正常人眼的多焦视诱发电位特征

研究31只正常眼视野中央8.6度的多焦（多刺激野）视诱发电位(multifocal visual evoked potential, MVEP)在视野各部位的特征.观察到平均反应密度随离心度增加而减少,并且在下半视野比在上半视野相应部位高;在上半视野,MVEP波形的极性反转发生率较高.MVEP在视野中的改变反映了视网膜和大脑视皮层解剖特征及其拓扑投射关系.     

基于小波和BP网络的视觉诱发电位分类识别

提出了小波分解与BP网络相结合的方法来识别视觉诱发电位（Visual Evoked Potential,VEP）。先用小波分解对VEP进行特征提取和降维。然后用BP网络进行分类识别。     

Early Clinical and Subclinical Visual Evoked Potential and Humphrey's Visual Field Defects in Cryptococcal Meningitis

Cryptococcal induced visual loss is a devastating complication in survivors of cryptococcal meningitis (CM). Early detection is paramount in prevention and treatment. Subclinical optic nerve dysfunction in CM has not hitherto been investigated by electrophysiological means. We undertook a prospective study on 90 HIV sero-positive patients with culture confirmed CM. Seventy-four patients underwent visual evoked potential (VEP) testing and 47 patients underwent Humphrey''s visual field (HVF) testing. Decreased best corrected visual acuity (BCVA) was detected in 46.5% of patients. VEP was abnormal in 51/74 (68.9%) right eyes and 50/74 (67.6%) left eyes. VEP P100 latency was the main abnormality with mean latency values of 118.9 (±16.5) ms and 119.8 (±15.7) ms for the right and left eyes respectively, mildly prolonged when compared to our laboratory references of 104 (±10) ms (p<0.001). Subclinical VEP abnormality was detected in 56.5% of normal eyes and constituted mostly latency abnormality. VEP amplitude was also significantly reduced in this cohort but minimally so in the visually unimpaired. HVF was abnormal in 36/47 (76.6%) right eyes and 32/45 (71.1%) left eyes. The predominant field defect was peripheral constriction with an enlarged blind spot suggesting the greater impact by raised intracranial pressure over that of optic neuritis. Whether this was due to papilloedema or a compartment syndrome is open to further investigation. Subclinical HVF abnormalities were minimal and therefore a poor screening test for early optic nerve dysfunction. However, early optic nerve dysfunction can be detected by testing of VEP P100 latency, which may precede the onset of visual loss in CM.     

稳态视觉诱发电位神经网络间的相互作用

稳态视觉诱发电位(steady-state visual evoked potential,SSVEP)不同于瞬态视觉诱发电位,有其独特的产生机理。当用两种不同频率的闪光同时刺激时,每种频率闪光诱发的SSVEP之间是否会相互影响?它们与对应单一频率闪光刺激时产生的SSVEP的关系怎样?作者用!波段频率8.3Hz与"波段频率20Hz的闪光分别及同时刺激10个被试的双眼,发现在同时刺激时,每种频率闪光的SSVEP比对应单频刺激时的SSVEP略小,但位置分布无明显变化。这说明不同频率SSVEP的产生网络是彼此独立的,在被同时激活时,每个网络产生的信号并不相互影响。     

视觉诱发电位波形的自动判别分析及其临床应用

计算诱发电位波形第一至第六次谐波的幅度和相位,把这12个参数作为判别分析的自变量.用32只正常眼、31只弱视眼和30只球后视神经炎患眼的诱发电位波形数据建立判别分析系统,再用另外32只正常眼、35只弱视眼和30只球后视神经炎患眼的诱发电位波形数据检验该判别分析系统的判别效果.     

Visual Evoked Cortical Potential (VECP) Elicited by Sinusoidal Gratings Controlled by Pseudo-Random Stimulation

The contributions of contrast detection mechanisms to the visual cortical evoked potential (VECP) have been investigated studying the contrast-response and spatial frequency-response functions. Previously, the use of m-sequences for stimulus control has been almost restricted to multifocal electrophysiology stimulation and, in some aspects, it substantially differs from conventional VECPs. Single stimulation with spatial contrast temporally controlled by m-sequences has not been extensively tested or compared to multifocal techniques. Our purpose was to evaluate the influence of spatial frequency and contrast of sinusoidal gratings on the VECP elicited by pseudo-random stimulation. Nine normal subjects were stimulated by achromatic sinusoidal gratings driven by pseudo random binary m-sequence at seven spatial frequencies (0.4–10 cpd) and three stimulus sizes (4°, 8°, and 16° of visual angle). At 8° subtence, six contrast levels were used (3.12–99%). The first order kernel (K1) did not provide a consistent measurable signal across spatial frequencies and contrasts that were tested–signal was very small or absent–while the second order kernel first (K2.1) and second (K2.2) slices exhibited reliable responses for the stimulus range. The main differences between results obtained with the K2.1 and K2.2 were in the contrast gain as measured in the amplitude versus contrast and amplitude versus spatial frequency functions. The results indicated that K2.1 was dominated by M-pathway, but for some stimulus condition some P-pathway contribution could be found, while the second slice reflected the P-pathway contribution. The present work extended previous findings of the visual pathways contribution to VECP elicited by pseudorandom stimulation for a wider range of spatial frequencies.     

Delayed P100-Like Latencies in Multiple Sclerosis: A Preliminary Investigation Using Visual Evoked Spread Spectrum Analysis

Conduction along the optic nerve is often slowed in multiple sclerosis (MS). This is typically assessed by measuring the latency of the P100 component of the Visual Evoked Potential (VEP) using electroencephalography. The Visual Evoked Spread Spectrum Analysis (VESPA) method, which involves modulating the contrast of a continuous visual stimulus over time, can produce a visually evoked response analogous to the P100 but with a higher signal-to-noise ratio and potentially higher sensitivity to individual differences in comparison to the VEP. The main objective of the study was to conduct a preliminary investigation into the utility of the VESPA method for probing and monitoring visual dysfunction in multiple sclerosis. The latencies and amplitudes of the P100-like VESPA component were compared between healthy controls and multiple sclerosis patients, and multiple sclerosis subgroups. The P100-like VESPA component activations were examined at baseline and over a 3-year period. The study included 43 multiple sclerosis patients (23 relapsing-remitting MS, 20 secondary-progressive MS) and 42 healthy controls who completed the VESPA at baseline. The follow-up sessions were conducted 12 months after baseline with 24 MS patients (15 relapsing-remitting MS, 9 secondary-progressive MS) and 23 controls, and again at 24 months post-baseline with 19 MS patients (13 relapsing-remitting MS, 6 secondary-progressive MS) and 14 controls. The results showed P100-like VESPA latencies to be delayed in multiple sclerosis compared to healthy controls over the 24-month period. Secondary-progressive MS patients had most pronounced delay in P100-like VESPA latency relative to relapsing-remitting MS and controls. There were no longitudinal P100-like VESPA response differences. These findings suggest that the VESPA method is a reproducible electrophysiological method that may have potential utility in the assessment of visual dysfunction in multiple sclerosis.     

Visual Evoked Response in Diagnosis of Multiple Sclerosis

The diagnostic value of the pattern-evoked response has been assessed in 73 patients referred because of suspected multiple sclerosis. Altogether 52 had delayed responses. Fifty-one patients in the group satisfied McAlpine''s criteria for diagnosing definite, probable, or possible multiple sclerosis. Of these, all but two had delayed responses in one or both eyes, while only three of the remaining 22 patients had delays. In those patients with multiple sclerosis but without any history of optic neuritis the incidence of delayed responses was only slightly less. Of 51 patients with delayed responses 23 had normal discs. Thus subclinical lesions of the visual pathways can be readily detected with this test. The high incidence of abnormal pattern responses, even in patients with no other ocular signs or symptoms, suggests that the test is of value in establishing the diagnosis.     

Mechanisms of Selective Attention during Competitive Discrimination of Visual and Auditory Verbal Information: Positron Emission Tomography and Cortical Evoked Potential Studies

The mechanisms of selective verbal attention were studied under conditions of simultaneous delivery of speech signals via the visual and auditory channels. The investigation was based on the comparison and synthesis of data obtained by two methods: positron emission tomography (PET) and brain evoked potentials (EPs). A new approach was developed: complementary tasks were constructed in such a way that, despite principal methodological problems, the same phenomenon could be investigated in one paradigm in EP and PET studies. The results obtained by the two methods are in rather good agreement with respect to topography: the secondary and tertiary areas, as well as the associative brain areas, are involved in attention concentration, that is, selection of verbal information occurs at the level of cognitive processes. The combination of two complementary methods, PET and EP, allowed the processes of processing of sensory information and brain mechanisms of selective attention to be investigated much more completely. The PET studies contributed to further understanding of brain mechanisms evidencing where processing occurs and the EP method provided insight into the mechanism of how this information is processed inside the corresponding cortical areas. The finding that the activation of primary areas of the visual cortex is accompanied by the inhibition of visual information deserves attention. This conclusion can be considered highly significant because of the concordance of the two independent methods. How to interpret it is not yet clear. It is possible that, in the case of primary importance of verbal information and priority of the visual channel for the repression from consciousness of artificially irrelevant information, a safety mechanism is activated: the amplified signal enters the brain cortex, where it is retained in the short-term iconic memory. This enables a reaction to this stimulus (if necessary), in the presence of any additional sign involving selective attention.     

Clinical Physiological Significance of Intraoperative Evoked Potential Monitoring

Modern approaches to intraoperative evoked potential (EP) monitoring in cerebral and spinal cord pathology are reviewed. The criteria of physiological permissibility of neurosurgery based on EP data and the possibilities of studying the neurophysiological mechanisms of somatosensory, auditory, and visual perception in unconscious patients are discussed.     

Cholinergic Pairing with Visual Activation Results in Long-Term Enhancement of Visual Evoked Potentials

Acetylcholine (ACh) contributes to learning processes by modulating cortical plasticity in terms of intensity of neuronal activity and selectivity properties of cortical neurons. However, it is not known if ACh induces long term effects within the primary visual cortex (V1) that could sustain visual learning mechanisms. In the present study we analyzed visual evoked potentials (VEPs) in V1 of rats during a 4–8 h period after coupling visual stimulation to an intracortical injection of ACh analog carbachol or stimulation of basal forebrain. To clarify the action of ACh on VEP activity in V1, we individually pre-injected muscarinic (scopolamine), nicotinic (mecamylamine), α7 (methyllycaconitine), and NMDA (CPP) receptor antagonists before carbachol infusion. Stimulation of the cholinergic system paired with visual stimulation significantly increased VEP amplitude (56%) during a 6 h period. Pre-treatment with scopolamine, mecamylamine and CPP completely abolished this long-term enhancement, while α7 inhibition induced an instant increase of VEP amplitude. This suggests a role of ACh in facilitating visual stimuli responsiveness through mechanisms comparable to LTP which involve nicotinic and muscarinic receptors with an interaction of NMDA transmission in the visual cortex.     

Modifications of Visual Evoked Potentials in Patients with Glaucoma

We compared the visual evoked EEG potentials (VEP) elicited by presentation of a reversal chess pattern in patients with glaucoma and in the control group. Amplitudes, peak latencies of the main VEP components (N75, P100, and N145), interpeak intervals, and interpeak magnitudes were measured, and a spectral analysis of the averaged VEP was performed. In patients suffering from glaucoma, the latencies of the N75 and P100 components were greater, while the interpeak intervals P100-N145 and N75-N145 were shorter, than those in the control group. Glaucoma-related changes in the VEP spectral characteristics, in particular a drop in the spectral power of oscillations corresponding to the alpha rhythm, were observed.     

A Comparison Study of Canonical Correlation Analysis Based Methods for Detecting Steady-State Visual Evoked Potentials

Canonical correlation analysis (CCA) has been widely used in the detection of the steady-state visual evoked potentials (SSVEPs) in brain-computer interfaces (BCIs). The standard CCA method, which uses sinusoidal signals as reference signals, was first proposed for SSVEP detection without calibration. However, the detection performance can be deteriorated by the interference from the spontaneous EEG activities. Recently, various extended methods have been developed to incorporate individual EEG calibration data in CCA to improve the detection performance. Although advantages of the extended CCA methods have been demonstrated in separate studies, a comprehensive comparison between these methods is still missing. This study performed a comparison of the existing CCA-based SSVEP detection methods using a 12-class SSVEP dataset recorded from 10 subjects in a simulated online BCI experiment. Classification accuracy and information transfer rate (ITR) were used for performance evaluation. The results suggest that individual calibration data can significantly improve the detection performance. Furthermore, the results showed that the combination method based on the standard CCA and the individual template based CCA (IT-CCA) achieved the highest performance.     

Visual Evoked Potentials and Disorders of Visual Function in Children Suffering from Cerebral Palsy

Using recording of visual evoked potentials (VEP), we examined 126 children (from 1 to 14 years old) suffering from spastic forms of cerebral palsy. In the overwhelming majority of cases (84.1%), we found in these patients significant modifications of the VEP related to dysfunctions of the visual analyzer system at different levels of the latter. We analyzed correlation of clinical manifestations of the disease with deviations of the VEP characteristics from the age norm. We conclude that an EEG examination, including VEP recording, allows one to obtain objective estimates of disorders of the visual function in the studied population of patients.     

Olfactory Evoked Potential Produced by Electrical Stimulation of the Human Olfactory Mucosa

Most physiological studies of the human olfactory system haveconcentrated on the cortical level; the olfactory bulbar levelhas been studied rarely. We attempted to stimulate the humanolfactory mucosa by electrical pulse to detect the bulbar potentials.Electrical stimulation (2 mA, 0.5 ms) of the human olfactorymucosa evoked a change in potential recorded from the frontalsector of the head. A negative peak of the evoked potentialthat occurred at 19.4 ms (grand means, n = 5) after stimulationwas the clearest. The highest amplitude of the potential wasrecorded from the frontal sector of the head on the stimulatedside. Our findings were similar to the experimental resultsobtained from the olfactory bulbs of animals. This evoked potentialwas considered to be the human olfactory bulbar potential. Whenthe subjects were stimulated by applying electricity to theolfactory mucosa, no sensation of smell occurred even thoughevoked potentials were recorded. Evoked potentials were recordedonly when the stimulating electrode was located in the olfactorycleft. When the stimulating electrode was outside the olfactorycleft, the stimulation caused pain. The trigeminal nerve seemedto be stimulated by electricity. Olfactory evoked potentialsproduced by the electrical stimulation of the human olfactorymucosa should aid the research on human olfactory physiology,and may be applicable to clinical tests of olfactory dysfunction.Chem. Senses 22: 77–81, 1997.     

Clinical Utility and Limitations of Intraoperative Monitoring of Visual Evoked Potentials

Objectives

During surgeries that put the visual pathway at risk of injury, continuous monitoring of the visual function is desirable. However, the intraoperative monitoring of the visual evoked potential (VEP) is not yet widely used. We evaluate here the clinical utility of intraoperative VEP monitoring.

Methods

We analyzed retrospectively 46 consecutive surgeries in 2011-2013. High luminance stimulating devices delivered flash stimuli on the closed eyelid during intravenous anesthesia. We monitored VEP features N75 and P100 and took patients'' preoperative and postoperative visual function from patient charts. Postoperative ophthalmologic workup was performed in 25 (54%) patients and preoperatively in 28 (61%) patients.

Results

VEP recordings were feasible in 62 of 85 eyes (73%) in 46 patients. All 23 eyes without VEP had impaired vision. During surgery, VEPs remained stable throughout surgery in 50 eyes. In 44 of these, visual function did not deteriorate and three patients (6 eyes) developed hemianopia. VEP decreased transiently in 10 eyes and visual function of all was preserved. VEPs were lost permanently in 2 eyes in two patients without new postoperative visual impairment.

Conclusions

Satisfactory intraoperative VEP monitoring was feasible in all patients except in those with severe visual impairment. Preservation of VEPs predicted preserved visual function. During resection of lesions in the visual cortex, VEP monitoring could not detect new major visual field defects due to injury in the posterior visual pathway. Intraoperative VEPs were sensitive enough to detect vascular damage during aneurysm clipping and mechanical manipulation of the anterior visual pathway in an early reversible stage. Intraoperative VEP monitoring influenced surgical decisions in selected patients and proved to be a useful supplement to the toolbox of intraoperative neurophysiological monitoring.