Biomedical subjects

D Boussaoud

Publications and source records attributed to D Boussaoud.

At least 19 recordsLinked to original sources

PubMed1999

Origin of thalamic inputs to the primary, premotor, and supplementary motor cortical areas and to area 46 in macaque monkeys: a multiple retrograde tracing study.

The origin of thalamic inputs to distinct motor cortical areas was established in five monkeys to determine whether the motor areas receive inputs from a common thalamic nucleus and the extent to which the territories of origin overlap. To not rely on the rough definition of cytoarchitectonic boundaries in the thalamus, monkeys were subjected to multiple injections of tracers (four to seven) in the primary (M1), premotor (PM), and supplementary (SMA) motor cortical areas and in area 46. The cortical areas were distributed into five groups, each receiving inputs from a specific set of thalamic nuclei: 1) M1; 2) SMA-proper and the caudal part of the dorsal PM (PMdc); 3) the rostral and caudal parts of the ventral PM (PMvr and PMvc); 4) the rostral part of the dorsal PM (PMdr); and 5) the superior and inferior parts of area 46 (area 46sup and area 46inf). A major degree of overlap was obtained for the origins of the thalamocortical projections directed to areas 46inf and 46sup and for those terminating in SMA-proper and PMdc. PMvc and PMvr received inputs from adjacent and/or common thalamic regions. In contrast, the degree of overlap between M1 and SMA was smaller. The projection to M1 shared relatively limited zones of origin with the projections directed to PM. Thalamic inputs to the motor cortical areas (M1, SMA, PMd, and PMv), in general, were segregated from those directed to area 46, except in the mediodorsal nucleus, in which there was clear overlap of the territories sending projections to area 46, SMA-proper, and PMdc.

Afferent Pathways↗

PubMed1998

Dual morphology and topography of the corticothalamic terminals originating from the primary, supplementary motor, and dorsal premotor cortical areas in macaque monkeys.

In the motor, somatosensory, and auditory systems of rodents and cats, the corticothalamic connection is composed of a main projection formed by small endings and a minor projection terminating with giant endings. To establish whether the corticothalamic projection originating from motor cortical areas in primates exhibits the same duality, the anterograde tracer biotinylated dextran amine was injected in eight macaque monkeys in the primary motor (M1; n = 3), the supplementary motor (SMA; n = 3) and the dorsal premotor (PMd; n = 2) cortical areas to label corticothalamic axons. The corticothalamic projection originating from these three motor cortical areas was characterized by the presence of axon terminals constituting the same two types of endings, observed both as boutons en passant and terminaux. The population of small endings exhibited a mean cross-sectional maximum diameter of 0.95 microm (S.D. = 0.23), a range of diameters not overlapping that of giant endings (mean diameter = 3.46 microm, S.D. = 0.74 microm). Topographically, the giant endings originating from M1 were located in the same thalamic nucleus (ventroposterolateral nucleus, oral part) in which the small endings were found. In contrast, the giant endings originating from SMA and PMd were located in a thalamic nucleus (mediodorsal nucleus) distinct from the main termination zone formed by small endings. Along the rostrocaudal axis, the giant endings were distributed in a restricted zone, irrespective of the origin of the projection (M1, SMA, PMd). The dual morphology of corticothalamic endings, previously found in rodents and cats, is present in the motor system of subhuman primates for both primary and nonprimary motor cortical areas.

Animals↗

PubMed1998

Eye position effects on the neuronal activity of dorsal premotor cortex in the macaque monkey.

Visual inputs to the brain are mapped in a retinocentric reference frame, but the motor system plans movements in a body-centered frame. This basic observation implies that the brain must transform target coordinates from one reference frame to another. Physiological studies revealed that the posterior parietal cortex may contribute a large part of such a transformation, but the question remains as to whether the premotor areas receive visual information, from the parietal cortex, readily coded in body-centered coordinates. To answer this question, we studied dorsal premotor cortex (PMd) neurons in two monkeys while they performed a conditional visuomotor task and maintained fixation at different gaze angles. Visual stimuli were presented on a video monitor, and the monkeys made limb movements on a panel of three touch pads located at the bottom of the monitor. A trial begins when the monkey puts its hand on the central pad. Then, later in the trial, a colored cue instructed a limb movement to the left touch pad if red or to the right one if green. The cues lasted for a variable delay, the instructed delay period, and their offset served as the go signal. The fixation spot was presented at the center of the screen or at one of four peripheral locations. Because the monkey's head was restrained, peripheral fixations caused a deviation of the eyes within the orbit, but for each fixation angle, the instructional cue was presented at nine locations with constant retinocentric coordinates. After the presentation of the instructional cue, 133 PMd cells displayed a phasic discharge (signal-related activity), 157 were tonically active during the instructed delay period (set-related or preparatory activity), and 104 were active after the go signal in relation to movement (movement-related activity). A large proportion of cells showed variations of the discharge rate in relation to limb movement direction, but only modest proportions were sensitive to the cue's location (signal, 43%; set, 34%; movement, 29%). More importantly, the activity of most neurons (signal, 74%; set, 79%; movement, 79%) varied significantly (analysis of variance, P < 0.05) with orbital eye position. A regression analysis showed that the neuronal activity varied linearly with eye position along the horizontal and vertical axes and can be approximated by a two-dimensional regression plane. These data provide evidence that eye position signals modulate the neuronal activity beyond sensory areas, including those involved in visually guided reaching limb movements. Further, they show that neuronal activity related to movement preparation and execution combines at least two directional parameters: arm movement direction and gaze direction in space. It is suggested that a substantial population of PMd cells codes limb movement direction in a head-centered reference frame.

Action Potentials↗

PubMed1997

Encoding behavioral context in recurrent networks of the fronto-striatal system: a simulation study.

This research addresses the hypothesis that behavioral context is encoded in recurrent networks of the fronto-striatal system. Behavioral context influences the processing of subsequent brain events, including responses to sensory inputs, thus providing a basis for context-dependent behavior. We define context-dependent behavior as the adaptive ability to produce the appropriate response to a given stimulus, dependent upon the context in which it appears. Behavioral context can change with a time-scale on the order of seconds to tens of seconds or more. This suggests a flexible mechanism that encodes context via an ensemble of neural activation that will appropriately influence the processing of subsequent sensory stimuli. We present a functional model of context encoding in recurrent connections of the fronto-striatal system with simulation results that correspond closely to empirical data. Neuronal activity in monkeys that perform a context-dependent task indicate that the prefrontal cortex and striatum participate differentially in this kind of context encoding. Likewise, simulated neurons in our model of the fronto-striatal system, which performs the context-dependent task, display task-related activity remarkably similar to that found in monkey frontal cortex and striatum, supporting our hypothesis.

Adaptation, Psychological↗

PubMed1997

The primate striatum: neuronal activity in relation to spatial attention versus motor preparation.

The primate basal ganglia are known to be involved in the initiation and control of visually guided movements. However, the precise role of these structures is not clear, partly because most neurophysiological studies have not dissociated neuronal activity related to visuomotor processing from that reflecting other aspects of behaviour, such as shifts of spatial attention. Moreover, the way the basal ganglia function together with the frontal cortex during movement initiation and execution is still a matter of debate. In an effort to clarify these issues, we recorded single neurons from the striatum (caudate nucleus and putamen) in two rhesus monkeys trained to perform a conditional visuomotor task, and compared their properties with those of the frontal cortex. The experimental paradigm was designed to distinguish neuronal activity associated with shifts of attention from that reflecting motor preparation. In a given trial, an identical visual stimulus could serve as a cue for the reorientation of spatial attention or as a cue for establishing a motor set depending on when it occurred during that trial. Additional aspects of the paradigm were designed to identify neurons whose activity differed when various stimulus configurations instructed the same action (stimulus effect), as well as neurons whose activity differed when two different actions were instructed by the same stimulus (movement effect). The majority of cells (60%) were preferentially active after instructional cues, 38% discharged preferentially after attentional cues, and the remaining 2% of cells discharged equally after both types of cue. Neurons active after instructional cues were further analysed for stimulus and movement effects. During movement preparation, the activity of the vast majority of striatal cells (putamen, 81%; caudate, 76%) varied significantly when different stimuli instructed the same action. Likewise, when different movements were instructed by the same stimulus, preparatory activity of a majority of cells (putamen, 92%; caudate, 82%) changed. Consequently, a substantial proportion of cells showed combined stimulus and movement effects. Comparison of these neuronal properties with those of the dorsal premotor cortex showed significantly higher proportions of cells in the striatum whose activity reflected sensory or sensorimotor processing. These results suggest that the basal ganglia are involved in shifting attentional set and in high-order processes of movement initiation, including the linking of sensory information with behavioural responses.

Animals↗

PubMed1997

Premotor and parietal cortex: corticocortical connectivity and combinatorial computations.

The dorsal premotor cortex is a functionally distinct cortical field or group of fields in the primate frontal cortex. Anatomical studies have confirmed that most parietal input to the dorsal premotor cortex originates from the superior parietal lobule. However, these projections arise not only from the dorsal aspect of area 5, as has long been known, but also from newly defined areas of posterior parietal cortex, which are directly connected with the extrastriate visual cortex. Thus, the dorsal premotor cortex receives much more direct visual input than previously accepted. It appears that this fronto-parietal network functions as a visuomotor controller-one that makes computations based on proprioceptive, visual, gaze, attentional, and other information to produce an output that reflects the selection, preparation, and execution of movements.

Animals↗

PubMed1996

Evidence for direct connections between the hand region of the supplementary motor area and cervical motoneurons in the macaque monkey.

In primates the corticospinal neurons of the hand representation of the primary motor cortex (M1) give rise to direct contacts with the cervical motoneurons that control distal forelimb muscles. We investigated, at the light-microscopy level, whether corticospinal cells present in the hand area of the supplementary motor area (SMA) also establish direct connections with cervical motoneurons, particularly those innervating hand and finger muscles. The hand representation of the M1 (two monkeys) or SMA (two monkeys) was located using intracortical microstimulation and injected with the anterograde tracer biotinylated dextran amine to label corticospinal terminals. Forearm muscles acting on the wrist and hand as well as hand muscles acting on the thumb and index finger, thus including those activated by intracortical stimulation, were injected with the retrograde tracer cholera-toxin B subunit, in order to label the motoneurons. A consistent zone of overlap between the two markers was found in the cervical cord. Close appositions between corticospinal axonal terminals and the somata or dendrites of motoneurons were found after injection in the M1, confirming previous observations. The new finding is the observation of similar close appositions after injection in the SMA, suggesting its control of hand movements in parallel with the M1.

Animals↗

PubMed1996

The premotor cortex and nonstandard sensorimotor mapping.

We often gaze at and attend to an object while preparing to reach toward and grasp it, and continue doing so when the plan is executed. Elaborate machinery, much of it in the brainstem and spinal cord, provides control systems for the spatially congruent guidance of the eyes, limbs, and body toward targets in visual space. We will use the term standard mapping for the sensorimotor transformations that underlie such behavior. Despite the common sense character of standard mapping, the targets of gaze, attention, and reaching can be dissociated from each other. We can attend to stimuli in locations that differ from the target of action. We can gaze in one direction while reaching in another. And we can guide spatial action with nonspatial stimuli, such as when, in conditional motor tasks, the color of an object instructs a movement elsewhere in space. All of these situations, and many others, call for a process that we term nonstandard mapping, wherein the central nervous system must reject the commonplace correspondences among visuospatial stimuli, gaze, attention, and reaching movements. We focus in this article on the possibility that premotor cortex underlies nonstandard mapping and, therefore, the behavioral flexibility that such a process allows.

Animals↗

PubMed1995

Direct visual pathways for reaching movements in the macaque monkey.

The brain seems to process the location of objects faster than their intrinsic features, such as size, when these parameters are used to guide action. To uncover a potential anatomical substrate of these different processing speeds, we investigated in the monkey the pathways linking extrastriate visual cortex with the dorsal premotor area, a frontal area known to be involved in visually guided reaching movements. Retrogradely transported anatomical tracers were injected at physiologically defined sites and the distribution of labelled cells was examined in the ipsilateral cortex. We found a projection to the dorsal premotor cortex from the parieto-occipital area (PO). This area receives direct projections from the primary visual cortex (V1), and is part of the dorsal visual stream involved in the processing of spatial information. No direct projections to the dorsal premotor cortex arise from the ventral visual areas, thought to process object features. Our finding provides evidence for direct pathways from the dorsal visual stream to the dorsal premotor cortex and supports the view that the location of objects is processed faster by the brain than their intrinsic features.

Animals↗

PubMed1995

Frontal lobe mechanisms subserving vision-for-action versus vision-for-perception.

In the typical course of daily events, we often gaze at an object, attend to its features and its place, reach toward it and grasp it, all with an awareness of what we are doing at the time. But behavior is not always thus. Gaze, attention, limb movement direction and awareness can be behaviorally dissociated from each other, and this review focuses on one such dissociation: that between the perception of an object and the use of that object's inherent spatial and nonspatial information for mediating visuomotor control. We review evidence that partially different neuronal systems underlie these two aspects of visual information processing. In neurophysiological studies of the primate frontal lobe, it has been possible to demonstrate that neural signals appearing to be visual responses reflect, at least in part, the motor significance of a stimulus. This finding has been confirmed, in separate studies, for both spatial and nonspatial visual information and supports the hypothesis that some frontal cortex activity reflects the selection and guidance of action rather than the properties of visual stimuli, per se. These findings are discussed in the context of neuropsychological studies indicating that accurate and appropriate movements are possible without perceptual awareness of the information guiding those movements.

Animals↗

PubMed1995

Role of the primate striatum in attention and sensorimotor processes: comparison with premotor cortex.

The present study was aimed at distinguishing neuronal activity associated with shifts of attention from that reflecting motor set. Our behavioural paradigm allowed a given visual stimulus to serve as a cue for the reorientation of spatial attention or as a cue for establishing a motor set, depending on when it occurred during a trial. Other aspects of the paradigm were designed to identify neurones whose activity differed when various stimulus configurations instructed the same action, as well as neurones whose activity differed when two different limb movements were instructed by the same stimulus. We found that many striatal cells discharge preferentially in relation to cues which reorient spatial attention, although they may also discharge after cues which instruct a motor act. In contrast to the dorsal premotor area (PMd, dorsolateral area 6), in both the caudate nucleus and putamen a larger proportion of the neuronal sample reflected both movement direction and stimulus attributes. These results support a role for striatal neurones in both attentional set shifting and the preparation for context-specific actions.

Animals↗

PubMed1995

Primate premotor cortex: modulation of preparatory neuronal activity by gaze angle.

1. This study investigated whether the neuronal activity of a cortical area devoted to the control of limb movements is affected by variations in eye position within the orbit. Two rhesus monkeys were trained to perform a conditional visuomotor task with an instructed delay period while maintaining gaze on a fixation point. 2. The experimental design required each monkey to put its hand on a metal touch pad located at arm's length and fixate a small spot of light presented on a computer screen. Then a visual cue came on, at the fixation point or elsewhere, the color of which instructed the monkey to move its limb to one of two touch pads according to a conditional rule. A red cue meant a movement to the left, whereas a green one instructed a movement to the right. The cue lasted for a variable delay period (1-3 s), and the monkey had to wait for its offset, the go signal, before performing the correct response. The fixation point and the cues were presented at various screen locations in a combination that allowed examination of whether eye position and/or target position modulate the neuronal activity. Because the monkeys' heads were fixed, all changes in eye position reflected movements in a craniocentric, head-centered, coordinate space. 3. The activity of single neurons was recorded from dorsal premotor cortex (PMd). For most neurons (79%), the activity during the instructed delay period (set-related activity) reflects the direction of the upcoming limb movement but varies significantly with eye position.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Cortical connections of inferior temporal area TEO in macaque monkeys.

In macaque monkeys, lesions involving the posterior portion of the inferior temporal cortex, cytoarchitectonic area TEO, produce a severe impairment in visual pattern discrimination. Recently, this area has been shown to contain a complete, though coarse, representation of the contralateral visual field (Boussaoud, Desimone, and Ungerleider: J. Comp. Neurol. 306:554-575, '91). Because the inputs and outputs of area TEO have not yet been fully described, we injected a variety of retrograde and anterograde tracers into 11 physiologically identified sites within TEO of seven rhesus monkeys and analyzed the areal and laminar distribution of its cortical connections. Our results show that TEO receives feedforward, topographically organized inputs from prestriate areas V2, V3, and V4. Additional sparser feedforward inputs arise from areas V3A, V4t, and MT. Each of these inputs is reciprocated by a feedback projection from TEO. TEO was also found to have reciprocal intermediate-type connections with the fundus of the superior temporal area (area FST), cortex in the most posteromedial portion of the superior temporal sulcus (the posterior parietal sulcal zone [area PP]), cortex in the intraparietal sulcus (including the lateral intraparietal area [area LIP]), the frontal eye field, and area TF on the parahippocampal gyrus. The connections with V3A, V4t, and PP were found only after injections in the peripheral field representations of TEO. Finally, TEO was found to project in a feedforward pattern to area TE and to areas anterior to FST on the lateral bank and floor of the superior temporal sulcus (areas TEm, TEa, and IPa, Seltzer and Pandya: Brain Res. 149:1-24, '78), all of which send feedback projections to TEO. Feedback projections also arise from parahippocampal area TH, and areas TG, 36, and possibly 35. These are complemented by only sparse feedforward projections to TG from central field representations in TEO and to TH from peripheral field representations. The results thus indicate that TEO forms an important link in the occipitotemporal pathway for object recognition, sending visual information forward from V1 and prestriate relays in V2-V4 to anterior inferior temporal area TE.

Animals↗

PubMed1993

Effects of gaze on apparent visual responses of frontal cortex neurons.

Previous reports have argued that single neurons in the ventral premotor cortex of rhesus monkeys (PMv, the ventrolateral part of Brodmann's area 6) typically show spatial response fields that are independent of gaze angle. We reinvestigated this issue for PMv and also explored the adjacent prearcuate cortex (PAv, areas 12 and 45). Two rhesus monkeys were operantly conditioned to press a switch and maintain fixation on a small visual stimulus (0.2 degree x 0.2 degree) while a second visual stimulus (1 degree x 1 degree or 2 degrees x 2 degrees) appeared at one of several possible locations on a video screen. When the second stimulus dimmed, after an unpredictable period of 0.4-1.2 s, the monkey had to quickly release the switch to receive liquid reinforcement. By presenting stimuli at fixed screen locations and varying the location of the fixation point, we could determine whether single neurons encode stimulus location in "absolute space" or any other coordinate system independent of gaze. For the vast majority of neurons in both PMv (90%) and PAv (94%), the apparent response to a stimulus at a given screen location varied significantly and dramatically with gaze angle. Thus, we found little evidence for gaze-independent activity in either PMv or PAv neurons. The present result in frontal cortex resembles that in posterior parietal cortex, where both retinal image location and eye position affect responsiveness to visual stimuli.

Animals↗

PubMed1993

Primate frontal cortex: neuronal activity following attentional versus intentional cues.

We examined neuronal activity in three parts of the primate frontal cortex: the dorsal (PMd) and ventral (PMv) premotor cortex and a ventrolateral part of the dorsolateral prefrontal (PF) cortex. Two monkeys fixated a 0.2 degrees white square in the center of a video display while depressing a switch located between two touch pads. On each trial, a spatial-attentional/mnemonic (SAM) cue was presented first. The SAM cue consisted of one 2 degrees x 2 degrees square, usually red or green, and its location indicated where a conditional motor instruction would appear after a delay period. The stimulus event containing the motor instruction, termed the motor instructional/conditional (MIC) cue, could be of two general types. It might consist of a single 2 degrees x 2 degrees square stimulus identical to one of the SAM cues presented at the same location as the SAM cue on that trial. When the MIC cue was a single square, it instructed the monkey to move its forelimb to one of the two touch pads according to the following conditional rule: a green MIC cue meant that contact with the right touch pad would be rewarded on that trial and a red MIC cue instructed a movement to the left touch pad. Alternatively, the MIC cue might consist of two 2 degrees x 2 degrees squares, only one of which was at the SAM-cue location: in those cases, one square was red and the other was green. The colored square at the SAM cue location for that trial was the instructing stimulus, and the other part of the MIC cue was irrelevant. When, after a variable delay period, the MIC cue disappeared, the monkey had to touch the appropriate target within 1 s to receive a reward and could break visual fixation. The experimental design allowed comparison of frontal cortical activity when one stimulus, identical in retinocentric, craniocentric, and allocentric spatial location as well as all other stimulus parameters, had two different meanings for the animal's behavior. When a stimulus was the SAM cue, it led to either a reorientation of spatial attention to its location, or the storage of its location in spatial memory. By contrast, when it was the MIC cue, the same stimulus instructed a motor act to be executed after a delay period. For the majority of PMd neurons (55%), post-MIC cue activity exceeded post-SAM cue activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1993

Primate frontal cortex: effects of stimulus and movement.

We compared neuronal activity in the dorsal premotor cortex (PMd), ventral premotor cortex (PMv), and prefrontal (PF) cortex of two rhesus monkeys. The behavioral design was a variant of the instructed delay task which established that: (1) a given visual stimulus could, on different trials, instruct different limb movements and (2) several different visual stimuli could instruct the same movement. Neurons in all frontal areas displayed the often replicated activity patterns that occur during instructed delay tasks, including phasic increases after instruction stimuli (signal-related activity), tonic discharge during an instructed delay period (set-related activity), and phasic premovement discharge (movement-related activity). For signal-, set-, and movement-related activity, the majority of neurons in PMd (51-64%), but only a minority in PF (16-18%) and PMv (32-40%), showed activity levels that significantly depended on the action instructed by that stimulus rather than simply the characteristics of the stimulus per se. Thus, most PMd activity, including the aspects that most resembled a sensory response, reflected factors in addition to the signal. Taken together with the results of related studies, it seems most likely that these other factors are dominated by the motor instructional significance of the stimulus. In addition, many neurons (17-37%) in all examined areas showed activity that significantly depended on which of various stimuli guided the same movement. This finding shows that, in those frontal areas, neuronal activity can be affected by both the action to be taken and the events guiding that action.

Animals↗

PubMed1992

Primate premotor cortex: dissociation of visuomotor from sensory signals.

1. If we assume adequate control for attention, memory, and stimulus location, a bona fide sensory response would be unaffected by whether a visuospatial stimulus instructs (1) one limb movement versus another or (2) limb movement versus a shift in spatial attention or memory. Two behavioral methods tested whether apparently sensory responses in the monkey's premotor cortex are strictly that, or, alternatively, whether they reflect the action instructed by a stimulus. 2. When an identical stimulus leads to two different responses, phasic discharge after a visuospatial stimulus is significantly, often dramatically, affected by the response. Similarly, premotor cortex neurons discharge more after a stimulus instructs a limb movement than after the same stimulus instructs a shift in spatial attention or memory. Thus, for the majority of premotor cortex neurons, the hypothesis that phasic poststimulus activity modulation represents a sensory response can be rejected.

Animals↗

PubMed1991

Visual topography of area TEO in the macaque.

Previous studies have mapped the visuotopic organization of visual areas from V1 through V4 in the occipital cortex and of area TE in the temporal cortex, but the cortex in between, at the occipito-temporal junction, has remained relatively unexplored. To determine the visuotopic organization of this region, receptive fields were mapped at 1,200 visually responsive sites on 370 penetrations in the ventral occipital and temporal cortex of five macaques. We identified a new visual area, roughly corresponding to cytoarchitectonic area TEO, located between the ventral portion of V4 and area TE. Receptive fields in TEO are intermediate in size between those in V4 and TE and have a coarse visuotopic organization. Collectively, receptive fields in TEO appear to cover nearly the entire contralateral visual field. The foveal and parafoveal representation of TEO is located laterally on the convexity of the inferior temporal gyrus, and the peripheral field is represented medially on the ventral surface of the hemisphere, within and medial to the occipitotemporal sulcus. Beyond the medial border of TEO, within cyteoarchitectonic area TF, is another visually responsive region, which we have termed VTF; this region may also have some crude visual topography. Bands of constant eccentricity in TEO appear to be continuous with those in V2, V3v, and V4. The upper field representation in TEO is located adjacent to that in ventral V4, with a representation of the horizontal meridian forming the boundary between the two areas. The lower field representation in TEO is located just anterior to the upper field but is smaller. In contrast to the orderly representation of eccentricity in TEO, we found little consistent representation of polar angle, other than the separation of upper and lower fields. The results of injecting anatomical tracers in two animals suggest that TEO is an important link in the pathway that relays visual information from V1 to the inferior temporal cortex. TEO is thus likely to play an important role in pattern perception.

Animals↗