, in the quiescent phase, without signs of brain stem involvement. BAEP abnormalities were found in 64% of the cases and BR abnormalities in 60%. A good correlation between the two tests was found in most patients. The abnormalities consisted of delayed latencies and/or high intraindividual variability in shape and latency of BAEP and BR components. It seems that demyelination of brain stem pathways results not only in conduction slowing but also in more serious dysfunction of the generators of the evoked components.

Adolescent↗
PubMedDate not supplied

The Kinelite Project: a new powerful motion analyser for Spacelab and space station.

The goal of the Kinelite Project is to develop a space qualified motion analysis system to be used in space by the scientific community, mainly to support neuroscience protocols. The measurement principle of the Kinelite is to determine, by triangulation mean, the 3D position of small, lightweight, reflective markers positioned at the different points of interest. The scene is illuminated by Infra Red flashes and the reflected light is acquired by up to 8 precalibrated and synchronized CCD cameras. The main characteristics of the system are: Camera field of view: 45 degrees; Number of cameras: 2 to 8; Acquisition frequency: 25, 50, 100, or 200 Hz; CCD format: 256 x 256; Number of markers: up to 64; 3D accuracy: 2mm; Main dimensions: 45 cm x 45 cm x 30 cm; Mass: 23 kg; Power consumption: less than 200 W. The Kinelite will first fly aboard the NASA Spacelab; it will be used, during the NEUROLAB mission (4/98), to support the "Frames of References and Internal Models" (Principal Investigator: Pr. A. Berthoz, Co Investigators: J. McIntyre, F. Lacquaniti).

Aerospace Medicine↗
PubMedDate not supplied

Representing spatial information for limb movement: role of area 5 in the monkey.

How is spatial information for limb movement encoded in the brain? Computational and psychophysical studies suggest that beginning hand position, via-points, and target are specified relative to the body to afford a comparison between the sensory (e.g., kinesthetic) reafferences and the commands that generate limb movement. Here we propose that the superior parietal lobule (Brodmann area 5) might represent a substrate for a body-centered positional code. Monkeys made arm movements in different parts of 3D space in a reaction-time task. We found that the activity of area 5 neurons can be related to either the starting point, or the final point, or combinations of the two. Neural activity is monotonically tuned in a body-centered frame of reference, whose coordinates define the azimuth, elevation, and distance of the hand. Each spatial coordinate tends to be encoded in a different subpopulation of neurons. This parcellation could be a neural correlate of the psychophysical observation that these spatial parameters are processed in parallel and largely independent of each other in man.

Animals↗