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Biomedical subjects

M Gentilucci

Publications and source records attributed to M Gentilucci.

54 records · Page 3Linked to original sources
PubMed1992

Prehension movements directed to approaching objects: influence of stimulus velocity on the transport and the grasp components.

In this investigation we studied the influence of object velocity on the transport and on the grasp components of prehension movements directed to approaching objects. Three experiments were carried out. In the first experiment six subjects were required to reach and grasp a sphere that approached them with a constant velocity. The effects of four velocities were studied. The results showed that the end point of the arm movement changed with object velocity: nearer the body with higher than with lower object velocities. Transport velocity increased with movement amplitude and the deceleration phase decreased in duration with higher object velocities. On the contrary the grasp component was not affected by object velocity. The second experiment was a control experiment carried out in order to verify whether a possible influence of object velocity on the grasp could be revealed in an experimental condition in which grasp planning relies without doubt on visual computation of all object features. In this experiment object velocity and object size were randomly varied. The results showed that the grasp was not influenced by object velocity, whereas it was sensitive to changes of object size. The third experiment had the two-fold aim of establishing (1) whether transport velocity was influenced by object velocity once the location in space at which the object had to be grasped was fixed and (2) whether the grasp kinematics differed for prehension movements directed respectively to stationary or to moving objects. Results showed that the first part of the transport is affected only by distance, whereas the deceleration phase decreased with increasing object velocity. This last result suggests that subjects minimized object displacements in order to grasp the sphere correctly. The grasp component differed between the conditions of stationary and moving stimuli only in the relative timing between finger aperture and closure phases. The closure phase decreased in the condition of moving stimuli. The results of the three experiments indicate the dependence of transport parameters on object velocity, whereas grasp parameters appear to be unaffected.

Acceleration↗
PubMed1991

Influence of different types of grasping on the transport component of prehension movements.

The main aim of the present study was to clarify whether different types of grasping may affect the transport component of prehension movements. To this purpose two experiments were carried out. In the first experiment the kinematics of arm movements (transport and manipulation components) were studied in eight normal subjects instructed to reach and grasp different objects located either 20 or 30 cm from their hand. The objects employed required two different types of grip: prehension with the whole hand and prehension with the index finger and the thumb (precision grip). In the second experiment subjects were instructed to point to the same objects employed in the first experiment. This experiment served as a control for the precision requirements related to the object size. The results showed that, once the precision requirements were taken into account, the transport component remained unmodified with the different types of grip. The time course of the manipulation component and its temporal relations with the transport component changed with the type of grasping. The maximal hand aperture was reached earlier in the precision grip than in the whole hand prehension and the temporal coupling with the transport component was weaker in the former condition than in the latter. The data are interpreted as further evidence in favour of independence between the transport and the manipulation "channels".

Adolescent↗
PubMed1991

[Kinematic study of reaching-grasping movements in the monkey].

Kinematics of reaching-grasping movement towards stimuli of three different sizes located at two different distances were studied in one monkey (Macaca nemestrina). Transport and manipulation components were analyzed using the ELITE system. Transport time, peak velocity and deceleration phase of velocity were influenced by stimulus size, whilst acceleration phase remained unmodified. Peak velocity clearly increased with distance, while transport time remained constant (isochrony ). The main parameters of manipulation component were all influenced by stimulus size but they did not vary with distance. A comparison with kinematic data obtained from human subjects was made.

Animals↗
PubMed1991

[Kinematic study of the temporal coupling between the components of transport and manipulation during reaching and grasping movements].

In this study the temporal coupling between transport and manipulation components of prehension movements was tested. For this purpose two experiments were carried out. In Experiment 1 six normal subjects were required to reach and grasp one of three spheres located at three different distances (Blocked trials). In Experiment 2 a visual perturbation paradigm was used in which the location of the object to be reached and grasped could change at onset of arm movement (Perturbed trials). The results of this study exclude a temporal coupling between events of transport and manipulation components. On the contrary they suggest that manipulation component organizes its time course having information about the time required to reach the object.

Animals↗
PubMed1990

Neurons related to reaching-grasping arm movements in the rostral part of area 6 (area 6a beta).

Single neurons were recorded from the rostral part of the agranular frontal cortex (area 6a beta) in awake, partially restrained macaque monkeys. In the medialmost and mesial sectors of this area, rostral to the supplementary motor area, neurons were found which were activated during arm reaching-grasping movements. These neurons ("reaching-grasping neurons") did not appear to be influenced by how the objects were grasped nor, with some exceptions, by where they were located. Their activity changed largely prior to the arm movement and continued until the end of it. The premovement modulation (excitatory or inhibitory) could start with stimulus presentation, with the saccade triggered by the stimulus or after stimulus fixation. The distance of the stimulus from the monkey was an important variable for activating many neurons. About half of the recorded neurons showed a modulation of the same sign during movement and premovement period. The other half showed an increase/decrease in activity which was of the opposite sign during movement and premovement period or part of it. In this last case the discharge changes were of the same sign when the stimulus was close to the monkey and when the monkey moved its arm to reach the objects, whereas they were of opposite sign when the stimulus was outside the animal's reach. Microstimulation of area 6a beta and the reconstruction of the locations of eye movement and arm movement related cells showed that the arm field was located more medially (and mesially) than the eye field described by Schlag and Schlag-Rey (1987). It is suggested that, unlike inferior area 6, which is mostly involved in selection of effectors on the basis of the physical properties of the objects and their spatial location (Rizzolatti and Gentilucci 1988), area 6a beta plays a role in the preparation of reaching-grasping arm movements and in their release when the appropriate conditions are set.

Animals↗
PubMed1989

Somatotopic representation in inferior area 6 of the macaque monkey.

On the basis of its cytoarchitectonic and enzymatic properties area 6 of the macaque monkey can be subdivided into two large sectors: a superior sector lying medial to the spur of the arcuate sulcus (superior area 6 or F2) and an inferior sector lying lateral to it (inferior area 6). Inferior area 6 is constituted by two enzymatic areas: F4 and F5. In this study we investigated the somatotopic organization of inferior area 6 and the adjacent area 4 combining single-neuron recording and intracortical electrical microstimulation. We found that two separate movement representations exist in this region. The caudal one corresponds to area F1 (primary motor cortex), the rostral one to inferior area 6. The two representations are mirror images one of the other with the axioproximal movements being adjacently located. In the rostral map the proximal movements are mostly located in F4, the distal movements in F5. Neuronal properties indicate that the rostral map has characteristics that are more complex than the caudal map. We propose that the rostral map is involved in transforming visual information in motor commands. F4 should be involved in the control of arm movements based on the location of the objects in respect to the body, whereas F5 should play a role in the control of grasping movements on the basis of the size of the stimuli.

Animals↗
PubMed1989

[Kinematic study of reaching-grasping movements].

The experiment was conducted to investigate, by using kinematic parameters, the influence of the type of prehension on the transportation component in reaching-grasping movements. The main question was whether the transportation component is influenced by the type of prehension besides the distance of the object. The experiment was carried out on eight subjects who performed reaching-grasping movements toward objects located at different distances. Two types of prehension were examined: whole hand prehension and precision grip. The following kinematic parameters of the transportation component (wrist movement) were studied: movement times, profiles of velocity and accelerations. Our results have shown that the transportation component is affected by the two factors. However the kinematic parameters were influenced differently by the distance and the type of prehension. Our conclusion is that, although distance and type of prehension affect the transportation component, they are computed separately in programming this component.

Adolescent↗
PubMed1988

Functional organization of inferior area 6 in the macaque monkey. I. Somatotopy and the control of proximal movements.

Two series of experiments are reported in this paper. The first concerns the movement representation in the macaque inferior area 6, the second the functional properties of neurons located in the caudal part of this area (histochemical area F4). By combining single neuron recording and intracortical microstimulation, we found that inferior area 6 is somatotopically organized. The axio-proximal movements are represented caudally, the distal movements are represented near the arcuate sulcus. The mouth field is located laterally, the hand field medially. There is no leg field. A comparison between neuron properties and histochemical characteristics of inferior area 6 showed that the proximal movements representation includes most of area F4, whereas the distal movements representation corresponds to area F5 and to the rostral part of F4. Neurons located in that part of F4 where proximal movements are represented respond very well to tactile stimuli. They have large receptive fields mostly located on the face and on the upper part of the body. A large number of these neurons respond to visual stimuli. Objects approaching the animal are particularly effective. The tactile and the visual receptive fields are in register. The most represented movements are reaching movements, movements bringing the hand to the mouth or to the body and facial movements. There is a congruence between location of visual fields and preferred arm movements. It is argued that the receptive field arrangement and the response properties are more complex in area F4 than in the primary motor cortex and that area F4 neurons are involved in the control of arm movements towards different space sectors.

Animals↗
PubMed1988

Functional organization of inferior area 6 in the macaque monkey. II. Area F5 and the control of distal movements.

The functional properties of neurons located in the rostral part of inferior area 6 were studied in awake, partially restrained macaque monkeys. The most interesting property of these neurons was that their firing correlated with specific goal-related motor acts rather than with single movements made by the animal. Using the motor acts as the classification criterion we subdivided the neurons into six classes, four related to distal motor acts and two related to proximal motor acts. The distal classes are: "Grasping-with-the-hand-and-the-mouth neurons", "Grasping-with-the-hand neurons", "Holding neurons" and "Tearing neurons". The proximal classes are: "Reaching neurons" and "Bringing-to-the-mouth-or-to-the-body neurons". The vast majority of the cells belonged to the distal classes. A particularly interesting aspect of distal class neurons was that the discharge of many of them depended on the way in which the hand was shaped during the motor act. Three main groups of neurons were distinguished: "Precision grip neurons", "Finger prehension neurons", "Whole hand prehension neurons". Almost the totality of neurons fired during motor acts performed with either hand. About 50% of the recorded neurons responded to somatosensory stimuli and about 20% to visual stimuli. Visual neurons were more difficult to trigger than the corresponding neurons located in the caudal part of inferior area 6 (area F4). They required motivationally meaningful stimuli and for some of them the size of the stimulus was also critical. In the case of distal neurons there was a relationship between the type of prehension coded by the cells and the size of the stimulus effective in triggering the neurons. It is proposed that the different classes of neurons form a vocabulary of motor acts and that this vocabulary can be assessed by somatosensory and visual stimuli.

Animals↗
PubMed1987

Neurons related to goal-directed motor acts in inferior area 6 of the macaque monkey.

A new class of neurons was identified in the rostral part of inferior area 6 in the macaque monkey (Macaca nemestrina). These neurons fire in relation to motor acts which have a particular aim such as reaching, grasping or holding. The same neuron discharges when the animal uses the right hand, the left hand and, frequently, also the mouth. Furthermore most of these neurons specify how the aim can be achieved (e.g. precision grip vs whole hand prehension). Different types of goal-related neurons form a vocabulary of simple motor acts localized in inferior area 6.

Action Potentials↗
PubMed1984

[Functional organization of the intermediate and deep layers of the superior colliculus of the monkey].

Single neurons and polispike activity were recorded from the superior colliculus of anesthetized, behaving monkeys. In agreement with previous findings neurons of the superficial layers responded exclusively to visual stimuli. In the intermediate layers most neurons were oculomotor, although some of them showed also a visual receptive field. No neurons responding to tactile or auditory stimuli were found. Occasionally the discharge of an oculomotor neuron increased if the ocular movement was triggered by a visual or an acoustical stimulus. Rare tacticle and auditory neurons were recorded in deep layers. However their receptive fields were difficult to map and their responses lacked the precision of the responses of the specific acoustic and tactile areas. Electrical stimulation of the SC produced contralateral eye and head movements, the threshold being high in the superficial layers and low in the intermediate and deep ones. In the deep layers complex limb and trunk movements could be also elicited. In conclusion, in contrast with carnivores and other mammals, the primate superior colliculus appears to be dominated by the visual modality.

Animals↗
PubMed1983

Visual responses in the postarcuate cortex (area 6) of the monkey that are independent of eye position.

The visual responses of postarcuate neurons have been studied in alert behaving monkeys (Macaca nemestrina). In particular, the effect of eye position on the location of visual responses in respect to the body has been examined. It was found that a large percentage of bimodal (visual and somatosensory) neurons have visual receptive fields that are independent of eye position. The location of the visual receptive field does not change when the eyes move, but remains in register with the tactile receptive field (soma-related visually responsive neurons).

Animals↗
PubMed1981

Response properties and behavioral modulation of "mouth" neurons of the postarcuate cortex (area 6) in macaque monkeys.

Single neurons were recorded from the "mouth area" of the postarcuate cortex in macaque monkeys. According to their responses to somatosensory stimuli and their activity during the animal's movements, the neurons were subdivided into three classes: (1) neurons activated only by external stimuli; (2) neurons showing an enhancement of their response when a specific motor act followed the external stimulation; (3) neurons responding reliably to external stimuli only if the stimulation triggered a specific, related motor act. Of the recorded neurons, 50% also responded to visual stimuli.

Animals↗
PubMed1981

Afferent properties of periarcuate neurons in macaque monkeys. I. Somatosensory responses.

The afferent properties of single neurons of the periarcuate cortex have been studied in the macaque monkey. Most of the recorded neurons responded to stimuli in one or two sensory modalities and, accordingly, they were classified as somatosensory, visual or bimodal (visual and somatosensory) neurons. Visual neurons were located rostral to the arcuate sulcus, whereas the somatosensory and the bimodal neurons were found predominantly caudal to this sulcus. Somatosensory neurons (n = 102) and bimodal neurons (n = 69) had identical somatic afferent properties. They were subdivided into 'tactile' neurons, 'joint' neurons and 'tactile and joint' neurons. 'Tactile' neurons (70%) had their receptive fields formed either by one or by two or more spatially separated responding areas. The parts of the body most represented were the hands and the mouth. 'Joint' neurons (10%) were activated by the rotation of one or, more often, of two or more articulations. The movement of the hand towards the mouth was the most frequently represented movement. 'Tactile and joint' neurons (20%) responded to both tactile and joint stimulation having receptive field locations and properties like those of the other two classes of neurons. Some 'joint' and 'tactile and joint' neurons had summing properties, i.e. their response to tactile or joint stimulation was conditional upon a simultaneous stimulation of another articulation. The data are interpreted as evidence in favor of the existence of an area in the agranular cortex that organizes the mouth and the hand to mouth movements.

Afferent Pathways↗
PubMed1981

Afferent properties of periarcuate neurons in macaque monkeys. II. Visual responses.

The visual response of single neurons of the periarcuate cortex have been studied in the macaque monkey. Two sets of neurons responding to visual stimuli have been found. The first set, located rostral to the arcuate sulcus, was formed by units that could be activated by stimuli presented far from the animal. These neurons had large receptive fields and were neither orientation nor direction selective. The second set, found predominantly caudal to the arcuate sulcus, was formed by units that were maximally or even exclusively activated by stimuli presented in the space immediately around the animal. These neurons were bimodal, responding also to somatosensory stimuli. According to the location of their visual responding regions the bimodal neurons were subdivided into pericutaneous (54%) and distant peripersonal neurons (46%). The former responded best to stimuli presented a few centimeters from the skin, the latter to stimuli within the animal's reaching distance. The visual responding regions were spatially related to the tactile fields. It is argued that neurons with a receptive field consisting of several responding areas, some in one sensory modality, some in another, have a praxic function and that they are involved in organizing sequences of movements.

Animals↗