EEG-EMG Zeitschrift fur Elektroenzephalographie, Elektromyographie und verwandte Gebiete最新文献

By means of transcranial magnetic stimulation bilateral compound muscle action potentials of long latency and ipsilateral potentials of short latency can be obtained in muscles supplied by cranial nerves. In this study motor evoked potentials were recorded from the mentalis muscle of 14 patients with traumatic brain lesions. These results were compared with clinical and radiological as well as other neurophysiological examinations. In spite of the absence of paralysis in muscles supplied by the facial nerve, 9 patients showed pathological long-latency responses, which correlated with the localisation of the paralysis of the limbs. In contrast to this, the degree of pathological latencies of motor evoked potentials did not correspond with the degree of paresis in different patients. A prediction concerning the clinical outcome could not be made by the results of motor evoked potentials. The clinical data showed a poor correlation with the structural brain lesions seen in the CT-scan and the results of EEG, BAEP and orbicularis oculi reflex examination. In conclusion, transcranial magnetic stimulation of cranial nerves proved to be a sensitive method for the evaluation of degree and localization of motor deficits following traumatic brain lesion and seems to be superior to the other examinations compared.

From the right m. biceps brachii and the right m. rectus femoris of 28 healthy women aged 19 to 30 years and 16 possible and obligate Duchenne-carriers aged 26 to 40 years we recorded 20 motor unit action potentials each. A satellite potential was defined as electrical activity following or preceding the main component and separated from it by an isoelectrical interval of at least 1, 2 or 3 ms. The most appropriate of these 3 satellite potential definitions is the one that proceeds from a 1 ms minimum interval, because it allows the detection of more satellite potentials than the two others. Applying this definition (minimum interval between the main component and the satellite potential 1 ms) to our controls data we computed a mean interval duration of 5 (m. biceps brachii) respectively 3.4 ms (m. rectus femoris), a mean satellite potential duration of 4.4 (m. biceps brachii) respectively 3.7 ms (m. rectus femoris) and a mean satellite rate of either 3.9 (m. biceps brachii) or 1.6% (m. rectus femoris). We observed up to 3 motor unit action potentials with a satellite potential and up to 1 polyphasic motor unit action potential with a satellite potential per 20 motor unit action potentials. There was little difference between the controls and the Duchenne-carriers satellite parameter means. Only the m. rectus femoris satellite potential duration was increased in Duchenne-carriers.(ABSTRACT TRUNCATED AT 250 WORDS)

In 20 healthy volunteers, a bilateral masseter silent period (Mass SP) was constantly evoked by stimulating the mental nerve (latency: x = 13.95 +/- 4.3 ms) and cervical plexus (latency: x = 20.2 +/- 3.7 ms). This was also the case with median nerve stimulation (latency: x = 54.4 +/- 13.1 ms) in 19 of the 20 subjects. Utilizing magnetic stimulation of the lumbal roots, the Mass SP was elicited in 3 of 10 subjects and showed marked habituation. No Mass SP was observed with stimulation of the long nerves of the lower limbs. The central loop of the reflex represents a stable connection between the spinal cord cervical region and the trigeminal motor nuclei. The Mass SP may be abolished in circumscribed brainstem lesions and thus may serve for localizing lower brainstem involvement.

The discharge frequency of primary muscle spindle afferents was recorded out of the tibial anterior muscle of the cat under a ramp-and-hold stretch. The rate of the ramp stretch was increased stepwise from 1 to 100 mm/s. Its amplitude was kept constant and was 7 mm. Whereas the initial length of the host muscle was enhanced in steps of 3 mm to reach a maximal augmentation of the muscle length of 12 mm. The decrease of the discharge frequency from the dynamic peak (the discharge frequency at the end of the dynamic phase of stretch) onto the static value (the discharge frequency 3 s after the end of the dynamic phase of stretch) comprises the receptor adaptation which had been analysed. Two components could be defined in the course of the adaptation, the fast and the slow decay (fig. 2). The border between the two components is the discharge frequency of static maximum. The static maximum is the first discharge frequency at the beginning of static phase of stretch. The static maximum increases with the initial length (fig. 3) and is independent of the stretch rate. The fast decay, the decrease of the discharge frequency from the dynamic peak onto the static maximum, lasts for only some 10 ms. The degree of the fast decay turns out to the dependent on the rate of ramp stretch by a power function whose exponent has in the mean a value of 0.5 (fig. 4).(ABSTRACT TRUNCATED AT 250 WORDS)

A number of 57 normal subjects was investigated using transcranial magnetic stimulation of the motor cortex and transcutaneous magnetic stimulation of the spinal nerve root in order to obtain normative data for central and peripheral motor latencies. Under standardized conditions (site of stimulation, stimulus intensity, degree of voluntary tonic background activation) muscle compound action potentials were recorded from different muscles of the upper and lower extremity: M. biceps brachii, M. extensor carpi radialis, M. interosseus dorsalis I, M. vastus medialis, M. tibialis anterior, and M. extensor digitorum brevis. Onset latency, peak to peak amplitude (% of maximal M-wave), duration and configuration of the muscle compound action potentials were evaluated (Fig. 1 and Tab. 1-6). Central and peripheral motor latencies were determined by stimulation over two different points of the neuraxis (cortex/cervical or lumbar nerve roots). Central motor latencies were calculated by subtracting the peripheral conduction time from the onset latency of the fastest cortically evoked muscle response. Not only the peripheral but also the central motor latencies were found to increase in higher ages (Tab. 6). This has to be taken into account when elderly patients are examined for diagnosis of disorders of the descending motor tracts.

Strategies for the evaluation of EP and ERP maps are discussed. Spatial interpolation is presented. The reference does not change the landscape but the wave shapes, the baselines change the landscape but not the wave shapes. Electric strength of the map is assessed using Global Field Power, whereby non-ambivalent component latencies can be established. Map landscapes are compared using Global Dissimilarity. Maps are classified using extracted landscape descriptors: locations of minimal and maximal potential, locations of the centroids of the positive and negative map area, reduction to a three-dimensional model dipole source. Adaptive segmentation into echoes of stable landscape (functional microstates) based on landscape descriptors is discussed. Diagnostic and physiological-functional interpretation of the results ought to be distinguished.

Electrically evoked blink reflexes were studied in 24 healthy subjects in different conditions of elicitation. In one condition the electrical shock was delivered by the experimenter; in a second condition the subject triggered the stimulus himself by manually operating a switch. The different conditions were investigated relaxed or clenching the fist with left hand. Moreover, in 3 subjects the stimulus was given in various delays after the occurrence of the EMG activity of the forearm flexor muscles due to a ballistic wrist flexion. The latencies and peak to peak amplitudes of the ipsi- and contralateral early and late responses were analysed. Voluntary sustained contraction of the left hand (fist) caused no significant modification of the blink reflex. Self-triggering of the stimulus had a facilitating influence on the early components (R1, R1') and an inhibitory effect on the late components (R2, R2'). In EMG triggered self-stimulation the R2-inhibition could already be seen at a delay of 0 ms. From a delay of 10 ms on the suppression was still more pronounced and recovered over the following 500-1000 ms. We conclude, that the reflex alterations are not due to the outflow of the motor cortex, but to the conditioning effect of self-elicitation. The influence on the excitability of the blink reflex resemble that described in the literature for the conditioning effect of an acoustic or visual stimulus. We suggest involvement of the same interneuron network on the condition of self-eliciting.

The spatial contrast transfer function of the visual system of the pigeon was determined by recording from the optic tectum evoked potentials or extracellular unit activity in response to a pattern stimulus contrast transfer function, determined as a "response function", describes the relationship between the contrast in the pattern--which consisted of vertically oriented stripes of sinusoidally varying luminance--and the amplitude of the response at various spatial frequencies (c/deg). The transfer function yields an estimate of the high frequency limit, which in turn is a measure of visual resolving power. Action potentials were recorded extracellularly using glass microelectrodes; for evoked potentials, stainless steel electrodes were used. Recordings were made from the stratum griseum et fibrosum superficiale of the optic tectum. The highest spatial frequency detectable in a visual system is limited by various factors, including the diffraction of light at the pupil and the anatomical spacing of the photoreceptors. The pupil factor can be controlled in experiments in a suitable way. In this paper, the electrophysiologically determined high-frequency limit was compared with the theoretical resolution limit imposed by the photoreceptor mosaic. The experimental results show that the visual system of the pigeon has a high-frequency limit at a spatial frequency of 15.5 c/deg, corresponding to a visual acuity of 1.9 min of arc. The attempt to relate visual acuity in the pigeon to the anatomical spacing of the photoreceptors shows that the Nyquist frequency of the photoreceptor mosaic, the theoretical upper bound of the spatial resolution, agrees with measurement.

The event-related potentials after a competitive visual stimulation are presented. The stimulation with target stimuli results in two pronounced positive potentials in the grand-average, the P2 and the P3 component of the ERP, and a long-lasting positivity following the P3 wave. Similar but smaller potential components are elicited by non-target stimuli. Some examples of individual ERP demonstrate the high degree of inter-individual variability, as in the positive components as in the restoration of the poststimulus baseline. Some aspects of a possibly fundamental difference between visually and acoustically elicited P300 waves are demonstrated.

Impairment or loss of vision due to optic nerve injury occurs in about 10% of patients with cranio-facial fractures. The assessment of optic nerve function is important for decisions regarding optic nerve decompression. But examination of vision and pupillary reflexes may be difficult, especially in uncooperative patients with reduced consciousness and primary disturbances of pupillary functions. In these cases, optic nerve function can be monitored by means of flash-evoked visual potentials elicited by use of a LED-goggle stimulator. VEPs were recorded in ten patients with head injuries comprising cranio-facial fractures and cerebral concussion with prolonged alteration of consciousness. Recordings were obtained in the acute phase upon admission. Visual acuity and visual fields were examined after regaining consciousness and the clinical findings correlated to the initial VEPs. Upon clinical examinations, four patients with initially normal VEPs had normal vision on both eyes. One patient initially revealed unilateral reduction of the VEP-amplitude of more than 50% and clinically showed a concentric visual field defect. Three patients with unilateral loss of potentials were amaurotic on this side. Perception of light was preserved in one patient in whom VEPs were absent. One patient with bilateral loss of potentials was blind when consciousness was regained. In general, pupillary light reflexes tested at admission corresponded to the VEP-findings. In two cases, however, pupillary reactivity was lost, but VEPs were still present. These patients had normal vision, but exhibited a lesion of the efferent pathways of pupillary reflexes. In two other patients, examination of pupillary reactivity could not be performed due to extreme edema of the eyelids.(ABSTRACT TRUNCATED AT 250 WORDS)