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Biomedical subjects

J Decety

Publications and source records attributed to J Decety.

At least 55 records · Page 3Linked to original sources
PubMed1994

Dissociating visual and kinesthetic coordinates during pointing movements.

Goal-directed movements imply that the visual coordinates in which the localisation of the goal is coded are transformed into proprioceptive coordinates in which the arm movement is coded. The two systems of coordinates are normally superimposed. Using a virtual reality device attached to the subject's head, we have created a situation where these systems were dissociated from each other. The virtual environment involved virtual visual targets and an image of the subject's hand reconstructed from the output of a data glove wore by the subject's right hand. When the subject's head was rotated, the visual targets and the image of the hand rotated by the same amount. Movements of the real hand were thus in conflict with those of the reconstructed hand, which appeared to err in the direction of head rotation. Pointing movements directed at five targets (0 degree, 26 degrees and 52 degrees on each side) were studied for five different head positions (0 degree, 45 degrees and 80 degrees to the right and to the left). The results showed a significant pointing bias towards head position, except for the left-most targets in the right head rotations. Constant errors in azimuth were proportional to the amount of head rotation. When the head was rotated to the right, constant errors in azimuth were greater during pointing towards right than left targets. Similarly, they were greater for left than for right stimuli when the head was rotated to the left. Errors in amplitude were not influenced by the direction nor the amount of head rotation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Impairment of grasping movements following a bilateral posterior parietal lesion.

The observation of a patient (A.T.) with a bilateral posterior parietal lesion of vascular origin is reported. A.T. presented a bilateral (more marked on the right) deficit in grasping simple objects (neutral cylindrical dowels) without deficit in reaching toward the location of these objects. The major symptom was an exaggerated anticipatory opening of the fingers with poor correlation with object size, resulting in awkward grasps. It was present both when the hand was visible to the subject and when it was not. This deficit was much less marked if the neutral objects were replaced by usual objects of the same sizes. Finally, in tasks where she had to indicate with her fingers the size of visual objects presented as virtual images through a mirror, or the size of imagined usual objects, A.T. performed normally. These results are discussed within the framework of a dual representation of objects. Only the "pragmatic" representation for steering object-oriented actions would be impaired in this patient as a result of posterior parietal damage. By contrast the semantic representation for object identification would be intact.

Adult↗
PubMed1993

Analysis of actual and mental movement times in graphic tasks.

This paper reports on a study of movement times and movement time variability of graphic gestures which were executed either physically or mentally. The results revealed that temporal parameters for actual as well as mental graphic movements in the same subject and for the same hand were very similar, irrespective of the writing amplitude. It is suggested that the programming of motor acts, whether they are physically executed or only virtually, share to a considerable extent the same timing mechanism.

Adult↗
PubMed1993

Motor imagery activates the cerebellum regionally. A SPECT rCBF study with 99mTc-HMPAO.

Our earlier findings of a cerebellar activation during motor imagery (Brain Res., 535 (1990) 313-317) were made with a technique with low regional resolution. Therefore we could not elucidate the distribution of the cerebellar activation. In the present study the cerebellar regional cerebral blood flow (rCBF) changes during motor imagery (MI) was measured with a single photon emission computed tomography (SPECT) rCBF method (99mTc-HMPAO) with higher regional resolution during (1) silent counting, and (2) MI (which included silent counting) in 17 normal subjects. Comparing the SPECT results from the two tasks revealed the regional activations during MI. We confirmed that the most pronounced regional activations during MI were found in the cerebellum, especially in its infero-lateral parts on both sides.

Adult↗
PubMed1993

Central activation of autonomic effectors during mental simulation of motor actions in man.

1. Healthy subjects actually performed and mentally simulated a leg exercise at two levels of work (15 and 19 kg loads). Heart rate, respiration rate and end-tidal PCO2 were measured in both conditions. In addition, muscular metabolism was simultaneously measured using 31P nuclear magnetic resonance (NMR) spectroscopy. 2. During actual exercise, heart and respiration rates increased, first abruptly and then gradually in relation to the level of work. End-tidal PCO2 was unaltered. NMR spectra showed a drop in phosphocreatine (PCr) and an increase in inorganic phosphate (Pi) concentrations. Intracellular pH fell to 6.65 at maximal effort with a 19 kg load. 3. During mental simulation, both heart and ventilatory rate increased immediately after mental exercise was begun. This increase was proportional to the amount of simulated exercise. Heart rate remained about 25% below the level observed during actual exercise. The increase in respiration rate, by contrast, was more marked than during actual exercise. Finally, end-tidal PCO2 decreased progressively to about 18% of the resting value. 4. During mental simulation, NMR spectra were unchanged with respect to the resting values. 5. Subjects rated their sensation of fatigue using an analog rating scale, during both actual exercise and mental simulation. During mental exercise, the sensation of fatigue was greater with the 19 kg load than with the 15 kg load. 6. These results demonstrate that mental simulation of action can activate heart and respiration control mechanisms. They suggest that autonomic activation during imagined action pertains to the more general phenomenon of preparation for action.

Adult↗
PubMed1992

Preparation for reaching: a PET study of the participating structures in the human brain.

The regional cerebral blood flow (rCBF) was measured as an indicator of regional metabolic activity with positron emission tomography (PET) in eight subjects who, after seeing a screen with seven targets prepared themselves with their eyes closed to reach these targets. The preparation phase was associated with increases of rCBF in the prefrontal cortex, several remote visual association areas in the parietal lobe, the supramarginal gyrus, the ventrolateral thalamus and the cerebellar vermis. During the course of learning the activations in the parietal visual areas, the supramarginal gyrus and the prefrontal cortex prevailed as a sign of the visual spatial information; its transformation being kept in working memory. The other activations vanished. No activations were seen in the motor cortices, indicating that reaching is a task which does not require substantial preparatory activity of motor cortices prior to the go signal.

Adult↗
PubMed1991

Vegetative response during imagined movement is proportional to mental effort.

Measurement of cardiac and respiratory activity during mental simulation of locomotion at increasing speed revealed a covariation of heart rate and pulmonary ventilation with the degree of imagined effort. The degree of vegetative activation of a subject mentally running at 12 km/h was comparable to that of a subject actually walking at 5 km/h. This effect cannot be explained by an increase in peripheral (e.g. muscular) metabolic demands. Indeed, oxygen uptake decreased during motor imagery. This finding is suggestive of a commonality of neural structures responsible for mental imagery of movement and those responsible for programming actual movement. In addition, it provides an quantifiable way of testing mental imagery in relation to movement by using easily accessible biological markers.

Adolescent↗
PubMed1991

Sensation of effort and duration of mentally executed actions.

The aim of this study was to examine whether a sensation of effort would arise in subjects requested, by verbal instructions, to mentally perform motor tasks with an internal imagery strategy. Sixteen subjects had to imagine themselves, from a first person perspective, writing a sentence and drawing a Necker's cube either with their right dominant hand or with their left hand, as well as hopping around a square either on their right or left foot. The time needed to mentally execute these actions was measured. The sensation of effort following the mental performance and the difficulty of imaging the tasks were assessed by means of two analog rating scales. The results indicate that the sensation of effort increased across the trials. Furthermore, a negative correlation coefficient (mean r = -0.99) was found between the difficulty to imagining a given motor task and the subjective sensation of effort across the trials. Moreover, the sensation of effort was more pronounced when the tasks involved the non-dominant limb.

Adult↗
PubMed1990

The cerebellum participates in mental activity: tomographic measurements of regional cerebral blood flow.

Measurements in man of regional cerebral blood flow (rCBF) have demonstrated a number of cortical and subcortical events coupled to sensory stimulation or motor performance. It has also been shown that local activity changes take place in the cortex during 'pure' mental activity such as motor imagery (unaccompanied by sensory input or motor output). Thus, our group has previously shown that imagination of hand movements gives predominantly a frontal cortical rCBF activation while the corresponding hand movement activates the rolandic hand area mainly. In this paper we report tomographic rCBF measurements with a 133-Xenon SPECT technique during imagined tennis movements and silent counting. Both procedures gave rise to a significant cerebellar activation in addition to cortical rCBF changes. Apparently, the cerebellum may participate in pure mental activity. It possibly plays a role for the temporal organization of neuronal events related to cognition.

Adult↗
PubMed1990

Effect of brain and spinal cord injuries on motor imagery.

The timing of mentally executed movements was measured in ten patients with hemiplegia, tetraplegia and paraplegia. In hemiplegic patients a significant difference in mental duration times was found between the paralysed and the normal "represented limb". The paralysed limb was mentally much slower than the healthy one. In contrast, movement times in tetraplegic and paraplegic patients did not differ from those in normal subjects. All patients reported a sensation of subjective effort accompanying the execution of the mental tasks. These observations are compatible with an outflow processing underlying motor imagery.

Adult↗
PubMed1990

Brain structures participating in mental simulation of motor behavior: a neuropsychological interpretation.

This paper reviews findings from cognitive and sport psychology, as well as from neurophysiology, concerning mental simulation of movement. A neuropsychological hypothesis is advanced to explain why mental practice can improve motor skill learning. Mental practice activates certain brain structures selectively as shown by measurements of regional cerebral blood flow. It appears likely that this activation improves the subsequent control of execution of movements. It is pointed out that the study of simulation of movements may not only be of value for sport training but also have importance for the rehabilitation of patients with motor disturbances following lesions of the central nervous system.

Brain↗
PubMed1989

The timing of mentally represented actions.

The performance of subjects walking blindly to previously inspected visual targets (located at 5, 10 or 15 m from the subjects) was studied in 2 experiments. In Expt. 1, subjects selected as good visual imagers were instructed to build up a mental representation of the target. Then they had to either actually walk or imagine themselves walking to the target. Walking time was measured in both the actual and the mental performance. It was found that subjects took almost exactly the same time in the two conditions. Accuracy of these subjects was also measured in the actual walking task. They were found to make no direction errors and to slightly overshoot target location. Subjects from another, control, group, who received no instructions about visual imagery made much larger errors. In Expt. 2, actual and mental walking times were measured in the same subjects as in Expt. 1, while they carried a 25-kg weight on their shoulders. In this condition, actual walking time was the same as in Expt. 1, although mental walking time was found to increase systematically by about 30%. These results are discussed in terms of the neural parameters encoded in the motor program for actually executing or mentally performing an action.

Adult↗
PubMed1989

Comparative analysis of actual and mental movement times in two graphic tasks.

This study compared the temporal organization of graphic movements executed either actually or mentally. Six subjects had to perform two tasks, writing a sentence and drawing a cube, either as a real performance or as an imagined one, with either the right or the left hand, and with either a small or a large tracing amplitude. In the same subject, for the same hand, mental and actual movement times were both very stable and very close from trial to trial regardless of the tracing amplitude. Thus, mental movements mimic closely real movements in their temporal organization and are likely to involve the same planning program.

Adult↗
PubMed1988

rCBF landscapes during motor performance and motor ideation of a graphic gesture.

The regional cerebral blood flow (rCBF) distribution was measured by 133xenon inhalation using a gamma camera in 18 right-handed volunteers, 6 subjects performing a graphic task (writing numbers in letters) with the right hand, 6 subjects imagining the same task, and 6 subjects were assessed during two rest periods to determine the reproducibility of the technique. The mean rCBF increased between 10% and 25% (P less than 0.01) during both motor performance and motor ideation. However, there were regional differences. While motor performance activated mainly the rolandic regions bilaterally, motor ideation gave prefrontal and premotor rCBF augmentations. In both situations there was significant bilateral increase in regions corresponding to the cerebellum.

Adult↗
PubMedDate not supplied

Visual pathways for object-oriented action and object recognition: functional anatomy with PET.

The purpose of this study was to identify the functional anatomy of the mechanisms involved in visually guided prehension and in object recognition in humans. The cerebral blood flow of seven subjects was investigated by positron emission tomography. Three conditions were performed using the same set of stimuli. In the 'grasping' condition, subjects were instructed to accurately grasp the objects. In the 'matching' condition, subjects were requested to compare the shape of the presented object with that of the previous one. In the 'pointing' condition (control), subjects pointed towards the objects. The comparison between grasping and pointing showed a regional cerebral blood flow (rCBF) increase in the anterior part of the inferior parietal cortex and part of the posterior parietal cortex. The comparison between grasping and matching showed an rCBF increase in the cerebellum, the left frontal cortex around the central sulcus, the mesial frontal cortex and the left inferior parietal cortex. Finally, the comparison between matching and pointing showed an rCBF increase in the right temporal cortex and the right posterior parietal cortex. Thus object-oriented action and object recognition activate a common posterior parietal area, suggesting that some kind of within-object spatial analysis was processed by this area whatever the goal of the task.

Adult↗
PubMedDate not supplied

Neural representations for action.

Goal directed behaviour is often internally generated which implies that the generation of action involves a representational step. One of the challenges of cognitive neuroscience is to discover the neural mechanism that underlies the representation of both intention and goal and fuses them into an integrated action. This paper reviews neurophysiological data gathered from different sorts of paradigms that reveal the presence of underlying neural processes which can be related to representations for action. Taken together, these data lead to the notion of distributed representations stored as patterns of activation networks.

Cognition↗
PubMedDate not supplied

[Naturalizing empathy].

Empathy is the ability to share emotions with others. It is acknowledged to be a powerful means of tacit communication, a key ingredient in any therapeutic relationship as well as in psychotherapy. Empathy is the cornerstone in the humanist perspective (Ego-psychology) in clinical psychology. This approach is often considered as poorly grounded on scientific and objective evidence. It is however acknowledged that empathetic therapists are more effective than less empathetic therapists. I shall argue that this paradox, i.e. it is the least scientific and the less validated psychotherapeutic approach that is the most efficient, can be eliminated if one considers the nature of empathy, its biological foundation, its evolutionary origin and its cognitive architecture. In this paper I will suggest that empathy is based on specific information processing modules which have been designed by natural selection to cope with social regularities in expressing and reading emotional states. This has provided adaptive benefits to individuals living in large groups bestowing them with mechanisms for cooperativity, altruism and more generally various aspects of prosocial behaviour. The capacity to express emotions, and to read and understand emotions of others also ensures implicit communication with others and may be at the root of intersubjectivity. This perspective on empathy is then articulated with two concurrent hypotheses regarding theory of mind (the simulation and the theory-theory) which aim to explain the human capacity to understand that the behaviors of other intelligent agents are caused by intentions, desires and beliefs. In this context, empathy can be considered as a simulation (or analogical) process that is necessary to understand but not sufficient to interpret other people. This last issue is relevant to clinical practice.

Biological Evolution↗