Electroretinogram in response to x-ray stimulation

The retina of the grass frog, Rana pipiens, responds to flashes of highintensity x-rays and produces an electroretinogram indistinguishable in form from the electroretinogram produced in response to light stimulation at low and intermediate intensities. At higher intensities the form changes and, for maximal responses, the electroretinogram in response to x-rays shows a lower amplitude and a longer latent period than that in response to light. The prolonged latent period indicates additional intermediate reactions for the x-rays response.     

Electroretinogram of the frog during embryonic development

Eyes removed from frog embryos at various stages of development gave a definite pattern of change in the electroretinogram. From the 7th to 9th days the electroretinogram consisted of slow, purely cornea-negative potentials. From the 9th to 10th days the responses were negative but included a prominent fast, negative component superimposed on the slow potentials. During the 11th to 17th days positive potentials appeared and developed. From the 20th day on, the typical electroretinogram of the adult obtained.     

Membrane fatty acids associated with the electrical response in visual excitation

The fatty acid composition of rat photoreceptor membranes was altered by dietary manipulation. A functional alteration was also observed in the component of the electroretinogram which is generated by the photoreceptors. A membrane fatty acid, docosahexaenoic acid, appears to be involved in the transduction process of visual excitation.     

Vitamin A deficiency effect on retina: dependence on light

The effects of vitamin A deficiency in the rat eye, as measured by the electroretinogram and changes in rhodopsin content, are critically dependent upon the levels of illumination to which the animals are exposed daily. Depleted animals kept in darkness maintained virtually normal electroretinogram function and rhodopsin content for 5 to 6 months while those kept in weak cyclic light lost rhodopsin continuously. A fraction of the retinol released from rhodopsin during illumination disappears presumably from the pigment epithelium into the blood and becomes unavailable for rhodopsin regeneration. A sequence of three first-order reactions was assumed to estimate the rate constant of this disappearance (0.03 per hour). Computer simulation supporting the experimental data illustrates the dependence of the retinal abnormalities on light.     

Mycoplasma pneumoniae: proposed nomenclature for atypical pneumonia organism (Eaton agent)

The light intensity-fusion frequency relationship of the goldfish electroretinogram follows the Ferry-Porter law except at the higher intensities. Maximum fusion frequency increases with temperature thus contradicting the results of studies elsewhere on the behavioral responses in sunfish.     

Electroretinogram of the visually deprived cat

Cats kept in darkness from birth show a subnormal b-wave in the electroretinogram to 4 weeks of age but quickly develop the full response upon stimulation. When the cats are kept without light for 1 year, the response recovers slowly after intense stimulation. A 2-day exposure to light is sufficient to reverse this diminution in response.     

Ecology of colors of firefly bioluminescence

Dark-active North American fireflies emit green bioluminescence and dusk-active species emit yellow, in general. Yellow light and yellow visual spectral sensitivity may be adaptations to increase the signal-to-noise (that is, foliage-reflected ambient light) ratio for sexual signaling during twilight. The peaks of the electroretinogram visual spectral sensitivities of four species tested, two dark- and two dusk-active, correspond with the peak of their bioluminescent emissions.     

Light adaptation in the rat retina: evidence for two receptor mechanisms

Light adapting the rat retina with transient white flashes too dim to bleach a substantial amount of visual pigment produces a change in electroretinogram spectral sensitivity and an increase in flicker fusion frequency. Increment threshold curves obtained with a long wavelength adapting stimulus and a short wavelength test stimulus show rod saturation.     

Metacontrast: its relation to evoked potentials

Electrophysiological correlates of metacontrast were studied by means of averaged evoked potentials recorded from the scalp in man. Under conditions in which the brightness of the first of two successive stimuli appears diminished there is no accompanying attenuation of the evoked potentials to that stimulus. The results suggest that the amplitude and latency of evoked potentials correlate with stimulus intensity but not with brightness.     

Insect photoreceptor: an internal ocellus is present in sphinx moths

Adult sphinx moths lack external ocelli. In Manduca sexta and other anocellate moths structures homologous to ocelli have been observed. Histological examination of such a structure in Manduca sexta has shown structural similarities to ocelli of other insects. Electrophysiological studies revealed a response to light stimuli stimilar to the electroretinogram of external ocelli. The evidence strongly suggests that the structures are internal ocelli.     

Self-stimulation alters human sensory brain responses

Human electrocortical potentials evoked by self-administered auditory and visual stimuli manifest much smaller amplitude and faster poststimulus timing than do average brain responses evoked by identical machine-delivered stimuli. Auditory evoked potentials show this "self-stimulation effect" to a greater degree than do visual responses. For visual evoked potentials, the effect appears greater at the vertex association area than over the occipital cortex. Individual differences in the magnitude of the "self-stimutlation effect" relate to level of intelligence.     

Metacontrast and evoked potentials: a reappraisal

Stimulation of the parafoveal retina may give rise to visual evoked responses generated in large part by stray light impinging upon the fovea. This effect appears to account for the absence of changes in the visual evoked response to parafoveal stimulation during metacontrast suppression. When the central retina is directly stimulated, the spatiotemporal interactions associated with brightness suppression during metacontrast may be readily demonstrated in a late component of the visual evoked response.     

Evoked potential correlates of expected stimulus intensity

The electrophysiological responses to a flash of medium intensity have different wave shapes in trials in which the occurrence of bright stimuli or dim stimuli is expected. When a bright or dim stimulus is signaled, the potentials evoked by the medium stimulus resemble the responses evoked by a real bright or dim flash.     

Specificity of peptides; new aspects of the specificity of peptides with vitamin and hormone action are described

The data now at hand show that specificity among biologically active peptides is probably not as exquisite as might have been deduced from experiences with some of the water-soluble vitamins. It is plain that a given biological effect can be evoked by peptides which differ considerably. It is likewise plain that the effect cannot be evoked by a number of other peptides. There is apparently some specificity, but more is involved than that incorporated in the classical view.     

Effects of visual form on the evoked response

The average visual evoked potentials elicited from relaxed human subjects are different for a blank visual field and one containing a geometric form, are different for different geometric forms of equal area, are similar for versions of the same geometric fortn of unequal area, and are different for two printed words equated for total letter area. These findings suggest that the waveform of evoked responses is not determined solely by the set of peripheral receptors which is stimulated, but it also reflects the perceptual content of the stimulus.     

Evoked potential correlates of generalization

Late components of evoked potentials recorded during the occurrence and nonoccurrence of generalization are different. During generalization the evoked response waveshapes resembled those elicited by the conditioned stimulus during correct performance. The differences are statistically significant.     

Evoked response and behavior in cats

Electroencephalographic averaged evoked responses to flashing lights of four different intensities were recorded in ten cats and correlated with behavior. Animals showing a high degree of exploratory behavior, aggressiveness, and activity and little withdrawal showed relatively large increases in amplitude of the averaged evoked response with increases of stimulus intensity. Those showing opposite behavioral traits had small increases or decreases of average evoked response amplitude with increases of stimulus intensity. These findings are compatible with those reported for human subjects. Inference is made about a neurophysiological mechanism for stimulus intensity modulation.     

Evoked potential correlates of signal recognition between and within modalities

Electrical responses evoked by clicks, flashes, changes in noise level, and changes in light level were recorded from the scalps of human subjects set to detect one of the stimuli. An early negative component of the evoked responses reflects selection between sensory modalities, whereas the later positive component reflects a more complex intramodal discrimination.     

Visual evoked response correlates of unconscious mental processes

Average evoked responses and accompanying free associations elicited by subthreshold visual stimuli were studied to determine if a differential discrimination between two stimuli would be reflected in either or both of these responses. The results indicate that the effects of subliminal perception are encoded in the average evoked response and also influence the content of free associations.     

Evoked potentials: modifications by classical conditioning

Visual evoked potentials to a positive discriminative stimulus change systematically during sensory conditioning and extinction. Changes due to conditioning are manifested in the increased amplitude of the late component of the evoked response. This effect is attenuated during extinction and reappears after reconditioning.