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BMC veterinary research2016; 12(1); 120; doi: 10.1186/s12917-016-0743-3

Visual evoked potentials in the horse.

Abstract: Electrical potentials generated in the central nervous system in response to brief visual stimuli, flash visual evoked potentials (FVEPs), can be recorded non-invasively over the occipital cortex. FVEPs are used clinically in human medicine and also experimentally in a number of animal species, but the method has not yet been evaluated in the horse. The method would potentially allow the ophthalmologist and equine clinician to evaluate visual impairment caused by disorders affecting post-retinal visual pathways. The aim was to establish a method for recording of FVEPs in horses in a clinical setting and to evaluate the waveform morphology in the normal horse. Methods: Ten horses were sedated with a continuous detomidine infusion. Responses were recorded from electrodes placed on the scalp. Several positions were evaluated to determine suitable electrode placement. Flash electroretinograms (FERGs) were recorded simultaneously. To evaluate potential contamination of the FVEP from retinal potentials, a retrobulbar nerve block was performed in two horses and transection of the optic nerve was performed in one horse as a terminal procedure. Results: A series of positive (P) and negative (N) peaks in response to light stimuli was recorded in all horses. Reproducible wavelets with mean times-to-peaks of 26 (N1), 55 (P2), 141 (N2) and 216 ms (P4) were seen in all horses in all recordings. Reproducible results were obtained when the active electrode was placed in the midline rostral to the nuchal crest. Recording at lateral positions gave more variable results, possibly due to ear muscle artifacts. Averaging ≥100 responses reduced the impact of noise and artifacts. FVEPs were reproducible in the same horse during the same recording session and between sessions, but were more variable between horses. Retrobulbar nerve block caused a transient loss of the VEP whereas transection of the optic nerve caused an irreversible loss. Conclusions: We describe the waveform of the equine FVEP and our results show that it is possible to record FVEPs in sedated horses in a clinical setting. The potentials recorded were shown to be of post-retinal origin. Further studies are needed to provide normative data and assess potential clinical use.
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Publication Date: 2016-06-21 PubMed ID: 27329086PubMed Central: PMC4915148DOI: 10.1186/s12917-016-0743-3Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The research article investigates the use of non-invasive visual evoked potentials (FVEPs) as a method for evaluating visual impairment in horses, particularly conditions affecting post-retinal visual pathways.

Objective

This study aimed to determine the practicality and efficacy of using Flash Visual Evoked Potentials (FVEPs), a non-invasive method of recording electric potentials in response to visual stimuli, to evaluate visual impairment in horses due to disorders affecting post-retinal visual pathways. Until this study, the FVEP method had been deployed in human clinical medicine and various animal species, but not in horses.

Methodology

  • Ten horses were chosen for the experiment, and they were sedated with continual detomidine infusion.
  • Responses, prompted by visual stimuli, were recorded from electrodes placed on various positions on the horses’ scalps in order to analyze from where the most optimal responses could be gathered.
  • Flash electroretinograms (FERGs) were simultaneously recorded to measure the electrical responses of the retina.
  • In order to evaluate the potential of retinal potentials contaminating the FVEP, a retrobulbar nerve block and transection of the optic nerve were performed on two horses and one horse, respectively.

Results

  • Responses to light stimuli were recorded, taking the form of a series of positive and negative peaks.
  • Constant waveforms were recorded with times-to-peaks at 26 (N1), 55 (P2), 141 (N2), and 216 ms (P4).
  • Implementation of the active electrode in a midline rostral location to the horses’ nuchal crest rendered the most reliable results.
  • Lateral electrode placements resulted in more variable outcomes, possibly due to ear muscle artifacts.
  • Averaging over 100 responses minimized the impact that noise and artifacts had on the results.
  • FVEPs were repeatable within the same recording session and between different sessions for the same horse but varied between different horses.
  • A temporary loss of the VEP occurred after the retrobulbar nerve block, whereas the transection of the optic nerve generated an irreversible loss.

Conclusion

The study demonstrated that it is possible to record FVEPs from horses in a clinical setting. These potentials were shown to originate from a post-retinal source. The authors concluded that further studies are needed to establish normative data and assess the potential clinical usage of the collected data.

Cite This Article

APA
Ström L, Ekesten B. (2016). Visual evoked potentials in the horse. BMC Vet Res, 12(1), 120. https://doi.org/10.1186/s12917-016-0743-3

Publication

BMC veterinary research
ISSN: 1746-6148
NlmUniqueID: 101249759
Country: England
Language: English
Volume: 12
Issue: 1
Pages: 120

Researcher Affiliations

Ström, L
  • Department of Clinical Sciences, Swedish University of Agricultural Sciences, PO Box 7054, SE-750 07, Uppsala, Sweden. lena.strom@slu.se.
Ekesten, B
  • Department of Clinical Sciences, Swedish University of Agricultural Sciences, PO Box 7054, SE-750 07, Uppsala, Sweden.

MeSH Terms

  • Animals
  • Diagnostic Techniques, Ophthalmological / veterinary
  • Evoked Potentials, Visual
  • Female
  • Horses / physiology
  • Male

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Citations

This article has been cited 4 times.
  1. Itoh K, Kikumura N, Maeda T, Hirata S, Ringhofer M. Non-invasive scalp recording of electroencephalograms and evoked potentials in unanesthetized horses using a 12-channel active electrode array. Front Vet Sci 2024;11:1470039.
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  2. Castoldi V, d'Isa R, Marenna S, Comi G, Leocani L. Non-invasive visual evoked potentials under sevoflurane versus ketamine-xylazine in rats. Heliyon 2021 Nov;7(11):e08360.
    doi: 10.1016/j.heliyon.2021.e08360pubmed: 34816047google scholar: lookup
  3. Graïc JM, Peruffo A, Corain L, Finos L, Grisan E, Cozzi B. The primary visual cortex of Cetartiodactyls: organization, cytoarchitectonics and comparison with perissodactyls and primates. Brain Struct Funct 2022 May;227(4):1195-1225.
    doi: 10.1007/s00429-021-02392-8pubmed: 34604923google scholar: lookup
  4. Ström L, Bröjer J, Ekesten B. Variability, repeatability and test-retest reliability of equine flash visual evoked potentials (FVEPs). BMC Vet Res 2020 Jul 29;16(1):261.
    doi: 10.1186/s12917-020-02463-8pubmed: 32727477google scholar: lookup
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