Biomedical subjects

L Fogassi

Publications and source records attributed to L Fogassi.

10 recordsLinked to original sources

PubMed1992

Space coding by premotor cortex.

Many neurons in inferior area 6, a cortical premotor area, respond to visual stimuli presented in the space around the animal. We were interested to learn whether the receptive fields of these neurons are coded in retinotopic or in body-centered coordinates. To this purpose we recorded single neurons from inferior area 6 (F4 sector) in a monkey trained to fixate a light and detect its dimming. During fixation visual stimuli were moved towards the monkey both within and outside the neuron's receptive field. The fixation point was then moved and the neuron retested with the monkey's gaze deviated to the new location. The results showed that most inferior area 6 visual neurons code the stimulus position in spatial and not in retinal coordinates. It is proposed that these visual neurons are involved in generating the stable body-centered frame of reference necessary for programming visually guided movements.

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PubMed1992

Understanding motor events: a neurophysiological study.

Neurons of the rostral part of inferior premotor cortex of the monkey discharge during goal-directed hand movements such as grasping, holding, and tearing. We report here that many of these neurons become active also when the monkey observes specific, meaningful hand movements performed by the experimenters. The effective experimenters' movements include among others placing or retrieving a piece of food from a table, grasping food from another experimenter's hand, and manipulating objects. There is always a clear link between the effective observed movement and that executed by the monkey and, often, only movements of the experimenter identical to those controlled by a given neuron are able to activate it. These findings indicate that premotor neurons can retrieve movements not only on the basis of stimulus characteristics, as previously described, but also on the basis of the meaning of the observed actions.

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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.

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PubMed1991

Saccade-related activity in the lateral intraparietal area. I. Temporal properties; comparison with area 7a.

1. The cortex of the inferior parietal lobule (IPL) contains neurons whose activity is related to saccadic eye movements. The exact role of the IPL in relation to saccades remains, however, unclear. In this and the companion paper, we approach this problem by quantifying many of the spatial and temporal parameters of the saccade-related (S) activity. These parameters have hitherto been largely unstudied. 2. The activity of single neurons was recorded from Macaca mulatta monkeys while they were performing a delayed-saccade task. The analysis presented here is based on 161 neurons recorded from the lateral intraparietal area (LIP), a recently defined subdivision of the IPL; and 54 neurons recorded from the neighboring part of the IPL, area 7a. Overall, 409 IPL neurons were isolated in this study. 3. The typical activity of IPL neurons during the delayed-saccade task has three basic phases: light sensitive (LS), memory (M), and S. These basic phases are common to neurons of both areas LIP and 7a. In each phase (LS, M, and S), individual neurons may or may not be active. Most LIP neurons, however, are active in more than one phase. 4. To compare the activity levels of different neurons, the actual firing rate was weighted by each neuron's background level, yielding an "activity index" for each neuron, in each phase of the task. We calculated the activity index for the LS and M phases and for three phases related to the saccade: a presaccadic (Pre-S), a saccade-coincident (S-Co), and a postsaccadic (Post-S) phase. For area LIP neurons the median values of the activity index were high for the LS, M, Pre-S, and S-Co activities, and slightly lower in the Post-S period. In area 7a the median values were low for the LS phase and, in particular, for the M and Pre-S phases, somewhat higher coincident with the saccade, and high post-saccadically. 5. In area LIP, in each phase, 49-63% of the neurons had excitatory activity, and 10-17% had inhibitory responses. 6. In contrast, in area 7a excitatory responses were most frequent in the Post-S phase (56%). Excitation was particularly infrequent during M (28%) and Pre-S (22%). The incidence of inhibitory responses varied too (4-18%). The time course of inhibition was roughly opposite that of excitation; the highest frequency of inhibitory responses occurred during the saccade.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1991

Saccade-related activity in the lateral intraparietal area. II. Spatial properties.

1. Single-neuron activity was recorded from the inferior parietal lobule (IPL) of Macaca mulatta monkeys while they were performing delayed saccades and related tasks. Temporal characteristics of this activity were presented in the companion paper. Here we focus on the spatial characteristics of the activity. The analysis was based on recordings from 145 neurons. All these neurons were from the lateral intraparietal area (LIP), a recently defined subdivision of the IPL. 2. Delayed saccades were made in eight directions. Direction-tuning curves were calculated for each neuron, during each of the following activity phases that were described in the companion paper: light sensitive (LS), delay-period memory (M), and saccade related (S); the latter further partitioned into presaccadic (Pre-S), saccade coincident (S-Co), and postsaccadic (Post-S). 3. Width and preferred direction were calculated for each direction-tuning curve. We studied the distributions of widths and preferred directions in LIP's neuronal population. In each case we included only neurons that showed clear excitatory activity in the phases in question. 4. Width was defined as the angle over which the response was higher than 50% of its maximal net value. Width distributions were similar for all phases studied. Widths varied widely from neuron to neuron, from very narrow (less than 45 degrees) to very wide (close to 360 degrees). Median widths were approximately 90 degrees in all phases. 5. Preferred-direction distributions were also similar for various phases. All directions were represented in each distribution, but contralateral directions were more frequent (e.g., 69% for S-Co). 6. For each neuron the alignment of the preferred directions of its various phases was determined. Distributions of alignments were calculated (again, phases that were not clearly excitatory were disregarded). On the level of the neuronal population LS, M, and Pre-S were well aligned with each other. S-Co was also aligned with these phases, but less precisely. 7. A set of "narrowly tuned" neurons was selected by imposing a constraint of narrow (width, less than 90 degrees) LS and S-Co direction tuning. In this set of neurons, the LS and S-Co preferred directions were very well aligned (median, 12 degrees). The fraction of narrowly tuned neurons in the population was 40% (25/63). Thus, in a large subpopulation of area LIP, a fairly precise alignment exists between sensory and motor fields. 8. An additional set of 82 area LIP neurons were recorded while the monkey performed delayed saccades to 32 targets located on small, medium, and large imaginary circles.(ABSTRACT TRUNCATED AT 400 WORDS)

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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.

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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.

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PubMed1990

Eye position effects on visual, memory, and saccade-related activity in areas LIP and 7a of macaque.

We studied the effect of eye position on the light-sensitive, memory, and saccade-related activities of neurons of the lateral intraparietal area and area 7a in the posterior parietal cortex of rhesus monkeys. A majority of the cells showed significant effects of eye position, for each of the 3 types of response. The direction tuning of the light-sensitive, memory and saccade responses did not change with eye position but the magnitude of the response did. Since previous work showed a similar effect for the light-sensitive response of area 7a neurons (Andersen and Mountcastle, 1983; Andersen et al., 1985b), the present results indicate that this modulating effect of eye position may be a general one, as it is found in 3 types of responses in 2 cortical areas. Gain fields were mapped by measuring the effect of eye position on the magnitude of the response at 9 different eye positions for each neuron. The gain fields were usually planar or largely planar for all 3 types of response in both areas, indicating that the magnitude of the response usually varies linearly with both horizontal and vertical eye position. A similar observation was made previously for the gain fields of the light-sensitive response of area 7a neurons (Andersen et al., 1985b). Although gain fields sloped in all directions for the population of cells, the gain field slopes of the light-sensitive, memory and saccade responses for individual cells were usually similar. It is proposed that these eye position effects play an important role in making coordinate transformations for visually guided movement.

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PubMed1989

Thalamic input to inferior area 6 and area 4 in the macaque monkey.

Recent cytoarchitectonic, histochemical, and hodological studies in primates have shown that area 6 is formed by three main sectors: the supplementary motor area, superior area 6, which lies medial to the spur of the arcuate sulcus, and inferior area 6, which is located lateral to it. Inferior area 6 has been further subdivided into two histochemical areas: area F5, located along the inferior limb of the arcuate sulcus, and area F4, located between area F5 and area 4 (area F1). The present study traced the thalamocortical projections of inferior area 6 and the adjacent part of area 4 by injecting small amounts of WGA-HRP in specific sectors of the agranular frontal cortex. Our data showed that each histochemical area receives a large projection from one nucleus of the ventrolateral thalamus (motor thalamus) and additional projections from other nuclei of this thalamic sector. Area F5 receives a large projection from area X of Olszewski ('52) and additional projections from the caudal part of the nucleus ventralis posterior lateralis, pars oralis (VPLo), and the nucleus ventralis lateralis, pars caudalis (VLc) (VPLo-VLc complex). Area F4 receives a large projection from the nucleus ventralis lateralis, pars oralis (VLo), and additional projections from area X and the VPLo-VLc complex. The rostral part of area F1 is innervated chiefly by VLo, plus smaller contributions from rostral VPLo and the VPLo-VLc complex. The caudal part of F1 receives its greatest input from VPLo, with a small contribution from VLo. In addition, each histochemical area receives projections originating from the intralaminar thalamic nuclei, the posterior thalamus, and--for area F4 and area F5--also from the nucleus medialis dorsalis (MD). Analysis of the physiological properties of the various histochemical areas in relation to their main thalamic input showed that those cortical fields in which distal movements are predominant (area F5, caudal part of area F1) are innervated chiefly by area X and VPLo, whereas those cortical fields in which proximal movements are predominant receive their main input from VLo. Because VPLo and area X are targets of cerebellothalamic pathways, whereas VLo receives a pallidal input, we propose that the cortical fields in which distal movements are most heavily represented are mainly under the influence of the cerebellum, whereas the cortical fields in which proximal movements are most heavily represented are mainly under the influence of the basal ganglia.

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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.

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