Chapter 6 Visual evoked potentials

Repetitive Paired-Pulse Transcranial Magnetic Stimulation Over the Visual Cortex Alters Visual Recovery Function

Chapter 34 - Visually evoked potentials

Visual evoked potentials (VEP) are visually evoked signals that extract electroencephalographic activity in the visual cortex that can detect retinal ganglion cells, optic nerves, chiasmal and retrochiasmal dysfunction, including optic radiations, and the occipital cortex. Because diabetes causes diabetic retinopathy due to microangiopathy and neuropathy due to metabolic abnormalities and intraneural blood flow disorders, assessment of diabetic visual pathway impairment using VEP has been attempted. In this review, evidence on the attempts to assess the visual pathway dysfunction due to abnormal blood glucose levels using VEP is presented. Previous studies have provided significant evidence that VEP can functionally detect antecedent neuropathy before fundus examination. The detailed correlations between VEP waveforms and disease duration, HbA1c, glycemic control, and short-term increases and decreases in blood glucose levels are evaluated. VEP may be useful for predicting postoperative prognosis and evaluating visual function before surgery for diabetic retinopathy. Further controlled studies with larger cohorts are needed to establish a more detailed relationship between diabetes mellitus and VEP.

Aging effects on functional auditory and visual processing using fMRI with variable sensory loading

BackgroundMigraine attacks might be triggered by a disruption of cerebral homeostasis. During the interictal period migraine patients are characterized by abnormal sensory information processing, but this functional abnormality may not be sufficient to disrupt the physiological equilibrium of the cortex unless it is accompanied by additional pathological mechanisms, like a reduction in energetic reserves. The aim of this study was to compare resting cerebral glucose uptake (using positron emission tomography (18fluorodeoxyglucose-PET)), and visual cortex activation (using visual evoked potentials (VEP)), between episodic migraine without aura patients in the interictal period and healthy volunteers.MethodsTwenty episodic migraine without aura patients and twenty healthy volunteers were studied. 18FDG-PET and VEP recordings were performed on separate days. The overall glucose uptake in the visual cortex-to-VEP response ratio was calculated and compared between the groups. Additionally, PET scan comparisons adding area under the VEP curve as a covariate were performed. For case-wise analysis, eigenvalues from a specific region exhibiting significantly different FDG-PET signal in the visual cortex were extracted. Standardized glucose uptake values from this region and VEP values from each subject were then coupled and compared between the groups.ResultsThe mean area under the curve of VEP was greater in migraine patients compared to healthy controls. In the same line, patients had an increased neuronal activation-to-resting glucose uptake ratio in the visual cortex. Statistical parametric mapping analysis revealed that cortical FDG-PET signal in relation to VEP area under the curve was significantly reduced in migraineurs in a cluster extending throughout the left visual cortex, from Brodmann’s areas 19 and 18 to area 7. Within this region, case-wise analyses showed that a visual neuronal activation exceeding glucose uptake was present in 90% of migraine patients, but in only 15% of healthy volunteers.ConclusionThis study identifies an area of increased neuronal activation-to-resting glucose uptake ratio in the visual cortex of migraine patients between attacks. Such observation supports the concept that an activity-induced rupture of cerebral metabolic homeostasis may be a cornerstone of migraine pathophysiology.This article has been selected as the winner of the 2018 Enrico Greppi Award. The Enrico Greppi Award is made to an unpublished paper dealing with clinical, epidemiological, genetic, pathophysiological or therapeutic aspects of headache. Italian Society for the Study of Headaches (SISC) sponsors this award, and the award is supported through an educational grant from Teva Neuroscience. This article did not undergo the standard peer review process for The Journal of Headache and Pain. The members of the 2018 Enrico Greppi Award Selection Committee were: Francesco Pierelli, Paolo Martelletti, Lyn Griffiths, Simona Sacco, Andreas Straube and Cenk Ayata.

Visual evoked potentials (VEPs) are widely used to objectively assess visual system function in animal models of ophthalmological diseases. Although use of chronically implanted electrodes is common in longitudinal VEP studies using rodent models, reliability of recordings over time has not been assessed. We compared VEPs 1 and 7 days after electrode implantation in the adult mouse. We also examined stimulus-independent changes over time, by assessing electroencephalogram (EEG) power and approximate entropy of the EEG signal. Stainless steel screws (600-μm diameter) were implanted into the skull overlying the right visual cortex and the orbitofrontal cortex of adult mice (C57Bl/6J, n = 7). Animals were reanesthetized 1 and 7 days after implantation to record VEP responses (flashed gratings) and EEG activity. Brain sections were stained for glial activation (GFAP) and cell death (TUNEL). Reliability analysis, using intraclass correlation coefficients, showed VEP recordings had high reliability within the same session, regardless of time after electrode implantation and peak latencies and approximate entropy of the EEG did not change significantly with time. However, there was poorer reliability between recordings obtained on different days, and a significant decrease in VEP amplitudes and EEG power. This amplitude decrease could be normalized by scaling to EEG power (within-subjects). Furthermore, glial activation was present at both time points but there was no evidence of cell death. These results indicate that VEP responses can be reliably recorded even after a relatively short recovery period but decrease response peak amplitude over time. Although scaling the VEP trace to EEG power normalized this decrease, our results highlight that time-dependent cortical excitability changes are an important consideration in longitudinal VEP studies. This study shows changes in VEP characteristics over time in chronically implanted mice. Thus, future preclinical longitudinal studies should consider time in addition to amplitude and latency when designing and interpreting research.

The visual physiology of the wild type mouse determined with pattern VEPs

Chapter 18 - Electrophysiological Correlates of Sensation Seeking Behavior in Rats, Cats, and Humans

Objective: To examine the association of visual evoked potential (VEP) latency and high-contrast visual acuity (VA) with cognitive function in MS patients using a standardized computerized battery. Background Cognition and vision are now recognized as important domains for clinical trials assessment in MS. The correlation of VEP conduction delay and VA with cognitive impairment has not been described. Design/Methods: Participants received a VEP evaluation as well as a Snellen vision test and completed a standardized, validated MindStreams battery designed to detect mild impairment (NeuroTrax Corp., NY) in their primary language. VEP latency categories were: normal =113 and =130 and =150 and 170 msec. Results: Among MS patients (n=435, 870 eyes), Accounting for age, disease duration, and within-patient, inter-eye correlations, abnormal VEP latency was associated with poorer overall battery performance (Global Cognitive Score, p Conclusions: Abnormal VEP latency and high-contrast VA in patients with MS may be associated with reduced cognitive function, particularly in domains related to executive function. Longer VEP latency may be particularly related to poorer visual spatial processing. Further studies will examine the role of afferent visual dysfunction and retinal axonal and neuronal loss in the relation of VEP latency to cognitive impairment and work disability in MS cohorts. Disclosure: Dr. Chahin has nothing to disclose. Dr. Balcer has received personal compensation for activities with Biogen Idec, Vaccinex and Bayer as a consultant and has received honoraria from Biogen Idec and Novartis. Dr. Zarif has received personal compensation for activities with Biogen Idec as a consultant. Ms. Bumstead has received personal compenstion for activities with Biogen Idec and Teva Neuroscience as a consultant. Dr. Fafard has nothing to disclose. Dr. Mebrahtu has nothing to disclose. Dr. Galetta has received personal compensation for activities with Biogen Idec Teva, and Novartis as a speaker.Dr. Galetta has received research support from Biogen Idec. Dr. Doniger has received personal compensation for activities with NeuroTrax Corporation as an employee. Dr. Gudesblatt has received personal compensation for activities with Biogen Idec, Teva Neuroscience, Lundbeck Research USA, Inc. and Medtronic as a consultant.

Cochlear implantation is the primary treatment for severe-to-profound hearing loss, yet outcomes vary significantly among recipients. While visual-auditory cross-modal reorganization has been identified as a contributing factor to this variability, its impact in early-implanted children remains unclear. To address this knowledge gap, we investigated visual processing and its relationship with auditory outcomes in children who received early bilateral cochlear implants. To examine potential cross-modal reorganization, we recorded visual evoked potentials (VEPs) in response to pattern-reversal stimuli in 25 children with cochlear implants (CIs) (mean implantation age: 1.44 years) and 28 age-matched normal-hearing (NH) controls. Analysis focused on both the occipital region of interest (ROI: O1, OZ, and O2 electrode sites) and right temporal ROI, examining VEP components and their correlation with speech perception outcomes. Unlike previous studies in later-implanted children, the overall occipital ROI showed no significant differences between groups. However, the left occipital electrode (O1) revealed reduced P1 amplitudes and delayed N1 latencies in CI users. Importantly, O1 N1 latency negatively correlated with speech-in-noise performance (r = -0.318; p = 0.02). The right temporal region showed no significant differences in VEP N1 between groups and no correlation with speech performance in CI users. Early bilateral cochlear implantation appears to preserve global visual processing, suggesting minimal maladaptive reorganization. However, subtle alterations in left occipital visual processing may influence auditory outcomes, highlighting the importance of early intervention and the complex nature of sensory integration in this population.

Electrophysiological evidence for an early attentional mechanism in visual processing in humans

Background Lactate, once considered merely a byproduct of anaerobic metabolism, is now recognized as a crucial neuromodulator in the brain, particularly during high-energy demands. Recent studies have explored its role in neuroprotection, cognitive enhancement, and neural plasticity. This study investigates the effects of elevated blood lactate levels, induced by acute exercise, on visual evoked potentials (VEPs), which reflect neural activity in the visual cortex. Methodology This interventional study was performed in theDepartment of Physiology, Indira Gandhi Institute of Medical Sciences, Patna, BR, IND. Fifty healthy male subjectsaged 18 to 40 years, participated in the study. Baseline blood lactate levels and VEP were recorded after 30 minutes of rest. Subjects then performed aerobic exercise until exhaustion, following the Bruce protocol. Blood lactate levels and VEPs were measured immediately at the end of exercise and again at 10 and 20 minutes post-exercise. Visual evoked potentials (the N75, P100, and N145 waves) were recorded according to the International 10-20 system, using the MEP Neurosoft four-channel machine (Neurosoft, Ivanovo, RUS). Data were analyzed using repeated measures ANOVA, Pearson's correlation, and linear regression via SPSS Statistics version 29.0.2.0 (IBM Corp, Armonk, NY, USA). Results Post-exercise, blood lactate levels were raised, which was statistically significant. The VEP analysis showed a statistically significant decrease in P100 latency immediately after exercise, which correlated with the rise in lactate levels having a p-value <0.001. The increase in N145 latencyat 10 minutes post-exercise was statistically significant, whichcorrelated with changes in lactate levels. The N75 latency exhibited a statistically significant decrease at 10 minutes post-exercise, though it had no statistically significant correlation with lactate levels. Conclusion The study demonstrates that elevated blood lactate levels post-exercise influence VEPs, particularly by decreasing P100 latency and increasing N145 latency. These findings suggest that elevated lactate levels post-exercise may enhance primary visual cortex activity, possibly as a protective mechanism to maintain essential visual processing. However, this enhancement may impair communication with extrastriate areas, potentially reducing the accuracy of perceiving complex visual features such as color, depth, and motion.

Purpose/aim: The aim of the study was to investigate the long-term functional changes that may occur in the retina and visual cortex in a rat ocular hypertension (OHT) model of glaucoma, used in our lab for treatment studies, using electroretinogram (ERG) and visual-evoked potential (VEP) cortical recordings in order to test the hypothesis that experimental glaucoma has differential retinal and central effects.Materials and methods: Experimental glaucoma was induced unilaterally in Dark Agouti rats using hypertonic saline injection into the episcleral veins. After 3, 8, 16 and 26 weeks, ERGs and VEPs were recorded under scotopic conditions using brief full-field white flashes (10 μcd s m−2 to 10.4 cd s m−2) and under photopic conditions using a rod-adapting background and white light flashes (0.13–10.4 cd s m−2).Results: At 16 and 26 weeks after OHT induction, there was a significant reduction in the amplitudes of the a- (50% and 30% of unoperated eye values, respectively) and b-waves (55% and 40%, respectively) of the scotopic ERG and the b-waves of the photopic ERG (55% and 45%, respectively) in the glaucomatous eyes. However, no significant changes in the VEPs simultaneously recorded over the visual cortex were seen at any of the time points.Conclusions: The reductions in ERG amplitudes suggest that this model of glaucoma not only causes retinal ganglion cell (RGC) degeneration but also degeneration of the outer retinal cells, and this was confirmed by histology showing a reduction in the outer retinal layers in the glaucomatous eyes. Cortical VEPs did not show detrimental effects suggesting that the retinal damage in this model was not extensive enough to be detected with the VEP methods used or that there could be central compensation in this model of glaucoma.

Recently, many computational models have been proposed to simulate visual cognition process. For example, the hierarchical Max-Pooling (HMAX) model was proposed according to the hierarchical and bottom-up structure of V1 to V4 in the ventral pathway of primate visual cortex, which could achieve position- and scale-tolerant recognition. In our previous work, we have introduced memory and association into the HMAX model to simulate visual cognition process. In this paper, we improve our theoretical framework by mimicking a more elaborate structure and function of the primate visual cortex. We will mainly focus on the new formation of memory and association in visual processing under different circumstances as well as preliminary cognition and active adjustment in the inferior temporal cortex, which are absent in the HMAX model. The main contributions of this paper are: 1) in the memory and association part, we apply deep convolutional neural networks to extract various episodic features of the objects since people use different features for object recognition. Moreover, to achieve a fast and robust recognition in the retrieval and association process, different types of features are stored in separated clusters and the feature binding of the same object is stimulated in a loop discharge manner and 2) in the preliminary cognition and active adjustment part, we introduce preliminary cognition to classify different types of objects since distinct neural circuits in a human brain are used for identification of various types of objects. Furthermore, active cognition adjustment of occlusion and orientation is implemented to the model to mimic the top-down effect in human cognition process. Finally, our model is evaluated on two face databases CAS-PEAL-R1 and AR. The results demonstrate that our model exhibits its efficiency on visual recognition process with much lower memory storage requirement and a better performance compared with the traditional purely computational methods.

Visual evoked potentials (VEP)were recorded in a large normal population. Significant age differences were found, and the P2 component (latency 116 m.sec.) was the most consistent component of the VEP both between and within the individuals. The validity of the normal VEP criteria were tested in two groups of patients with known visual field defects. One group with central lesions and hemianopia, and a second with senile macula degeneration. The VEP varied with the degree of visual impairment with low amplitudes, long latencies and no localization at either occiput being consistent with poor acuity. The P2 component appeared to be particularly effected by the loss of central retinal function. Two prospective studies were carried out on patients with dense opacities of the optic media. One group of patients had unilateral longstanding cataracts, the second group had recently sustained severe eye injuries with penetration of the globe. The VEP was graded to predict a good visual recovery or no useful function remaining and the gradings were significantly correlated with the final visual outcome. It was concluded that the flash VEP is particularly useful to monitor visual function with dense opacities of the optic media if there is damage to the central retina or visual pathways and cortex.