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Biomedical subjects

G Rizzolatti

Publications and source records attributed to G Rizzolatti.

At least 109 records · Page 6Linked to original sources
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↗
PubMed1980

[Selective interference of a motor task on the reaction time to stimuli presented to the visual field of the left hemisphere].

Simple reaction time to a lateralized visual stimulus was studied in normal subjects while they were carrying out a concomitant task. The concomitant task consisted in a flexion of a single finger or pairs of finger at the middle joint. Regardless of the hand used the concomitant tasks produced a specific lengthening of responses to stimuli located in the left visual field. It is concluded that isolated finger movements, separate from a sequence of movement, are function of the right hemisphere.

Adult↗
PubMed1980

[Cognitive tasks and simple reaction times: new observations].

Simple reaction times to lateralized unstructured visual stimuli were studied in normal subjects while they were carrying out a concomitant task. In one task strings of four digits, randomly chosen from 1 to 9, were acoustically presented to the subjects who had to repeat them at the end of each presentation, in a second task again strings of four digits were presented and the subjects were asked to pay attention to the stimuli without memorizing them. In order to compel the subjects to listen carefully to the stimuli, in the second experiment, intermixed with the digits, a letter was occasionally presented and the subjects had to repeat it. It was found that the memory task facilitates reaction times mediated by the left hemisphere, whereas no hemispheric differences were found in the purely attentional task.

Acoustic Stimulation↗
PubMed1980

[Reaction time experiment on absolute or relative functional specialization of the cerebral hemispheres in man].

Lateralized presentations of verbal stimuli yield faster reaction times in the right visual field-left hemisphere, whereas nonverbal stimuli yield faster reaction times in the left visual field-right hemisphere. However, the problem of how lateral asymmetries in response latency are determined is still unsolved. The hypothesis of an absolute functional specialization of the two hemispheres suggests that information presented in the visual field connected with the unspecialized hemisphere has to travel along a less direct pathway, implying a crossing through the forebrain commissures, to reach the processing center. The hypothesis of a relative functional specialization assumes that stimuli are processed by the hemisphere contralateral to the field of presentation but speed of processing varies as a function of hemispheric specialization. The present study tried to find empirical evidence in favor of one of the two hypotheses. Choice reaction times to lateralized verbal stimuli were studied in normal subjects. In half of the trials the subjects had to carry out a concomitant task known to interfere selectively with mechanisms responsible of the organization of the responses of the left hemisphere. Both with and without concomitant task reaction times were significantly faster in the right visual field-left hemisphere. While the concomitant task produced an overall lengthening of reaction time, it did not affect interhemispheric asymmetry. This finding was discussed as evidence in favor of the absolute specialization hypothesis.

Acoustic Stimulation↗
PubMed1980

[Spatial stimulus-response compatibility: presentation of stimuli within one visual hemifield].

Choice reaction times of two lateralized unstructured visual stimuli located within the same (right or left) visual hemifield were studied in subjects with hands crossed and uncrossed. The subjects were instructed to respond with their right or left hand depending on the position of the stimulus. In one experimental condition they have to use their right hand for responding to the right light and their left hand for responding to the left light. In another experimental condition the reverse arrangement was used. The two light stimuli were presented, one at a time and 3 degrees apart, in both visual fields. Thus, the analyzed factors were: hand position (crossed or uncrossed), responding hand (right or left), field of presentation (right or left), and relative position of the light stimulus (right or left). The main finding of the present study was that spatial compatibility effects were present even when both stimuli were presented within the same visual field. That means that the factor determining which hand is faster in responding is the relative position of the two stimuli and of the two hands and not the position of the stimuli with reference to the vertical meridian.

Functional Laterality↗
PubMed1980

Neurons with complex visual properties in the superior colliculus of the macaque monkey.

Single neurons were recorded from the superficial layers of the superior colliculus of immobilized monkeys (Macaca mulatta and Macaca irus). Two main functional types of neurons were found. The neurons of the first type (Type I neurons) responded well to simple stationary and moving stimuli such as spots, bars or slits of light. The latency of their response was 41 +/- 6 ms. They were not directionally selective and responded to a large range of velocities. The neurons of the second type (Type II neurons) responded very poorly to simple visual stimuli and their activation required real objects or certain two-dimensional patterns. The mean latency of response of these units was 66 +/- 26 ms. Habituation was always present. Type II neurons were located in the lower part of the superficial layers. The characteristics of Type II neurons suggest that in the primate superior colliculus there is a mechanism that allows the recognition of the complexity and the novelty of a stimulus and guides orienting responses to those stimuli that are worth analyzing in detail.

Animals↗
PubMed1979

The effect of hemidecortication on the inhibitory interactions in the superior colliculus of the cat.

Single neurons were recorded extracellularly from the superficial layers of the superior colliculus (SC) in 21 curarized cats. Four animals were normal unoperated cats, 17 were animals in which all cortical visual areas were ablated on one side from 7 to 69 days before the electrophysiological experiments. After cortical ablation all animals were blind in the visual field contralateral to the ablated side. In both normal and hemianopsic cats the effect of a visual stimulus located very far from the excitatory part of the unit receptive field, on the neuron responses to visual stimuli was studied. The remote stimulus (extra-field stimulus) was a hand moved black spot 10 degrees in diameter. In normal animals the introduction of the extra-field stimulus in the hemifield contralateral or ipsilateral to the recorded SC produced a marked reduction of unit responses to visual stimuli presented in their receptive field. This effect was particularly strong when the extra-field stimuli were introduced in the hemifield contralateral to the recorded side. In the hemianopsic animals the neurons of the SC ipsilateral to the lesion (receptive fields in the behaviorally blind hemifield) responded well to visual stimuli, but were only weakly inhibited by the extra-field stimuli presented in the blind hemifield. The neurons of this colliculus with the exception of those in the upper part of stratum griseum superficiale were normally inhibited by stimuli presented in the normal hemifield. The neurons of the SC contralateral to the lesion responded well to visual stimuli and were normally inhibited by stimuli presented in the normal hemifield; they were virtually not affected by stimuli presented in the blind hemifield. Mechanisms responsible for the abnormal inhibitory interactions between and within colliculi after cortical lesions and the possible behavioral implications of the findings are discussed.

Animals↗
PubMed1979

Neurons responding to visual stimuli in the frontal lobe of macaque monkeys.

Responses to visual stimuli of single cortical neurons in arcuate and prearcuate regions were studied in 6 immobilized macaque monkeys. Neurons responding to visual stimuli were found in both regions, some of them responded to conventional light stimuli, others required more complex visual stimulation. The former were found posteriorly in the arcuate region, the latter anterioly and in the prearcuate region. According to their functional properties the latter neurons were subdivided into: (a) neurons responding to stimuli near the eyes; (b) neurons triggered by complex visual stimuli; (c) neurons inhibited by visual stimuli.

Animals↗
PubMed1977

Influence of the presentation of remote visual stimuli on visual responses of cat area 17 and lateral suprasylvian area.

Single units were recorded extracellularly from area 17 and lateral suprasylvian area (LSSA) in curarized cats. Visual stimuli, usually a 10 degree black spot, were introduced abruptly in the visual field remote from the discharge area of a neuron's receptive field and moved at a speed of about 30 degrees/sec. The effect of these remote stimuli (S2) on the reponse to a restricted visual stimulus (S1) crossing the discharge area was studied. It was found that most units in area 17 were not affected by the presentation of remote stimuli, the remainder being either slightly facilitated or slightly inhibited. In contrast the LSSA neurons were usually inhibited by the presentation of S2: this effect was strong, was present in all classes of LSSA neurons and was independent of the relative directions of movement of S1 and S2. On the basis of these data and those previously obtained from the superior colliculus it is concluded that the way the extrageniculate centres respond to a stimulus abruptly introduced in the visual field is substantially different from that of the striate cortex. Only in the extrageniculate centres a new stimulus, besides exciting the neurons which correspond to the position of the stimulus in the field, concomitantly decreases the responses of neurons located in positions of the visual field remote from that stimulus. Possible behavioral implications of the findings are discussed.

Animals↗