Evoked Potential: Use in Screening of Hearing and Vision

1982 ◽  
Vol 4 (3) ◽  
pp. 81-98
Keyword(s):  
Visual Acuity ◽  
Visual Cortex ◽  
Evoked Potential ◽  
Light Flash ◽  
Electrical Response ◽  
Sensory Information ◽  
Occipital Cortex ◽  
Small Children ◽  
Refractive Correction ◽  
Potential Use

An evoked potential (EP) is the electrical response of the CNS to an external stimulus. Each EP may be represented as a sequence of waves, the amplitude and length of which reflect the conduction and processing of sensory information through the CNS. Visual, auditory, and somatic EP are used clinically in pediatrics. Visual evoked potentials are the responses recorded from the occipital cortex of the scalp near the primary visual cortex to a stroboscopic light flash. The occipital potential orginates in the retina. This study can be used to assess the functional integrity of the visual system. Visual acuity can be assessed using refractive correction to enhance the amplitude of the recorded response in small children.

scholarly journals Vision AfterEarly-OnsetLesions of the Occipital Cortex: I. Neuropsychological and Psychophysical Studies

2002 ◽  
Vol 9 (1) ◽  
pp. 1-25 ◽  
Author(s):  
D. C. Kiper ◽  
P. Zesiger ◽  
P. Maeder ◽  
T. Deonna ◽  
G. M. Innocenti
Keyword(s):  
Visual Acuity ◽  
Visual Cortex ◽  
Motion Perception ◽  
Primary Visual Cortex ◽  
Visual Processing ◽  
Occipital Cortex ◽  
Adaptive Plasticity ◽  
Visual Functions ◽  
Color Form ◽  
Psychophysical Studies

We analyzed the visual functions of two patients (MS, FJ) with bilateral lesion of the primary visual cortex, which occurred at gestational age 33 wk in MS and at postnatal month 7 in FJ. In both patients basic visual functions— visual acuity, contrast sensitivity, color, form, motion perception—are similarly preserved or modestly impaired. Functions requiring higher visual processing, particularly figure-ground segregation based on textural cues, are severely impaired. In MS, studied longitudinally, the deficits attenuated between the ages of 4.5 and 8 y, suggesting that the developing visual system can display a considerable degree of adaptive plasticity several years after the occurrence of a lesion. In FJ (age 18:9 to 20:6 y), who is more impaired, the recovery, if any, was less.

Analysis of Visual-Evoked Potentials of Primary Visual Cortex under Flash Stimulations

2013 ◽  
Vol 749 ◽  
pp. 328-332
Author(s):  
Shu Li Chen ◽  
Zhi Zhong Wang ◽  
Li Shi ◽  
Xiao Ke Niu
Keyword(s):  
Visual Cortex ◽  
Evoked Potentials ◽  
Visual Evoked Potentials ◽  
Sensory Processing ◽  
Evoked Potential ◽  
Visual Stimulation ◽  
Neurological Diseases ◽  
Occipital Cortex ◽  
Pattern Evoked Potentials ◽  
Visual Evoked

Visual-evoked potentials (VEPs) which is made up of electrical signals generated by the nervous system in response to a stimulus can be easily recorded from the visual cortex of the experiment animal. There are several types of VEPs, for example, flash evoked potential (FEP), pattern evoked potential [1-3]. The FEP is produced by a visual stimulation with a brief and diffuse flash light. It is frequently used to evaluate the neural activity and sensory processing in the visual system [ and to identify and characterize the changes occurring in the retina and the occipital cortex [4, 5]. VEPs can also provide a further therapeutic approach through the stimulate of monitoring neurophysiologic changes related to diseases [6, 7]. The pattern evoked potentials have been used to assess parametric characteristics of visual perception, detect neuronal irritability and diagnose neurological diseases [8-1.

Phosphene perceptions and safety of chronic visual cortex stimulation in a blind subject

2020 ◽  
Vol 132 (6) ◽  
pp. 2000-2007 ◽  
Author(s):  
Soroush Niketeghad ◽  
Abirami Muralidharan ◽  
Uday Patel ◽  
Jessy D. Dorn ◽  
Laura Bonelli ◽  
...  
Keyword(s):  
Visual Cortex ◽  
Adverse Events ◽  
Clinical Intervention ◽  
Occipital Cortex ◽  
Neuronal Population ◽  
Serious Adverse Events ◽  
Stimulation Parameters ◽  
The Right ◽  
Visual Cortical ◽  
Stimulation Of

Stimulation of primary visual cortices has the potential to restore some degree of vision to blind individuals. Developing safe and reliable visual cortical prostheses requires assessment of the long-term stability, feasibility, and safety of generating stimulation-evoked perceptions.A NeuroPace responsive neurostimulation system was implanted in a blind individual with an 8-year history of bare light perception, and stimulation-evoked phosphenes were evaluated over 19 months (41 test sessions). Electrical stimulation was delivered via two four-contact subdural electrode strips implanted over the right medial occipital cortex. Current and charge thresholds for eliciting visual perception (phosphenes) were measured, as were the shape, size, location, and intensity of the phosphenes. Adverse events were also assessed.Stimulation of all contacts resulted in phosphene perception. Phosphenes appeared completely or partially in the left hemifield. Stimulation of the electrodes below the calcarine sulcus elicited phosphenes in the superior hemifield and vice versa. Changing the stimulation parameters of frequency, pulse width, and burst duration affected current thresholds for eliciting phosphenes, and increasing the amplitude or frequency of stimulation resulted in brighter perceptions. While stimulation thresholds decreased between an average of 5% and 12% after 19 months, spatial mapping of phosphenes remained consistent over time. Although no serious adverse events were observed, the subject experienced mild headaches and dizziness in three instances, symptoms that did not persist for more than a few hours and for which no clinical intervention was required.Using an off-the-shelf neurostimulator, the authors were able to reliably generate phosphenes in different areas of the visual field over 19 months with no serious adverse events, providing preliminary proof of feasibility and safety to proceed with visual epicortical prosthetic clinical trials. Moreover, they systematically explored the relationship between stimulation parameters and phosphene thresholds and discovered the direct relation of perception thresholds based on primary visual cortex (V1) neuronal population excitation thresholds.

scholarly journals Supersaturation of VEP in Migraine without Aura Patients Treated with Topiramate: An Anatomo-Functional Biomarker of the Disease

2021 ◽  
Vol 10 (4) ◽  
pp. 769
Author(s):  
Ciro De Luca ◽  
Sara Gori ◽  
Sonia Mazzucchi ◽  
Elisa Dini ◽  
Martina Cafalli ◽  
...  
Keyword(s):  
Visual Cortex ◽  
Cortical Neurons ◽  
Migraine Without Aura ◽  
Inverse Correlation ◽  
Primary Headache ◽  
Contrast Gain ◽  
High Prevalence ◽  
Functional Pathway ◽  
Inhibitory Signaling ◽  
Potential Use

Migraine is a primary headache with high prevalence among the general population, characterized by functional hypersensitivity to both exogenous and endogenous stimuli particularly affecting the nociceptive system. The hyperresponsivity of cortical neurons could be due to a disequilibrium in the excitatory/inhibitory signaling. This study aimed to investigate the anatomo-functional pathway from the retina to the primary visual cortex using visual evoked potentials (VEP). Contrast gain protocol was used in 15 patients diagnosed with migraine without aura (at baseline and after 3 months of topiramate therapy) and 13 controls. A saturation (S) index was assessed to monitor the response of VEP’s amplitude to contrast gain. Non-linear nor monotone growth of VEP (S < 0.95) was defined as supersaturation. A greater percentage of migraine patients (53%) relative to controls (7%) showed this characteristic. A strong inverse correlation was found between the S index and the number of days separating the registration of VEP from the next migraine attack. Moreover, allodynia measured through the Allodynia Symptoms Check-list (ASC-12) correlates with the S index both at baseline and after 3 months of topiramate treatment. Other clinical characteristics were not related to supersaturation. Topiramate therapy, although effective, did not influence electrophysiological parameters suggesting a non-intracortical nor retinal origin of the supersaturation (with possible involvement of relay cells from the lateral geniculate nucleus). In conclusion, the elaboration of visual stimuli and visual cortex activity is different in migraine patients compared to controls. More data are necessary to confirm the potential use of the S index as a biomarker for the migraine cycle (association with the pain-phase) and cortical sensitization (allodynia).

The Role of Neuronal Synchronization in Response Selection: A Biologically Plausible Theory of Structured Representations in the Visual Cortex

1996 ◽  
Vol 8 (6) ◽  
pp. 603-625 ◽  
Author(s):  
Pieter R. Roelfsema ◽  
Andreas K. Engel ◽  
Peter König ◽  
Wolf Singer
Keyword(s):  
Visual Cortex ◽  
Response Selection ◽  
Sensory Information ◽  
Motor Program ◽  
Dynamic Parameter ◽  
Object Identification ◽  
Multiple Objects ◽  
Structured Representations ◽  
Purposeful Behavior ◽  
Behavioral Requirements

Recent experimental results in the visual cortex of cats and monkeys have suggested an important role for synchronization of neuronal activity on a millisecond time scale. Synchronization has been found to occur selectively between neuronal responses to related image components. This suggests that not only the firing rates of neurons but also the relative timing of their action potentials is used as a coding dimension. Thus, a powerful relational code would be available, in addition to the rate code, for the representation of perceptual objects. This could alleviate difficulties in the simultaneous representation of multiple objects. In this article we present a set of theoretical arguments and predictions concerning the mechanisms that could group neurons responding to related image components into coherently active aggregates. Synchrony is likely to be mediated by synchronizing connections; we introduce the concept of an interaction skeleton to refer to the subset of synchronizing connections that are rendered effective by a particular stimulus configuration. If the image is segmented into objects, these objects can typically be segmented further into their constituent parts. The synchronization behavior of neurons that represent the various image components may accurately reflect this hierarchical clustering. We propose that the range of synchronizing interactions is a dynamic parameter of the cortical network, so that the grain of the resultant grouping process may be adapted to the actual behavioral requirements. It can be argued that different aspects of purposeful behavior rely on separable processes by which sensory input is transformed into adjustments of motor activity. Indeed, neurophysiological evidence has suggested separate processing streams originating in the primary visual cortex for object identification and sensorimotor coordination. However, such a separation calls for a mechanism that avoids interference effects in the presence of multiple objects, or when multiple motor programs are simultaneously prepared. In this article we suggest that synchronization between responses of neurons in both the visual cortex and in areas that are involved in response selection and execution might allow for a selective routing of sensory information to the appropriate motor program.

scholarly journals Effectiveness of refractive error correction for people with oculocutaneous albinism in Nepal

2017 ◽  
Vol 8 (6) ◽  
pp. 30-34 ◽  
Author(s):  
Arjun M Bhari ◽  
Kabindra Bajracharya ◽  
Hari B Thapa ◽  
Maria Gautam ◽  
Araniko Pandey ◽  
...  
Keyword(s):  
Visual Acuity ◽  
Error Correction ◽  
Oculocutaneous Albinism ◽  
Outreach Program ◽  
Refractive Errors ◽  
Medical Sciences ◽  
Telephone Contact ◽  
Refractive Correction ◽  
And Function ◽  
Objective Improvement

Background: Albinism is commonly associated with high refractive errors, but some clinicians are reluctant to prescribe glasses because reduced vision persists due to additional non-refractive visual problems.Aims and Objective: The purpose of this study was to evaluate the effectiveness of glasses in people with oculocutaneous albinism in Nepal.Materials and Methods: People with Oculocutaneous albinism (OCA) were prospectively examined through an outreach program of Lumbini Eye Institute, Nepal. Glasses were prescribed to determine the objective improvement in visual acuity (VA) and strabismus. Compliance with spectacles wear was assessed by telephone contact after 3 weeks and categorized as excellent: >75% of awake hours; good: 50–75% of awake hours; fair: 26–50% of awake hours and poor: <25%.Results: Thirty one people (65% male) mean age 18 years (range: 3 to 50) with OCA were examined. Mean refractive correction was –0.40±4.3 diopters spherical equivalents (range: −11.0 to +7.0 D). Mean visual acuity at distance was 0.9±0.28(6/50) corrected and 1.150.31(5/60) uncorrected (P = 0.000) in 62 eyes. Mean neat VA was1.74±0.89M corrected and 2.06±1.20M uncorrected (P = 0.004). Forty eight per cent (15 people) had fusion with or without glasses and one had fusion only with glasses. Compliance was excellent in 52% (16), fair in 26% (8), good in 12% (4), and poor in 10% (3).Conclusion: Providing eye glasses resulted in a clinically and functionally significant improvement in visual acuity and function in people with OCA.Asian Journal of Medical Sciences Vol.8(6) 2017 30-34

scholarly journals Posterior cortical atrophy: A rare variant of Alzheimer’s disease

2018 ◽  
Vol 10 (2) ◽  
Author(s):  
Michael A. Meyer ◽  
Stephen A. Hudock
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Visual Cortex ◽  
Primary Visual Cortex ◽  
Photon Emission ◽  
Occipital Cortex ◽  
Cortical Atrophy ◽  
Emission Computed Tomography ◽  
Posterior Cortical Atrophy ◽  
Homonymous Hemianopsia

Posterior cortical atrophy is a rare condition first described in 1988 involving progressive degeneration and atrophy of the occipital cortex, often recognized after an unexplained homonymous hemianopsia may be discovered. We report a case in association with Alzheimer’s disease in a 77-year-old female, who underwent brain single-photon emission computed tomography as well brain positron emission tomography using Florbetapir to further evaluate progressive cognitive decline. The patient had also been followed in Ophthalmology for glaucoma, where a progressive unexplained change in her visual field maps were noted over one year consistent with a progressive right homonymous hemianopsia. This rare combination of findings in association with her dementia led to a detailed review of all her imaging studies, concluding with the surprising recognition for a clear hemi-atrophy of the primary left occipital cortex was occurring, consistent with Alzheimer’s disease affecting the primary visual cortex. Further awareness of this disease pattern is needed, as Alzheimer’s disease typically does not affect the primary visual cortex; other conditions to consider in general include Lewy Body dementia, cortico-basal degeneration and prion disease.

scholarly journals Changes in thalamocortical connectivity as a potential mechanism of cross-modal plasticity in congenitally blind individuals

2018 ◽  
Author(s):  
Theo Marins ◽  
Maite Russo ◽  
Erika Rodrigues ◽  
jorge Moll ◽  
Daniel Felix ◽  
...  
Keyword(s):  
Visual Cortex ◽  
Cortical Thickness ◽  
Visual Information ◽  
Brain Plasticity ◽  
Temporal Cortex ◽  
Occipital Cortex ◽  
Brain Structures ◽  
Congenitally Blind ◽  
Blind Individuals ◽  
Neuroimaging Techniques

ABSTRACTEvidence of cross-modal plasticity in blind individuals has been reported over the past decades showing that non-visual information is carried and processed by classical “visual” brain structures. This feature of the blind brain makes it a pivotal model to explore the limits and mechanisms of brain plasticity. However, despite recent efforts, the structural underpinnings that could explain cross-modal plasticity in congenitally blind individuals remain unclear. Using advanced neuroimaging techniques, we mapped the thalamocortical connectivity and assessed cortical thickness and integrity of white matter of congenitally blind individuals and sighted controls to test the hypothesis that aberrant thalamocortical pattern of connectivity can pave the way for cross-modal plasticity. We described a direct occipital takeover by the temporal projections from the thalamus, which would carry non-visual information (e.g. auditory) to the visual cortex in congenitally blinds. In addition, the amount of thalamo-occipital connectivity correlated with the cortical thickness of primary visual cortex (V1), supporting a probably common (or related) reorganization phenomena. Our results suggest that aberrant thalamocortical connectivity as one possible mechanism of cross-modal plasticity in blinds, with potential impact on cortical thickness of V1.SIGNIFICANT STATEMENTCongenitally blind individuals often develop greater abilities on spared sensory modalities, such as increased acuity in auditory discrimination and voice recognition, when compared to sighted controls. These functional gains have been shown to rely on ‘visual’ cortical areas of the blind brain, characterizing the phenomenon of cross-modal plasticity. However, its anatomical underpinnings in humans have been unsuccessfully pursued for decades. Recent advances of non-invasive neuroimaging techniques allowed us to test the hypothesis of abnormal thalamocortical connectivity in congenitally blinds. Our results showed an expansion of the thalamic connections to the temporal cortex over those that project to the occipital cortex, which may explain, the cross-talk between the visual and auditory systems in congenitally blind individuals.

scholarly journals Relating excitatory and inhibitory neurochemicals to visual perception: a magnetic resonance study of occipital cortex between migraine events

2018 ◽  
Author(s):  
Yu Man Chan ◽  
Kabilan Pitchaimuthu ◽  
Qi-Zhu Wu ◽  
Olivia L Carter ◽  
Gary F Egan ◽  
...  
Keyword(s):  
Visual Cortex ◽  
Magnetic Resonance ◽  
Visual Perception ◽  
Binocular Rivalry ◽  
Occipital Cortex ◽  
Individual Variability ◽  
Healthy Individuals ◽  
Magnetic Resonance Study ◽  
Gaba Concentration ◽  
Inhibitory Neurotransmitter

AbstractCertain perceptual measures have been proposed as indirect assays of brain neurochemical status in people with migraine. One such measure is binocular rivalry, however, previous studies have not measured rivalry characteristics and brain neurochemistry together in people with migraine. This study compared spectroscopy-measured levels of GABA and Glx (glutamine and glutamate complex) in visual cortex between 16 people with migraine and 16 non-headache controls, and assessed whether the concentration of these neurochemicals explains, at least partially, inter-individual variability in binocular rivalry perceptual measures. Mean Glx level was significantly reduced in migraineurs relative to controls, whereas mean occipital GABA levels were similar between groups. Neither GABA levels, nor Glx levels correlated with rivalry percept duration. Our results thus suggest that the previously suggested relationship between rivalry percept duration and GABAergic inhibitory neurotransmitter concentration in visual cortex is not strong enough to enable rivalry percept duration to be reliably assumed to be a surrogate for GABA concentration, at least in the context of healthy individuals and those that experience migraine.

Interhemispheric EEG asymmetries during unilateral bright-light exposure and subsequent sleep in humans

2008 ◽  
Vol 294 (3) ◽  
pp. R1053-R1060 ◽  
Author(s):  
Christian Cajochen ◽  
Rosalba Di Biase ◽  
Makoto Imai
Keyword(s):  
Visual Cortex ◽  
Time Course ◽  
Visual Stimulation ◽  
Light Exposure ◽  
Bright Light ◽  
Occipital Cortex ◽  
Alpha Activity ◽  
Hemispheric Dominance ◽  
Eeg Activity ◽  
The Right

We tested whether evening exposure to unilateral photic stimulation has repercussions on interhemispheric EEG asymmetries during wakefulness and later sleep. Because light exerts an alerting response in humans, which correlates with a decrease in waking EEG theta/alpha-activity and a reduction in sleep EEG delta activity, we hypothesized that EEG activity in these frequency bands show interhemispheric asymmetries after unilateral bright light (1,500 lux) exposure. A 2-h hemi-field light exposure acutely suppressed occipital EEG alpha activity in the ipsilateral hemisphere activated by light. Subjects felt more alert during bright light than dim light, an effect that was significantly more pronounced during activation of the right than the left visual cortex. During subsequent sleep, occipital EEG activity in the delta and theta range was significantly reduced after activation of the right visual cortex but not after stimulation of the left visual cortex. Furthermore, hemivisual field light exposure was able to shift the left predominance in occipital spindle EEG activity toward the stimulated hemisphere. Time course analysis revealed that this spindle shift remained significant during the first two sleep cycles. Our results reflect rather a hemispheric asymmetry in the alerting action of light than a use-dependent recovery function of sleep in response to the visual stimulation during prior waking. However, the observed shift in the spindle hemispheric dominance in the occipital cortex may still represent subtle local use-dependent recovery functions during sleep in a frequency range different from the delta range.

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