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R Jech

Publications and source records attributed to R Jech.

18 recordsLinked to original sources
PubMed2005

[Time perception in functional brain imaging].

BACKGROUND: Knowledge of physiological mechanisms underlying time perception is still rather limited. The aim of our study was to search for a 'time accumulator', i.e. the part of the brain where information on the duration of time is stored. METHODS AND RESULTS: Nine healthy volunteers were given a time reproduction task during event-related fMRI. Subjects were instructed to retain the duration of the stimulus presented (presentation phase) and then to reproduce it by pressing a button (reproduction phase). Two different analyses were made: event-related (P < 0.05, FWR corrected) and parametric (BOLD signal increase/decrease during the presentation/reproduction phases correlated with the time intervals; P < 0.01, FDR corrected). When the event-related approach was employed, activation was noted bilaterally in the inferior prefrontal cortex (IPFC), supplementary motor area (SMA), precuneus and secondary visual cortex. On the right, there was activation in the dorsolateral prefrontal cortex (DLPFC), gyrus cinguli and inferior parietal lobule. On the left, the primary sensory-motor cortex was activated. While during the presentation phase the left DLPFC activity inversely correlated with the presented duration, a nearly identical area showed positive correlation in the reproduction phase. CONCLUSIONS: The event-related analysis did not allow distinguishing the process of time perception from many cognitive processes running simultaneously. In turn, the parametric analysis was based on visualizing regions, in which the signal correlated with the varying duration of the time interval provided the level of attention, decision-making and the processes of behavioral response planning and execution were constant. Moreover, the right and left DLPFC seem to play different roles in time perception. While the left one is functioning as a "time accumulator", the right one is rather involved in the recognition of previously perceived intervals.

Adult↗
PubMed2002

Rat spatial memory tasks adapted for humans: characterization in subjects with intact brain and subjects with selective medial temporal lobe thermal lesions.

In the present paper we describe five tests, 3 of which were designed to be similar to tasks used with rodents. Results obtained from control subjects, patients with selective thermo-coagulation lesions to the medial temporal lobe and results from non-human primates and rodents are discussed. The tests involve memory for spatial locations acquired by moving around in a room, memory for objects subjects interacted with, or memory for objects and their locations. Two of the spatial memory tasks were designed specifically as analogs of the Morris water task and the 8-arm radial-maze tasks used with rats. The Morris water task was modeled by hiding a sensor under the carpet of a room (Invisible Sensor Task). Subjects had to learn its location by using an array of visual cues available in the room. A path integration task was developed in order to study the non-visual acquisition of a cognitive representation of the spatial location of objects. In the non-visual spatial memory task, we blindfolded subjects and led them to a room where they had to find 3 objects and remember their locations. We designed an object location task by placing 4 objects in a room that subjects observed for later recall of their locations. A recognition task, and a novelty detection task were given subsequent to the recall task. An 8-arm radial-maze was recreated by placing stands at equal distance from each other around the room, and asking subjects to visit each stand once, from a central point. A non-spatial working memory task was designed to be the non-spatial equivalent of the radial maze. Search paths recorded on the first trial of the Invisible Sensor Task, when subjects search for the target by trial and error are reported. An analysis of the search paths revealed that patients with lesions to the right or left hippocampus or parahippocampal cortex employed the same type of search strategies as normal controls did, showing similarities and differences to the search behavior recorded in rats. Interestingly, patients with lesions that included the right parahippocampal cortex were impaired relative to patients with lesions to the right hippocampus that spared the parahippocampal cortex, when recall of the sensor was tested after a 30 min delay (Bohbot et al. 1998). No differences were obtained between control subjects and patients with selective thermal lesions to the medial temporal lobe, when tested on the radial-maze, the non-spatial analogue to the radial-maze and the path integration tasks. Differences in methodological procedures, learning strategies and lesion location could account for some of the discrepant results between humans and non-human species. Patients with lesions to the right hippocampus, irrespective of whether the right parahippocampal cortex was spared or damaged, had difficulties remembering the particular configuration and identity of objects in the novelty detection of the object location task. This supports the role of the human right hippocampus for spatial memory, in this case, involving memory for the location of elements in the room; learning known to require the hippocampus in the rat.

Adolescent↗
PubMed2001

Functional magnetic resonance imaging during deep brain stimulation: a pilot study in four patients with Parkinson's disease.

Functional magnetic resonance imaging (fMRI) was performed in patients with Parkinson's disease during deep brain stimulation of the subthalamic nucleus (three patients) and during deep brain stimulation of the ventral intermedius nucleus of the thalamus (one patient). All showed an increase in blood oxygenation level-dependent signal in the subcortical regions ipsilateral to the stimulated nucleus. This effect cannot be simply explained by a mechanism of depolarization blockade; rather, it is caused by overstimulation of the target nucleus, resulting in the suppression of its spontaneous activity. We confirm that fMRI during deep brain stimulation is a safe method with considerable potential for elucidating the functional connectivity of the stimulated nuclei.

Brain↗
PubMed2001

Efficacy and safety of a standardised 500 unit dose of Dysport (clostridium botulinum toxin type A haemaglutinin complex) in a heterogeneous cervical dystonia population: results of a prospective, multicentre, randomised, double-blind, placebo-controlled, parallel group study.

Results from a dose-ranging study in a selected group of de novo patients with rotational cervical dystonia (CD) suggest that 500 units of Dysport (Clostridium botulinum toxin type A haemaglutinin complex) is the optimal starting dose. The present study aimed to confirm the efficacy and safety profile of this dose in a population of CD patients more representative of those seen in a typical dystonia clinic. A total of 68 patients with moderate to severe CD (Tsui score > or = 9) were randomly assigned to receive placebo or Dysport 500 units. Treatment was administered according to the clinical pattern of head deviation, using a standardised injection protocol. A total of 21 patients (11 Dysport, 10 placebo) had not previously received botulinum toxin type A (BtxA) injections, and 47 patients (24 Dysport, 23 placebo) had received BtxA more than 12 weeks previously. Assessments were performed at baseline and weeks 4, 8 and 16. Patients defined as non-responders at week 4 were re-treated in an open phase with 500 units of Dysport at week 6, and were followed up at week 10. Significant between-group differences in Tsui scores were present at weeks 4 (p=0.001) and 8 (p=0.002). Similarly, there were significant between-group differences (p < 0.001) in patient and investigator assessments of response in favour of Dysport at weeks 4 and 8. Also, more Dysport (49%) than placebo (33%) patients were pain-free at week 4 (p=0.02). Overall, 30/35 (86 %) Dysport patients and 14/33 (42%) placebo patients were classified as responders at week 4. Adverse events were reported by 15/35 Dysport patients and 9/33 placebo patients. Open phase treatment produced improvements in Tsui (p < 0.001) and pain scores (p=0.011), and 23/24 patients were classified as responders. Although individual dose titration and muscle selection is desirable, this study demonstrated that a dose of 500 units of Dysport injected into clinically identified neck muscles without electromyographic guidance is safe and effective in the treatment of patients with the major clinical types of cervical dystonia.

Adolescent↗
PubMed2001

Colour discrimination impairment is not a reliable early marker of Parkinson's disease.

Disturbances of colour visual discrimination have been shown to occur frequently in Parkinson's disease (PD). To verify the potential utility of reduced colour sensitivity as a diagnostic marker of early PD, we examined 14 PD patients, mean age 55.4 years, disease duration 2.3 years, in Hoehn and Yahr stages 1, 1.5, or 2, previously untreated with levodopa. Colour discrimination was measured with the Farnsworth-Munsell 100-hue test in patients who were compared with age-matched controls. The examinations were performed under standard conditions in a room illuminated by a daylight lamp Biolux Osram 6500 K. The mean total error score (MTES) and partial error scores (green-yellow and red-green axis) were calculated for every person examined. No significant differences were found between PD patients (MTES 49.1 +/- SD 37) and controls (MTES 37.9 +/- SD 25). Similarly, the mean partial scores were not significantly elevated in PD patients. We found an elevation of error scores exceeding the upper limit of normality (control mean + 2SD) only in three patients. We conclude that colour visual discrimination is not consistently impaired in early stages of PD and does not appear as a reliable early marker of Parkinson's disease.

Adult↗
PubMed2001

Investigation of non-linear properties of multichannel EEG in the early stages of Parkinson's disease.

OBJECTIVES: Modifications of brain activity in the early stages of Parkinson's disease (PD) are difficult to detect using electroencephalography (EEG) signals and are often biased by L-DOPA treatment. We compare here the performances of both linear and non-linear methods in differentiating EEG of L-DOPA naive PD patients from that of control subjects. METHODS: Resting multichannel EEG (20 electrodes, 30 s epochs) of 9 patients with PD in Hoehn and Yahr stages 1-2 (4 women, 5 men, mean age 54.3 years, range 48-63 years) were compared with those of 9 control subjects (7 women, two men, mean age 51.3 years, range 43-61 years). The following measurements were computed: theta-, alpha- and beta-band relative powers constituted the linear indices; localized entropy, slope asymmetry and number of non-linear EEG segments constituted the non-linear indices. RESULTS: In the case of linear quantification, only a decrease in the beta-band was observed for patients. Significant non-linear structures were observed in our EEG data. Non-linear quantifiers demonstrate an increase in entropy and in the number of non-linear EEG segments for the patients. CONCLUSIONS: Changes in EEG dynamics observed here in L-DOPA naive PD patients may represent early signs of cortical dysfunction produced by subcortical dopamine depletion.

Algorithms↗
PubMed2001

Electromagnetic field of mobile phones affects visual event related potential in patients with narcolepsy.

The effects of the mobile phone (MP) electromagnetic fields on electroencephalography (EEG) and event-related potentials (ERP) were examined. With regard to the reported effects of MP on sleep, 22 patients with narcolepsy-cataplexy were exposed or sham exposed for 45 min to the MP (900 MHz, specific absorption rate 0.06 W/kg) placed close to the right ear in a double blind study. There were no changes of the EEG recorded after the MP exposure. A subgroup of 17 patients was studied on visual ERP recorded during the MP exposure. Using an adapted "odd-ball" paradigm, each patient was instructed to strike a key whenever rare target stimuli were presented. There were three variants of target stimuli (horizontal stripes in (i) left, (ii) right hemifields or (iii) whole field of the screen). The exposure enhanced the positivity of the ERP endogenous complex solely in response to target stimuli in the right hemifield of the screen (P < 0.01). The reaction time was shortened by 20 ms in response to all target stimuli (P < 0.05). In conclusion, the electromagnetic field of MP may suppress the excessive sleepiness and improve performance while solving a monotonous cognitive task requiring sustained attention and vigilance.

Brain Mapping↗
PubMed2000

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.

Administration, Oral↗
PubMed1999

Huntington's disease: the relationship between clinical signs, CAG repeats and the atrophy of the caudate nucleus in CT scans.

We compared clinical data from 45 patients with Huntington's Disease (HD) with CAG triplet repeats and the planimetric measurement of the caudate nucleus head area (CNHA) in CT scans. The mean age of patients was 50.4 yrs (SD +/- 10.2), the mean duration of HD 7.4 yrs (4.6), the mean age at the onset of HD 43.1 yrs (11.1). HD started with motor symptoms in 28 patients, with psychiatric symptoms in 14 patients, the history was unknown in 3 patients. The paternal transmission was observed in 29 patients, the maternal one in 12 patients, unknown in 4 patients. The mean number of CAG repeats was 46.6 (6.1). The mean CNHA was 0.4 cm2 (0.1). We found statistically significant reversed correlation between CAG repeats and the age at the onset of HD (p < 0.0001, r -0.6). The earlier onset of HD in patients with the paternal transmission compared to the maternal one was found statistically significant (p < 0.05). This phenomenon was not related to the larger number of CAG triplets in patients with the paternal transmission. No differences either of the age at the onset of HD or numbers of CAG repeats were found between subgroups of HD patients starting with motor or psychiatric symptoms. We also observed the significant reversed correlation between the duration of HD and CNHA measurement (p < 0.001, r -0.5). Even in the earliest stage of HD patients showed the marked atrophy of CNHA.

Atrophy↗
PubMed1998

Dose-dependent reduction of cerebral blood flow during rapid-rate transcranial magnetic stimulation of the human sensorimotor cortex.

Rapid-rate transcranial magnetic stimulation (rTMS) was used to stimulate the primary sensorimotor cortex in six healthy volunteers while regional changes in cerebral blood flow (CBF) were simultaneously measured by means of positron emission tomography. A figure-eight TMS coil (Cadwell Corticoil) was positioned, using frameless stereotaxy, over the probabilistic location of the left primary sensorimotor cortex, and a series of brief 10-Hz trains of TMS was delivered at subthreshold intensity during each of six 60-s scans. The scans differed in the number of trains delivered, namely 5, 10, 15, 20, 25, and 30 trains/scan, respectively. In the left primary sensorimotor cortex, CBF covaried significantly and negatively with the number of stimulus trains. These CBF decreases may reflect TMS-induced activation of local inhibitory mechanisms known to play a role in TMS-related phenomena, such as the electromyographic silent period.

Adult↗
PubMed1998

[Residual findings in retrobulbar neuritis during demyelinization].

Retrobulbar neuritis is a common clinical manifestation of multiple sclerosis. We evaluated and compared the results of visual field and fundus examinations, visual evoked response and nuclear magnetic resonance of the brain in 37 patients with the diagnosis of multiple sclerosis and retrobulbar neuritis. Diffuse, peripheral scotomas seemed to be the most often found scotomas on perimetry in these patients. In contrary, central scotomas formed just a little part of the visual field defects. Each threshold increasing of 0.10 log. units on perimetry was followed by increased latencies of 2.5 ms. Each other central scotoma on perimetry decreased the visual acuity of the patient for 1.6 lines on the Snellen chart. The central visual field examination without periphery in the patients with multiple sclerosis and retrobulbar neuritis seems to give false negative results.

Evoked Potentials, Visual↗
PubMed1997

Transcranial magnetic stimulation during positron emission tomography: a new method for studying connectivity of the human cerebral cortex.

We describe a new technique permitting the mapping of neural connections in the living human brain. The method combines two well established tools of brain research: transcranial magnetic stimulation (TMS) and positron emission tomography (PET). We use TMS to stimulate directly a selected cortical area while simultaneously measuring changes in brain activity, indexed by cerebral blood flow (CBF), with PET. The exact location of the stimulation site is achieved by means of frameless stereotaxy. In the first study using this technique, we found significant positive correlations between CBF and the number of TMS pulse trains at the stimulation site, namely the left frontal eye field (FEF) and, most importantly, in the visual cortex of the superior parietal and medial parieto-occipital regions. The pattern of these distal effects was consistent with the known anatomic connectivity of the monkey FEF. We suggest that the combined TMS/PET technique offers an objective tool for assessing the state of functional connectivity without requiring the subject to engage in any specific behavior.

Adult↗
PubMed1995

[Cognitive and visual functions in a sample of the aged population: analysis of evoked potentials].

BACKGROUND: There are significant changes of perception and cognition during aging. Goal of this study was to investigate these functions by means of evoked potentials, and to obtain normative data in older people for comparisons with cognitive disorders in the elderly. METHODS AND RESULTS: Twenty three healthy subjects (14 women and 9 men), aged 59 to 82 years (average 68 years), were examined for auditory event-related potentials (AERP) and somatosensory event-related potentials (SERP) using pattern reversal stimulation with large squares (1 degree 10') and small vertical bars (10'). The exogenous components N1 and P2 in both AERP and SERP exhibited significantly longer latencies and higher amplitude in response to target stimuli compared to an indifferent stimulus, a fact attributable to selective attention mechanisms (AERP: N1 delay 8 ms, p < 0.001; P2 delay 11 ms, p < 0.05; increase in amplitude N1/P2 2.2 microV, p < 0.01; SERP: N1 delay 8 ms, p < 0.05; P2 17 ms, p < 0.01; increase in amplitude N1/P2 8 microV, p < 0.001). As for the endogenous components N2 and P3, there were no latency differences between the two modalities (N2: p < 0.4; P3a: p < 02; P3b: p < 0.2). Significant correlations were found between P3 latencies AERP and SERP (r = 0.56, p < 0.01). N1, P2, N2 and P3b latencies of the AERP and P3a, P3b of the SERP correlated significantly with age. The average annual increase was 3.9 ms for P3b AERP (p < 0.01) and 3.2 ms for P3b SERP (p < 0.01). These values are markedly higher than the data reported by other authors for groups of lower average age. In the VEP, an age-related increase was seen in the N70 latency (0.6 ms/year, p < 0.05) and in the P100 latency (0.8 ms/year, p < 0.05) in response to the smaller bars stimulus and in the N140 latency (1.2 ms/year, p < 0.01) in response to the larger squares stimulus. CONCLUSIONS: We confirm an age-related increase in latencies of the AERP and SERP, which is markedly higher than the increase described in other studies with younger subjects. This finding is important to keep in mind in order to avoid false positives of cognitive deficits in older patients. The latencies of later components, compared with earlier components of the VEP, AERP and SERP are more dependent on age. This may suggest that there are universal aging influences on the neuronal conduction velocity. The latencies of the P3b SERP and N2 AERP were found to be correlated with the N140 VEP with the smaller bars stimulus. These findings suggest that parameters of some waves may be modulated by certain other factors than age.

Aged↗
PubMed1994

Apomorphine induced cognitive changes in Parkinson's disease.

Auditory event related potentials (ERPs) and visual evoked potentials (VEPs) were recorded from eight patients with Parkinson's disease, before and after a single dose of apomorphine. To assess the treatment effects, the patients' motor state, Benton visual retention test (BVRT), and digit span tests were also examined. After apomorphine, although motor performance improved, the ERP latencies were delayed and the N2-P3 ERP amplitude was significantly diminished by comparison with pretreatment values. These data suggest that apomorphine induces, besides its motor effects in patients with Parkinson's disease, a slowing down of cognitive processing. Preferential stimulation of dopamine autoreceptors in mesocortical and mesolimbic systems may represent a neural mechanism for these effects. Also, the posttreatment BVRT rotation errors significantly increased, suggesting an apomorphine induced impairment of visuospatial perception.

Apomorphine↗
PubMedDate not supplied

Apomorphine does not influence olfactory thresholds in Parkinson's disease.

In order to verify the presumed dopaminergic basis of olfactory dysfunction in Parkinson's disease (PD), we studied olfactory functions in 12 PD patients (mean age 60.1 yrs, mean duration of PD 9.0 yrs, mean Hoehn and Yahr score 2.8) before and after apomorphine (APO) administration. Amylacetate (banana smell) in 12 sequential dilutions (in 50% steps) was used for the examination of olfactory thresholds. The testing showed no significant differences in any olfactory parameters before and after APO. Furthermore, when analysing the subgroup of 7 hyposmic PD patients, we also found no significant differences before and after APO. We therefore believe that olfactory dysfunction in PD is not dependent on dopamine deficiency.

Aged↗