Retinal processes involved in the evoked cortical potential to patterned stimuli

The purpose of this investigation was to study the underlying physiological processes involved in the evoked potential to patterned visual stimulation. Specifically, the study was designed to assess the role of the photopic and scotopic visual systems as mediatory processes subserving occipitally elicited potentials to a series of checkerboard patterns. In addition, it was hoped that the research would provide further information with respect to the hypothetical mechanisms of lateral inhibition and receptive field size and their contribution to complex visual processes. Six subjects participated in the experiment. Evoked potentials were recorded to a series of patterned stimuli that were illuminated with red and blue flashes presented to central and peripheral retinal sites against high and low levels of background luminance. Statistical analysis of the data revealed significant relations between evoked potential amplitude and the main effects of background, site, and check-size. Amplitude was also significantly related to the interaction effects of background x site, check-size x background, check-size x color, and site x color x background. Discussion of the results was in terms of the differential functional behavior of photopic and scotopic visual processes. Several comments were directed to the possible importance of lateral inhibition and receptive field size in the generation of these data

The Endocannabinoid System in the Vervet Monkey Retina

The main active compound found in the marijuana plant, tetrahydrocannabinol, is responsible for its psychotropic effects but also for its numerous beneficial actions such as appetite stimulation, nausea reduction, analgesia, and muscle spasm suppressor. Although cannabis consumption leads to some visual disturbances, the exact role of the endocannabinoid system (ECS) in normal vision is still unknown. Many studies have looked into the localization of this complex system (receptors, ligands, and enzymes) throughout the various components of the visual system of different animal models in order to obtain clues about its role. In fact, the retina, optic nerve, dorsal lateral geniculate nucleus, and visual cortices all express parts of the ECS. Manipulating this system pharmacologically or genetically has also an impact on visual function. In this book chapter, we provide the current understanding of how the ECS is involved in the functioning of the visual system and special emphasis is put on data obtained in monkeys, representing the most relevant animal model for visual neuroscience research. The mechanisms that control endocannabinoid (eCB) release and activation of cannabinoid receptors are discussed. We also propose a model highlighting the mechanisms involved in the regulation of photopic and scotopic vision taking advantage of the spatial specificity of the eCB signaling system and its physiological activation conditions

Erg lens with built-in ganzfeld light-source for stimulation and adaptation

A contact lens for routine electroretinography which contains a Ganzfeld light source is described. The light source consists of six light-emitting diodes and serves both as a stimulus source and a background illumination. The response characteristics with this source are comparable with those of an integrating sphere stimulator

Erg lens with built-in ganzfeld light-source for stimulation and adaptation

A contact lens for routine electroretinography which contains a Ganzfeld light source is described. The light source consists of six light-emitting diodes and serves both as a stimulus source and a background illumination. The response characteristics with this source are comparable with those of an integrating sphere stimulator

Topographical distribution of visually evoked cortical potentials in relation to locus of retinal stimulation and check size

Visually evoked cortical potentials (VERs) to checkerboard stimulation were studied as a function of locus of retinal stimulation, check size, and relative distribution of response over the cortex. Pattern stimuli of checks subtending 7.5, 15, 30, and 60' of arc were presented to the upper, central, lower, and lower-peripheral visual field. Evoked responses were recorded simultaneously from scalp electrodes located approximately 5 cm to the right or left of a point 2.5 cm above the inion, and approximately 2.5, 7.5, and 12.5 cm above the inion. Results obtained from the four electrode locations illustrated the differential effect of visual field stimulation on VER waveform in relation to the topography of the visual cortex. When activity was recorded from electrodes near the inion, VERs decreased as retinal stimulation was moved from the central to the lower-peripheral visual field. Such results indicate only that neural activity in response to peripheral stimulation decreased in the cortical area concerned with macular activity and not that, in general, VERs are less to peripheral than central visual stimulation. Responses at electrodes placed anteriorly over the peripheral projection area increased in amplitude as stimulation was changed from the central to the peripheral visual field

Rod driven frequency entrainment and resonance phenomena

A controversy exists on photic driving in the human visual cortex evoked by intermittent photic stimulation. Frequency entrainment and resonance phenomena are reported for frequencies higher than 12 Hz in some studies while missing in others. We hypothesized that this might be due to different experimental conditions, since both high and low intensity light stimulation were used. However, most studies do not report radiometric measurements, which makes it impossible to categorize the stimulation according to photopic, mesopic, and scotopic vision. Low intensity light stimulation might lead to scotopic vision, where rod perception dominates. In this study, we investigated photic driving for rod-dominated visual input under scotopic conditions. Twelve healthy volunteers were stimulated with low intensity light flashes at 20 stimulation frequencies, leading to rod activation only. The frequencies were multiples of the individual alpha frequency (α) of each volunteer in the range from 0.40 to 2.30∗α. Three hundred and six-channel whole head magnetoencephalography recordings were analyzed in time, frequency, and spatiotemporal domains with the Topographic Matching Pursuit algorithm. We found resonance phenomena and frequency entrainment for stimulations at or close to the individual alpha frequency (0.90–1.10∗α) and half of the alpha frequency (0.40–0.55∗α). No signs of resonance and frequency entrainment phenomena were revealed around 2.00∗α. Instead, on-responses at the beginning and off-responses at the end of each stimulation train were observed for the first time in a photic driving experiment at frequencies of 1.30–2.30∗α, indicating that the flicker fusion threshold was reached. All results, the resonance and entrainment as well as the fusion effects, provide evidence for rod-dominated photic driving in the visual cortex

A Physiological and Psychometric Evaluation of Human Subconscious Visual Response and Its Application in Health Promoting Lighting.

Subconscious vision is a recent focus of the vision science community, brought on by the discovery of a previously unknown photoreceptor in the retina dedicated to driving non-image-forming responses, intrinsically photosensitive retinal ganglion cells (ipRGCs). In addition to accepting inputs from rod and cone photoreceptors, ipRGCs contain their own photopigment, melanopsin, and are considered true photoreceptors. ipRGCs drive various non-image-forming photoresponses, including circadian photoentrainment, melatonin suppression, and pupil constriction. In order to understand more about ipRGC function in humans, we studied its sensitivity to light stimuli in the evening and day. First, we measured the sensitivity threshold of melatonin suppression at night. Using a protocol that enhances data precision, we have found the threshold for human melatonin suppression to be two orders of magnitude lower than previously reported. This finding has far-reaching implications since there is mounting evidence that nocturnal activation of the circadian system can be harmful. Paradoxically, ipRGCs are understimulated during the day. Optimizing daytime non-image-forming photostimulation has health benefits, such as increased alertness, faster reaction times, better sleep quality, and treatment of depression. In order to enhance ipRGC excitation, we aimed to circumvent adaptation (i.e. desensitization) of the photoresponse by using flickering instead of steady light. We find that properly timed flickering light enhances pupillary light reflex significantly when compared to steady light with 9-fold more energy density. Employing our findings, a new form of LED light is proposed to enhance subconscious visual responses at a typical indoor illuminance level. Using the silent substitution technique, a melanopsin-selective flicker is introduced into the light. A linear optimization algorithm is used to maximize the contrast of the subconscious, melanopsin-based response function while keeping conscious, cone-driven responses to the pulsing light fixed. Additional boundary conditions utilizing test color samples as an environmental mimic are introduced to limit the amount of perceived color change in a simulated environment. Two examples of lights are given to illustrate potential applications for general illumination and therapeutic purposes. For the lighting and electronics industry, we hope our study of subconscious-stimulative thresholds at night will better inform their design guidelines for health conscious products.PhDMacromolecular Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/133226/1/garenv_1.pd

Aerospace Medicine and Biology: A continuing bibliography with indexes, supplement 127, April 1974

This special bibliography lists 279 reports, articles, and other documents introduced into the NASA scientific and technical information system in March 1974