1,721,162 research outputs found
The cortical network for eye–hand coordination and its relevance to understanding motor disorders of parietal patients
No full textCortical neurons in both superior (SPL) and inferior (IPL) parietal lobules are modulated by a variety of signals concerning planning and execution of eye and hand movement. Thanks to these properties, parietal neurons are ideally suited for eye–hand coordination during reaching. In SPL, a fundamental feature of neurons is the invariance of their directional tuning properties across tasks that require different forms of spatial relationships between the eye and the hand. In such conditions, the orientation of the preferred directions (PDs) of individual SPL cells cluster within a limited sector of space, the global tuning field (GTF), to be regarded as an ideal frame to dynamically match eye and hand signals on the basis of the orientation of their PDs. At the population level, the mean vectors of the GTF cover the direction continuum in a uniform fashion. These neurons are part of a parietal network richly interconnected with the premotor and motor areas of the frontal lobe. Thus, the reaching disorders of patients with optic ataxia might be interpreted as a consequence of the breakdown of the combinatorial mechanisms of the GTF of parietal neurons, and of their interplay with premotor cortex. In IPL, the main feature of eye and/or hand related neurons is the uneven distribution of their PDs, that mostly point toward the contralateral space. This anisotropy of the representation of directional motor space might explain the movement disorders that characterize directional hypokinesia in neglect patients. In conclusion, the study of the dynamic properties of parietal neurons and of their relationships with the premotor cortex via cortico-cortical connections provides a basis for an interpretation of movement disorders of parietal patients from a neurophysiological perspective
Cortical mechanisms for on-line control of hand movement trajectory. The role of posterior parietal cortex
No full textThe parietal mechanisms for the control of hand movement trajectory were studied by recording cell activity in area 5 of monkeys making direct reaches to visual targets and online corrections of movement trajectory, after change of target location in space. The activity of hand-related cells was fitted with a linear model including hand position, movement direction, and speed. The neural activity modulation mostly led, but also followed, hand movement. When a change of hand trajectory occurred, the pattern of activity associated with the movement to the first target evolved into that typical of the movement to the second one, thus following the corresponding variations of the hand kinematics. The visual signal concerning target location in space did not influence the firing activity associated with the direction of hand movement within the first 150 ms after target presentation. This might be the time necessary for the visuo-motor transformation underlying reaching. We conclude that online control of hand trajectory not only resides in the relationships between neural activity and kinematics, but, under specific circumstances, also on the coexistence of signals about ongoing and future hand movement direction
Toxicité des hydrocarbures et impacts des déversements sur les organismes marins et leur environnement
Full text linkLes risques liés aux déversements opérationnels et accidentels d’hydrocarbures seront intensifiés par l’augmentation des besoins mondiaux en pétrole. Les accidents, bien que rares, se multiplient et causent d’innombrables effets sur l’environnement et sur les organismes qui s’y trouvent. Ce chapitre fait un survol de l’impact potentiel des hydrocarbures sur les organismes et sur les habitats ainsi que des conséquences sur le fonctionnement et les services écologiques que procurent les écosystèmes marins. La nature et le comportement des pétroles déversés ainsi que les risques associés aux méthodes d’intervention, par exemple l’utilisation de dispersants ou le nettoyage physique, y sont abordés. Les voies d’exposition des divers organismes (microorganismes, phytoplancton, zooplancton, invertébrés, oiseaux et mammifères marins) et les effets sur leur population sont illustrés en prenant exemple parmi les événements malheureux de l’échouage de l’Exxon Valdez en 1989 ou de l’explosion de la plateforme Deepwater Horizon en 2010. L’influence des conditions de déversement sur la résilience des écosystèmes touchés sera abordée
Co-extinctions and co-compensatory species responses to climate change moderate ecosystem futures
No full textConsensus has been reached that the sequential loss of biodiversity leads to a non-linear and accelerating decline in ecosystem properties. The form of this relationship, however, is based on theory and empirically derived observations that do not include species co-extinctions. Here, we use data from marine benthic invertebrate communities to parameterise trait-based extinction models that adjust the probability of species extirpation and compensation by including the dependencies between different spe- cies across a gradient of climate-driven environmental change. Our simulations reveal that the inclusion of static co-extinctions leads to more pronounced declines in the trajectories of sediment bioturbation—a process of great importance to the functioning of marine ecosystems—than those observed with sequential losses of single species. Compensatory mechanisms and the allow- ance of the formation of new interactions derived from local and regional species pools moderate the compounding influence of co-extinction but introduce additional variability in community response depending on the composition and functional role of incoming and outgoing species. Our observations emphasise the importance of accounting for local and regional community dynamics, especially in highly connected systems that are prone to extinction cascades when projecting the ecosystem conse- quences of altered biodiversity
Impacts potentiels cumulés des facteurs de stress liés aux activités humaines sur l’écosystème marin du Saint-Laurent
Full text linkLes activités humaines modifient l’environnement naturel, perturbant par le fait même les organismes qui y habitent. Dans l’écosystème marin du golfe du Saint-Laurent, les diverses perturbations affectent les écosystèmes à différents degrés. Pour certains d’entre eux, les effets sont mal connus ou simplement inconnus. De plus, plusieurs perturbations peuvent affecter simultanément une composante de l’écosystème ou un système en entier. Les effets cumulés sont encore moins connus. Dans ce chapitre, nous synthétisons les connaissances actuelles sur les facteurs de stress liés aux activités humaines, puis essayons de déterminer leurs interactions et leurs effets cumulés sur l’écosystème du Saint-Laurent
Online control of hand trajectory and evolution of motor intention in the parietofrontal system
Full text linkThe frontal mechanisms of motor intention were studied in dorsal premotor and motor cortex of monkeys making direct reaches to visual targets and online corrections of hand trajectory, whenever a change of the target's location occurred. This study and our previous one of parietal cortex (Archambault et al., 2009) provide a picture on the evolution of motor intention and online control of movement in the parietofrontal system. In frontal cortex, significant relationships were found between neural activity and hand kinematics (position, speed, and movement direction). When a change of motor intention occurred, the activity typical of the movement to the first target smoothly evolved into that associated with the movement toward the second one, as observed during direct reaches. Under these conditions, parietal cells remained a more accurate predictor of hand trajectory than frontal ones. The time lags of neural activity with hand kinematics showed that motor, premotor, and parietal cortex were activated sequentially. After the first target's presentation and its change of location, the population activity signaled the change of motor plan before the hand moved to the initial target's position. This signaling occurred earlier in premotor than in motor and parietal cortex. Thus, premotor cortex encodes a higher-order command for the correction of motor intention, while parietal cortex seems responsible for estimating the kinematics of the motor periphery, an essential step to allow motor cortex to modify the hand trajectory. This indicates that the parietofrontal system can update an original and not-yet-accomplished motor plan during its execution
Occurrences of megabenthic organisms collected from Agassiz trawl catches taken in Canadian Arctic seas in 2007 and 2008
No full textThis dataset is a component of the PAN-Arctic data collection of benthic BIOtas (PANABIO) and has been collated during the Census of Marine Life project Arctic Ocean Diversity (ArcOD; http://www.arcodiv.org/). It contains a total of 667 presence records of 244 megabenthic taxa (species to genus level) identified in 30 Agassiz trawl catches taken at 30 stations located in various Canadian Arctic seas at water depths of 38–759 m during two cruises in 2007 and 2008. The dataset is also available in a PostgreSQL-based data warehouse that can be accessed and queried through an open-access frontend web service at https://critterbase.awi.de/panabio
Impairment of Online Control of Hand and Eye Movements in a Monkey Model of Optic Ataxia
No full textThe parietal mechanisms for online control of hand trajectory were studied by combining single-cell recording and reversible inactivation of superior parietal area 5 (PE/PEc; SPL) of monkeys while these made reaches and saccades to visual targets, when the target position changed unexpectedly. Neural activity was modulated by hand position, speed, and movement direction, and by pre- and/or postsaccadic signals. After bilateral muscimol injection, an increase in the hand reaction- and movement-time toward both the first and second targets was observed. This caused an increase in the time necessary for the trajectory correction, and therefore an elongation of the hand-path toward the first target location. Furthermore, hand trajectories were different in shape than control ones. An elongation of the eye reaction time to both first and second targets was also observed, which could partially explain the deficit of planning and correction of hand movement. These results identify the superior parietal lobule as a crucial node in the online control of hand and eye movement and highlight the role of the eye impairment in the emergence of the reaching disorder so far regarded as the hallmark of optic ataxia
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