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Biomedical subjects

M Lamarche

Publications and source records attributed to M Lamarche.

At least 19 recordsLinked to original sources
PubMed2001

Event-related potentials, CNV, readiness potential, and movement accompanying potential recorded from posterior thalamus in human subjects. A SEEG study.

Intracranial recordings were obtained from three patients with intractable chronic pain who underwent analgesic electrical stimulation of the contralateral thalamus. Multilead electrode made it possible to record from several thalamic nuclei. The electrode was targeted into the ventroposterolateral (VPL) nucleus of the thalamus. During separate recording sessions, the following tests were performed: somatosensory evoked potentials (SEP) of the median or posterior tibial nerve, event-related cognitive potentials (auditory oddball P3 wave), readiness potential (RP) and contingent negative variation (CNV) using auditory warning (S1) and visual imperative (S2) stimuli. The movement accompanying potential (MAP), which was present in the VPL in all but one of the recordings, behaved as a far-field potential. Recordings obtained from the VPL confirmed its established role as a relay nucleus, processing somatosensory information to the primary somatosensory cortex. The VPL generated the 'thalamic' SEP, which was the only potential regularly recorded in this nucleus. In the recordings from one patient (No. 3), auditory and visual evoked potentials of the CNV protocol, peaking at approximately 300 ms, were obtained from the VPL and appeared to be generated in situ. Neither RP, CNV nor 'oddball' ERPs appeared in the VPL. From the pulvinar, only a visually evoked potential was recorded. Oddball P3, RP, CNV, and middle and long latency auditory and visual potentials (evoked in the CNV paradigm) appeared to be generated 'dorsally' to the VPL, probably in the nucleus posterolateralis (PL). This structure may therefore be involved in both the processing of afferent information and in cognitive operations.

Aged↗
PubMed2001

Steep early negative slopes can be demonstrated in pre-movement bereitschaftspotential.

OBJECTIVES: The study presents data suggesting that the classic bereitschaftspotential hides in its early component (BP1) steep increases of negativity which precede the movement at varying intervals in repeated trials. METHODS: In 12 volunteers, surface EEG from Fz, Cz, C3, C4, and Pz electrodes and EMG from the flexor digitorum communis were recorded during self-paced wrist flexions. Two hundred trials were collected from each subject. The single trials were grouped for averaging in two different ways. In the first one, single trials for each subject were used to create individual averages. In the second, all single trials were divided into groups according to the point in time of small steep negative shift from the baseline detected on sweeps before the movement and time group averages were created. The identification of small shifts was based on the comparison of calculated mean amplitudes in the first and the second half of the 1 s time window moved along the time axis. RESULTS: The small negative shifts were identified in 97.2% of analyzed records. In each subject, their position on the time axis varied considerably. Individual averages exhibited the characteristics of classical readiness potential, i.e. slow early component, steep late component, laterality over motor cortices. On the other hand, all time group averages (26) displayed an early steep negative shift followed by plateau which, about 0.5 s before the movement, gave rise to the second, late steep negative shift. The slope values calculated in the definite segments of averaged curves were used as a measure of the amplitude of these shifts over various brain areas. MANOVA showed a significant effect of the electrode position both in the case of early slopes (F(4,115)=9.7; P<0.000) and in the case of late slopes (F(4,115)=22.5; P<0.000). In both cases, the largest value was demonstrated under Cz electrode. In contrast to the late slopes, the values of early slopes did not exhibit laterality and suggested greater importance of pre-frontal regions in their formation. CONCLUSION: We have suggested that the formation of steep early negative shifts from the baseline in time group averages was due to synchronization of a mental process which, under classical averaging procedure, was dispersed uniformly throughout the pre-movement period.

Adult↗
PubMed2001

Parieto-temporal rhythms in the 6-9 Hz band recorded in epileptic patients with depth electrodes in a self-paced movement protocol.

OBJECTIVES: Description of 6-9 Hz rhythmic electrical activity observed on recordings from electrodes implanted in the cortex of epileptic patients undergoing presurgical evaluation. METHODS: Recordings were obtained from 74 patients with multilead electrodes in the frontal, parietal and temporal cortex. The motor task consisted of a self-paced fist clenching movement at approximately 10 s intervals. Events within a window extending from 4 s before to 1 s after movement EMG onset were analyzed. RESULTS: (i) Spindle-like rhythmic activity at 6-9 Hz was observed in 29 patients. (ii) This activity was located in the inferior parietal and superior temporal areas. (iii) Enhancement of rhythmic activity occurred when patients were asked to perform the motor task. (iv) A striking tendency to phase-locking of rhythmic oscillations on consecutive trials was noted during the 3-2 s epoch before movement EMG onset. CONCLUSION: Whether this intracerebrally recorded 6-9 Hz rhythmic activity belongs to the mu-alpha class or is a special type of theta, and if it is related to the epileptic process or to drug treatment remain open to discussion. Motor-task related enhancement and phase-locking suggest that this activity may be one more indicator of movement preparation.

Electrodes, Implanted↗
PubMed2000

Synchronizing effect of clock rhythm on the 'when to move' decision in repeated voluntary movements.

In 13 volunteers, surface EEGs from F(z), C(z), C(3), C(4), and P(z) electrodes and EMG from the flexor digitorum communis were recorded during an experimental task in which the performance of wrist flexion was linked with the selection of a clock sound. In the epoch from 4 to 1 s before movement, more than 95% of the records exhibited a small negative shift from the baseline. The position of these shifts on the time axis made it possible to create groups of time trials. The average EEG curves from these groups showed one prominent negative shift from the baseline, which could be related to the position of particular clock sounds. The slope values of these shifts were highest under the F(z) and C(z) electrodes. We suggested that these negative shifts coincided with 'when to move' decisions, which preceded the execution of the movement at varying intervals.

Adult↗
PubMed1998

Presence of very early events preceding self-paced movements in epileptic patients. An intracerebral exploration.

In epileptic patients explored with depth electrodes kept within the brain for several days ("chronic conditions") to localize their focus, recordings were taken from the less perturbed deep brain areas, before and during the execution of self-paced movements. A few deep leads (some of which were located in areas which did not display a classical readiness potential) showed that phasic paroxystic events very often occurred 2,000 ms and, sometimes, even about 3,000 ms before the movement (movement-related events, MREs). This finding suggests that the preparation of a "voluntary" self-paced movement may begin well before the appearance of the readiness potential or, alternatively, that intracerebral paroxystic spikes delay the decision making. This type of phasic process may be undetectable in scalp recording from normal subjects and only be revealed when some brain structures have become hyper-reactive due to the epileptic process.

Brain↗
PubMed1998

Intracerebral recording of potentials accompanying simple limb movements: a SEEG study in epileptic patients.

OBJECTIVES: Slow potentials appearing during simple repetitive acral limb movement were investigated. Twenty-six patients suffering from drug resistant partial epilepsies and explored with implanted intracerebral electrodes were examined using two protocols. METHODS: In 18 patients, readiness potential (RP), in 13 patients contingent negative variation (CNV), and in 7 patients both protocols, were tested. The recordings from leads with evident pathological EEG activity were excluded from evaluation. The results concerning the slow potentials preceding the movements in RP and CNV protocols have already been published. RESULTS: The movement-accompanying slow potentials (MASP) were polyphasic or monophasic, started before or during the movement. In the primary motor cortex they followed the pre-movement potentials depending on the protocol: in the RP paradigm they were present only contralateral to the movement, but were bilateral in the CNV protocol. In other areas they either followed the potentials preceding the movement, in some cases with opposite polarity, or they occurred alone. MASP was recorded in motor and supplementary motor, premotor and prefrontal, midtemporal, somatosensory, superior parietal and cingular cortices. The cingular cortex was heavily involved in the self-paced movements but rarely in the cued movements. CONCLUSION: The major involvement of the cingular gyrus contrasted with the absence of slow potentials in temporal limbic structures. MASP is evidently a heterogenic phenomenon. Its genesis could be involved in a spread of information through the relevant structures.

Adolescent↗
PubMed1998

The early component of the premovement readiness potential and its behavioral determinants.

Fifteen healthy subjects were asked to randomly select a tick of a mechanical clock which was operating throughout the experiment and to flex their wrist at the chosen tick. The individual averages of EEG recordings collected during the period of the putative decision to begin the task exhibited steep slopes of negativity followed by plateaus. These slopes preceded the selection of the signal sound at varying intervals, the longest interval was 3 s. The grand average of individual averages depicted a waveform whose shape was identical to the early component of the classical readiness potential. Another interesting finding came from experiments with mental counting of clock sounds, which demonstrated that the generation of the first mentally-counted number is preceded by a distinct negative potential shift.

Acoustic Stimulation↗
PubMed1997

Can epileptologists without access to intracranial EEG use reliably the International League Against Epilepsy classification of the localization-related epileptic syndromes? A stereo-electroencephalographic study.

The goal of the present study was to investigate the reliability of clinical and electroencephalographic (EEG) criteria for the classification of localization-related epileptic syndromes as listed in the Proposals of Revised Classification of Epilepsies and Epileptic Syndromes 1989 (ICE). ICE distinguishes between multiple syndromes within epilepsies of a given lobe. Intracranial recordings were the main element in the development of the revised ICE. Considering that most epilepsy centers have no access to such invasive techniques for precise anatomic localization, it was of interest to assess how accurately the seizure origin could be determined from the scalp EEG and clinical data as reported in ICE. In this retrospective study, we compared the accuracy of the topographic diagnosis made by two groups of physicians evaluating the same patients-one group with and the other without access to results of stereo-EEG (SEEG). Medical files of 87 patients with intractable localization-related epilepsy were analyzed: 38 with frontal, 37 with temporal, 10 with parietal, and 2 with occipital lobe epilepsy were included in the study. All patients underwent previous SEEG and successful cortectomy. Minimum follow-up was 5 years. In most cases, noninvasive techniques and criteria suggested by ICE allowed topographic diagnosis of focal epilepsies according to brain lobe involvement. More detailed diagnosis, localizing the origin of critical activity within a lobe, was often unreliable. Further data are required for a definition of the epileptogenic zone. A spatiotemporal evaluation of critical events, including the intracranial EEG recording, remains the best method for topographic diagnosis of localization-related epilepsy.

Adolescent↗
PubMed1997

Differences in pain medication use in stroke patients with aphasia and without aphasia.

BACKGROUND AND PURPOSE: While individuals with stroke are known to experience pain for a variety of reasons including premorbid conditions and stroke-specific sequelae, there are some groups of individuals with stroke, who because of aphasia, are unable to express their pain. This study investigated whether there exists an association between severity of aphasia and overall pain medication use as indicated (1) by the proportion of individuals medicated according to aphasia severity and (2) by the dosage of pain medication used according to aphasia severity. METHODS: The study involved a retrospective chart review of 207 charts of patients with stroke admitted to the Jewish Rehabilitation Hospital (JRH), Laval, Canada. Patients were classified into three groups according to level of expressive aphasia: those without aphasia, those with mild-to-moderate aphasia, and those severe aphasia. Information on medications used primarily for pain management was elicited for the first 21 days and the last 5 days of hospitalization. Any substitution, increase, elimination, or addition of pain medication during hospitalization was also monitored. RESULTS AND CONCLUSIONS: While the findings indicate that pain medication prescriptions were similar for all patients, a significantly smaller number of individuals with aphasia received pro re nata (prn) "as required" pain medication when compared with those without aphasia, for the first 21 days and for the last 5 days of hospitalization at the JRH. Similarly, when daily dose was monitored for the same time periods, individuals with aphasia were found to have received less medication for pain than those without aphasia.

Aged↗
PubMed1996

The impact of a decision process upon scalp recorded premovement potential.

Twelve normal subjects were asked to select one finger after a warning signal and to move it. Using different modes of averaging the EEG responses, it is shown that: (i) the selection of a finger is accompanied by a distinct negative slow potential consisting of a rapid set-up and a following plateau which is the most prominent under the Fz electrode, and (ii) the decision process, when dispersed within a large interval in repeated trials, gives rise to a slow progressive increase of negativity resembling the early component of premovement slow cortical potential from the classical self-paced paradigm.

Adult↗
PubMed1996

[Multiple cortical photolesions and penicillin epileptogenic focus. Study of a model in rabbits].

Inactivation of an epileptogenic focus by dividing it into sub-unities unable to maintain epileptic activity has been demonstrated in animals. Based on these experiments, multiple subpial transections have been performed in patients suffering from partial drug-resistant epilepsies when resection of the epileptogenic cortex was not possible. In order to develop a new surgical technique for such epilepsies, the authors present an initial study of multiple cortical laser photolesions on the rabbit brain. The aim of this study is to assess the histological lesions created on the cortex with a laser at a chronic stage, and to compare the electrical paroxysmal activity of a penicillin focus on the laser irradiated cortex and on the non radiated cortex in the same animal. Twenty-five adult albino rabbits were used for this study. Both hemispheres of 19 rabbits have been exposed; 14 to 35 photolesions in a network were performed on one hemisphere using a 1.064 microns wavelength Nd-YAG laser. Six to twenty-one days later, a penicillin-induced focus was created on both hemispheres, a corticographic study was performed, and each animal was sacrificed for histological study of the brain. For the 6 last animals a high-power 0.805 micron wavelength diode laser was used with the same protocol. Histological study was solely performed in order to compare the effects of both lasers. In 11 animals electrocorticographic control was reliable. Time to first spike occurrence after penicillin application was significantly increased on the treated hemisphere as compared to the untreated one (1' to 14'30" and 10" to 6', respectively; p < 0.01) and the number of spikes per minute at early and late counts was significantly smaller on the treated hemisphere as compared to the untreated one (1 to 29 and 2 to 70, respectively; p < 0.02). Histologically the lesions appeared as cone-shaped coagulation necrosis surrounded by an area of macrophagic reaction, angiogenesis and gliosis. With the diode laser, some lesions included ischemic changes extended in the white matter. This study demonstrated the possibility of creating limited and reproducible photolesions using the laser light energy, without extensive destruction of the cortex. These lesions were reaching from one third to the totality of the cortical depth, depending on laser exposure parameters. This study also demonstrated that these photolesions arranged in a network and at a chronic stage were associated with a significantly reduced paroxysmal activity of a penicillin focus when compared to intact cortex. Since such lesions did not totally isolate cortical sub-unities, spiking was still recorded from the irradiated cortex, but at a lower rate, suggesting a disorganization of the local neuronal network responsible for paroxysmal activity.

Animals↗
PubMed1996

Readiness potentials related to self-initiated movement and to movement preceded by time estimation: a comparison.

Two procedures for eliciting premovement potentials were compared: (1) the estimation of a 3 s interval elapsed after a warning auditory signal, and (2) classical "self-pacing". Eleven healthy right-handed subjects participated in the experiment, EEG records from scalp electrodes placed at CZ, C3+ and C4+ were analyzed. It has been shown that both procedures induced similar premovement potentials except that in the first procedure the early component of the potential was longer. The time estimation itself induced a negative slow potential consisting of a rapid set-up and a subsequent plateau.

Adolescent↗
PubMed1995

Intracerebral recordings of slow potentials in a contingent negative variation paradigm: an exploration in epileptic patients.

While exploring epileptic patients with intracerebral multilead electrodes, we applied a forewarned reaction time task with two successive sound stimuli, a paradigm that is known to elicit a contingent negative variation (CNV). The second, imperative sound stimulus was followed by a hand or a foot movement. Eleven patients suffering drug-resistant partial epilepsies were tested. The slow potentials developing during the time between the two stimuli were usually not typical CNVs (sometimes comprising multiple successive components with distinct polarities). Such "CNV-like" potentials were obtained from two main cortical zones: a central one including premotor, motor, supplementary motor, postcentral and cingulate areas; and a temporal zone, mainly including the auditory cortex and its vicinity, and in some cases the amygdala. This restricted localization contrasted with the broader extent of the CNVs on the scalp. Intracerebral CNV-like events were obtained from both hemispheres, independent of the side of the performed movement. In some patients, readiness potentials (RPs) were also recorded for comparison and displayed a more restricted extent, being present only on the contralateral motor cortex and bilaterally in the supplementary motor areas. Our data suggest that the last part of the CNV cannot just be identified with the RP.

Adolescent↗
PubMed1994

Intracerebral recording of movement related readiness potentials: an exploration in epileptic patients.

Readiness potentials (RPs) preceding voluntary self-paced limb movements were recorded intracerebrally in 13 patients suffering drug resistant, intractable epilepsy. Multilead depth electrodes were positioned using the Talairach's coordinate system; they allowed simultaneous recording from the external and mesial cortices and from the interposed white matter during self-paced unilateral hand or plantar flexions. Our intracerebral explorations have shown RPs in the primary motor cortex (MC) contralateral to the movement and in both supplementary motor areas (SMAs), indicating that at least 3 cortical sites become active before the movement. At variance with the scalp RPs recorded in the same patients, the intracerebral potentials were either negative, or positive, depending on the recording site. No consistent differences in duration and time of onset could be established between the MC and the SMA RPs, at least with the used time resolution. RPs were only occasionally observed in the parietal cortex and hippocampus and none were recorded from the amygdala, the temporal, temporo-occipital, prefrontal, frontal and cingular cortices. The wide topographical distribution of the scalp RPs may not be fully explained by the above intracortical findings, leaving the possibility that other generators exist, whose locations remain to be determined.

Adolescent↗
PubMed1990

Suppression of motor seizures after specific thalamotomy in chronic epileptic monkeys.

In the monkey with a chronic motor epileptogenic focus, thalamic lesions restricted to the anterior part of the ventro-postero-lateral nucleus produced a long-lasting improvement, leading in most cases to almost complete seizure suppression. This improvement was attributed to the interruption of a long-loop recurrent excitatory mechanism, involving muscular afferents which are known to relay in the thalamic region where lesions were produced. The specific nature of this effect was suggested by the preliminary results of lesions performed in thalamic regions with non-specific cortical projections. Compared with the pre-lesional situation in which focal activity resulted in permanent motor troubles, the post-lesional state did not show any additional motor deficit. It is concluded that such lesions could be a new approach to controlling intractable motor epilepsies in man.

Animals↗
PubMed1986

Penicillin epileptogenic focus in the rat: requisites for transcortical reflex triggering.

Epileptiform discharges elicited by natural or electrical stimulations, proprioceptive or cutaneous, were studied in the rat with an experimental acute focus induced by penicillin application in the motor area. EEG paroxystic spikes were easily triggered with restricted foci (0.5 to 1 mm2) located in the representation area of the stimulated region. However, despite the large overlap of sensory and motor cortical limb areas in the rat, EEG spikes, either spontaneous or triggered, were followed by muscular jerks only with much larger foci: at least 2 and 4 mm2, respectively, for anterior and posterior limb areas. Cutaneous stimulations were the most efficient in discharge production; however, discharges were triggered indifferently by muscular or cutaneous afferent fibers in about three-fourths of the cases. The temporal relation between EEG spike and myoclonic jerk were very close. A latency analysis (delay between triggered EEG spike and EMG response, parallel latency fluctuation of both phenomena, delay between spontaneous EEG spike and jerk) supported the hypothesis that a transcortical reflex mechanism, rather than a spinal excitability rebound, was involved in the jerk genesis. Iontophoretic ejection of penicillin within layers III-IV resulted in the development of electroclinical paroxysms. However, similar penicillin ejection within layer V, did not allow efferent discharge production. It is concluded that the involvement of a large surface or volume of cortical tissue is required to produce efferent discharges following EEG paroxysms. This observation is likely related to the unexpectedly wide representation of individual muscles at the motor cortical level.

Animals↗
PubMed1985

A reappraisal of rat motor cortex organization by intracortical microstimulation.

The organization of the motor cortex was reinvestigated with intracortical microstimulation, in light-anaesthetized (ketamine) rats. A posterolateral (PL) vibrissae area was found in addition to the rostral one, and blinks of the contralateral eyelids were elicited from a part of this PL area. Several cortical representations such as neck or tail were largely overlapping with neighbouring areas. Vegetative effects (mainly myosis and swallowing) were obtained from a medial cortical strip. Within the PL vibrissae area, a topical arrangement related to the vibrissal rows was observed, whereas in the leg areas, no individual representation of muscles could be evidenced. These results are compared with the maps previously published, and discussed in terms of specificity, musculotopy and overlapping of motor areas.

Animals↗