Racial and cultural differences in sensitivity to flickering light

Latin America has been registering a fast decrease in fertility rates since the mid-twentieth century. This change can be linked to the modernization process these populations have been undergoing. However, research with Latin American indigenous populations, which are undergoing relatively similar lifestyle changes, shows very different trends in fertility. The aim of this study was to analyze fertility patterns in the indigenous Toba community of Cacique Sombrero Negro, which is experiencing a rapid process of economic and social Westernization. Fertility patterns were analyzed between 1981 and 1999, the period for which the most accurate records were found. Results showed an overall increase in fertility rates and changes in the age of peak fertility across time periods. It is hypothesized that the lifestyle transition this population is experiencing leads to better access to resources that, in the absence of contraception, allow for a higher number of offspring. Nevertheless, this higher resource availability would be differential, affecting mostly the fertility of younger mothers.     

Oscillatory activity in the neural networks of spiking elements

We study the dynamics of activity in the neural networks of enhanced integrate-and-fire elements (with random noise, refractory periods, signal propagation delay, decay of postsynaptic potential, etc.). We consider the networks composed of two interactive populations of excitatory and inhibitory neurons with all-to-all or random sparse connections. It is shown by computer simulations that the regime of regular oscillations is very stable in a broad range of parameter values. In particular, oscillations are possible even in the case of very sparse and randomly distributed inhibitory connections and high background activity. We describe two scenarios of how oscillations may appear which are similar to Andronov-Hopf and saddle-node-on-limit-cycle bifurcations in dynamical systems. The role of oscillatory dynamics for information encoding and processing is discussed.     

Reactions of neural elements of neocortex to action of hypoxia at the early neonatal period in rats

We studied reactions of neural elements from different neocortex regions (sensorimotor, visual, auditory) to acute normobaric hypoxia on the model of human incomplete pregnancy (the 2-day-old rat pups) and revealed similar and unidirectional reorganization in all these regions. The chosen parameters of hypoxia induced the earliest detectable changes as fast as in a day since exposure: a decrease in cell body size and cytoplasmic volume, intensification of apoptotic cell death. By the end of the neonatal period (day 5), several ultrastructural changes were observed by indicating deceleration of processes of nerve cell differentiation: arrest of complication of smooth and rough endoplasmic reticulum and Golgi apparatus, the reduced number of free ribosomes and polysomes in cytoplasm as well as of axonal and dendritic growth cones in neuropil, delayed and disordered myelination of nerve fibers. All these morphofunctional abnormalities may be the structural basis for development of neonatal encephalopathies.     

Effect of rhythmical light flickering on the stability of the human body

Influence of photostimulation upon the man's movements biomechanics (stabilogram, goniogram, electromiogram etc) according to the one-leg toe balance model was investigated on 500 persons. Lowering of the exercise biomechanical efficiency at the background of light gleams was established. Light gleams with the frequency of 8-12 Hz which violated movement control processes (the correction of the body GWC) had maximal confusing effect.     

Electrophysiology of the Insect Dorsal Ocellus : III. Responses to flickering light of the dragonfly ocellus

The ERG of the dragonfly ocellus has been analyzed into four components, two of which originate in the photoreceptor cells, two in the ocellar nerve fibers (Ruck, 1961 a). Component 1 is a sensory generator potential, component 2 a response of the receptor axons. Component 3 is an inhibitory postsynaptic potential, component 4, a discharge of afferent nerve impulses in ocellar nerve fibers. Responses to flickering light are examined in terms of this analytic scheme. It has been found that the generator potential can respond to higher rates of flicker—up to 220/sec.—than can the receptor axon responses, the postsynaptic potential, or the ocellar nerve impulses. The maximum flicker fusion frequency as measured by fusion of the ERG is that of the sensory generator potential itself.     

Galactosyltransferase activity of intact neural retinal cells from the embryonic chicken

Permeability of electrotonic junctions between isolated and reaggregated Fundulus blastomeres was evaluated with a new fluorescent dye, Lucifer yellow CH. The dye is readily shown to pass between coupled cells. It does not enter from the bathing medium, nor does it move between cells via the enlarged extracellular space sometimes seen between them. Thus, we conclude that passage is via a private pathway, presumably provided by the gap junctions described for this tissue. In contrast to previous findings, fluorescein (as the sodium salt, uranine) also passes between coupled Fundulus cells. Although it can enter from the bathing medium, it may be less concentrated in the space between a cell pair than in the uninjected cell. Again, passage via gap junctions is indicated. Molecular models demonstrate that Lucifer yellow and fluorescein are similar in size. Thus, similarity in ability to permeate junctional membranes is to be expected.     

Remodeling of retinal ganglion cell dendrites in the absence of action potential activity

The dendrites of ganglion cells in the retina have an excess number of spines and branches that are normally lost during the first postnatal month of development. We investigated whether this dendritic remodeling can be prevented when the action potential activity of ganglion cells is abolished by chronic intraocular injections of tetrodotoxin (TTX) during the first 4 or 5 postnatal weeks in the cat. Dendritic tree morphologies of alpha and beta ganglion cells from TTX-treated, non-TTX-treated (contralateral eye), and normal control retinae were compared after intracellular filling with Lucifer yellow. Qualitative observations and quantitative measurements indicate that TTX treatment does not prevent the normally occurring loss of spines and dendritic branches. Indeed, the dendritic trees of both alpha and beta cells in TTX injected eyes actually have even fewer spines and branches than normal cells at equivalent ages. However, because the total dendritic lengths of these cells are also reduced after TTX blockade, spine density is indistinguishable from untreated animals at the same age. In addition, although dendritic field areas are not altered with treatment, the complexity of the dendritic trees is reduced. These observations suggest that dendritic remodeling can occur in the absence of ganglion cell action potential activity. Thus, the factors that influence the dendritic and axonal development of retinal ganglion cells must differ, because similar TTX treatment during the period of axonal remodeling does have profound effects on the final pattern of terminal arborizations.     

Some quantitative characteristics of the frog retinal rod outer segments]

Retinal rod outer segments in frogs were studied by means of light microscopy, refractometry, microspectrophotometry, and electron microscopy. Analysis of the data obtained shows that an unidentified substance, which makes up about 50% of outer segment dry weight, is lost during routine biochemical investigations. The protein parts of the rhodopsin molecules make up 85% of the outer segments proteins and 25% of outer segment dry weight. Rhodopsin molecules can be arranged in a square array with a unit cell side of about 7 nm on one side of each disk membrane. Lipids in a single membrane occupy only 2 nm, and disk membranes are strongly hydrated.     

Responses of retinal rods of the frog to light

To study the effect of the intensity, duration, spectral composition, and diameter of the light spot on the amplitude and shape of the response of single rods of the frog retina, potentials were recorded intracellularly. The rods tested could be divided into two groups on the basis of their responses to light spots of different spectral composition: those with maxima of sensitivity at 507 ± 8 nm and 442 ± 8 nm. With an increase in the intensity of light the response amplitude rose gradually and the time for the response to rise to its maximum was shortened. A bright flash temporarily inhibited the sensitivity of the cell to subsequent test flashes. If light spots of larger diameter (1000–1500 µ) were presented a delayed depolarization wave, due to illumination of the distant surroundings of the receptor, was observed in the course of recovery of the photic response; this effect was maximal for stimulation with red light and it was evidently induced by horizontal cell activity. The possible functional role of the depolarizing effect of illumination of the distant surroundings of the receptor is discussed.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 7, No. 1, pp. 84–92, January–February, 1975.     

A functional statistical analysis of the action potentials in the brain multineuronal activity of waking cats

In the present work a method is substantiated of the correction of singled out impulses series by identification of parameters of neurones discharges (PD) during a long period of recording (up to 120 days) of the neuronal activity by means of chronically implanted nichrome semimicroelectrode in different brain part of alert cats.     

Remodeling of retinal ganglion cell dendrites in the absence of action potential activity.

The dendrites of ganglion cells in the retina have an excess number of spines and branches that are normally lost during the first postnatal month of development. We investigated whether this dendritic remodeling can be prevented when the action potential activity of ganglion cells is abolished by chronic intraocular injections of tetrodotoxin (TTX) during the first 4 or 5 postnatal weeks in the cat. Dendritic tree morphologies of alpha and beta ganglion cells from TTX-treated, non-TTX-treated (contralateral eye), and normal control retinae were compared after intracellular filling with Lucifer yellow. Qualitative observations and quantitative measurements indicate that TTX treatment does not prevent the normally occurring loss of spines and dendritic branches. Indeed, the dendritic trees of both alpha and beta cells in TTX injected eyes actually have even fewer spines and branches than normal cells at equivalent ages. However, because the total dendritic lengths of these cells are also reduced after TTX blockade, spine density is indistinguishable from untreated animals at the same age. In addition, although dendritic field areas are not altered with treatment, the complexity of the dendritic trees is reduced. These observations suggest that dendritic remodeling can occur in the absence of ganglion cell action potential activity. Thus, the factors that influence the dendritic and axonal development of retinal ganglion cells must differ, because similar TTX treatment during the period of axonal remodeling does have profound effects on the final pattern of terminal arborizations.     

Blinking suppresses the neural response to unchanging retinal stimulation

Blinks profoundly interrupt visual input but are rarely noticed, perhaps because of blink suppression, a visual-sensitivity loss that begins immediately prior to blink onset. Blink suppression is thought to result from an extra-retinal signal that is associated with the blink motor command and may act to attenuate the sensory consequences of the motor action. However, the neural mechanisms underlying this phenomenon remain unclear. They are challenging to study because any brain-activity changes resulting from an extra-retinal signal associated with the blink motor command are potentially masked by profound neural-activity changes caused by the retinal-illumination reduction that results from occlusion of the pupil by the eyelid. Here, we distinguished direct top-down effects of blink-associated motor signals on cortical activity from purely mechanical or optical effects of blinking on visual input by combining pupil-independent retinal stimulation with functional MRI (fMRI) in humans. Even though retinal illumination was kept constant during blinks, we found that blinking nevertheless suppressed activity in visual cortex and in areas of parietal and prefrontal cortex previously associated with awareness of environmental change. Our findings demonstrate active top-down modulation of visual processing during blinking, suggesting a possible mechanism by which blinks go unnoticed.