Biomedical subjects

F Cassim

Publications and source records attributed to F Cassim.

At least 19 recordsLinked to original sources

PubMed2003

Changes in oscillatory cortical activity related to a visuomotor task in young and elderly healthy subjects.

OBJECTIVE: In order to better understand the spatio-temporal interaction of the activated cortical areas when the movement is visuo-guided and to assess the age effect on the spatio-temporal pattern of cortical activity, we have compared a proximo-distal movement with visual-motor control and hand-eye coordination (targeting movement) with a distal and a proximal movement. METHODS: Brain's electrical activity was studied using the analysis of event-related (de)synchronizations (ERD/S) of cortical mu and beta rhythms in 17 subjects, 8 young and 9 elderly subjects. RESULTS: In both populations, we found an earlier and broader mu and beta ERD during the preparation of the targeting movement compared to distal and proximal movements, principally involving the contralateral parietal region. During the execution, a spreading over the parietocentral region during proximal movement and over the parietal region during targeting movement was observed. After the execution of proximal and targeting movements, a wider and higher beta ERS was observed only in the young subjects. In the elderly subjects, our results showed a significant decrease of beta ERS during the targeting task. CONCLUSIONS: These results suggest there was a larger recruitment of cortical areas, involving notably the parietal cortex when the movement is visuo-guided. Moreover, cerebral aging-related changes in the spatio-temporal beta ERS pattern suggests an impaired sensory integration.

Adult↗

PubMed2003

[Neurophysiology of parkinsonian syndromes].

Neurophysiological investigations may contribute to establish the diagnosis of different parkinsonian syndromes such as multiple system atrophy, progressive supranuclear palsy and corticobasal degeneration, which are often suspected in case of atypical parkinsonian syndrome. They provide a means of objective analysis of certain symptoms (myoclonus for example) and identify the pathophysiological processes underlying these parkinsonian syndromes. This article reviews especially the following electrophysiological tests: autonomic nervous system analysis (sympathetic sudomotor skin response, R-R interval variation, electromyography of the external anal sphincter), surface electromyography and movement recording to investigate myoclonus, somatosensory and motor evoked potentials, brainstem reflexes (mainly the blink reflex), startle reaction, monosynaptic and long latency reflexes and finally the premotor potentials (contingent negative variation, Bereitschaftspotential) and movement-related desynchronization).

Anal Canal↗

PubMed2003

[Clinical and electrophysiological features of "cortical tremor"].

The purpose of this paper is to draw attention to one particular variant of tremor named "cortical tremor," which corresponds to rhythmic cortical myoclonus whose principal differential diagnosis is essential tremor. Diagnosis may be established with electrophysiological explorations (electromyography, accelerometry, electroencelography with back averaging, long latency reflexes, giant somesthesic evoked potentials). Clinical and electrophysiological features of 15 patients are reported and compared to cases previously published. Association with generalized or partial seizures is possible. Other cases in the family are often mentioned with a dominant autosomal transmission. The therapeutic approach is based on the use of antiepileptic drugs.

Adolescent↗

PubMed2001

Does post-movement beta synchronization reflect an idling motor cortex?

After the completion of a voluntary movement, a synchronization of cortical beta rhythms is recorded over the contralateral central region, which is assumed to reflect the termination of the motor command. In order to test this hypothesis, we compared in eight healthy subjects the synchronization of EEG beta rhythms following active and passive index extension. The passive movement was also performed after deafferentation by ischaemic nerve block in three subjects. Beta synchronization was present in all subjects after both active and passive movements, and disappeared under ischaemia in all three subjects. Post-movement beta synchronization can not solely be explained by an idling motor cortex. It may also, at least in part, reflect a movement-related somatosensory processing.

Adult↗

PubMed2001

Intermuscular coherence in Parkinson's disease: relationship to bradykinesia.

We hypothesised that bradykinesia may be partly due to the failure of the corticomuscular system to engage in high frequency oscillatory activity in Parkinson's disease (PD). In healthy subjects such oscillations are evident in coherence between active muscles at 15--30 Hz. We therefore investigated the effects of therapeutic stimulation of the basal ganglia on this coherence and related it to changes in bradykinesia in the contralateral arm. Increases in coherence at 15--30 Hz and improvements in bradykinesia upon stimulation were correlated (r = 0.564, p < 0.001). This suggests that the basal ganglia modulate oscillatory activity in the corticomuscular system and that impairment of the motor system's ability to engage in synchronised oscillations at high frequency may contribute to bradykinesia in PD.

Electric Stimulation Therapy↗

PubMed2001

Autonomic dysfunction in multiple sclerosis: cervical spinal cord atrophy correlates.

Autonomic dysfunction has rarely been studied in patients suffering from multiple sclerosis (MS). Some hypotheses have concerned the pathophysiology, especially with regard to a possible spinal cord origin. However, there have been no previous studies on autonomic dysfunction in MS and spinal cord lesions. This study assessed the frequency of autonomic dysfunction (AD) in MS and the correlation to spinal cord magnetic resonance imaging (MRI) findings. We prospectively studied 75 MS patients (25 with relapsing-remitting forms, 25 with secondary progressive forms and 25 with primary progressive forms). We performed sympathetic skin response, R-R interval variability and orthostatic hypotension testing. Spinal cord MRI was performed to detect demyelinating lesions (sagittal and axial plane) or spinal cord atrophy. Clinical and laboratory evidence of AD was found in 84% and 56% of MS patients, respectively. The correlation of the latter with disability was evaluated using the Extended Disability Status Scale. AD was more frequent in primary progressive MS than in the other two forms. AD was correlated with spinal cord cross-sectional area reduction but not with spinal cord hyperintensities. This study confirms that the frequency of AD in MS, especially in primary progressive forms, has until now been underestimated. Furthermore, AD appears to be more closely related to axonal loss, as demonstrated by spinal cord atrophy, than to demyelinating lesions.

Adult↗

PubMed2001

Event-related variations in the activity of EEG-rhythms. Application to the physiology and the pathology of movements.

The averaging of the ongoing activity of the electroencephalogram (EEG) allows extracting the potentials that are time-locked and phase-locked to an event. These potentials are described as evoked potentials. There is another type of change in the ongoing EEG, which is time-locked but not phase-locked to an event: the EEG rhythm reactivity, also called "Event-Related Desynchronization and Synchronization" (ERD/ERS) by Pfurtscheller. These changes are often visible to the naked eye but they cannot be extracted by the averaging technique. Their quantification requires another method, which was suggested by Pfurtscheller and Aranibar in 1977. This method consists in measuring the temporal evolution of the power of EEG signal within a given frequency band before, during, and after an event. ERD corresponds to the decrease in power of an EEG rhythm related to an event. Conversely, ERS corresponds to an increase in amplitude of an EEG rhythm related to the event. ERD represents the activation of the subjacent cortical areas. ERS would partly traduce the setting at rest of the cortex; it would also be related to the somesthetics afferents inputs. This method can be applied to the study of cortical activation in many situations: memory tasks, auditory processing, attention, anticipatory behavior, and voluntary movement. Thus, a voluntary self-paced movement of the dominant hand is preceded by an ERD of mu and beta rhythms occurring respectively 2 000 and 1 500 ms before the movement onset. This ERD is recorded over the contralateral central region. It becomes bilateral at the movement onset and reaches its maximum at the movement offset. It is then followed by an ERS of the beta rhythms. We show that ERD/ERS phenomena vary with the type of movement, and that their study allows exploring the modifications of cortical excitability that are observed in Parkinson's disease and in epilepsy with focal motor seizures.

Journal Article↗

PubMed2000

Thalamic tremor: correlations with three-dimensional magnetic resonance imaging data and pathophysiological mechanisms.

Tremor associated with a single focal thalamic lesion has rarely been reported. Furthermore, the exact localization of the lesions is difficult to determine because of the imprecision of "conventional" radiology (computed tomography scan and/or "standard" magnetic resonance imaging). The aim of this study was to identify which thalamic structures are involved in tremor associated with a single focal thalamic lesion. We selected two patients who presented with unilateral postural and kinetic tremor of the upper limb related to a localized thalamic infarction. Three-dimensional T1-weighted magnetic resonance imaging sequence (MP-RAGE sequence) was used to determine the precise topography of the lesions by stereotactic analysis using the atlas of Hassler. The lesions were located within the pulvinar, the sensory nuclei, the mediodorsal nucleus, and the ventral lateral posterior nucleus (according to the classification of Hirai and Jones), the latter including the ventral intermediate nucleus (Vim according to the classification of Hassler). However, the Vim was spared. The subthalamic area, which can induce tremor, was not involved. After having compared the topography of the lesions with the clinical findings, we suggest that thalamic tremors may result from the interruption of the cerebellar outflow tract to the Vim within the thalamus.

Adult↗

PubMed2000

[Neurophysiologic study of tremor].

Tremor is frequently encountered in neurologic practice. Clinical examination supplies information regarding its approximative frequency, regularity, amplitude, topography and activation conditions. The neurophysiological study helps in confirming the tremor, in differentiating it from other movement disorders like myoclonus, and may provide distinctive features which are important for the aetiological diagnosis. The neurophysiological investigation includes accelerometry, which analyses the mechanics of the movement. Spectral analysis with FFT allows the determination of frequency and amplitude. Accelerometry is always associated with surface EMG of at least two antagonistic muscles. It may show rhythmic bursts, their frequency, duration and activation pattern (alternating or synchronous). This neurophysiological approach to tremor has multiple interests. It may help in differentiating a true rest tremor from a postural tremor seemingly persisting at rest. Brief interruptions or rhythm breaks during distraction manoeuvers are seen in psychogenic tremors. Surface EMG may also demonstrate positive myoclonic bursts, or brief silent periods corresponding to negative myoclonus, sometimes pseudorhythmic, thus appearing clinically like a tremor, but investigations, aetiologies and treatment are different. Several features, especially slow frequency, may suggest a midbrain tremor, thus requiring brain imagery centered around the posterior fossa. Finally, the neurophysiological examination is the only way to demonstrate a primary writing tremor, or a primary orthostatic tremor, the frequency of which is pathognomonic while clinical symptoms are rather misleading.

Diagnosis, Differential↗

PubMed2000

Brief and sustained movements: differences in event-related (de)synchronization (ERD/ERS) patterns.

OBJECTIVE: (1) To determine if there are changes in event-related desynchronization/event-related synchronization (ERD/ERS) patterns when the movement is sustained? (2) To determine, from a technical point of view for ERD calculation, if it is possible to take the reference period during muscular activation? METHODS: Eight healthy subjects performed two series of brief and sustained self-paced extensions with their dominant wrist. The end of the sustained movement was externally triggered by the examinator. ERD/ERS was calculated in mu and beta bands from 13 source derivations covering motor areas, computed from 29 scalp electrodes. Movement onset and offset were determined by electromyographic activity (EMG) of wrist extensors. RESULTS: When the movement was sustained, power in the mu and beta bands returned to baseline values within 4-5 s. Movement duration had little effect, if at all, on both pre and post-movement periods. Compared to brief movement, after the onset of the prolonged movement, mu ERD just returned to baseline, without synchronization. In contrast, beta ERS was still present though earlier and much lower. CONCLUSIONS: The reference period for ERD calculation may be taken during muscular activation if its duration is long enough. Beta synchronization may occur despite a non-deactivated motor cortex, suggesting a contribution from afferent somesthetic inputs.

Cortical Synchronization↗

PubMed1999

Motor programming is more affected in progressive supranuclear palsy than in Parkinson's disease: a spatiotemporal study of event-related desynchronization.

To determine the benefit of motor programming analysis for distinguishing patients with parkinsonism, we compared the spatiotemporal pattern of event-related desynchronization (ERD) preceding a self-paced voluntary wrist flexion between two groups of 10 patients with progressive supranuclear palsy (PSP) and Parkinson's disease (PD) and 10 control subjects. ERD of the mu rhythm was computed from 11 source derivations covering the medial frontocentral, central, and parietocentral areas during two successive left and right experimental conditions (80 self-paced wrist flexions). ERD began in the control group 1750 ms before movement onset over the contralateral central area and then appeared bilaterally on movement execution. In both patient groups, spatiotemporal distribution differed from that in the control group. In the PSP group, ERD had a shorter latency over the contralateral primary sensorimotor area compared with the PD group (PSP: 375 ms before movement onset for both conditions; PD: right flexion 1125 ms before movement onset, left flexion 1000 ms). ERD was observed over the parietocentral area in both groups but also with a clear reduction of latency before movement onset in the PSP group. In both groups, a bilateral central pattern appeared 250 ms before movement execution. In conclusion, our study indicates that ERD analysis is a useful method for observing the changes in cortical activation and for measuring motor programming impairment in parkinsonism, which was more affected in PSP than in PD.

Aged↗

PubMed1999

[Event-related desynchronization and synchronization. Reactivity of electrocortical rhythms in relation to the planning and execution of voluntary movement].

Cortical electroencephalographic rhythms reactivity may be quantified using event-related desynchronization (ERD) and synchronization (ERS) methods. We therefore studied cortical activation occurring during programming and performance of voluntary movement in healthy subjects. EEG power evolution within the reactive frequency bands (mu and beta central rhythms) was averaged before, during and after a minimum of 50 self-paced flexions of the thumb. Recordings in 18 normal adults showed that ERD (decrease in power) of mu rhythm started 2,000 ms before movement onset, while ERD of beta rhythm started 1,500 ms before movement onset. Early ERD of mu and beta rhythms were located over the contralateral central region covering primary motor cortex. They were followed by bilateral ERD occurring over ipsilateral and contralateral central regions during performance of the movement. At the end of the movement, an ERS (increase in power) of beta rhythm occurred. These results suggest that programming of voluntary movement induces early activation in contralateral sensorimotor areas, while performance of the movement induces bilateral activation in sensorimotor areas. ERS of beta rhythm occurring at the end of the movement could correspond to inactivation of motor areas activated by movement. Based on EEG activity, ERD and ERS prove to be useful methods to analyze cortical activation during programming and performance of voluntary movements with good spatial and temporal resolution.

Adult↗

PubMed1999

Analysis of the perception of and reactivity to pain and heat in patients with wallenberg syndrome and severe spinothalamic tract dysfunction.

BACKGROUND: The aim of the study was to assess the consequences of severe spinothalamic tract lesions resulting from lateral medullary infarct and to show that a specific pain perception can be elicited by strong thermal stimulation. CASE DESCRIPTIONS: Both patients examined presented with severe thermoalgic dissociation of the limbs contralateral to the lesion, with normal discriminative somatosensory perception and motor strength. They reported pain perception when touching very warm (>50 degrees C to 60 degrees C) objects and a brisk, occasionally uncontrolled withdrawal reaction of the arm and hand under the same conditions, without any perception of the heat nature of the stimulus. Warm stimulation, <45 degrees C, elicited no thermal perception or discrimination. Pain perception could be elicited in both patients by increasing the temperature, with a reproducible threshold of 47 degrees C to 49 degrees C. Pain always occurred after a prolonged delay of 8 to 10 seconds in response to threshold heat, and was described as deep and osseous, and clearly different from that perceived on the nonaffected side. The delay was much shorter when the temperature was increased by 4 degrees C to 5 degrees C. Cold stimulation elicited similar pain perception in one patient. Analysis of subjective perception of laser stimulation showed a much higher pain threshold on the affected hand. There were no laser-evoked potentials on this side, which suggested major spinothalamic injury. Assessment of the RIII noxious reflex revealed persistent response withdrawal reactions, with an increased threshold on the affected side, and partial consciousness of the noxious nature of the stimulus. CONCLUSIONS: To our knowledge, this is the first description of the appearance of pain perception of high temperatures in patients with severe spinothalamic injury who are suffering from a complete loss of temperature perception. This implies that noxious thermal stimulation can still be perceived via extra spinothalamic pathways (which are slow and multisynaptic), such as the spinoreticulothalamic tract. Patients with Wallenberg syndrome should be informed and made aware of their residual perception of and reactions to noxious stimulation.

Central Nervous System Diseases↗

PubMed1998

["Primary" orthostatic tremor. 10 clinical electrophysiologic observations].

Orthostatic tremor is an unusual kind of potentially disabiling tremor appearing immediately when standing. Clinical examination is normal in primary form except for wide base standing and unsteadiness which disappear when walking. Arm tremor resembling essential tremor is found present in one third of cases. Electrophysiological exploration is necessary for diagnosis and shows a regular rapid tremor (frequency around 16 Hz). We present 10 new cases, 3 men and 7 women, 37 to 74 years old. Unsteadiness when standing was the predominant complaint in 9 cases, the other first described pains in the lower limbs. All had visible or palpable tremor predominant in thighs. Four patients had postural arm tremor, one had neurogen syndrome in the lower limbs corresponding to toxic polyneuropathy which developed after tremor. Electromyographic study found high frequency (13-17.3 Hz) rhythmic discharge in weight-bearing muscles. Orthostatic tremor cannot be considered as a clinical variant of postural essential tremor. Its pathophysiology is unknown but the efficacy of clonazepam, primidone or barbiturates suggests the impairment of the gabaergic system.

Adult↗

PubMed1997

Abnormal cortical activation during planning of voluntary movement in patients with epilepsy with focal motor seizures: event-related desynchronization study of electroencephalographic mu rhythm.

PURPOSE: The spatiotemporal distribution of EEG mu rhythm desynchronization was analyzed in patients with partial epilepsy to determine whether frequent focal motor seizures could induce a change of cortical activation during the planning of a voluntary movement. METHODS: The event-related desynchronization (ERD) of the mu rhythm was quantified during a self-paced voluntary movement of the thumb. The results were compared between two groups of patients with epilepsy: in one group (n = 12), the patients had frontal lobe epilepsy with frequent focal motor seizures (FMS); in the second group (n = 12), they had temporal lobe epilepsy (TLE) with complex partial seizures but no ictal movement disorder. The results were also compared with those of control subjects of same age (n = 10). RESULTS: In the control group, desynchronization of mu rhythm began over the contralateral central region 2,000 ms before the movement onset. In the FMS group, the desynchronization of mu rhythm was delayed, appearing only 500 ms before the movement onset, and the amplitude of ERD was increased over the frontocentral region. In the TLE group, the spatiotemporal pattern of ERD was the same as in normal subjects, but the amplitude of ERD was increased. CONCLUSIONS: These results indicate that there is a change of reactivity of mu rhythm in patients with partial epilepsy. The change in spatiotemporal pattern of ERD in patients with frequent focal motor seizures suggests that there is an abnormal cortical activation during the planning of a voluntary movement.

Adult↗

PubMed1997

Hereditary chin trembling or hereditary chin myoclonus?

Hereditary chin trembling is a rare autosomal dominant disease often considered as an "essential tremor variant". The clinical and neurophysiological data obtained in a new white family lead to the suggestion that this abnormal involuntary movement is a focal variant of hereditary essential myoclonus.

Adult↗

PubMed1996

Late contralateral hyperhidrosis in lateral medullary infarcts.

BACKGROUND AND PURPOSE: This study describes unilateral increases of sweating reactions observed in the months after contralateral medullary infarct; evaluation of sympathetic cutaneous response may help to explain sweating disorders. SUMMARY OF REPORT: After the discovery of the clinical phenomenon in one case, patients admitted between 1990 and 1993 were systematically evaluated clinically and electrophysiologically. In a group of five patients presenting with lateral or dorsal medullary lesions, two exhibited an increase of contralateral sweating reactions that appeared 6 to 8 months after stroke, were elicited by effort and exposure to heat and stress, and were more severe over the forehead, face, and upper trunk. In one case, this was clinically associated with an absence of sweating on the side of the lesion. During the late phase after stroke, in three patients presenting with lateral medullary lesions, electrophysiological evaluation revealed significant asymmetry of the sympathetic skin response, which was higher on the side contralateral to the lesion than on the ipsilateral side. In one patient, no response could be elicited by stimulations applied on the side of the lesion. CONCLUSIONS: Contralateral hyperhidrosis can be observed in the late phase after lateral medullary infarct and is likely due to lesion of the sympathetic pathway passing through the lateral medulla, which inhibits sudomotor neurons. Evaluation of sympathetic skin response may help to explain such clinical disorders.

Adult↗

PubMed1996

[Dystonia and tremor in bilateral lesion of the posterior mesencephalon and the vermis].

The aim of this study is to report the association of diffuse dystonia and tremor in a bilateral and extended lesion of the posterior mesencephalon. After surgery on a meningioma of the upper part of the fourth ventricle, this patient presented with facial dystonia, predominating on orbicularis muscles and peribuccal area, and limb dystonia, with tonic extension of fingers and first toes. The tremor was associated with a rhythmic and most often alternate agonist-antagonist muscular activation, whose frequency varied from 3 to 7 Hz. These disorders were increased by the standing position, voluntary movement, somatosensory stimulations, stress or emotion. Pyramidal and somatosensory tracts were spared. Therapeutic trials showed that both the dystonia and tremor were improved by subcutaneous injection of apomorphine, the dystonia by trihexyphenidyle, and the tremor by carbamazepine and propranolol, but not by levodopa and benserazide. The cerebral blood flow study using HMPAO showed a relatively important activity on the cerebellum, which could play a role in the onset of these disorders.

Adult↗