Electroencephalography and clinical neurophysiology最新文献

EEG has been used widely in diagnosing encephalitis, as it demonstrates rather typical abnormalities, especially in herpes simplex virus encephalitis (HSVE). We analysed 204 EEG recordings from 98 consecutive acyclovir-treated patients with acute encephalitis between 1984 and 1994. Periodic complexes (PC) in the acute phase predicted poor outcome (Kendall tau 0.40, P<0.001). However, unlike in many other diseases, e.g. stroke and intracerebral haemorrhage, the diffuse slowing of the background activity at acute phase did not predict outcome (Kendall tau −0.6, P=0.35). At follow-up, the emergence of diffuse slow background activity was significantly associated with a less favourable outcome (Kendall tau 0.33, P=0.0016). Among clinical variables, only epileptic seizures early during the course of the disease correlated significantly with outcome. EEG does have value as a prognostic indicator in acute encephalitides, but it seems that diffuse slowing of background activity or irritative features acutely are not as important as previously thought, based on the experiences of the pre-acyclovir era.

Objective: The aim of this study was to determine the otolithic and semicircular canal effects of galvanic vestibular stimulation with increasing current strengths on eye movements and the perception of verticality.

Methods: We measured (1) 3-dimensional eye movements, (2) subjective tilt of the peripheral visual field, and (3) subjective tilt of a central vertical line in 12 healthy subjects during galvanic vestibular stimulation. A rectangular, unipolar binaural electric current was applied to each subject's mastoid.

Results: Anodal stimulation of the right mastoid led to an ipsiversive tonic ocular torsion of up to 5.4°, to a contralateral tilt of both the peripheral visual field (1–9°), and a central vertical line (0.5–6.2°) increasing in amplitude with increasing current strengths applied. This reflects otolith stimulation. In most subjects, current strengths of 3 mA or more elicited a slight (horizontal-) torsional nystagmus (amplitude 1–2°) that was superimposed on static torsion. This reflects horizontal and vertical semicircular canal stimulation. A correlation was found in the amount of the 3 measured parameters and the strength of the applied current.

Conclusions: Thus, galvanic vestibular stimulation at low current intensities (1– 3 mA) preferably excites otolith responses, which increase with increasing current intensity. With higher current intensity above 3 mA, additional semicircular canal responses are elicited in the form of horizontal-rotatory nystagmus superimposed on static torsional deviations. The lack of a vertical deviation and nystagmus can be explained by the counterdirected vertical components of the anterior and posterior semicircular canal.

Objective: To present clinical electrophysiologic studies performed on the pallido-ponto-nigral degeneration (PPND) family linked to chromosome 17q21–22.

Methods: Nine patients from this kindred were studied with 11 electroencephalograms (EEGs), 4 electroencephalographic background frequency analysis (BFA) studies, 4 electromyographic recordings (EMGs) including nerve conduction studies (NCSs), 4 electromyographic multichannel surface recordings (MSRs), one pattern visual evoked potential (VEP) study and one median nerve somatosensory evoked potential (SEP) study.

Results: EEGs revealed normal findings early in the disease and diffuse slowing which became more prominent with disease progression. BFA studies demonstrated rapid decrease in mean parietal frequencies with disease progression. EMGs and NCSs showed no abnormalities. MSRs revealed action myoclonus and a dystonic process. Long loop reflexes were absent in resting hand muscles. VEPs and SEPs were normal.

Conclusions: Clinical neurophysiologic studies were consistent with a cortical and subcortical degenerative process. With clinical deterioration, there is a progressive decline in the mean parietal frequency and background rhythms. Tremor studies were consistent with action myoclonus and a dystonic process and did not show parkinsonian features of resting tremor or agonist-antagonist cocontraction. There was no evidence of peripheral nerve involvement or slowing in central sensory pathways. Electrophysiologic findings are characteristic for this illness.

Myoclonus is defined as a sudden, brief, jerky, shock-like, involuntary movement, arising from the central nervous system that can be caused by a muscular contraction, i.e. positive myoclonus, or by an interruption of muscular activity, i.e. negative myoclonus. Myoclonus can characterize a variety of neurological disorders, and often both positive and negative myoclonus can coexist. In this paper, we outline some relevant clinical aspects and neurophysiological features of the different types of myoclonus, with particular emphasis on the physiological findings. Indeed, since most myoclonus depend on enhancement of neuronal activities which are inherently present in normal subjects, electrophysiological studies are useful for elucidating the underlying pathophysiological mechanisms and for establishing the correct diagnosis. To reveal and discuss the peculiarities of soleus muscle in comparison with electrophysiological features of other leg muscles.

Purpose: Localization of hippocampal paroxysmal activities in temporal lobe epilepsy (TLE) by means of dipole modeling has often been criticized because of the supposed inaccuracy of this technique in localizing deep sources of EEG signals. This study aimed at assessing the relevance of mesio-temporal dipoles, as identified by modeling of scalp recorded spikes in TLE.

Methods: Surface and depth EEG activities were simultaneously recorded using scalp and intracranial electrodes implanted through the foramen ovale (FO) in 3 patients with refractory TLE seizures. Intracranial FO spikes were used as triggers for scalp EEG averaging. The averaged signals were modeled by current dipoles, the localization of which were fused with patients' 3D-MRI.

Results: Individual FO spikes were undetectable on visual analysis of raw scalp EEG but were reflected by low-amplitude scalp EEG transients on averaged signal. Dipole modeling of this EEG deflection consistently identified a mesio-limbic source in a position close to that of the FO pole recording the intracranial spike with its maximal amplitude.

Conclusion: This result suggests that mesio-temporal sources can be accurately localized by modeling the signals recorded on the scalp, thus validating the anatomical and clinical relevance of hippocampal sources identified by modeling scalp interictal averaged spikes in TLE.

Changes of the second suppressive period (ES2) of the exteroceptive suppression of the temporalis muscle activity are found in patients with chronic tension-type headache (TTH) and are suggested to reflect an abnormal endogenous pain control system. We investigated whether similar changes are found in patients with the fibromyalgia syndrome (FMS) that is also believed to result from disturbed central pain processing. The ES2 values of 27 patients with FMS were compared with those of 18 patients with TTH and 40 healthy volunteers. The duration of ES2 (±SD) in FMS patients was 30.6±7.5 ms and was not significantly different from the control group (33.1±7.8 ms), whereas it was significantly shortened in TTH patients (22.9±11.5 ms). Our results indicate that, despite similar concepts on the pathophysiology of the two chronic pain disorders, there are no comparable changes of this brain stem reflex activity in FMS.

Objectives: To compare maintenance of wakefulness test (MWT) data gathered at baseline in the course of two, multicenter studies on the therapeutic efficacy of modafinil with published MWT norms. Methods: The MWT is a procedure that uses electrophysiological measures to determine the ability to remain awake while sitting in a quiet, darkened room. The test consists of 4 20 min trials conducted 4 times at 2 h intervals commencing 2 h after awakening from a night of sleep. MWT data were gathered at baseline in the course of two, multicenter studies on the therapeutic efficacy of modafinil. Subjects were 17–68 year old men (n=239) and women (n=291) diagnosed with narcolepsy according to the International Classification of Sleep Disorders (ICSD). All patients were free of psychoactive medication for a minimum of 14 days. Results: Mean MWT sleep latency was 6.0±4.8 min. However, the mean for the first MWT trial was 7.0 min which was longer that the means for the following 3 trials (5.8, 5.6 and 5.7 min, respectively). The 4 distributions of the individual MWT trials were similar and adequately summarized by the distribution of the average MWT sleep latency. As a group, patients with narcolepsy were less able to remain awake than normals; only 8 of 530 (1.5%) patients were able to remain awake on 4 20 min MWT trials compared with 35 of 64 (54.7%) normals in another study. However, using a mean MWT sleep latency of 12 min (the 5th percentile for normals) as the lowest cut-point for normalcy, 15% of patients with narcolepsy appeared to have an unimpaired ability to remain awake. Conclusions: The diagnosis of narcolepsy did not always predict inability to remain awake on the MWT. Age, gender and the duration of illness did not predict ability to remain awake. Patients with severe cataplexy and other ancillary symptoms were least able to remain awake on MWT trials. Patients who used tobacco and caffeine moderately had the lowest MWT sleep latencies relative to patients with heavy and light use.

Objective: To determine the effect of intermittent photic stimulation (IPS) and frequency of asymmetric driving responses in patients with occipital spikes. Methods: The amplitude of the driving response at 4 flash frequencies was measured from a referential montage in 60 patients with occipital spikes and in 60 normal EEG records from age-matched patients. Responses were classified as asymmetric if the amplitude at one occipital area was less than 50% of the amplitude at the other. Results: A measurable photic response occurred significantly less frequently in patients with occipital spikes (48%) compared to the control group (70%; Fisher's test P<0.05). The driving response was asymmetric in 7/36 patients (37%) with unilateral spike foci versus none in the control group (Fisher's test, P<0.001). The amplitude was suppressed ipsilateral to the focus in 5 patients, all of whom had an ipsilateral structural lesion or focal slowing. In two cases the amplitude was higher ipsilateral to the focus, neither having slowing or a structural lesion. Conclusions: Patients with occipital spikes have an increased frequency of asymmetric driving response. An attenuated response ipsilateral to the focus seems to be related to an underlying lesion while the presence of an epileptiform focus in some cases with no slowing on EEG and normal imaging studies may lead to an accentuation of this response.

Objectives: Event-related potentials (ERPs) elicited by subthreshold visual stimuli were studied to assess the relationship between unconscious cognitive processing and the electrical activity of the brain.

Methods: A new method of modified visual oddball paradigm with supraliminal and subliminal stimuli was applied. Prior to the experiment, the individual `subjective' threshold for the conscious discrimination between frequent and target stimuli was established for each subject. Supraliminal and subliminal, frequent and target visual stimuli were then alternatively presented in random order to each subject.

Results: Both the individual and the grand average ERPs revealed a typical response (P3) in the parietal region after supraliminally presented target stimuli. In subliminal conditions an analogous positive deflection in the central-parietal region was observed, which was elicited by the target stimulus, but not the frequent stimulus. Its latency could be clearly distinguished from the latency of the classical P3, the time difference between the two waveforms was approximately 100 ms.

Results: The results of this study revealed the impact of unconscious processing to target stimuli on the configuration of event-related responses.