Biomedical subjects
I Rektor
Publications and source records attributed to I Rektor.
Intracerebral recording of readiness potential induced by a complex motor task.
While exploring 11 epileptic patients with intracerebral electrodes, we recorded readiness potential (RP) preceding a complex motor task. Multilead depth electrodes were positioned stereotactically into the cortex. In three patients, it was also possible to record RP from the putamen. The movement triggering the recording was the turning of a page in an architectural book. The movement was performed under two conditions: in the first condition, without looking at the pictures on the page (typical self-pacing); and in the second condition, following the inspection of the pictures. There were no significant differences in the appearance of RP under these two conditions, neither in duration nor in amplitude. That could be explained by the fact that "self-paced" does not mean "spontaneous," but covers the internal non-conscious program related to a given task. RP were present in the contralateral primary sensorimotor cortex and the bilateral supplementary motor area (SMA), and in the anterior caudal cingulate cortex. No difference between the cortical topography of RP preceding a simple motor task and the topography of RP occurring in connection with complex movement was observed.
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.
Intracerebral event-related potentials to subthreshold target stimuli.
OBJECTIVES: Event-related potentials (ERPs) elicited by subthreshold visual stimuli were recorded directly from human frontal and temporal lobe structures to study unconscious perception. METHODS: Thirteen intractable epileptic patients undergoing depth electrode recordings prior to their surgical treatment participated in the study. An original method of modified visual oddball paradigm with supraliminal and subliminal stimuli was applied, and the averaged responses to both kinds of stimuli were subsequently compared. RESULTS: The results clearly prove that, at least from an electrophysiological viewpoint, the mechanism of unaware processing of visual stimuli in the human brain does not differ substantially from the aware processing. Finding the subliminal P3 waveform in a number of cortical structures (hippocampus and parahippocampal gyrus bilaterally, and left-sided mesiofrontal, orbitofrontal and lateral temporal cortex) indicates their involvement in unconscious processing, in spite of the fact that typical large-scale neurocognitive networks are not completely activated. The absence of activation consistently observed bilaterally in dorsolateral prefrontal cortices, in connection with right-sided cortical frontal lobe structures and right-sided lateral temporal neocortex in unconscious perception, supports the importance of these structures for the awareness of visual stimuli. The proof of the significantly faster unaware information processing represents another distinctive feature of implicit visual perception. CONCLUSIONS: Based on the presented findings and comparisons with the results of previous ERP, functional magnetic resonance imaging, positron emission tomography, and clinical neuropsychological studies, a crucial role of the large-scale neural system for conscious experience of perception is suggested, which is distributed extensively among the dorsal posterior association areas and the prefrontal cortex, with the dominant part being that of the right hemisphere.
Movement-related potentials in the basal ganglia: a SEEG readiness potential study.
OBJECTIVES: The brain potentials preceding and accompanying self-paced acral limb movements (Bereitschaftspotential/readiness potential (RP) paradigm) were studied in 12 patients. METHODS: Intracranial electrodes were implanted in order to explore intractable epilepsy. The electrodes were introduced into sites corresponding to the electroclinical characteristics of each patient's epileptic seizures. In 7 patients, several depth electrodes were implanted orthogonally, in the temporal, fronto-orbital and prefrontal cortex. In 4 patients, subdural strip electrodes were used for the exploration of the fronto-temporal convexity. There were no RPs recorded in these areas. No contacts were placed in the central region known to generate cortical RP. In all the patients, one or two diagonal electrodes passed through or touched the basal ganglia to reach the amygdala and the hippocampus. The putamen was explored in 11 patients (in 3 of them bilaterally); the caudate head was explored in two patients, and the pallidum was explored in two patients. RESULTS: RP with a clear amplitude gradient was present in all explored structures, however a phase reversal was never observed. RP was observed in the caudate in all recordings, and in the pallidum in one patient. It was recorded in the putamen in 8 out of the 11 explored patients. RPs were displayed contralaterally to the movement 9 times in 13 explorations, and ipsilaterally 4 times in 9 explorations. The shape of RP resembled the RP shape in the cortex and on the scalp. Movement accompanying potentials (MAPs) were also present in all 3 explored structures. The electrophysiological characteristics of MAP differed from RP, indicating separate generators. In the basal ganglia, RPs preceded the onset of movement by 500-1500 ms, at an average of 1080 (+/-330) ms. It seems that the RP in the basal ganglia starts slightly later than the RP in the motor cortices. That should be definitely demonstrated in patients with simultaneous recordings from cortical and subcortical structures. RP and MAP were displayed synchronously in the cortex and in the basal ganglia during most of the premovement period, as well as during the execution of movement. RP generators were reported by several authors in other deeply located structures, i.e. in the thalamus and in the brain-stem. CONCLUSIONS: Based on all these recordings, we presume that the RPs recorded on the scalp are generated simultaneously in several cortical as well as subcortical structures.
Basal ganglia involvement in sensory and cognitive processing. A depth electrode CNV study in human subjects.
OBJECTIVE: Intracranial recordings were taken from the basal ganglia (BG) in order to explore the possible role of the BG in the cognitive processing of sensory information. METHODS: Ten patients with intractable temporal lobe epilepsy, who were candidates for epilepsy surgery, underwent intracranial recordings with depth electrodes. A frontal approach was used for the insertion of diagonal depth electrodes into the amygdalo-hippocampal complex (AH complex). These electrodes passed through the BG. The putamen was explored in 8 patients; the nucleus caudatus and pallidum were explored in two patients. The contingent negative variation (CNV) paradigm was tested using auditory warning stimuli and visual imperative stimuli followed by a hand flexion. The auditory and visual middle and late latency potentials evoked by the warning and imperative stimuli were analyzed. RESULTS: (1) Auditory evoked potentials (EPs): the amplitude potential gradient was observed with latencies of (a) 150-195ms (9 patients); (b) 215-290ms (9 patients); and (c) 350-600ms (10 patients). Negative potentials, with latencies of 100 and 110ms were observed in two patients. (2) Visual EPs: (a) 160-195ms (9 patients); (b) 210-295ms (9 patients); and (c) 330-550ms (7 patients). Negative potentials with latencies between 100 and 120ms were observed in 4 patients. CNV was obtained from the BG in 8 patients; a phase reversal was observed twice. CONCLUSIONS: (1) The BG generate middle and late latency EPs in a cognitive paradigm linked to the motor task. (2) The BG generate CNV. (3) The BG could play an integrative role in the processing of sensory, cognitive, and motor information.
Effect of vagal nerve stimulation on auditory and visual event-related potentials.
Chronic unilateral vagal nerve stimulation (VNS) has been recently introduced into the therapy for intractable epileptic seizures. Its effect on cognitive functions in VNS-treated patients remains controversial. The aim of the present study was to evaluate the possible impact of therapeutic VNS on cognitive functions by means of event-related potentials analysis. Ten patients with medically intractable epilepsy, who had been implanted with VNS devices, participated in the study. Auditory and visual event-related potentials (ERPs) were repeatedly recorded, first just before the implantation of VNS devices, and then again 3-6 months after the device activation. The effect of lower intensity stimulation on the P3 component of ERPs was assessed. No significant differences were found in auditory ERPs; the latencies of P3 as well as N2/P3 peak-to-peak amplitudes were virtually identical. The same was true for mean P3 latencies of visual ERPs. However, higher visual N2/P3 peak-to-peak amplitudes were observed in the responses to targets that followed VNS, with a significant finding at the electrodes investigated. When comparing the effect of VNS on visual N2/P3 amplitude in each electrode separately, the most expressive differences were found in the frontal region. This observation supports the theory of a possible positive effect of low-intensity VNS on the cognitive functions.
Cortical activation in self-paced versus externally cued movements: a hypothesis.
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Amantadine infusion in treatment of motor fluctuations and dyskinesias in Parkinson's disease.
Efficiency and safety of amantadine sulfate (AMS) infusions were investigated in late stage complications of Parkinson's disease (PD). In an open-label study, 21 PD patients suffering from motor fluctuations and/or dyskinesias were administered AMS infusions (PK-Merz, 400 mg per day) during seven days. Oral AMS treatment followed. Significant improvement of UPDRS motor scores was observed between day 0 and day 7, remaining improved until day 21. Based on patients' diary notes, both severity and occurrence of hypokinetic "off" state significantly decreased (from 6.6 to 3.1 hours, p < 0.001, average "off" time per day) as well as dopaminergic-induced dyskinesias (from 2.5 to 1.3 hours, p < 0.05, average duration of dyskinesias per day). AMS infusions followed by oral administration appeared as a safe method for improvement of both motor fluctuations and dyskinesias in advanced PD. In advantage to simple oral therapy, AMS infusions allowed fast introduction of a profound and durable treatment effect.
Long-lasting simultaneous activation of cortical and subcortical structures in movement preparation and execution.
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Parallel information processing in motor systems: intracerebral recordings of readiness potential and CNV in human subjects.
We performed intracerebral recordings of Readiness Potential (RP) and Contingent Negative Variation (CNV) with simple repetitive distal limb movement in candidates for epilepsy surgery. In 26 patients (in Paris), depth electrodes were located in various cortical structures; in eight patients (in Brno), in the basal ganglia and the cortex. RPs were displayed in the contralateral primary motor cortex, contralateral somato-sensory cortex, and bilaterally in the SMA and the caudal part of the anterior cingulate cortices. CNVs were recorded in the same cortical regions as the RP, as well as in the ipsilateral primary motor cortex, and bilaterally in the premotor fronto-lateral, parietal superior, and middle temporal regions. In the basal ganglia, the RP was recorded in the putamen in six of seven patients, and in the head of the caudate nucleus and the pallidum in the only patient with electrodes in these recording sites. We suggest that our results are consistent with a long-lasting, simultaneous activation of cortical and subcortical structures, before and during self-paced and stimulus-triggered movements. The particular regions that are simultaneously active may be determined by the task context.
Lateralization of the P22/N30 precentral cortical component of the median nerve somatosensory evoked potentials is different in patients with a tonic or tremulous form of cervical dystonia.
Somatosensory evoked potentials (SEPs) of the median nerve were recorded in 40 patients with the tonic and tremulous form of torticollis and in 40 healthy volunteers. Polymyographic recordings of the activity of cervical muscles were performed in all patients with cervical dystonia to determine the dystonic and antagonistic muscles. Patient SEPs were recorded during abnormal head movement. SEPs in 20 healthy volunteers were recorded with the head in the middle position. SEPs in another 20 healthy volunteers were recorded with the head rotated 60 degrees to the right. The mean peak-to-peak amplitude values of the precentral P22/N30 and the postcentral N20/P25 complexes and their mean side-to-side ratios were calculated in the F3 (F4), C3' (C4'), and C3+ (C4+) electrode positions in all four groups. In patients with the tonic form of torticollis (group I), an apparent mean P22/N30 amplitude increase was found above the hemisphere contralateral to the direction of head deviation in both precentral electrode positions, F3(4) and C3(4)'. A statistically significant difference was observed between group I and other patient and control groups. In patients with the tremulous form of torticollis (group II), an increase in the mean P22/N30 amplitude was found above both hemispheres in both precentral electrode positions F3(4) and C3(4)'; a significant difference was found between group II and both control groups. Lateralization of the P22/N30 component was found only in patients with the tonic form of torticollis. The mean side-to-side ratio of the precentral P22/N30 component amplitude was significantly different when group I was compared with either group II or control groups. No significant difference between group II and either control group was found. No significant abnormalities in the postcentral N20/P25 component were found in either the dystonic patients or in healthy control subjects. These results might indicate a different pattern of cortex excitability in patients with tonic versus tremulous forms of torticollis and therefore may implicate different underlying pathophysiological mechanisms in these two forms of disorder.
The role of frontal and temporal lobes in visual discrimination task--depth ERP studies.
Visual event-related potentials were simultaneously recorded from different anatomical structures within frontal and temporal lobes in 12 epileptic patients. A simple discrimination task was performed to complement previous studies on the localization of P3 generators in the human brain. The role of multiple cortical structures in the generation of both P3a and P3b components was confirmed. Activities contemporary to a visual P3b were recorded in the hippocampus, amygdala and temporal pole. Anterior cingulate and orbitofrontal cortices-generated activities more closely related in time to the surface P3a. Earlier events related to visual discrimination took place in more lateral sites of the frontal lobe, but their contribution to the scalp P3 remains uncertain. Subsequently, mutual temporal relations among single generators were analyzed. The results suggested a processing-level hierarchy within the neural network for directed attention with a key role played by the dorsolateral prefrontal cortex.
Change in lateralization of the P22/N30 cortical component of median nerve somatosensory evoked potentials in patients with cervical dystonia after successful treatment with botulinum toxin A.
The precentral P22/N30 cortical component of the median nerve somatosensory evoked potentials (SEPs) was recorded in 16 patients (11 women and five men) suffering from cervical dystonia before and after botulinum toxin therapy. Cervical dystonia was diagnosed as idiopathic in all patients: 13 patients suffered from right-sided torticollis, and three suffered from left-sided torticollis. The amplitude of the P22/N30 component and the side-to-side ratio of amplitude values were measured. Normal values were obtained by acquiring measurements in two groups of healthy volunteers (n1 = 20 and n2 = 20). The recordings in the first control group were done with the patient's head in a normal position, whereas, in the second control group, the patient kept the head intentionally rotated 60 degrees to the right. Patients were treated with local injections of botulinum toxin A (BTX-A). The mean duration of treatment was 8.3 months, and the mean total amount of BTX injected was 295 U. The P22/N30 precentral component was repeatedly recorded in patients after head posture had been corrected to the normal plane by BTX-A treatment. The recordings showed that the amplitude of the P22/N30 precentral component recorded contralaterally to the direction of head deviation was significantly higher in patients before treatment than after treatment. Contralateral pretreatment amplitudes were also significantly higher (p < 0.01 and p < 0.05, respectively) than amplitudes in both groups of healthy volunteers. The mean side-to-side ratio of precentral P22/N30 component amplitudes was significantly higher in patients before treatment compared with after treatment and also compared with both control groups. These changes in dystonic patients probably reflect the direction of head rotation, the muscle pattern of torticollis, and the change in force of dystonic contraction after the treatment. The changes presumably could be the result of higher excitability of the precentral cortex contralateral to head rotation in patients with cervical dystonia and its change after successful BTX-A treatment.
Effect of subthreshold target stimuli on event-related potentials.
OBJECTIVES: Event-related potentials (ERPs) elicited by subthreshold visual stimuli were studied to assess the relationship between unconscious cognitive processing and the electrical activity of the brain. METHODS: A new method of modified visual oddball paradigm with supraliminal and subliminal stimuli was applied. Prior to the experiment, the individual 'subjective' threshold for the conscious discrimination between frequent and target stimuli was established for each subject. Supraliminal and subliminal, frequent and target visual stimuli were then alternatively presented in random order to each subject. RESULTS: Both the individual and the grand average ERPs revealed a typical response (P3) in the parietal region after supraliminally presented target stimuli. In subliminal conditions an analogous positive deflection in the central-parietal region was observed, which was elicited by the target stimulus, but not the frequent stimulus. Its latency could be clearly distinguished from the latency of the classical P3, the time difference between the two waveforms was approximately 100 ms. RESULTS: The results of this study revealed the impact of unconscious processing to target stimuli on the configuration of event-related responses.
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.
Lateralization of the P22/N30 component of somatosensory evoked potentials of the median nerve in patients with cervical dystonia.
Somatosensory evoked potentials (SEPs) of the median nerve were recorded in 40 patients suffering from cervical dystonia and in 40 healthy volunteers as a control. Before recording the median nerve SEPs, polymyographic recordings were performed in all patients with cervical dystonia. The activity of cervical muscles was recorded, and the leading muscle of cervical dystonia was determined. Patients were divided into two groups according to the results of polymyography. The leading muscle was sternocleidomastoid in the first group and the splenius capitis in the second group. Patient SEPs were recorded during abnormal head rotation. SEPs in 20 healthy volunteers were recorded with the head in the middle position. SEPs of another 20 healthy volunteers were recorded with the head rotated 60 degrees to the right. The mean peak-to-peak amplitude values of the precentral P22/N30 complex and the mean ratio of the P22/N30 amplitudes between both hemispheres were calculated in the F3 (F4) and C3' (C4') electrode positions in all four groups. No significant lateralization of the precentral P22/ N30 component was found in either group of healthy volunteers. In dystonic patients in whom the sternocleidomastoid was determined as the leading muscle of dystonia, a statistically significant lateralization of the P22/N30 component toward the ipsilateral side of the leading muscle was found. In the group with the splenius capitis determined as the leading muscle of dystonia, a statistically significant lateralization of the P22/N30 component toward the contralateral side of the leading muscle was found. The possibility that the precentral cortex is activated differently in cervical dystonia patients who have different muscle patterns of dystonia is discussed.
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.