Biomedical subjects

J Decety

Publications and source records attributed to J Decety.

At least 19 recordsLinked to original sources

PubMed1999

MRI measurement of the functional blood flow changes in a large superficial vein draining the motor cortex.

In this study, phase-contrast MR techniques are applied in order to measure the blood flow changes induced by a motor task in a large superficial vein draining the motor cortex. The measurements were applied to six healthy volunteers, in motor rest conditions and during performance of a motor task. The latter consisted of sequential finger-to-thumb opposition. The task was actually executed and mentally simulated. Significant blood flow increases were found when changing from from mental simulation to actual execution of the motor task (increases ranging between 1.6 and 10.3 ml/min, i.e. 9% and 45%, respectively) and from resting conditions to actual execution of the motor task (increases ranging between 1.7 and 14.0 ml/min, i.e. 32% and 72%, respectively).

Adult↗

PubMed1999

Human brain activity related to the perception of spatial features of objects.

The role of the parietal cortex in visuospatial analysis of object was investigated by cerebral blood flow measurements in seven objects using positron emission tomography. Data were acquired while subjects performed a matching task requiring the discrimination of simultaneously presented objects based on one of their spatial properties. Three properties were studied separately during three scanning conditions repeated twice:surface orientation, principal axis orientation, and size. Scans were also obtained during a sensorimotor control task (similar visual stimulation, same motor action, voluntary saccades toward each object) as well as during rest (no stimulation, eyes closed). Compared to rest, the three property matching tasks showed the same pattern of activation: the whole occipital lobe, the right intraparietal sulcus (IPS), and the right occipitotemporal (OT) junction. Compared to the control condition, only right IPS and OT junction were significantly activated during discrimination of the spatial properties. The IPS focus was located between the superior parietal lobule and the angular gyrus, and the OT activation overlapped the posterior part of the inferior temporal gyrus and the middle occipital gyrus. These results indicate that discrimination of spatial attributes requires the activation of both the parietal and the temporal cortices of the right hemisphere and provide further evidence that the IPS plays a critical role in visuospatial analysis of objects.

Adult↗

PubMed1999

Neural mechanisms subserving the perception of human actions.

Our ability to generate actions and to recognize actions performed by others is the bedrock of our social life. Behavioral evidence suggests that the processes underlying perception and action might share a common representational framework. That is, observers might understand the actions of another individual in terms of the same neural code that they use to produce the same actions themselves. What neurophysiological evidence, if any, supports such a hypothesis? In this article, brain imaging studies addressing this question are reviewed and examined in the light of the functional segregation of the perceptual mechanisms subtending visual recognition and those used for action. We suggest that there are not yet conclusive arguments for a clear neurophysiological substrate supporting a common coding between perception and action.

Journal Article↗

PubMed1999

Neuroanatomical correlates of visually evoked sexual arousal in human males.

Brain areas activated in human male sexual behavior have not been characterized precisely. For the first time, positron emission tomography (PET) was used to identify the brain areas activated in healthy males experiencing visually evoked sexual arousal. Eight male subjects underwent six measurements of regional brain activity following the administration of [15O]H2O as they viewed three categories of film clips: sexually explicit clips, emotionally neutral control clips, and humorous control clips inducing positive but nonsexual emotions. Statistical Parametric Mapping was used to identify brain regions demonstrating an increased activity associated with the sexual response to the visual stimulus. Visually evoked sexual arousal was characterized by a threefold pattern of activation: the bilateral activation of the inferior temporal cortex, a visual association area; the activation of the right insula and right inferior frontal cortex, which are two paralimbic areas relating highly processed sensory information with motivational states; and the activation of the left anterior cingulate cortex, another paralimbic area known to control autonomic and neuroendocrine functions. Activation of some of these areas was positively correlated with plasma testosterone levels. Although this study should be considered preliminary, it identified brain regions whose activation was correlated with visually evoked sexual arousal in males.

Adult↗

PubMed1999

The effects of learning and intention on the neural network involved in the perception of meaningless actions.

PET was used to explore the neural network involved in the perception of meaningless action. In two conditions, subjects observed learned and unknown meaningless actions without any purpose. In two other conditions, subjects observed the same type of stimuli for later imitation. The control condition, which consisted of the presention of stationary hands, served as a baseline. Unsurprisingly, a common network that forms part of the dorsal pathway was engaged in all conditions when compared with stationary hands, and this was interpreted as being devoted to the analysis of hand movements. One of the most striking results of the present study was that some brain areas were strongly modulated by the learning level, independent of the subject's intention. Two different effects were observed: a reduced activity in posterior regions within the common network, which correlated with specific increases in the frontopolar area 10 and in the angular gyrus during the perception of learned meaningless actions compared with the perception of unknown actions. Finally, the major effect of the subject's intention to imitate was a strong increase in the dorsal pathway extending to the lateral premotor cortex and to the dorsolateral prefrontal cortex, which reflects the information processing needed for prospective action. Overall, our results provide evidence for both an effect of the visuomotor learning level and of the subject's intention on the neural network involved during the perception of human meaningless actions.

Adult↗

PubMed1998

Brain regions involved in the perception of gaze: a PET study.

Mutual gaze may be described as a psychological process during which two persons have the feeling of a brief link between their two minds. In the monkey, specific cell assemblies in the superior temporal cortex of the brain are responsive to gaze. This suggests that the brain may have evolved mechanisms for interpreting direct eye contact. These mechanisms could depend on the activation of specific brain regions. Positron emission tomography was used to measure activity in brain regions in healthy volunteers while they were looking at faces featuring, respectively, eye contact, averted gaze, or no gaze. As expected a region known to be involved in face processing was found to be activated in the ventral occipito-temporal region, especially in the right hemisphere. Averted gaze and mutual gaze triggered blood flow responses in similar areas which were different from those involved in face processing. These areas included the occipital part of the fusiform gyrus, the right parietal lobule, the right inferior temporal gyrus, and the middle temporal gyrus in both hemispheres. These results are consistent with the hypothesis that perception of eyes regardless of the direction of the gaze is subserved by a distributed network. However, no conclusive evidence was found for specific area(s) devoted to mutual gaze processing.

Adult↗

PubMed1997

Visual working memory for shape and 3D-orientation: a PET study.

In order to determine the neural substrate of working memory for shape and 3D-orientation, regional cerebral blood flow (rCBF) changes were estimated using positron emission tomography (PET). Subjects were scanned during the performance of two delayed-matching-to-sample tasks using flat polydedrical objects of different shapes and 3D-orientations presented in a virtual environment. The shape matching task was associated with activation in the occipito-temporal junction, occipito-parietal cortex and mesial frontal pole of the right hemisphere. During the orientation matching task, rCBF increased in the mesial occipito-temporal cortex, superior temporal gyrus and middle frontal gyrus of the left hemisphere. The right supramarginal gyrus was also activated. These results suggest that both visual pathways are engaged in the processing of objects presented in different orientations. The dorsal stream is involved mainly in working memory of 3D-orientation, while the ventral stream is involved especially in shape working memory.

Adult↗

PubMed1997

Mental simulation of an action modulates the excitability of spinal reflex pathways in man.

The question of whether mental simulation of an action has an effect on the spinal reflex circuits was examined in normal humans. Subjects were instructed either to exert or to mentally simulate a strong or a weak pressure on a pedal with the left or the right foot. Changes in the H- and T-reflexes activated by electrical and mechanical stimuli were measured on both legs during motor performance as well as during mental simulation of the same task. Asynchronous EMG activity of the soleus muscles was simultaneously recorded. Reflex excitability increased during performance of the pressure. It was larger when the H-reflex was triggered in the muscle involved in the task as compared to the contralateral side. Because actual performance modified the tension of the tendon and the location of the stimulus, ipsilateral changes of T-reflex amplitude could not be evaluated. Mental simulation of foot pressure in this condition resulted in a large increase of spinal reflex excitability, which was only slightly weaker than the reflex facilitation associated with the actual performance. Changes in T-reflex amplitude, but not in H-reflex amplitude, depended upon the lateralization and force of the simulated pressure, being larger in the leg involved in the simulation than in the contralateral leg, and larger for a strong than for a weak simulated movement. EMG activity was found to be weakly increased during mental imagery. This increase was significantly, although slightly, modulated by the lateralization and intensity of the imagined movement. However, no correlation was found across subjects between reflex amplitude and the amplitude of EMG activity.

Adult↗

PubMed1997

Brain activity during observation of actions. Influence of action content and subject's strategy.

PET was used to map brain regions that are associated with the observation of meaningful and meaningless hand actions. Subjects were scanned under four conditions which consisted of visually presented actions. In each of the four experimental conditions, they were instructed to watch the actions with one of two aims: to be able to recognize or to imitate them later. We found that differences in the meaning of the action, irrespective of the strategy used during observation, lead to different patterns of brain activity and clear left/right asymmetries. Meaningful actions strongly engaged the left hemisphere in frontal and temporal regions while meaningless actions involved mainly the right occipitoparietal pathway. Observing with the intent to recognize activated memory-encoding structures. In contrast, observation with the intent to imitate was associated with activation in the regions involved in the planning and in the generation of actions. Thus, the pattern of brain activation during observation of actions is dependent both on the nature of the required executive processing and the type of the extrinsic properties of the action presented.

Adult↗

PubMed1996

Possible involvement of primary motor cortex in mentally simulated movement: a functional magnetic resonance imaging study.

The role of the primary motor cortex (M1) during mental simulation of movement is open to debate. In the present study, functional magnetic resonance imaging (fMRI) signals were measured in normal right-handed subjects during actual and mental execution of a finger-to-thumb opposition task with either the right or the left hand. There were no significant differences between the two hands with either execution or simulation. A significant involvement of contralateral M1 (30% of the activity found during execution) was detected in four of six subjects. Premotor cortex (PM) and the rostral part of the posterior SMA were activated bilaterally during motor imagery. These findings support the hypothesis that motor imagery involves virtually all stages of motor control.

Adult↗

PubMed1996

Differential influence of the visual framework on end point accuracy and trajectory specification of arm movements.

In this study the influence of visual scene on both arm end point accuracy and spatial path kinematics was evaluated. Eight subjects, immersed in a virtual environment, were required to point to one of ten targets located at two distances and in five directions. Targets were presented in frameworks of different complexity. The simplest framework was constituted by a uniform background, the most complex framework was constituted by a perspective-arranged grid. In the other two conditions it consisted of lines having a direction parallel to either the subject's sagittal or frontal body axis. Movements were executed without vision of both target and framework. The results showed that pointing movements were hypometric in all conditions. No difference in end point localization was observed between movements executed after presentation of the simplest and the most complex scenes. However, hypometria significantly increased when the scene was formed by lines parallel to the subject's sagittal axis. Visual information on the scene was also used to specify hand path parameters. Trajectory curvature increased with decreasing complexity of the framework. Correspondingly, the pointing kinematics varied. Taken together, these results suggest that visual analysis of cues surrounding the target can influence both target localisation and hand path planning. However, scene complexity is directly related only to determining trajectory curvature. We conclude that planning an arm movement consists of at least two processes: target localisation and hand path specification. Environmental visual cues forming the scene are taken into account differently during the two processes.

Adult↗

PubMed1996

The neurophysiological basis of motor imagery.

Motor imagery may be defined as a dynamic state during which representations of a given motor act are internally rehearsed in working memory without any overt motor output. What neural processes underlie the generation of motor imagery? This paper reviews physiological evidence from measurements of regional brain activity and from measurements of autonomic responses in normal subjects and behavioral observations from brain damaged patients. It is proposed that motor imagery shares neural mechanisms with processes used in motor control. This review emphasizes the importance of the prefrontal cortex and its connections to the basal ganglia in maintaining dynamic motor representations in working memory. This view fits with the general idea that the prefrontal cortex is responsible for the creation and maintenance of explicit representations that guide thought and action.

Arousal↗

PubMed1996

Do imagined and executed actions share the same neural substrate?

This paper addresses the issue of the functional correlates of motor imagery, using mental chronometry, monitoring the autonomic responses and measuring cerebral blood flow in humans. The timing of mentally simulated actions closely mimic actual movement times. Autonomic responses during motor imagery parallel the autonomic responses to actual exercise. Cerebral blood flow increases are observed in the motor cortices involved in the programming of actual movement (i.e. premotor cortex, anterior cingulate, inferior parietal lobule and cerebellum). These three sources of data provide converging support for the hypothesis that imagined and executed actions share, to some extent, the same central structures.

Autonomic Nervous System↗

PubMed1995

Mentally simulated movements in virtual reality: does Fitts's law hold in motor imagery?

This study was designed to investigate mentally simulated actions in a virtual reality environment. Naive human subjects (n = 15) were instructed to imagine themselves walking in a three-dimensional virtual environment toward gates of different apparent widths placed at three different apparent distances. Each subject performed nine blocks of six trials in a randomised order. The response time (reaction time and mental walking time) was measured as the duration between an acoustic go signal and a motor signal produced by the subject. There was a combined effect on response time of both gate width and distance. Response time increased for decreasing apparent gate widths when the gate was placed at different distances. These results support the notion that mentally simulated actions are governed by central motor rules.

Adult↗

PubMed1995

Imagination of dynamic exercise produced ventilatory responses which were more apparent in competitive sportsmen.

1. The cardiorespiratory response to imagination of previously performed treadmill exercise was measured in six competitive sportsmen and six non-athletic males. This was compared with the response to a control task (imaging letters) and a task not involving imagination ('treadmill sound only'). 2. In athletes, imagined exercise produced increases in ventilation which varied within and between subjects. The mean maximal increase (11.71 min-1) was approximately 20% of the ventilatory response to actual exercise. This was primarily due to treadmill speed-related increases in respiratory frequency (mean maximal increase, 14.8 breaths min-1) and resulted in significant reductions in end-tidal PCO2 (mean maximal fall, 7 mmHg). These effects were greater (P < 0.01) than any observed during the control tasks. 3. Changes in heart rate (mean increase, 12 beats min-1) were not significantly different from those observed during the control tasks (P > 0.2). 4. In non-athletes, imagination of exercise produced no changes in cardiorespiratory variables. No significant differences were detected in subjective assessments of movement imagery ability between athletes and non-athletes (P = 0.17). 5. This study demonstrates that ventilatory effects, when observed, are specific to imagination of exercise. The greater likelihood of generating ventilatory responses in highly trained athletes, experienced in 'rhythmic' sports, may be related to awareness of breathing and its role in exercise imagination strategy. A volitional component of the response cannot be discounted.

Adult↗

PubMed1995

Motor imagery of a lateralized sequential task is asymmetrically slowed in hemi-Parkinson's patients.

We examined seven right-handed, asymmetrical (right side affected) Parkinson's disease patients and seven age-matched controls in a manual finger sequencing test using left and right hands in vision, no vision, and motor imagery conditions. All patients displayed motor asymmetry, favoring the left hand. They also displayed motor imagery asymmetry, mentally simulating movement more slowly with their right affected hand than with their left hand. Additionally, impairment in mental hand rotation correlated significantly with the imagery asymmetry. These data support two related hypotheses: (a) Motor sequence imagery and execution share common neural structures. (b) The frontostriatal system is among these shared structures.

Adult↗

PubMed1995

Mental motor imagery: a window into the representational stages of action.

The physiological basis of mental states can be effectively studied by combining cognitive psychology with human neuroscience. Recent research has employed mental motor imagery in normal and brain-damaged subjects to decipher the content and the structure of covert processes preceding the execution of action. The mapping of brain activity during motor imagery discloses a pattern of activation similar to that of an executed action.

Animals↗

PubMed1995

Intracranial gradient-echo and spin-echo functional MR angiography in humans.

PURPOSE: To investigate the predominance of venous signal intensity at 1.5-T gradient-echo (GRE) functional magnetic resonance (MR) imaging of motor activity and to demonstrate the contribution from task-induced changes in flow velocity to the functional MR imaging signal intensity. MATERIALS AND METHODS: Functional MR imaging of motor activity was performed in healthy volunteers. In a first examination, conventional two-dimensional GRE blood oxygenation level-dependent (BOLD) functional MR imaging techniques were used, and the image planes were carefully positioned with respect to the veins that responded to the motor task. In a second examination, two-dimensional spin-echo (SE) techniques were used, and the image planes were oriented axially and measured in a sequential multisection manner. The areas of hyperintensity on functional MR images were eventually processed by means of maximum intensity projection. RESULTS: Functional MR angiograms were obtained in both examinations. The possibility to generate SE functional MR angiograms demonstrates that venous inflow effects may contribute substantially to signal intensity in conventional two-dimensional GRE BOLD functional MR imaging of motor activity. CONCLUSION: Veins have a substantial role in BOLD functional MR imaging of motor activity.

Adult↗