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C Lucchetti

Publications and source records attributed to C Lucchetti.

16 recordsLinked to original sources
PubMed2001

Time-modulated neuronal activity in the premotor cortex of macaque monkeys.

A voluntary motor act, executed in response to a stimulus, requires both spatial and temporal computation. Even though electrophysiological and positron emission tomography (PET) investigations on humans suggest that SMA, medial prefrontal cortex and primary motor cortex play a role in temporal mechanisms, we have few data about neuronal time computation in the premotor cortex. The involvement of monkey premotor area (PM) in motor learning and cognitive processes, and the presence of buildup neurons, whose activity is closely related to the motor action, prompted us to investigate the involvement of these set-related neurons in the time domain. To this end we manipulated the duration of a pre-cue in a visuomotor task while recording unit activity. We found that, when the duration of the pre-cue was predictable and long (5 s), delay of the onset of cell activity in consecutive trials gradually increased. On the other hand, when the duration was unpredictable or predictable and short (1 s), this phenomenon could not be detected. The inconsistent discharge correlations with expected reward and attentional processes, and the specific discharge relationship to the time instruction, suggest that these buildup neurons reflect a learning process in the time domain.

Action Potentials↗
PubMed1998

Neglect syndrome for aversive stimuli in a macaque monkey with dorsomedial frontal cortex lesion.

After a session of unit activity recording, one of our monkeys presented an epileptic attack, which provoked contralateral tilting movements. The following days, the animal performed saccades and fixation tasks correctly in all directions, while contralateral arm reaching movements were severely impaired. To establish if the neurological lesion had changed the orienting performance we considered two types of stimuli, pleasant and aversive. Pleasant stimuli, presented in the ipsilateral or contralateral hemifield, readily drew the attention of the animal. If the same stimuli were presented simultaneously in both hemifields, the monkey oriented itself only toward the ipsilateral one. Aversive stimuli evoked an aggressive reaction only when the stimulus was localized in the ipsilateral hemifield. The animal clearly neglected the aversive stimulus presented in the contralateral hemifield. The animal recovered completely in 30 days. The postmortem examination revealed a lesion in the dorsomedial frontal cortex. The combined attentional and motor deficits suggest that this area may be involved in the preparation and execution of movements triggered by the affective meaning of the stimulus.

Animals↗
PubMed1997

Attention-related neurons in the supplementary eye field of the macaque monkey.

This study investigated whether the neuronal activity of a cortical area involved in the control of eye fixation is affected by the covert orienting of attention. We recorded single-unit activity from the supplementary eye field (SEF) of two macaque monkeys performing fixation and peripheral-attention tasks. Ninety-nine out of four hundred and fifteen cells were related to eye movements. The other neurons showed relationship with postural adjustments, and arm and ear movements. Fifty-five neurons were active during fixation (fixation cells) and 44 discharged in relation to saccades. The experiments reported here primarily concern the fixation cells. The activity of 64% (35/55) of fixation cells started with the onset of visual stimulus, before the visual input reached the fovea, and continued during active fixation. The activity of 27% (15/55) of fixation cells started with the onset of fixation. The activity of 9% (5/55) of fixation cells modified their timing trial by trial. Sixty-four percent of the fixation cells (35/55) were position-dependent, showing a selective spatial field of activity, 36% (20/55) were position-independent and characterized by a full spatial field. None of the 55 cells showed a visual receptive field. We tested both types of fixation cells by means of a peripheral attention task. When attention was oriented peripherally toward a target located in the selective spatial field, the cells discharged as if the gaze was held toward it. When attention was oriented peripherally toward a target, lying outside the selective spatial field the cells were inactive as if gaze was held in that position. These results suggest that the supplementary eye field neurons may code for oriented attention in space and might be involved in the preparation of motor action.

Animals↗
PubMed1997

Motor programs of spontaneous and visually guided saccades in macaque monkey: an electrophysiological approach.

The discharge activity of 37 burst neurons in the paramedian pontine reticular formation and the saccades performed in the dark (spontaneous saccades) and between visual targets (attentive visually guided) were recorded in two macaque monkeys. Forty-five % of spontaneous saccades showed more than one maximum of velocity (irregular velocity profiles), while visually guided saccades were always characterized by a single maximum of velocity (regular velocity profiles). The discharge pattern of each burst neuron (short lead neuron) was different according to the saccade velocity profile. We observed a clear inhibition within the burst neuron discharge for irregular velocity profiles, thus giving rise to multiple maxima of discharge frequency, and to a clearly interrupted saccade. The same neuron showed only one maximum of discharge frequency for regular saccades. Then the hypothesis of two different neural networks generating the different motor programs of spontaneous and attentive visual guided saccades is put forward and discussed.

Animals↗
PubMed1997

Activity of neurons related to eye movements during drowsiness in the frontal cortex of the macaca monkey.

During our extensive study of the supplementary eye field (SEF) in relation to eye and arm movements, we had the opportunity to record the activity of 25 out of 315 cells during both saccade task and drowsiness states. All 25 cells showed a phasic, spatially selective postsaccadic activity that was not related to fixation. During drowsiness, the discharge was time locked with the onset of the slow movement, had increased duration, and was not spatially selective. These preliminary data suggest that saccade neurons present in SEF are also involved in the motor processes of slow eye movements during drowsiness.

Animals↗
PubMed1994

Ear and eye representation in the frontal cortex, area 8b, of the macaque monkey: an electrophysiological study.

We evoked both ear and eye movements in area 8b, the rostral area of frontal cortex, in two monkeys. In some sites it was possible to evoke only ear movements or only eye movements; in other locations we evoked both ear and eye movements by varying the intensity of electrical stimulation. The electrically evoked ear movements were forward, or backward, or oblique (upward-forward; upward-backward). In two penetrations the ear movements were bilateral, in the other penetrations they were contralateral. Ipsilateral ear movements were not observed. The evoked eye movements were mainly fixed-vector saccades, contralateral and with an upward orientation of about 45 degrees. If we considered only the sites where the threshold was equal to or lower than 50 microA, the stimulation of this area evoked mainly ear movements. In addition we recorded the electrical activity of 195 neurons. Of these neurons: 74% (145/195) discharged before ear movements (ear cells); 20% (40/195) discharged before ear and eye movements (ear-eye cells); 5% (10/195) discharged only before eye movements (eye cells). Ninety-one percent (132/145) of ear cells presented a preferred direction; 90% (36/40) of ear-eye cells presented a preferred direction for ear movements, and 15% (6/40) presented a preferred direction for eye movements. Eighty-five percent (34/40) of cells did not present a preferred direction for visually guided saccades and were active when the monkey made saccades toward the unlit targets (checking saccades). Our results show that a field of area 8b is related to ear movements and to eye-ear movements. The findings that it is possible to obtain both ear and eye movements with low-intensity currents and that there are cells firing for the two types of movements suggest that area 8b may be involved in the orientation and coordination of both ear and eye. This area might be considered a rostral extension of supplementary eye field (SEF) or a different region. However, based on its distinct functional characteristics and connectivity, it is probably better regarded as a separate field. Regardless, the combination of 8b and SEF may constitute a cortical center for orienting processes.

Animals↗
PubMed1992

The dorsomedial frontal cortex of the macaca monkey: fixation and saccade-related activity.

The activity of 249 neurons in the dorsomedial frontal cortex was studied in two macaque monkeys. The animals were trained to release a bar when a visual stimulus changed color in order to receive reward. An acoustic cue signaled the start of a series of trials to the animal, which was then free to begin each trial at will. The monkeys tended to fixate the visual stimuli and to make saccades when the stimuli moved. The monkeys were neither rewarded for making proper eye movements nor punished for making extraneous ones. We found neurons whose discharge was related to various movements including those of the eye, neck, and arm. In this report, we describe the properties of neurons that showed activity related to visual fixation and saccadic eye movement. Fixation neurons discharged during active fixation with the eye in a given position in the orbit, but did not discharge when the eye occupied the same orbital positions during nonactive fixation. These neurons showed neither a classic nor a complex visual receptive field, nor a foveal receptive visual field. Electrical stimulation at the site of the fixation neurons often drove the eye to the orbital position associated with maximal activity of the cell. Several different kinds of neurons were found to discharge before saccades: 1) checking-saccade neurons, which discharged when the monkeys made self-generated saccades to extinguish LED's; 2) novelty-detection saccade neurons, which discharged before the first saccade made to a new visual target but whose activity waned with successive presentations of the same target. These results suggest that the dorsomedial frontal cortex is involved in attentive fixation. We hypothesize that the fixation neurons may be involved in codifying the saccade toward a target. We propose that their involvement in arm-eye-head motor-planning rests primarily in targeting the goal of the movement. The fact that saccade-related neurons discharge when the saccades are self initiated, implies that this area of the cortex may share the control of voluntary saccades with the frontal eye fields and that the activation is involved in intentional motor processes.

Animals↗
PubMed1992

The effects of maturation on spontaneous eye movements in the macaque monkey.

The spontaneous eye movements of infant and adult monkeys were studied both in the dark and in the laboratory light by a magnetic search-coil technique and analysed comparatively. The spatio-temporal organization of the infant monkey's eye movements is predominantly vertical; by contrast it is predominantly horizontal in adults. Moreover, the infant monkey's eye movements have smaller amplitudes and slower velocities than adult's in both visual conditions. The linear relationships between amplitude and maximum velocity suggest that rapid eye movements of the infant monkey are saccades but with a lower rate of velocity increase than the adult's. We conclude that the eye movements in the infant and in the adult monkeys differ in many aspects and that maturation acts on both the static and dynamic characteristics of ocular motility.

Aging↗
PubMed1991

Behavioral and motor mechanisms of dorsomedial frontal cortex of macaca monkey.

The activity of 249 neurons in the dorsomedial frontal cortex was recorded in two macaca monkeys. The animals had been trained for saccades and fixation tasks in an unrestrained condition. We found 51 burst neurons that showed a double-firing discharge. We observed two different patterns of discharge. In one case the first burst occurred before the arm movement, the second before the related eye movement. In the second case, the first discharge took place before a neck contraction followed by a second burst before eye movement. Some cells showed two discharges, one that preceded the bar-press and the other the saccade. With other cells the discharges preceded the bar-release and then saccade. Still other cells discharged three times: first before the bar-press, second before release and third before the orienting saccade. Some cells were active for the bar-press and for the first orienting saccades. These cells were active also for a large range of movement tested at the presentation of natural stimuli. Electrical stimulation failed to evoke either arm or eye movement. Neck-eye cells are related to movement of the eye and to an increase of EMG activity independent of eye position. The electrical stimulation evoked eye movements and EMG increases at low threshold. The activity of arm-eye cells related to purposeful movement with the ineffectiveness of electrical stimulation may be ascribed to a motor reactivation or an ordering signal. The neck-eye cells may be considered trigger commands for neck-eye coordination.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Neurons signalling the maintenance of attentive fixation in frontal area 6a beta of macaque monkey.

Twelve out of 140 neurons recorded in a restricted region of the frontal agranular cortex (area 6a beta) of trained macaque monkeys, discharged only during attentive fixation of a target in the straight ahead position. These cells, lacking a visual receptive field, were silent when the animal's eye was in the same position during spontaneous oculomotor behaviour. Our preliminary results suggest that this area is involved in the codification of attentive fixation.

Acoustic Stimulation↗
PubMed1990

Does attention affect the motor programs of pharmacologically induced eye movements?

Attention plays an important role in oculomotor function. We studied the effect of attentional stimuli on eye movements induced by ketamine. The experiments were carried out on three monkeys. Ketamine injected intramuscularly induced nystagmus. When we switched on a new stimulus these eye movements stopped and the animal made a saccade toward it. This may be due to a new motor program, triggered by a visual stimulus, that among its characteristics is able to engage the animal's attention. The program of evoked saccade is overwritten on induced oculomotor activity. Our results suggest that attentional processes modify the dynamic characteristics and induce in particular behavioral condition a new motor program.

Animals↗
PubMed1988

The motor programs of monkey's saccades: an attentional hypothesis.

We analyzed the dynamics of saccadic eye movements performed by monkeys in three different conditions: as a part of an ocular motor task, spontaneously when the monkey was alert but not performing a task in ordinary room illumination, and spontaneously when the monkey was alert but not performing a task in total darkness. We found three general classes of saccades: 1) regular-symmetric, in which the rise time of the velocity profile was equal to the falling time; 2) regular-asymmetric, in which the rise time was less than the falling time; 3) irregular, in which there were multiple velocity maxima or inflection points. The monkeys made irregular saccades half the time in the two spontaneous saccade conditions, and almost never during the task. In order to see if the regularity of saccades was an artifact of reward, we then evoked saccades by presenting the monkeys with novel visual and acoustic stimuli to which they made saccades. Such guided saccades to novel stimuli had regular velocity profiles. We suggest that saccades made as a part of attentive behavior differ in their motor programming from saccades made spontaneously in darkness, or saccades made in the light without a purpose relevant to visual behavior.

Acoustic Stimulation↗
PubMed1985

The spontaneous eye movements in the awake kitten.

The spontaneous eye movements were analysed comparatively in the kitten and in the cat. The eye movements were recorded in the dark by a magnetic search coil technique. The spatio-temporal organization of eye movements in the kitten has a prevailing vertical orientation and differs completely from that of the cat. In the kitten the amplitude of eye movements is smaller than in the cat and only a few movements are followed by fixation. It results, by correlating amplitude-peak velocity, that rapid eye movements in the awake kitten are saccades. From our results we conclude that the eye movements in the kitten and in the cat differ in many aspects and that the visual system is responsible for the development of the correct oculomotor behaviour.

Aging↗