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Biomedical subjects

P Maquet

Publications and source records attributed to P Maquet.

At least 19 recordsLinked to original sources
PubMed1999

Functional neuroanatomy of hypnotic state.

BACKGROUND: The aim of the present study was to describe the distribution of regional cerebral blood flow during the hypnotic state (HS) in humans, using positron-emission tomography (PET) and statistical parametric mapping. METHODS: The hypnotic state relied on revivification of pleasant autobiographical memories and was compared to imaging autobiographical material in "normal alertness." A group of 9 subjects under polygraphic monitoring received six H215O infusions and was scanned in the following order: alert-HS-HS-HS with color hallucination-HS with color hallucination-alert. PET data were analyzed using statistical parametric mapping (SPM95). RESULTS: The group analysis showed that hypnotic state is related to the activation of a widespread, mainly left-sided, set of cortical areas involving occipital, parietal, precentral, premotor, and ventrolateral prefrontal cortices and a few right-sided regions: occipital and anterior cingulate cortices. CONCLUSIONS: The pattern of activation during hypnotic state differs from those induced in normal subjects by the simple evocation of autobiographical memories. It shares many similarities with mental imagery, from which it differs by the relative deactivation of precuneus.

Adult↗
PubMed1999

Impaired effective cortical connectivity in vegetative state: preliminary investigation using PET.

Vegetative state (VS) is a condition of abolished awareness with persistence of arousal. Awareness is part of consciousness, which itself is thought to represent an emergent property of cerebral neural networks. Our hypothesis was that part of the neural correlate underlying VS is an altered connectivity, especially between the associative cortices. We assessed regional cerebral glucose metabolism (rCMRGlu) and effective cortical connectivity in four patients in VS by means of statistical parametric mapping and [18F]fluorodeoxyglucose-positron emission tomography. Our data showed a common pattern of impaired rCMRGlu in the prefrontal, premotor, and parietotemporal association areas and posterior cingulate cortex/precuneus in VS. In a next step, we demonstrated that in VS patients various prefrontal and premotor areas have in common that they are less tightly connected with the posterior cingulate cortex than in normal controls. These results provide a strong argument for an alteration of cortical connectivity in VS patients.

Adult↗
PubMed1999

Idiopathic rolandic epilepsy with "interictal" facial myoclonia and oromotor deficit: a longitudinal EEG and PET study.

PURPOSE: The prognosis of benign epilepsy with centrotemporal spikes (BECTS) is always favorable as far as the epilepsy is concerned. However, some data suggest that affected children may be at risk for minor cognitive impairment. We report here the longitudinal study of a young girl demonstrating that BECTS also may be associated with severe motor disturbances. METHODS: BECTS (rare left oromotor seizures, right rolandic spike-waves activated during sleep) started at the age of 3 years 6 months in a girl with normal initial psychomotor development. Her clinical, neuropsychological, and EEG status was assessed every 3-6 months. Regional cerebral glucose metabolism was measured by using the [18F]fluorodeoxyglucose-positron emission tomography (FDG-PET) method. RESULTS: Between the age of 5 and 6 years, the girl had (a) increased seizure frequency; (b) brief perioral and palpebral myoclonic jerks, concomitant with the spike component of interictal spike-waves, and (c) persistent but fluctuating oromotor deficits (drooling, dysarthria, dysphagia). The EEG showed a marked increase in abundance and amplitude of wake and sleep interictal abnormalities, which became bilateral. Awake FDG-PET revealed a bilateral increase of glucose metabolism in opercular regions. A complete and definitive EEG and clinical remission occurred at age 5 years 11 months and has persisted since (present age, 7 years 9 months). CONCLUSIONS: This case confirms that during BECTS, epileptiform dysfunctions within rolandic areas may induce "interictal" positive or negative oromotor symptoms, independent of classic seizures.

Brain↗
PubMed1999

Brain mechanisms of sleep: contribution of neuroimaging techniques.

Functional brain neuroimaging essentially relies on two basic principles: functional segregation and functional interaction. Recent studies of the functional segregation of the human brain during sleep, using positron emission tomography and statistical parametric mapping, indicate that human brain function is organized in a very specific way in each state of vigilance. During slow wave sleep, the most deactivated areas are the upper brainstem, thalamic nuclei and basal forebrain; deactivation of the basal ganglia is also seen. In the cortex, the least active areas are the associative cortices of the frontal and parietal cortex. The anatomical extent of this deactivation remains uncertain. In rapid eye movement (REM) sleep there is significant activation of the dorsal tegmentum of the ponto-mesencephalic region and the thalamic nuclei. Within the cortex, the limbic areas (amygdala, hippocampus, orbito-frontal cortex and anterior cingulate cortex) are activated. In contrast, the associative areas of the frontal and parietal cortices are less active than other parts of the brain. The functional interactions between the amygdala and the temporal cortex during REM sleep differ markedly from those during other states of vigilance, and there is also an inverse relationship between the activities of the primary and secondary visual areas.

Brain↗
PubMed1999

Biomechanics of hip dysplasia.

When walking, each hip alternately carries the body mass minus the supporting leg. This mass exerts a force K acting on the hip with a lever arm h'; it is counter-balanced by a force M exerted by the abductor muscles, which acts on the hip with a lever arm h. The hip joint transmits the resultant R of forces K and M. Force R evokes compressive stresses in the joint. In a normal hip, force R is exerted at the center of the force transmitting surface of the joint, and the stresses are evenly distributed over this surface. This is reflected by the narrow ribbon of subchondral sclerosis in the roof of the socket. The normal femoral neck is stressed in bending with shear. It has a medial bundle of cancellous trabeculae, stressed in compression, intersecting with a lateral bundle, stressed in tension. Dysplasia and an imbalance of the muscles may have similar mechanical consequences: a shortening of the lever arm h and a more vertical orientation of force M. Shortening of h results in an increase of the force M necessary to counterbalance the moment of force K; the change in direction of force M displaces the resultant R towards the edge of the socket. The result is an increased resultant force R which becomes unevenly distributed over a smaller surface. Subluxation of the femoral head due to a shallow socket will also result in an uneven distribution of force R on a smaller surface. The abnormal distribution of compressive stresses is reflected by the development of a triangular sclerosis at the edge of the socket. This is the beginning of subluxating osteoarthritis of the hip. In a coxa valga the femoral neck may be stressed in a pure compression. This appears in the structure of the cancellous bone of the neck. Coxa vara has opposite consequences: lengthening of the lever arm h of the abductor muscles and a more horizontal orientation of force M. This results in a decrease of the resultant force R, which is displaced medially over a larger surface, resulting into smaller compressive stresses in the joint. If the acetabular cartilage of the socket does not develop further medially, the distribution of compressive stresses may become uneven with a maximum medially, where a dense triangular sclerosis develops. This is the beginning of protrusive osteoarthritis of the hip. In coxa vara, the femoral neck is stressed in bending more than in a normal hip, which is reflected by more marked cancellous trabeculae which intersect at right angles in the femoral head. The medial bundle is stressed in compression, the lateral bundle in tension.

Biomechanical Phenomena↗
PubMed1998

Functional brain imaging of human sleep.

This paper presents an overview of the contribution of functional brain mapping to the study of human sleep. Early studies were essentially successful in describing the variations of the global level of cerebral metabolism. More recently, regional distribution of cerebral blood flow was reported. The results suggest that the permissive and executive processes of slow wave sleep and REM sleep are similar in humans and in animals. They also show cortical blood flow distributions specific to each sleep stage. The cellular mechanisms underlying the involvement of these cortical areas in sleep are not yet precisely known. They should be looked for by further investigations in animals. Future research in functional neuroimaging will attempt to explore functional and, hopefully, effective connectivity between cerebral areas involved in sleep processes. This final goal will probably require the co-registration of two or more brain imaging techniques to precisely describe the spatio-temporal course of neuronal interactions occurring during sleep.

Brain↗
PubMed1997

The basic pattern of activation in motor and sensory temporal tasks: positron emission tomography data.

Positron emission tomography (PET) data were obtained from subjects performing a synchronization task (target duration 2700 ms). A conjunction analysis was run to identify areas prominently activated both in this task and in a temporal generalization task (target duration 700 ms) used previously. The common pattern of activation included the right prefrontal, inferior parietal and anterior cingulate cortex, the left putamen and the left cerebellar hemisphere. These areas are assumed to play a major role in time processing, in relation to attention and memory mechanisms.

Adult↗
PubMed1997

Functional neuroanatomy of human slow wave sleep.

The distribution of regional cerebral blood flow (rCBF) was estimated during sleep and wakefulness by using H215O positron emission tomography (PET) and statistical parametric mapping. A group analysis on 11 good sleepers (8 with steady slow wave sleep, SWS) showed a significant negative correlation between the occurrence of SWS and rCBF in dorsal pons and mesencephalon, thalami, basal ganglia, basal forebrain/hypothalamus, orbitofrontal cortex, anterior cingulate cortex, precuneus, and, on the right side, in a region that follows the medial aspect of the temporal lobe. Given the known decrease in global cerebral blood flow levels during SWS, these negative correlations suggest that rCBF is decreased significantly more in these cerebral areas than in the rest of the brain. The marked rCBF decreases in the pons, mesencephalon, thalamic nuclei, and basal forebrain reflect their close implication in the generation of SWS rhythms. The influence of these rhythms on the telencephalon usually are thought to be global and homogeneous. In contrast, our results show that rCBF is decreased more in some cortical areas (especially in orbitofrontal cortex) than in the rest of the cortex. We hypothesize that cellular processes taking place during SWS might be modulated differently in these regions. Given the functions of the ventromedial frontal areas, we surmise that SWS might be particularly critical for the adaptation of behavior to environmental pressures. This hypothesis is supported indirectly by results of sleep deprivation experiments.

Adult↗
PubMed1997

Positron emission tomography studies of sleep and sleep disorders.

Using positron emission tomography (PET) it is possible to perform an in vivo study of cerebral physiological and biochemical processes in man. Employing this technique in sleep studies, decreased cerebral metabolic rates for glucose during slow wave sleep compared with those seen during wakefulness were first demonstrated, whereas similar rates of cerebral glucose metabolism were observed during paradoxical sleep and wakefulness. More recently, regional modifications of cerebral blood flow during sleep have also been demonstrated. During slow wave sleep, cerebral blood flow is decreased particularly in the prefrontal cortex. Rapid eye movement sleep is characterized by activation of the pons, thalami, amygdaloid complexes and a number of cortical areas (e.g. the anterior cingulate cortex). Although data remain incomplete, a variety of sleep disorders, including narcolepsy, fatal familial insomnia and continuous spike-and-wave discharges during slow sleep have been investigated. These results are briefly reviewed.

Brain↗
PubMed1996

Functional neuroanatomy of human rapid-eye-movement sleep and dreaming.

Rapid-eye-movement (REM) sleep is associated with intense neuronal activity, ocular saccades, muscular atonia and dreaming. The function of REM sleep remains elusive and its neural correlates have not been characterized precisely in man. Here we use positron emission tomography and statistical parametric mapping to study the brain state associated with REM sleep in humans. We report a group study of seven subjects who maintained steady REM sleep during brain scanning and recalled dreams upon awakening. The results show that regional cerebral blood flow is positively correlated with REM sleep in pontine tegmentum, left thalamus, both amygdaloid complexes, anterior cingulate cortex and right parietal operculum. Negative correlations between regional cerebral blood flow and REM sleep are observed bilaterally, in a vast area of dorsolateral prefrontal cortex, in parietal cortex (supramarginal gyrus) as well as in posterior cingulate cortex and precuneus. Given the role of the amygdaloid complexes in the acquisition of emotionally influenced memories, the pattern of activation in the amygdala and the cortical areas provides a biological basis for the processing of some types of memory during REM sleep.

Adult↗
PubMed1996

Brain activation induced by estimation of duration: a PET study.

Duration information about a visual stimulus requires processing as do other visual features such as size or intensity. Using positron emission tomography, iterative H215O infusions, and statistical parametric mapping, we investigated the neural correlates of time processing. Nine normal subjects underwent six serial rCBF. Three tasks were studied: (a) A temporal generalization task (D task) in which the subjects had to judge (by pressing one of two keys) whether the duration of the illumination of a green LED was equal to or different from that of a previously presented standard; (b) An intensity generalization task (I task) in which the judgment concerned the intensity of the LED; and (c) A control task (C task) in which the subjects had to press one of the two keys at random in response to LED illumination. A significant increase in rCBF during the D task, compared to that during the C task, was observed in right prefontal cortex, right inferior parietal lobule, anterior cingulate cortex, vermis, and a region corresponding to the left fusiform gyrus. A significant increase in rCBF during the I task, compared to that during the C task, was observed in right prefontal cortex, right inferior parietal lobule, right extrastriate cortex, anterior cingulate cortex, left inferior parietal lobule, vermis, and two symmetrical regions corresponding to the fusiform gyri. No significant activation was observed in the D task when compared to that in the I task. We propose that these cortical maps are best explained by the recruitment of visual attention and memory structures, which play a major role in prospective time judgements as indicated by behavioral studies. The data also suggest that the temporal dimension of a visual stimulus is processed in the same areas as other visual attributes.

Adult↗