Biomedical subjects

J Kremlácek

Publications and source records attributed to J Kremlácek.

7 recordsLinked to original sources

PubMed2001

Electrophysiological testing of dyslexia.

We enlarged our previous study (Kubová Z. et al. Physiol Res 1995;44:87-89) giving an evidence about magnocellular pathway involvement (delayed motion-onset visual evoked potentials (M-VEPs)) in 70% of dyslexic children. In the new group presented here, only 48% of 25 dyslexics displayed prolonged latencies of cortical responses to motion stimuli. However, there was no correlation of this defect with the used quantification of the reading skills (reading quotients). No significant EEG frequency spectrum changes were found. 10 subjects from the former group, who were re-examined 4 years after the previous study at the mean age of 14 years, exhibited significant shortening of the M-VEP latencies compared to the original values. Also in control subjects a distinct improvement in magnocellular pathway function was proved (in M-VEP re-examination after 4 years). These results document rather late maturation of the magnocellular pathway, which is evident mainly in dyslexic children. In both groups of dyslexics an effect of colour in moving stimuli was also tested to verify the reported effect of light wavelengths onto the magnocellular pathway function. However, no latency differences among grey, green, pink, yellow and blue stimuli were observed.

Adolescent↗

PubMed1999

Simple and powerful visual stimulus generator.

We describe a cheap, simple, portable and efficient approach to visual stimulation for neurophysiology which does not need any special hardware equipment. The method based on an animation technique uses the FLI autodesk animator format. This form of the animation is replayed by a special program ('player') providing synchronisation pulses toward recording system via parallel port. The 'player is running on an IBM compatible personal computer under MS-DOS operation system and stimulus is displayed on a VGA computer monitor. Various stimuli created with this technique for visual evoked potentials (VEPs) are presented.

Color↗

PubMed1999

Global brain dynamics of transient visual evoked potentials.

The independent component analysis was applied to multichannel transient visual evoked potentials elicited by a high contrast pattern-reversal and motion-onset (motion velocity of 7 and 23 deg/s). Three overlapping independent components with different topographical distribution over the scalp were described. The first component displayed similar timing in response to all three stimuli (40-200 ms) but was a different in shape and scalp projection. This activation component is considered to reflect the stimulus properties. The second component (100-227 ms), related to negativity at about 160 ms, can be referred to visual processing of motion. The last component, attributed to positivity at 230 ms dominates in the fronto-central area and might represent a cognitive process.

Brain↗

PubMed1998

[Oscillatory potentials in human electroretinography during adaptation to light and dark].

In 20 healthy subjects no changes of the peak-latencies of the four wavelets of electroretinographic oscillatory potentials (OP) was found in the course of dark- and light-adaptation. On the other hand, their peak-to-peak amplitudes and dominant frequencies diminish significantly with rising levels of light adaptation. No single OP wavelet was affected by these changes selectively. The OP peak latencies are well suited for clinical diagnostic testing owing to their stability and low variability. On the other hand, because of the great interindividual variability of the peak-to-peak amplitude values of the OP a better clinical tool appears to be a sum of their amplitudes.

Adaptation, Ocular↗

PubMed1998

Cognitive evoked potentials related to visual perception of motion in human subjects.

A method was tested for simultaneous recordings of evoked potentials from the secondary visual cortex (mediotemporal) and from the brain cognitive areas (fronto-central). Visual moving stimulations with cognitive tasks seem to be suitable for combined examination of visual motion perception and cognitive processes based on the magnocellular system activity. This arrangement enhances the analysis of visual information processing and evaluation of central nervous system functions.

Adult↗

PubMed1996

Advanced electrophysiological diagnostics of hepatic and portosystemic encephalopathy.

In 28 patients with liver cirrhosis, pre- and post-TIPS (transjugular intrahepatic porta-caval shunt), pattern-reversal visual evoked potentials (PREPs) and motion-onset visual evoked potentials (M-VEPs) examinations, EEG spectral analysis and Number Connection Test were performed. The M-VEPs (representing an activity of the magnocellular system of the visual pathway and reactions of the mediotemporal associate visual area) displayed the highest sensitivity (latencies delay) for detection of subclinical hepatic encephalopathy. The PREPs (originating in the primary visual cortex -area striata) were not significantly changed in comparison with a group of age matched controls. The EEG frequency spectrum exhibited significant slowing of the dominant frequency which was more pronounced in the post-TIPS examination. Combined analysis of the M-VEPs latency and EEG dominant frequency seem to be a recommendable method for early detection and objective classification of subclinical hepatic or portosystemic encephalopathy.

Adolescent↗

PubMed1996

Video-signal synchronizes registration of visual evoked responses.

Autodesk Animator software offers the suitable technique for visual stimulation in the registration of visual evoked responses (VERs). However, it is not possible to generate pulses that are synchronous with the animated sequences on any output port of the computer. These pulses are necessary for the synchronization of the computer that makes the registration of the VERs. The principle of the circuit is presented that is able to provide the synchronization of the analyzer with the stimulation computer using Autodesk Animator software.

Computer Graphics↗