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

The spinal and subcortical median nerve SEPs were recorded in 65 patients with lesions of the cervical cord, medulla oblongata, pons and in brain death. A recording technique including cephalic, non-cephalic and anterior neck referenced leads was used. The location of the lesions corresponded to different types of SEP alterations: Cervical extramedullary lesions compressing the spinal cord corresponded to a prolonged P9-P14 interpeak latency. Cervical intramedullary lesions corresponded to the loss of N13, normally generated in the spinal interneurons. Vascular lesions of the medulla oblongata (Wallenberg's syndrome) showed normal SEPs. Space occupying medulla oblongata lesions corresponded to reduction in amplitude or loss of P14. Pontine lesions showed normal spinal and subcortical SEPs. In brain death P14 showed a graduate decrease in amplitude or alternatively vanished abruptly. The spinal and subcortical SEPs provide a good tool for testing the function of the lemniscal pathways and the spinal interneurons.

The characteristics of a newly developed computerized EMG-analysis system are lined out. The analysis steps include segmentation and parametrization of digitized EMG segments followed by automatic classification of single potentials into motor units. Comparison of parameters is used rather than a template matching algorithm for classification. For each motor unit a set of parameters can be computed in addition to duration and amplitude. Normative data are given for four muscles. 60 normal volunteers (50% female, 50% below age 50) were recorded from for each muscle. The recording conditions required to move the electrode until a motor unit could be recorded with its individual maximum. Furthermore, it was attempted to attain the maximum discharge rate of a particular motor unit. A highly significant correlation of the amplitude of the motor unit potentials with age was found for all four muscles. For the duration of the potentials a correlation with age was found only for the M. ext. digitorum brevis. Significant sex differences were found for nearly all parameters and all muscles. Pairwise comparisons of the muscles revealed significant differences of all muscles. The analysis showed, that a muscle can be regarded pathological if more than two of a total of seven recorded motor units show pathological parameters.

In multiple sclerosis and stroke the muscle responses to transcranial magnetic stimulation are frequently delayed, reduced in amplitude or absent. To investigate the underlying pathophysiological mechanisms, responses of single motor units to transcranial magnetic stimulation were analysed using peri-stimulus time histograms. The following response patterns were detected: 1. prolongation of latency and duration of the primary peak which occurs in healthy controls 17 to 30 ms after the stimulus and has a duration of 2 to 8 ms, 2. lack of an excitatory response, 3. prolongation of the interval between sub-peaks within the primary peak and 4. multimodal responses. Possible mechanisms for these changes are: reduction and dispersion of conduction velocities in corticospinal axons associated with impaired summation of excitatory post-synaptic potentials at the spinal motoneurone, frequency-dependent or complete conduction block in corticospinal neurones and compensatory activation of other descending motor pathways.

There is a hotly debated question as to whether the meaning of a word can be assessed in the lexicon before conscious identification of this word is possible. Some authors have reported shorter lexical decision times for words, which had been preceded by primes, that had been masked below threshold. This effect was taken as evidence for an automatic activation of the lexicon by the unidentified prime. We report an ERP study using the N400 potential and lexical decision time as an index for associative activation of the lexicon. In a condition with supra-threshold primes the typical acceleration of lexical decision time and reduction of N400 amplitude was found for semantically related target words. In the sub-threshold condition, however, no evidence was found for priming in RT and ERP data. This pilot data, as well as previous RT studies, question the findings gathered on sub-threshold priming. No dissociation between RT and ERP parameters was found in the present study.

In 15 schizophrenic patients event-related potentials were recorded during an auditory two-tone-discrimination task in the acute phase and after remission. The control group consisted of ten healthy subjects of the same age. The schizophrenic patients showed reduced amplitudes of N1, P2 and P3 and prolonged latencies of N2 and P3 independent of neuroleptic medication and clinical state. We found no differences in the topographical distribution of P3 between schizophrenic patients and controls. The changes of the event-related potentials in the schizophrenic patients may be interpreted as electrophysiological correlates of basic disturbances in information processing in schizophrenia.

A patient with severe organophosphate intoxication received Neostigmine 1 mg IV during the intermediate syndrome. This dose resulted clinically and neurophysiologically in a marked deterioration of neuro-muscular transmission. This effect of neostigmine on the neuromuscular block during the intermediate syndrome (deterioration) differs from its effect on a similar pattern (improvement), which is seen in the delayed neuropathy following organophosphate exposure. The administration of therapeutic doses of cholinesterase inhibitors in patients with a reduced safety margin due to inhibition of endplate acetylcholinesterase may be dangerous.

Magnetic stimulation of the motor cortex and spinal nerve roots was investigated in a group of 45 normal subjects using double coils. Figure of eight coils allows for an isolated excitation of the motor cortex of one hemisphere which cannot be achieved with circular coils. To evoke compound responses in hand muscles the optimal position of the figure of eight coil is with its centre about 5 cm lateral of the vertex and contralateral to the target muscle. The coil handle is in frontal position (occipito-frontal direction of the stimulation current in the coil; physical current definition is used resembling the electron flow from - to +). For the excitation to leg muscles the double coil centre is over the vertex with the handle contralateral to the target muscle (frontal current direction). Cervical roots can easily be stimulated using figure of eight coils with the handle contralateral to the target muscle and the coil centre over the root segment.

For the analysis of saccadic eye movements two values were to be computed: the latency of the reaction and the maximum velocity reached by the eye finding the new visual point. The waveform is disturbed especially by noise. With this method, the impurity level can be reduced nearly completely without destroying the curve shape of the saccade.

The surface-EMG becomes more and more important because computer assisted analysing systems can be applied. The occurrence of artefacts makes it very difficult to compare several recorded EMG channels with each other. In this study a frequency related quantification of movement artefacts and ECG-related influences on the EMG is carried out to select a suitable lower cut-off frequency for surface-EMG investigations. In 764 monopolar surface-EMG-recordings of the neck and back muscles the solely artefact-caused part of EMG-segments was analysed and quantified by means of modelling methods.