Recording of Visual‐Evoked Potentials in Dogs With Scalp Electrodes

Abstract

Following unsuccessful attempts to record visual-evoked potentials (VEPs) in dogs with scalp electrodes, adoption of a new stimulation technique seems to be beneficial. Previously, flashes of white light administered after dark adaptation induced relatively high amplitude electroretinograms (ERGs) covering any VEP activity over the surface of the skull. ERG amplitude, however, can be significantly reduced using flashes of red light after light adaptation (mostly cone stimulation). Simultaneous ERG and VEP recording allows identification of VEPs composed of three significantly different negative peaks (Nl, N2, and N3) measured in dogs anesth2tized with chloralnse and halothane. No more than two of the three peaks were seen in one recording. Only the N1 and N3 waves were consistently recorded in dogs anesthetized with thiopental and thiopental combined with halothane. In 50% of all recordings, N1 was seen alone. The other VEPs consisted of N l and N2, or N l and N3 occurring concurrently. The simultaneous occurrence of N2 and N3 waves, however, was never seen. Among all recordings, N1 was most frequently recorded (85% of measurements), followed by N3 and N2 (38% and 31% of measurements, respectively).Peaks of less than 90 ms are highly reproducible. Anesthesia is necessary to eliminate frequent artifacts obtained in conscious and sedated dogs. Thiopental and/or halothane had no effect on measured latencies compared with chloralose. (Journal of Veterinary Internal Medicine 1988; 2:145-149) THE LARGE VOLUME of literature on visuel-evoked potentials (VEPs) in humans reflects the importance given to this noninvasive electrophysiological tool in the diagnosis of brain dysfunction. ' In animals, direct cortical measurement after implantation of electrodes on the cerebral cortex has been used to record potentials from the visual occipital cortex2-6 and to define the normal VEP.3,7 Recording of evoked cortical potentials (ECPs) with implanted electrodes is not applicable to clinical cases. Nearly atraumatic ECP recordings with scalp electrodes are performed routinely in humans. Until recently, however, VEP recording in animals with scalp electrodes was unsuccessful. The difficulty encountered in attempts to record VEPs in dogs has been attributed to the high amplitude far-field electroretinogram (ERG) conducted over the skull masking the localized lower amplitude VEP activity.8 High amplitude ERGs result when using flashes of white light after dark adaptation, i.e., when the photoreceptors of the retina, rods, and cones are maximally loaded with their respective photopigments. Under this circumstance, retinal stimulation with white light flashes gives rise to a response from most of the reactive cells of the retina. ' Because the retinas of dogs contain more rods than cones in an approximate proportion of 95: 1 , l o a lower amplitude ERG should be obtained by stimulation of the cones only. The lower amplitude of the ERG might allow easier recording of the VEP. The objective of the present study was to design a suita...

Reactivity of Dogs' Brain Oscillations to Visual Stimuli Measured with Non-Invasive Electroencephalography

“…Our current data confirm that, via extensive behavioral training with positive reinforcement, it is possible to conduct non-invasive EEG measurement and group-level studies with fully conscious, non-medicated and unrestrained domestic dogs—an endeavor that has been deemed unsuccessful in the past [14], [34]. In our study, the training and the EEG recordings were optimized for the relatively short attention span, as well as vibrant habitude of dogs, compared with the standard measurements in human subjects.…”

“…Brain function of dogs has been studied in the past mainly by recording activity with electroencephalography (EEG) directly from the brain, by sedating the animals and restraining their movements, and by putting them down after the experiment. Most of the functional brain research of dogs has explored epilepsy [e.g., [11], although some studies have described features of the nervous system functionality, such as oscillatory EEG activity during sleep [12] or awake state [13], or visual evoked potentials to flashes of light [14]–[16]. However the intracranial measurements, with the need to restrain and medicate the animals, do not readily allow the study of the nervous system function during cognitive events.…”

Visual Evoked Potentials in the Clinically Normal Dog

“…A recent study described VEP recorded from anesthetized dogs in response to flashes of red light. 26 The authors reported an inability to record reliable responses in conscious or sedated dogs, and described three negative peaks in the VEP that were inconsistently present in all dogs. They proposed that their stimulation protocol would reduce masking of early VEP components by farfield ERG signals, as reported in their earlier s t~d y .~ Because both studies used general anesthesia (halothane or chloralose), which, as the authors reported, may affect VEP recordings, it is difficult to draw conclusions from their results.…”

Topographic Analysis of Flash Visual Evoked Potentials in Dogs

“…The flash VEP stimulated by the flashlight has also been recorded in dogs [1,5,6,[9][10][11], however the generators of potentials in amplitude and/or latency of the waves, are not well known. Recently, topographic analysis of evoked potentials have been applied in human using multiple electrodes on the scalp for elucidating generators of the waves in the flash VEP [3,7,8,12].…”