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Biomedical subjects

I Rektor

Publications and source records attributed to I Rektor.

At least 55 records · Page 3Linked to original sources
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↗
PubMed1995

Spatiotemporal analysis of interictal epileptic spikes. A stereoelectroencephalographic study.

Interictal epileptic spikes (IES) were recorded and averaged in 4-15 channels, in seven adult epileptics with intracerebral electrodes. IES relations were revealed by comparing the onset of the averaged IES in each channel, with one being used alternatively as the triggering channel. The records were analysed and sorted by comparing the morphology of individual IES and the final average morphology. There was a dominant group of IES on each recording site channel representing about 65-80% and decidedly influencing the average morphology of all IES. The major limitation of IES averaging is the loss of information due to the IES relative heterogeneity. Nevertheless, it reveals the main basic relationships in the large numbers of IES. On the other hand, IES averaging helps to minimize fortuitous spatiotemporal relations between recording sites. The relationship between IES in two channels was considered as significant only when these channels were observed both before and after the mutual switching of the role of triggered and triggering channel. The relations were then considered significant in only about 18% of all possible relations.

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↗
PubMed1993

The cholinergic system-dependent myoclonus of the baboon Papio papio is a reticular reflex myoclonus.

Neurophysiological studies were performed on four Papio papio baboons presenting with nonepileptic myoclonus (a startle response resembling stimulus-sensitive jerk). Investigations of the EEG, back-averaged EEG, and somatosensory evoked potentials revealed the absence of cortical correlates preceding the jerks, and exclusion of cerebral cortex involvement. No long-latency reflexes could be recorded in these animals. The jerks were symmetric when evoked by unilateral stimulation in normal baboons as well as in a split-brain animal. Polymyographic records showed that the first muscle involved during the jerk was the trapezius; other muscles were involved with latencies increasing in both cranial and caudal directions. From these data, nonepileptic myoclonus of baboons can be classified as a reticular reflex myoclonus. The involvement of cranial nerves did not follow the layout of the nuclei in the brainstem, indicating that the jerk is most likely generated as a complete movement. The generating structure is probably under cholinergic control. Finally, the Papio papio baboon, which was already known as a model for cortical myoclonus elicited by intermittent photic stimulation in predisposed animals, can also be considered a model for the study of the reticular reflex myoclonus.

Animals↗
PubMed1992

Influence of cholinergic system on myoclonus in myoclonic epilepsies.

The effect of two drugs upon multifocal myoclonic jerks was evaluated. The drugs influence the central cholinergic system in opposite ways. Eight patients with progressive and nonprogressive myoclonic epilepsy were tested. The single blind test was used. The number of myoclonic jerks after intravenous physostigmine (mean dose 0.02 mg/kg) and that after atropine (0.04 mg/kg) was compared to number of myoclonic jerks in the drug-free periods and with placebo. Placebo was without an effect. Physostigmine slightly increased the number of jerks. Atropine decreased the number significantly. In most patients the results were not striking. It is suggested that the cholinergic system may participate in the physiopathology of the studied myoclonus in a rather indirect, perhaps modulating way.

Adolescent↗
PubMed1992

Inhibition of the startle reaction by physostigmine in patients with early brain damage.

The influence of physostigmine and atropine on the startle reaction and EEG epileptic paroxysmal activity was examined in 24 severely impaired children with early brain damage. The startle motor reaction could be regularly evoked by tapping on the sternum in 12 of the patients. Physostigmine inhibited this reaction significantly, while atropine was without effect. In 12 patients without a previous startle reaction, atropine had a possible activating effect, however, the result was not significant. Physostigmine had no effect. The EEG paroxysmal activity was inhibited by physostigmine and activated by atropine in both groups of patients. A cholinergic system disturbance was suggested in the pathophysiology of the paroxysmal activity. The disturbance which is probably present in early brain damage, is presumed to be also involved in the genesis of the startle reaction.

Adolescent↗
PubMed1991

Drugs influencing the GABAergic neurotransmission have no effect on the non-epileptic myoclonus of baboons.

In Papio papio baboons benzodiazepines can facilitate the appearance of a naturally occurring non-epileptic myoclonus, suggesting a possible role of GABAergic transmission in their physiopathology. Nevertheless, as this myoclonus is blocked by physostigmine, the effect of benzodiazepines is probably due to their indirect action on the cholinergic system. Therefore, in this study, we report the effects on the non-epileptic myoclonus of drugs influencing GABAergic transmission. Systemic injections of progabide (GABA precursor), baclofen (GABAB receptor agonist) and allylglycine (glutamic acid decarboxylase inhibitor) did not modify or induce the non-epileptic myoclonus. In the same way, localized chronic injections of GABA into various cerebral structures (prefrontal and motor cortical areas, reticular magnocellular nucleus and substantia nigra) had no effect. When the two types of myoclonus were present in the same photosensitive animal, the epileptic myoclonus induced by photic stimulation was blocked by benzodiazepines but was not influenced by physostigmine, thus differing from the non-epileptic myoclonus. This suggests that different neurochemical mechanisms are involved in the two types of myoclonus, the non-epileptic myoclonus not being directly influenced by the GABAergic transmission.

Animals↗
PubMed1991

Reflex reticular myoclonus: relationship to some brainstem pathophysiological mechanisms.

Two patients with reflex reticular myoclonus [RRM] were tested electrophysiologically and pharmacologically. In one of the cases the underlying disease was chronic Lyme borreliosis. In the other, the RRM attacks may have been associated with procarbazine therapy applied for Hodgkin's disease. No cortical lesion could be demonstrated either clinically or electrophysiologically [EEG, averaged EEg preceeding the jerks, SSEP]. An EMG analysis of the jerks revealed the shortest latency in the muscles innervated by the accessory nerve. The latencies became longer in a more rostral muscle [masseter], as well as in a more caudal one, the muscles innervated by the facial nerve were spared. it is presumed that the complete movement pattern of the myoclonus residues in the jerk generating structure. RRM in the described cases differs from the startle by sparing the facial nerve and from the Papio papio baboon non-epileptic myoclonus by the activating effect of physostigmine. A partial therapeutic effect was achieved with a serotonine precursor, but a GABAergic therapy proved to be the most effective.

Adult↗
PubMed1990

Unexpected potentializing effect of a tacrine derivative (9-amino-7-methoxy-1,2,3,4 tetrahydroacridine) upon the non-epileptic myoclonus in baboons Papio papio.

1. The influence of 7-methoxytacrine (7-MEOTA) on the non epileptic myoclonus of the Papio papio baboon was studied in 5 animals. 2. This type of myoclonus is thought to depend on a cholinergic system dysfunction since it can be induced by atropine and blocked by physostigmine. 3. 7-MEOTA, a tacrine derivative, is believed to display a conspicuous anticholinesterase activity but, surprisingly, it here potentiated the non epileptic myoclonus occuring either spontaneously or induced by atropine. 4. In baboons not spontaneously presenting the non epileptic myoclonus, 7-MEOTA induced the myoclonus in a fashion similar to atropine; such a myoclonus was blocked by physostigmine. 5. These data indicate a possible antagonist action of tacrine on the muscarinic acetylcholine receptor. From these data, it is suggested that caution is necessary when introducing a tacrine derivative in clinical practice.

Animals↗
PubMed1990

Cholinergic system disturbance in the West syndrome.

The effects of drug on the cholinergic system (atropine and physostigmine) were evaluated in acute tests in 12 infant patients with the West syndrome (WS) and in 12 older ones who had suffered from WS at typical ages, displaying various types of epileptic symptoms. In both groups paroxysmal EEG activity was inhibited by physostigmine and enhanced by atropine. In two infants who had frequent clinical seizures, the seizures were temporarily blocked by physostigmine. These effects in WS are different from those reported in some other experimental and clinical epilepsies, where physostigmine has a proepileptic and atropine often an antiepileptic effect, thus indicating that a cholinergic system disturbance may occur in patients with WS.

Acetylcholine↗