Electroencephalography and clinical neurophysiology最新文献

Photosensitivity is usually tested by intermittent photic stimulation. Photoparoxysmal responses in the EEG are enhanced when the eyes remain closed during stimulation. We tested the hypothesis that this is due to diffusion of light by the eyelids. In 25 photosensitive patients, conditions `eye closure', `eyes closed', `eyes open' and `eyes open with diffuser' were tested for frequencies of 2–60 Hz. Additional influences of a red filter and fixation were also examined. The photosensitivity range was maximal in the condition `eyes open with diffuser', due to an increase of the upper limit to a median 60 Hz (range 25–60), from 35 (15–50) Hz with eyes open, 37.5 (25–60) Hz with eyes closed and 40 (23–60) Hz with eye closure (P=0.0002). This effect was attenuated in patients on valproic acid and with the use of a red or white filter. Testing with a diffuser was more sensitive than without, except for one patient who was photosensitive only in the eye closure condition. The influence of the eyelids on photosensitivity can be explained by diffusion of light, attentuated by an intensity loss. Use of a diffuser may simplify testing for photosensitivity in the EEG laboratory. The diffusion effect may explain seizure susceptibility in front of 50 and 60 Hz television screens.

Event-related EEG spectral perturbation (ERSP) was studied in 20 right-handed subjects during selective response (SRP) and selective mental arithmetic (SMA). The input signals were one-digit number sounds (single syllable). The subjects were asked to make switch response (for SRP) or accumulative summation (for SMA) as soon as odd numbers (T) were heard and to ignore even ones (N). EEG powers were derived from 3 successive 0.5 s segments post input signal from 9 locations on scalp in 4 conditions (srT, srN, maT and maN). The ERSP was taken as the spectral change relative to that under rest control. The main results were: (i) the power of delta and theta activity increased significantly in the 1st 0.5 s in all 4 conditions but decreased in the following epochs; (ii) the theta activity revealed greatest spatial differentiation, prominent theta activity remained at Fz in the 2nd and 3rd 0.5 s in maT but not in srT; (iii) the power of alpha activity was lowest in the 1st 0.5 s and remained low level during SMA but increased in the 2nd 0.5 s during SRP; (iv) the 11–18 Hz activity augmented after the 1st 0.5 s, its dominance remained at P6 during SMA but switched from P6 to frontal locations during SRP; (v) the power of high frequency activities beyond 30 Hz decreased significantly during SRP at all locations. The temporal and spatial feature of ERSP in the 4 conditions provided further evidence indicating the functional correlates of EEG activities in each frequency band. The high frequency activity might reflect the general attention state. The dynamic change of attentional demand during information processing was probably reflected by alpha activity. The delta, theta and beta activities seemed related to different aspects of cognitive processes.

A simple method for the quantitative description of sleep microstructure is proposed. This method is based on the computation of descriptors which provide a normalized measure of how the amplitude of the activity in a frequency band differs, at a given instant, from its background. The use of these descriptors makes it possible to identify epochs of transient increase in band activity, to measure their length, and to measure the time distance between two successive epochs.

We determined the diagnostic value of the EEG in young children with Angelman syndrome (AS) and Rett syndrome (RS). EEGs, recorded before 5 years of age, of 10 patients with AS, 10 with RS and 10 with mental retardation of other origin were studied blindly by two examiners for the presence of the following items: (A) 4–6 Hz rhythmic activity of over 200 μV; (B) 2–3 Hz frontal activity of 200–500 μV; (C) posterior spikes; (D) triphasic frontal waves; (E) central and/or centro-temporal spike-wave complexes; and (F) other epileptic discharges. Based on these items the EEGs were scored as AS (A–D); RS (E–F); or other. Examiners never made a mistake between AS and RS. One examiner labeled 6 of 10 AS cases correctly, the other 5; 4 (5) were characterized as `other.' In RS cases 5 were labeled as `other' by the first examiner and 3 by the second one. We conclude that EEG patterns of AS and RS are sufficiently different to help differentiate between AS and RS at a young age, which has a bearing on genetic counseling.

Objectives: We developed a method to register EEG and MRI data used for the source reconstruction of electric brain activity. Methods: The method is based on matching of the head surfaces as obtained by 3D scanning after the EEG recording, and by segmentation of MRI data. The registration accuracy was estimated by calculating the residual error of the surface matching and its intra-individual and inter-individual variability. In addition, the test-retest reliability concerning the transformation of electrode positions was studied, to estimate how inaccuracies resulting from the 3D scanning of the head surface translate into registration uncertainty. Results: For 61 measurements, performed on 20 subjects, the average root mean square of the Euclidean distances between the 3D-scanned and the MRI-derived head surfaces amounted to 3.4 mm. An inter-individual standard deviation of 0.24 mm, and an intra-individual standard deviation of 0.003–0.31 mm proved a high inter- and intra-subject stability of the surface matching technique. The variation of transformation results when studying the test-retest reliability amounted to 1.6 mm on average. The maximum error of transformation was smaller than the diameter of the electrodes. Conclusions: The findings suggest that the surface matching technique is a precise method for determination of the transformation of electrode positions and MRI data into a single co-ordinate system and can successfully be used in a routine laboratory setting.

In order to specify the locations and to clarify the electrophysiological significance of the transitory rhythmic theta activities detected on scalp electrodes in infants, we performed simultaneous EEG and video recording with power spectral map analysis in 29 normal infants of less than 1 year of age. The rhythmic theta activities appeared in posterior temporal regions with sucking or crying, in the parietal region with gazing, and in the frontal region with handling. Each specific location of the theta rhythm seemed to correspond to the functional localization in the infant's brain. We thus concluded that these rhythmic theta activities might originate from direct cortical activation, or from the cortical activation driven by the neuronal impulses from the limbic system through the connection between that system and the cortex.

Auditory evoked responses and spontaneous cortical activity were recorded with a whole-scalp 122-channel neuromagnetometer from 7 patients, who had small thalamic infarctions in the region of the left anterior tuberothalamic artery and associated memory defects. In contrast to healthy control subjects, with dominant rhythmic activity at 10.6±0.6 Hz in the parieto-occipital region, the spectral maximum in the patients was at 8.9±0.4 Hz. Abnormal acceleration of rhythmic activity was also observed bilaterally in rolandic areas. Our findings imply that lesions of non-specific thalamic nuclei may disturb human brain rhythms in widespread cortical areas. `Mismatch responses' to deviant tones (1.1 kHz) among standards (1.0 kHz), suggested to reflect sensory auditory memory in healthy subjects, were absent in 2 patients, markedly decreased in 3, and normal in 2, implying that pathways passing through the anteromedial thalamus contribute to modulation of these responses. We conclude that local unilateral lesions in the anteromedial thalamus may cause extensive, bilateral alterations in brain's electric activity.

Objectives: Event-related desynchronization (ERD) and synchronization (ERS) of the 8–10 and 10–12 Hz frequency bands of the background EEG were studied in 10 subjects performing an auditory lexical matching task.

Methods: The stimuli were words and pseudowords presented sequentially in pairs. The subject was prompted to answer whether the two stimuli shared the same lexical status (words or pseudowords).

Results: Regardless of lexicality, the presentation of the first stimulus elicited a significant late frontal ERD in both alpha frequency bands. When preceded by a pseudoword, the presentation of the second stimulus elicited a significant ERS at 200–400 ms and a significant, long-lasting and topographically-widespread ERD at 600–2200 ms in both frequency bands. When preceded by a word, the second stimulus did not elicit ERS in the initial time window, but a late ERD which was similar to the one observed in the previous condition. The complexity of ERD/ERS changes in the present task was revealed by significant interactions that time had with frequency band, stimulus type, stimulus order and lexicality of the preceding stimulus.

Conclusions: The results suggest that ERD/ERS does not reflect primary auditory stimulus processing. Rather, the ERD/ERS observed in this experiment most probably reflected task difficulty and differences between lexical–semantic and phonological memory functions.