Electroencephalography and Clinical Neurophysiology/Evoked Potentials Section最新文献

The topography of the middle-latency N110 after radial nerve stimulation suggested a generator in SII. To support this hypothesis, we have tried to identify a homologous component in the tibial nerve SEP (somatosensory evoked potential). Evoked potentials following tibial nerve stimulation (motor+sensory threshold) were recorded with 29 electrodes (bandpass 0.5–500 Hz, sampling rate 1000 Hz). For comparison, the median nerve was stimulated at the wrist. Components were identified as peaks in the global field power (GFP). Map series were generated around GFP peaks and amplitudes were measured from electrodes near map maxima. With median nerve stimulation, we recorded a negativity with a maximum in temporal electrode positions and 106±12 ms peak latency (mean±SD), comparable to the N110 following radial nerve stimulation. After tibial nerve stimulation the latency of a component with the same topography was 131±11 ms (N130). Both N110 and N130 were present ipsi- as well as contralaterally. Amplitudes were significantly higher on the contralateral than the ipsilateral scalp for both median (3.1±2.4 μV vs. 1.7±1.6 μV) and tibial nerve (1.9±1.2 μV vs. 0.6+1 μV). The topography of the N130 can be explained by a generator in the vicinity of SII. The latency difference between median and tibial nerve stimulation is related to the longer conduction distance (cf. N20 and P40). The smaller ipsilateral N130 is consistent with the bilateral body representation in SII.

This study aimed at assessing the effects of midazolam (MDZ) sedation on auditory brainstem (BAEP) and middle latency (MLAEP) evoked potentials in intensive care conditions. Ten ventilated comatose patients were receiving an intravenous MDZ bolus dose (0.2 mg/kg) followed by a 2 h continuous infusion (0.1 mg/kg/h). MLAEPs and BAEPs elicited by clicks (90 dB HL+masking) were simultaneously and continuously monitored during the first 6 h and for 30 min the next morning. We found no effect of MDZ sedation on BAEPs. Only MLAEP components were modified. However, none of the patients presented any total abolition of the MLAEPs. Bolus injection led to very early alteration of cortical responses, beginning after 5 min and lasting almost 1 h (maximum Pa latency increase, 3.1 ms; maximum Pa-Nb amplitude decrease, 46%). During continuous infusion, MLAEPs remained slightly, although significantly, altered (Pa latency, +1.3 ms; Pa-Nb amplitude, 27%). The Nb wave seemed to be modified earlier and to return to normality later than the Pa wave. These findings incite a careful interpretation of MLAEP tracings acquired during the first hour following MDZ bolus injection. If possible, MDZ should be administered as continuous infusion for reliable interpretation of evoked potential changes in intensive care unit, or during surgery.

Among single sweep records of event-related potentials (ERPs), the peak latency of P300, which is one of the most prominent positive peaks in the ERP obtained in the oddball paradigm, may vary depending on the conditions of the subject. In the analysis of characteristics of the variability in the peak latency, it is important to know to what extent the variability of the measured peak latency (measured variability) is actually caused by physiological factors (physiological variability). In our previous study, a method was developed for judging whether the physiological variability really exists or not, and if it does exist, the developed method extracts the physiological variability from the measured variability based on a limited number of single sweep records. In the present study, based on the P300 waveforms which were detected by blinded visual inspection of the ERP data obtained by an auditory oddball paradigm from 12 healthy adults, the physiological variability was shown to exist with a confidence level of 95% for all subjects. Furthermore, its interval estimate was calculated by subtracting noise variability from the measured variability with a confidence level of 80%, and it was found to range from 17 to 57 ms for all subjects.

In this study the H-reflex and M-wave were evoked in a group of ALS patients, to correlate the findings with the clinical state, and to investigate whether a statistical approach for assessing H-reflex changes in the presence of a constant M-wave could be reproducible and helpful in monitoring the course of amyotrophic lateral sclerosis (ALS). The H-reflex and M-wave from the soleus muscle were evoked at different stimulus strengths in 35 patients with definite ALS during the course of their illness. The mean amplitude of the H-reflexes (H-mean) obtained in different sessions within an established range of mean M-response amplitude (M-mean) was calculated. For each patient, M-mean was made constant across sessions. H-mean showed high reproducibility and two different trends of changes which emerged in a 1 year follow-up within the population: a significant progressive increase and a steady decrease. When grouped on the basis of their H-mean trend, the patients did not differ in terms of any clinical variables considered. However, the group with progressive increase of H-mean showed a better prognosis. This study has shown that H-mean is effective in assessing the clinical course of ALS and could be useful in monitoring drug effects during clinical trials.

We studied 20 patients with ataxia caused by various disorders using magnetic stimulation over the cerebellum. Results were compared with normal values found for 12 normal volunteers. In normal subjects, a magnetic stimulus over the cerebellum reduced the size of responses evoked by magnetic cortical stimulation when it preceded cortical stimulus by 5, 6 and 7 ms. The grand average of the ratios of the areas of conditioned responses at intervals of 5, 6 and 7 ms to those of control responses was designated the average area ratio (5–7 ms). Suppression of motor cortical excitability was reduced or absent in patients with a lesion in the cerebellum or cerebellothalamocortical pathway, but was normal in patients with a lesion in the afferent pathway to the cerebellum. Normal suppression was observed in Fisher's syndrome. The average area ratio (5–7 ms) correlated well with the severity of ataxia in patients with degenerative late-onset ataxia. These results are consistent with those for electrical stimulation of the cerebellum reported previously. We conclude that magnetic stimulation over the cerebellum produces the same effect as electrical stimulation even in ataxic patients. This less painful method can be used clinically to clarify the pathomechanisms for ataxia. Two other clinical uses of this technique were that it revealed clinically undetectable cerebellar dysfunction in patients whose extrapyramidal signs masked cerebellar signs, and that the slow progression of ataxia could be followed quantitatively in patients with degenerative late-onset ataxia.

Event-related potentials (ERPs) of the rat were recorded at the frontal, temporal and parietal areas on the skull during active and passive auditory oddball paradigms, and consisted of P1 (12.7–37.7 ms), N1 (40.0–80.6 ms), P2 (91.7–202.7 ms), N2 (183.7–246.7 ms) and P3 (265.7–462.7 ms) components. Topography and relationship to the paradigm and stimulus types were examined, and unique features were found for each component. P1, N1 and N2 were prominent frontally. However, P2 showed maximum amplitude at the parietal area. N2 and P3 were consistently present only for rare stimuli. During the passive paradigm P3 had a tendency to be greater at the parietal area, but during the active paradigm it had a longer latency and a larger amplitude than during the passive paradigm. No significant difference between the recording sites was observed for P3 latency and amplitude during the active paradigm. The relationship to the paradigm and stimulus types indicates that the rat P3 corresponds to that of the human. There are differences, however, in surface distribution of the ERP components between the rat and the human. The topographical characteristics of the rat ERP, which are possibly due to differences in brain architecture and function, should be taken into consideration when the rat is used for ERP research.

The somatosensory evoked magnetic fields (SEFs) and evoked potentials (SEPs) following passive toe movement were studied in 10 normal subjects. Five main components were identified in SEFs recorded around the vertex around the foot area of the primary sensory cortex (SI). The first and second components, 1M and 2M, were identified at approximately 35 and 46 ms. Equivalent current dipoles (ECDs) of both 1M and 2M were estimated around SI in the hemisphere contralateral to the movement toe, and were probably generated in area 3a or area 2, which mainly receive inputs ascending through muscle and joint afferents. The large inter-individual difference of 1M and 2M in terms of ECD orientation was probably due to a large anatomical variance of the foot area of SI. The third and fourth components, 3M and 4M, were identified at approximately 62 ms and 87 ms, respectively. They appeared to be a single large long-duration component with two peaks. Since the 3M and 4M components were significantly larger than the 1M and 2M components in amplitude and their ECD location was significantly superior to that of 1M and 2M, we suspected that they were generated in different sites from those of 1M and 2M, probably area 3b or area 4. Four components, 1E, 2E, 3E and 4E, were identified in SEPs, which appeared to correspond to 1M, 2M, 3M and 4M, respectively. The variation observed in the scalp distribution of the primary component, 1E, could be accounted for by the variation of the orientation of ECD of the 1M component. There was a large difference in the waveform of the long-latency component (longer than 100 ms) between SEFs and SEPs. The 5E of SEPs was a large amplitude component, but the 5M of SEFs was small or absent. We speculate that this long-latency component was generated by multiple generators.

Event-related potentials (ERPs) from 50 children (6–11 years) and 10 adults were elicited by auditory passive, and by rare target and frequent non-target stimuli, and analyzed in the time and frequency domains. The latency of the maximal theta response (or the theta frequency component of the ERP) was evaluated with respect to age and scalp topography effects. The major findings were: (1) The latency of the maximal theta response decreased with increasing age in children, although for each stimulus type and location adults had shorter latencies than the children. (2) The developmental time course of latency reduction depended on the electrode location, with the most prominent reduction occurring at 8 years at Cz, and no differences between children groups obtained for the frontal site. (3) Maximal theta response latency was strongly associated with the latency of the late parietal P400–700 (P3b) component in children. The results suggest that the developmental latency decrease in P300 processes originate from a decrease in the preceding theta-related processes and may reflect a speeding of cognitive stimulus evaluation.

Pudendal nerve somatosensory evoked potentials (PN-SSEPs) were recorded in 21 healthy children (age range: 3.3–13.3 years). The dorsal nerve of the penis/clitoris was stimulated and SSEPs were recorded at spinal L1-D12 and at cortical Cz′-Fz. Morphology, latency and amplitude of the cortical SSEPs were evaluated. A cortical response was obtained in all but two subjects. Cortical SSEPs were broader and less defined in shape in the youngest subjects. There was a progressive shortening of the latency of the P and N components during growth. Spinal responses were obtained only in 6 cases. Nine subjects also underwent tibial nerve stimulation. Pudendal and tibial SSEPs differed in their degree of maturation.

Mismatch negativity (MMN) responses were collected from 86 normal school-age children in response to synthesized speech syllables, /wa/ and two variants of /ba/. Waveform characteristics and statistical properties of the responses were analyzed across stimulus conditions in order to assess methods for determining response validity in individuals. Methods were compared using signal detection theory techniques. Criteria based on measurements of response area, onset latency, and duration were the best indicators of response validity. Also a promising indicator of validity was the interval of significance based on Z transformations determined by considering the variance of the underlying noise distribution. Correlations of individual responses with the grand average and integral calculations of the response negativity showed somewhat lower d′ values. Statistical methods which utilized response subaverages were the poorest indicators of response validity. Likely the methods are limited primarily by the signal to noise ratio of the MMN compared to the underlying physiologic noise. Improvement of the signal to noise ratio remains a significant factor in the interpretation of MMN for individual subjects.