Biomedical subjects

Driss Boussaoud

Publications and source records attributed to Driss Boussaoud.

12 recordsLinked to original sources

PubMed2006

Conditional visuo-motor learning and dimension reduction.

Conditional visuo-motor learning consists in learning by trial and error to associate visual cues with correct motor responses, that have no direct link. Converging evidence supports the role of a large brain network in this type of learning, including the prefrontal and the premotor cortex, the basal ganglia BG and the hippocampus. In this paper we focus on the role of a major structure of the BG, the striatum. We first present behavioral results and electrophysiological data recorded from this structure in monkeys engaged in learning new visuo-motor associations. Visual stimuli were presented on a video screen and the animals had to learn, by trial and error, to select the correct movement of a joystick, in order to receive a liquid reward. Behavioral results revealed that the monkeys used a sequential strategy, whereby they learned the associations one by one although they were presented randomly. Human subjects, tested on the same task, also used a sequential strategy. Neuronal recordings in monkeys revealed learning-related modulations of neural activity in the striatum. We then present a mathematical model inspired by viability theory developed to implement the use of strategies during learning. This model complements existing models of the BG based on reinforcement learning RL, which do not take into account the use of strategies to reduce the dimension of the learning space.

Basal Ganglia↗

PubMed2005

Callosal connections of dorsal versus ventral premotor areas in the macaque monkey: a multiple retrograde tracing study.

BACKGROUND: The lateral premotor cortex plays a crucial role in visually guided limb movements. It is divided into two main regions, the dorsal (PMd) and ventral (PMv) areas, which are in turn subdivided into functionally and anatomically distinct rostral (PMd-r and PMv-r) and caudal (PMd-c and PMv-c) sub-regions. We analyzed the callosal inputs to these premotor subdivisions following 23 injections of retrograde tracers in eight macaque monkeys. In each monkey, 2-4 distinct tracers were injected in different areas allowing direct comparisons of callosal connectivity in the same brain. RESULTS: Based on large injections covering the entire extent of the corresponding PM area, we found that each area is strongly connected with its counterpart in the opposite hemisphere. Callosal connectivity with the other premotor areas, the primary motor cortex, prefrontal cortex and somatosensory cortex varied from one area to another. The most extensive callosal inputs terminate in PMd-r and PMd-c, with PMd-r strongly connected with prefrontal cortex. Callosal inputs to PMv-c are more extensive than those to PMv-r, whose connections are restricted to its counterpart area. Quantitative analysis of labelled cells confirms these general findings, and allows an assessment of the relative strength of callosal inputs. CONCLUSION: PMd-r and PMv-r receive their strongest callosal inputs from their respective counterpart areas, whereas PMd-c and PMv-c receive strong inputs from heterotopic areas as well (namely from PMd-r and PMv-r, respectively). Finally, PMd-r stands out as the lateral premotor area with the strongest inputs from the prefrontal cortex, and only the PMd-c and PMv-c receive weak callosal inputs from M1.

Animals↗

PubMed2005

Prehension movements in the macaque monkey: effects of perturbation of object size and location.

While the neural bases of prehension have been extensively studied in monkeys, a few kinematic studies have examined their prehension behavior. Recently (Roy et al. 2000, 2002), we have described the kinematics of reaching and grasping in freely behaving monkeys under normal conditions by applying the high-resolution recording techniques (Optotrak system) and behavioral paradigms used in humans. Here we determined whether online movement reorganization observed in monkeys following sudden changes of either object size or location at movement onset is similar to that observed in humans. We found that changing object size led to rapid on-flight re-calibration of the different movement parameters, eventually preserving the unitary aspect of the movement with a minor time cost. By contrast, a shift in object location triggered a massive time-consuming reorganization. Re-directed movements appeared as a concatenation of two sub-movements: a first one directed to the initial object and a second one directed to the new object location. These findings first complement our earlier studies in providing further evidence of the similarities between monkey and human prehension. Second, they suggest that the two components of prehension, reaching and grasping, interact through coordination mechanisms that are more efficient to correct for size than for location perturbation. This difference may reflect a hierarchical organization in which reaching would be the subordinate of grasping in both primate species.

Animals↗

PubMed2005

High gamma frequency oscillatory activity dissociates attention from intention in the human premotor cortex.

The premotor cortex is well known for its role in motor planning. In addition, recent studies have shown that it is also involved in nonmotor functions such as attention and memory, a notion derived from both animal neurophysiology and human functional imaging. The present study is an attempt to bridge the gap between these experimental techniques in the human brain, using a task initially designed to dissociate attention from intention in the monkey, and recently adapted for a functional magnetic resonance imaging (fMRI) study [Simon, S.R., Meunier, M., Piettre, L., Berardi, A.M., Segebarth, C.M., Boussaoud, D. (2002). Spatial attention and memory versus motor preparation: premotor cortex involvement as revealed by fMRI. J. Neurophysiol., 88, 2047-57]. Intracranial EEG was recorded from the cortical regions preferentially active in the spatial attention and/or working memory task and those involved in motor intention. The results show that, among the different intracranial EEG responses, only the high gamma frequency (60-200 Hz) oscillatory activity both dissociates attention/memory from motor intention and spatially colocalizes with the fMRI-identified premotor substrates of these two functions. This finding provides electrophysiological confirmation that the human premotor cortex is involved in spatial attention and/or working memory. Additionally, it provides timely support to the idea that high gamma frequency oscillations are involved in the cascade of neural processes underlying the hemodynamic responses measured with fMRI [Logothetis, N.K., Pauls, J., Augath, M., Trinath, T. and Oeltermann, A. (2001). Neurophysiological investigation of the basis of the fMRI signal. Nature, 412, 150-7], and suggests a functional selectivity of the gamma oscillations that could be critical for future EEG investigations, whether experimental or clinical.

Adult↗

PubMed2004

Functional connectivity during real vs imagined visuomotor tasks: an EEG study.

It is proposed that real and imagined movements activate identical neural networks. Cortical oscillatory activity is proposed as a mechanism through which distributed neuronal networks may bind into coherent ensembles and coupling of oscillators is used as a tool to investigate modulations of cortical connectivity. The aim of the present study was to test the hypothesis that, although the same brain network is involved in both real and imagined movements, the functional connectivity within the network differs. To do so, we measured interregional coupling, quantified using coherence between scalp EEG electrodes, during different periods of a prehension task during real and imagined movements. The results demonstrated a different pattern of coupling in the beta frequency range between electrodes overlying occipital and motor cortices during executed and imagined movements. These findings are consistent with the hypothesis that the neural networks during real and imagined movements are not identical.

Adult↗

PubMed2003

Neuronal activity in the monkey striatum during conditional visuomotor learning.

The frontostriatal system has been implicated in linking sensory information and action through arbitrary rules. The aim of the present study was to investigate the role of the striatum, a key, integrative structure in such behavior. We recorded single neuronal activity from the anterior striatum of two macaque monkeys as they learned to associate new visual cues with motor responses. Monkeys held a joystick which they could move in one of four constrained directions. During the recording sessions, they were presented with a set of well-learned associations (familiar condition), and with sets of new cues which they were required to map, by trial and error, with joystick movements (novel condition). A sample of 50 striatum neurons were studied during execution of familiar and novel conditions. Activity of most of them was strongly modulated during learning. These modulations were either transient or long lasting changes of neuronal firing rate. The findings suggest that the striatum is involved in early stages of conditional visuomotor learning, and are interpreted in relation with previous data on frontal cortex.

Action Potentials↗

PubMed2003

[The planning of action: can one separate attention from intention?].

Attention and motor preparation are two intimately linked processes. However, they can be dissociated in the laboratory in order to study their neuronal basis. Behavioral neurophysiology has thus shown that neurons that discharge in relation with attention or with motor preparation (or intention) exist in a variety of brain regions in the monkey, especially the prefrontal and premotor cortices. When examined more carefully, these two regions appear different in both the proportion of cells that respond during attention versus intention, and in the information coded in the so-called "preparatory activity". This activity reflects sensory selection in the prefrontal cortex (spatial attention/memory), motor selection in the premotor cortex. Furthermore, two regions in the dorsal aspect of premotor cortex can be distinguished on the basis of their relative involvement in attention: a rostral (anterior) region, functionally close to prefrontal cortex, and a caudal one, which appears functionally close to motor cortex. Using an experimental design derived from monkey experiments, a functional magnetic resonance imaging (fMRI) study recently indicated that the functional specialization within the premotor cortex is similar in monkey and man.

Animals↗

PubMed2002

Projections of the claustrum to the primary motor, premotor, and prefrontal cortices in the macaque monkey.

The claustrum is interconnected with the frontal lobe, including the motor cortex, prefrontal cortex, and cingulate cortex. The goal of the present study was to assess whether the claustral projections to distinct areas within the frontal cortex arise from separate regions within the claustrum. Multiple injections of tracers were performed in 15 macaque monkeys, aimed toward primary motor area (M1), pre-supplementary motor area (pre-SMA), SMA-proper, rostral (PMd-r) and caudal (PMd-c) parts of the dorsal premotor cortex (PM), rostral (PMv-r) and caudal (PMv-c) parts of the ventral PM, and superior and inferior parts of area 46. The distribution of retrogradely labeled neurons showed no clear segregation along the rostrocaudal axis of the claustrum; they were usually located along the entire anteroposterior extent of the claustrum. For all motor cortical areas, there was a general trend of the labeled neurons to occupy the dorsal and intermediate parts of the claustrum along the dorsoventral axis. The same territories were labeled after injection in area 46, but in addition numerous labeled neurons were found in the most ventral part of the claustrum. At higher resolution, however, there was clear evidence that the territories projecting to pre-SMA and SMA-proper formed separate, interdigitating, clusters along the dorsoventral axis. A comparable local segregation was observed for the two subdivisions of area 46, whereas there was more local overlap among the subareas of PM. The projections from the claustrum to the multiple subareas of the motor cortex and to area 46 arise from largely overlapping territories, with, however, some degree of local segregation.

Amidines↗

PubMed2002

Parietal inputs to dorsal versus ventral premotor areas in the macaque monkey: evidence for largely segregated visuomotor pathways.

The lateral premotor cortex plays a crucial role in visually guided limb movements. Visual information may reach this cortical region from the parietal cortex, the highest stage in the dorsal visual stream. Anatomical studies indicate that the parietal projections to the dorsal (PMd) and ventral (PMv) premotor areas arise from separate parietal regions, supporting the notion of parallel visuomotor pathways. We tested the degree of segregation of these pathways by injecting retrograde tracers into PMd and PMv in the same monkeys, under physiological control. Eleven injections were made in four animals, and the analysis of retrograde labelling revealed that parietal cells projecting to PMd and those projecting to PMv are largely segregated. The strongest projections to PMd arise from the superior parietal lobule, including the medial intraparietal area (MIP), PEc and PGm, and the parieto-occipital area. These areas were devoid of labelling following injections into PMv, which receives its major projections from the anterior intraparietal area (AIP), area PEip, the anterior portion of the inferior parietal gyrus (area 7b), and the somatosensory areas. In addition to their strong projections to PMv, areas 7b and PEip send minor projections to PMd as well. Additional projections to PMd arise from the ventral intraparietal area and the inferior parietal lobule. The present findings are direct anatomical evidence for largely segregated visuomotor pathways linking parietal cortex with PMd and PMv.

Animals↗

PubMed2002

Prehension movements in the macaque monkey: effects of object size and location.

Prehension movements were examined in freely behaving monkeys and compared with the well-known characteristics of human movements. The degree of independence of the components of movements (i.e., reaching and grasping) was investigated in animals trained to reach for and grasp three-dimensional objects. To this aim, the kinematics of prehension movements was recorded using an Optotrak system in two tasks. In one task, monkeys grasped a small or a large object (size task), in the other, they grasped an object of constant size placed at three different spatial locations (location task). We found that object size and its location affected both reaching and grasping. In particular, in the size task, we found that the maximum grip aperture strongly depended on the selection of the grip and not only on the size of an object. Our results also revealed that, in monkeys as well as in humans, the reaching parameters are highly sensitive to task-related constraints such as accuracy demands. The results of the location task showed a difference between rightward and leftward movements, a pattern of grip aperture that varied across animals, and a large degree of coordination between the two components. These findings argue against a strict postulate of independence between the visuo-motor channels, favoring instead the idea of variable degrees of coordination between the reach and grasp components depending on the task demands. Finally, this work emphasizes the relevance of studying monkey's prehension movements as a useful step to the understanding of visuo-motor control in humans.

Animals↗

PubMed2002

Spatial attention and memory versus motor preparation: premotor cortex involvement as revealed by fMRI.

Recent studies in both monkeys and humans indicate that the dorsal premotor cortex participates in spatial attention and working memory, in addition to its well known role in movement planning and execution. One important question is whether these functions overlap or are segregated within this frontal area. Single-cell recordings in monkeys suggest a relative specialization of the rostral portion of dorsal premotor cortex for attention and/or memory and of the caudal region for motor preparation. To test whether this possibility also holds true in humans, we used functional magnetic resonance imaging (fMRI) to compare, in the same set of subjects, brain activation related to strong spatial attention and memory demands to that elicited by long motor preparatory periods. The behavioral protocol was based on a task that had proved effective for dissociating neuronal properties related to these two functions in the monkey brain. The principle of the monkey task was that a first cue guided the focus of spatial attention and memory, whereas a second one instructed an arm movement. Based on this principle, two tasks were developed. One maximized spatial attention and memory demands by presenting long series of stimuli (4, 8, or 12) before the motor instructional cue, whereas the other extended the motor preparation phase by imposing long and variable delays (1-5.5 s) between the onset of the instructional cue and movement execution. The two tasks and their respective control conditions were arranged in two blocked-design sequences. The results indicate that the brain networks underlying the two functional domains overlap in the caudate nucleus and presupplementary motor area, and possibly in lateral prefrontal cortex as well, but involve different dorsal premotor fields. Motor preparation primarily recruited a dorsal premotor area located caudally, within the precentral gyrus (together with the supplementary motor area), whereas spatial attention and memory preferentially activated a more rostral site, in and anterior to the precentral sulcus (in addition to the posterior parietal cortex). These findings strengthen the idea that the primate dorsal premotor cortex contributes to both motor and nonmotor processes. Moreover, they corroborate emerging evidence from monkey physiology suggesting a relative functional segregation within this cortex, with attention to short-term storage of visuospatial information engaging a more rostral region than motor preparation.

Adult↗

PubMedDate not supplied

Conditional visuo-motor learning in primates: a key role for the basal ganglia.

Sensory guidance of behavior often involves standard visuo-motor mapping of body movements onto objects and spatial locations. For example, looking at and reaching to grasp a glass of wine requires the mapping of the eyes and hand to the location of the glass in space, as well as the formation of a hand configuration appropriate to the shape of the glass. But our brain is far more than just a standard sensorimotor mapping machine. Through evolution, the brain of advanced mammals, in particular human and non-human primates, has acquired a formidable capacity to construct non-standard, arbitrary mapping using associations between external events and behavioral responses that bear no direct relationship. For example, we have all learned to stop at a red traffic light and to go at a green one, or to wait for a specific tone before dialing a phone number and to hang up when hearing a busy signal. These arbitrary associations are acquired through experience, thereby providing primates with a rich and flexible sensorimotor repertoire. Understanding how they are learned, and how they are recalled and used when the context requires them, has been one of the challenging issues for cognitive neuroscience. Valuable insights have been gained over the last two decades through the convergence of multiple complementary approaches. Human neuropsychology and experimental lesions in monkeys have identified a network of brain structures important for conditional sensorimotor associations, whereas imaging studies in healthy human subjects and electrophysiological recordings in awake monkeys have sought to identify the different functional processes underlying the overall function. The present review focuses on the contribution of a network linking the prefrontal cortex, basal ganglia, and dorsal premotor cortex, with special emphasis on results from recording experiments in monkeys. We will first review data pointing to a specific contribution of each component of the network to the performance of well-learned arbitrary visuo-motor associations, as well as data suggesting how novel associations are formed. Then we will propose a model positing that each component of the fronto-striatal network makes a specific contribution to the formation and/or execution of sensorimotor associations. In this model, the basal ganglia are thought to play a key role in linking the sensory, motor, and reward information necessary for arbitrary mapping.

Animals↗