Photic Inhibition of Brain Stimulated Firefly Flashes

A study of the effects of photic stimulation on the abilityto induce flash luminescence in the female Photuris fireflyby electrical brain stimulation was made. Pulses of light deliveredto the eye of the firefly aie not only able to inhibit spontaneousflashing but also reduce the ability of electrical biain stimulito induce firefly flashes. Inhibition by photic pulses is mosteffective when the pulses are delivered approximately 300–400msec prior to brain stimulation. Only flashes of biain stimulus—flashonset latency greater than 120 msec can be inhibited in thisfashion, while driven flashes of 90 msec were immune from theinhibitory effect. It is suggested that the inhibilory effectsof photic stimulation provide some physiological explaintionof the male-female response latency found in the courting fireflies.     

A disjunctive analysis of neonatal approach stimulus prepotence

Preliminary results of a disjunctive procedure developed to ascertain the relative attractiveness for domestic chicks of auditory and visual stimuli are promising. A detailed account of the procedure and initial results is presented. Seventy-two Canadian Athens random bred chicks were tested at 24 or 36 h posthatch. A repetitive tone (4 per sec, 50 msec duration, 500 Hz) served as the auditory stimulus, and a flickering light (3.5 flashes per sec, 0.8 foot candle) served as the visual stimulus. An age-dependent change in the attractiveness of auditory and visual stimuli obtained with the disjunctive procedure. No change in stimulus preference obtained when the stimuli were presented individually.     

Mechanisms of synchrony in the North American fireflyPhotinus carolinus (Coleoptera: Lampyridae)

Photometric recordings combined with computer stimulation, acquisition and analysis were used to study synchrony in the North American fireflyPhotinus carolinus. A computer-generated burst of simulatedP. carolinus flashes was used to trigger a firefly flash burst. We found that the first triggered firefly flashes occurred after the second or third flashes in the stimulus burst, that there were fewer flashes in a triggered burst than a spontaneous burst, and that extending the stimulus flashes into the firefly's interburst interval inhibited firefly flashing. When the stimulus flash interval (389–560 ms) was changed, no change was seen in the interflash interval. When the stimulus flash interval was changed, the average time between stimulus flash and firefly flash (flash delay) changed as if the firefly interflash interval was constant. Thus, interflash interval inP. carolinus does not change its length, making it similar to the Southeast Asian synchronizerPteroptyx cribellata and different fromPteroptyx malaccae, which can change its interval. We suspect that the time between bursts is functionally analogous to the time between flashes in Southeast Asian synchronizers.     

The initial response of Limulus ventral photoreceptors to bright flashes. Released calcium as a synergist to excitation

The leading edge of the response of Limulus ventral photoreceptors to brief flashes was investigated using a voltage clamp. The leading edge of responses increases linearly with flash intensity when dim flashes produce less than one photoisomerization per square micron of cell surface. Brighter flashes accelerate the initial portion of the response, resulting in a fourth-power relationship between the magnitude of the response at brief times after the flash and the flash intensity. The onset of this nonlinearity with increasing flash intensity is determined by the local density of photoisomerizations within the receptor. Responses to bright 10-15-mum-diam spots therefore rise faster than responses to diffuse flashes producing the same number of photoisomerizations within the receptor. Background illumination shortens the response latency and suppresses the initial nonlinearity. These phenomena can be explained by a model of transduction in which light activates two parallel cascades of reactions. Particles released by the first of these cascades open ionic channels, while the second produces an agent that accelerates the rate of production of particles by the first. Injection of the calcium buffer EGTA slows the initial portion of the response to bright flashes and suppresses its nonlinearity, which suggests that the accelerating agent released by the second cascade is calcium.     

Effects of light flashes on the dark closure of Albizzia julibrissin pinnules

An electronic flash unit is used to deliver, at the beginning of a 10 min dark period and within a few ms, large doses of light to Albizzia julibrissin pinnules, to ascertain their effects on the rate of pinnule closing. In a series of alternating light flashes at 710 and 550 nm, the first 710 nm light flash significantly retards closing. A following light flash at 550 nm negates the far-red induced delay. The second 710 nm light flash delays closing less effectively than the first when given within 4 s after the green flash, but is just as effective when given after 30 s. The delay brought about by the second 710 nm light flash is again abolished by a light flash at 550 nm. A light flash at 660 nm has no effect on pinnule closing by itself and is also ineffective in reversing the far-red induced delay. A series of ten 710 nm light flashes becomes most effective in delaying closure when there is a dark interval of one min between flashes. The closing delay induced by a 710 nm light flash escapes reversal by a 550 nm light flash when the dark interval between the two flashes exceeds 2–3 min. A 750 nm light flash has no retarding effect on pinnule closing, but it becomes effective when preceded by a 660 nm or 550 nm light flash. The results obtained are suggested to be due to light absorbed by phytochrome and an unknown photoreceptor with green, far-red photoreversal property.     

Detection of red and green flashes: evidence for cancellation and facilitation.

Green and red flashes of light will differentially stimulate the middle- and long-wavelength sensitive cones. Interaction of cone signals was studied by measuring increment thresholds for combinations of green and red flashes on a yellow adapting field. When the yellow adapting field was at 10.000 trolands (td), green and red incremental flashes (1 degree, 200-msec duration) produced cancellation when presented simultaneously and facilitation when presented sequentially. A green incremental flash (1.15 degrees, 200 msec, 5000-td adaptation field) and red decremental flash, or vice versa, produced facilitation when presented simultaneously. The results can be explained by color-differencing, opponent-mechanisms. The cancellation effect for the simultaneous incremental flashes largely disappeared when the flashes were exposed briefly (10 msec) or reduced in size (0.04 degrees). It is unlikely that the stimuli were exclusively detected by achromatic, luminance channels, as suggested by previous work, since observers could partially distinguish the hue of threshold flashes of 570- and 590-nm light (0.04 degrees, 10 msec) on a bright yellow field.     

Temporal acuity of honeybee vision: behavioural studies using flickering stimuli

ABSTRACT. Temporal resolution of freely-flying bees was measured by training bees, Apis mellifera (Linn.), to discriminate between a steady light and a flickering light. Two kinds of experiments were conducted: those using a homochromatic flicker, in which the intensity of the flickering light varied periodically with time; and ones using a heterochromatic flicker, in which the colour of the flickering light varied periodically. In either case, the time-averaged properties (intensity and colour) of the flickering light matched those of the steady light, and the bees' ability to discriminate between the two stimuli was measured for various flicker frequencies. The results indicate that bees perform poorly in the homochromatic flicker experiments, regardless of the colour of the light (u.v., blue or green), but well in those with heterochromatic flicker. Heterochromatic flicker experiments using various pairwise combinations of the colours U.V., blue and green (corresponding to the three known spectral receptor-types in the bee's retina) reveal that temporal resolution is much better when blue is one of the component colours, than when it is not. The simplest interpretation of the results is in terms of colour channels possessing different response speeds. Heterochromatic flicker promises to be a useful tool in investigating the temporal properties of colour vision in bees.     

Visual responses in crayfish 3. Further studies on transmission through the brain

Responses to illumination of the eyes of the crayfish were studied by gross recording from one of the circumesophageal connectives. Two-thirds of the spontaneous activity at this level of the CNS consists of ascending activity, which is eliminated by cutting a connective posterior to the recording electrode. An average of about eight fibers in a connective responded to 1 sec illumination of the homolateral eye. The fibers were of four types: pure-on units, on-sustained units, on-and-off units and pure-off units. The average latency was 74 msec for the on-response and 26 msec for the off-response. The latency of responses to 10 μsec flashes of increasing intensity shortened from 72 to 52 msec. This was demonstrated to be mainly a peripheral effect since ERG latency showed a parallel reduction while the ERG-connective response interval remained more nearly constant at 40–50 msec. ERG amplitude, frequency, and usually the duration of the connective spike discharge increased at greater stimulus intensities, yet the average number of responding fibers was greatest at intermediate intensities. The results indicate minimal processing of response patterns by the brain.     

The Rat Electroretinogram : II. Bloch's law and the latency mechanism of the b-wave

Electroretinograms were obtained from the all-rod eye of the rat with uniform illumination of the entire retina and stimulus flashes of less than 3 msec. duration. Bloch's law of temporal summation was verified for the b-wave latency by varying the time between two equal intensity flashes and observing that no change occurred in the latency when measured from the midpoint of the two flashes. The results of this and other experiments are described in terms of a simple but general model of the latency-determining mechanism. It is shown that this latency mechanism acts as if it depends on a linear additive process; and also that a hypothetical excitatory substance which triggers activity in the sources of the b-wave must accumulate rapidly in time after the flash, approximately as t⁸. The rate at which this substance accumulates is accurately represented by the diffusion equation for more than 4 to 6 log units in the flash intensity. This suggests that the rate-determining step in the latency mechanism may be diffusion-limited.     

The Dependence of the Photopupil Response on Flash Duration and Intensity

The changes in pupil size were recorded by infrared pupillographic methods in response to light flashes of different durations and intensities for a 13 degree 34 minute centrally fixated circular field. For such stimuli, the threshold intensities for (rod) vision and for the pupil response were found to be about the same. The response amplitudes were related to the logarithm of the flash energy, the reciprocity law remaining valid up to about one-half second. The curve relating flash energy and pupil response was clearly divisible into two parts commensurate with the duplex character of the human retina. A similar dichotomy appears in curves relating response amplitude to response latency. Since the pupil response is determined by total flash energy, intense long flashes produce larger pupil responses than shorter (and perceptually brighter) ones of the same intensity.     

Suppression of cone signal in the dark-adapted frog retina as indicated by the electroretinogram.

Electroretinogram (ERG) cone acitvity is depressed in the dark-adapted frog retina. The strength of this effect is examined over a large range of flash energy, for 618 nm flashes extending up to about 4 log10 units above the "threshold" (10-25 micron V b-wave) of the cone ERG "released" in the early stage of rapid dark-adaptation (RDA). Cone signal depression is remarkably strong over this flash energy range. The cone ERG is practically absent for flashes up to about I log unit above cone RDA threshold. For stronger flashes, the suppression becomes time-dependent, that is, cone signal is very small for the first few hundred msec. after the flash, cone intrusion then becoming detectable. The results suggest that the cone suppression phenomena arises distally in the retina, probably near the receptor layer, and that cone signal intrusion a few hundred msec. after a strong flash may be due to light-adaptation of rods by the flash itself.     

Linear Superposition of Retinal Action Potentials to Predict Electrical Flicker Responses from the Eye of the Wolf Spider, Lycosa baltimoriana (Keyserling)

Retinal action potentials were elicited from light-adapted posterior median ocelli of the wolf spider Lycosa baltimoriana (Keyserling) by rectangular shaped photic stimuli representing 8 per cent increments or decrements of the background illumination. Responses to trains of recurrent incremental or decremental flashes were successfully predicted by graphical linear superposition of a single flash response, which was repeatedly drawn and added to itself at intervals equal to the period of the intermittent stimulus. Incremental stimuli inverted to form decremental stimuli elicited responses which were also inverted. Responses to single incremental flashes were successfully predicted by linear superposition of the response to one incremental step stimulus, which was inverted and added to itself at an interval equal to the duration of the flash.     

Intensity and motion responses of giant vertical neurons of the fly eye

There are nine “giant vertical” neurons in the lobula plate of the fly optic lobe. Intracellular recordings were obtained from the three most peripheral of these cells. These cells respond to a light flash with graded changes in the membrane potential. The response consists of an “on” transient, a sustained depolarization, an increase in membrane potential fluctuations, and an “off” transient. Signal averaging showed that only the “on” and “off” transients are correlated to the stimulus. A pattern of horizontally oriented stripes moving in the vertical direction evokes a response larger than the response to a stationary pattern. The response is most sensitive to vertical movement; motion in the downward direction evokes a net membrane potential depolarization, and upward motion results in a net hyperpolarization. We conclude that the giant vertical cells function primarily as vertical motion detectors and that the direction of the motion is encoded in the polarity of the shift in the membrane potential.     

Frequency dependent flicker response enhancement in the lamina ganglionaris ofDrosophila

Summary At low light intensity and within the narrow frequency range of 55 to 66 s^–1, the eye ofDrosophila will follow a flashing light source by enhancing it's flicker response to every other flash. By contrast, at lower and higher frequencies the eye will follow every cycle of a respective flash frequency upto a fusion point around 200 s^–1.While the receptor cells involved are retinula cells R1–6, the flicker response enhancement is established to originate postsynaptically in the Large Monopolar Cells of the lamina with which the peripheral retinula cells synapse, and which respond with the cornealpositive on-transient component of the ERG. Not only is a prescribed frequency required for the enhancement, but also continuity of cue — since brief periods of light flashes within the required frequency range are resolved at every cycle.The flicker response behaviour provides further credence to the existence of fine tuning mechanisms together with amplification within the lamina neuropile.We are grateful to the late Dr. Richard Wright for his comments, and to Professor Aubrey Manning for the hospitality his Department gave to N.L.     

Conscious awareness of flicker in humans involves frontal and parietal cortex

Even when confined to the same spatial location, flickering and steady light evoke very different conscious experiences because of their distinct temporal patterns. The neural basis of such differences in subjective experience remains uncertain . Here, we used functional MRI in humans to examine the neural structures involved in awareness of flicker. Participants viewed a single point source of light that flickered at the critical flicker fusion (CFF) threshold, where the same stimulus is sometimes perceived as flickering and sometimes as steady (fused) . We were thus able to compare brain activity for conscious percepts that differed qualitatively (flickering or fused) but were evoked by identical physical stimuli. Greater brain activation was observed on flicker (versus fused) trials in regions of frontal and parietal cortex previously associated with visual awareness in tasks that did not require detection of temporal patterns . In contrast, greater activation was observed on fused (versus flicker) trials in occipital extrastriate cortex. Our findings indicate that activity of higher-level cortical areas is important for awareness of temporally distinct visual events in the context of a nonspatial task, and they thus suggest that frontal and parietal regions may play a general role in visual awareness.     

Superoxide flashes: early mitochondrial signals for oxidative stress-induced apoptosis

Irreversible mitochondrial permeability transition and the resultant cytochrome c release signify the commitment of a cell to apoptotic death. However, the role of transient MPT (tMPT) because of flickering opening of the mitochondrial permeability transition pore remains elusive. Here we show that tMPT and the associated superoxide flashes (i.e. tMPT/superoxide flashes) constitute early mitochondrial signals during oxidative stress-induced apoptosis. Selenite (a ROS-dependent insult) but not staurosporine (a ROS-independent insult) stimulated an early and persistent increase in tMPT/superoxide flash activity prior to mitochondrial fragmentation and a global ROS rise, independently of Bax translocation and cytochrome c release. Selectively targeting tMPT/superoxide flash activity by manipulating cyclophilin D expression or scavenging mitochondrial ROS markedly impacted the progression of selenite-induced apoptosis while exerting little effect on the global ROS response. Furthermore, the tMPT/superoxide flash served as a convergence point for pro- and anti-apoptotic regulation mediated by cyclophilin D and Bcl-2 proteins. These results indicate that tMPT/superoxide flashes act as early mitochondrial signals mediating the apoptotic response during oxidative stress, and provide the first demonstration of highly efficacious local mitochondrial ROS signaling in deciding cell fate.     

Plastic response changes in neurons from lateral geniculate body in rats submitted to conditional reflectory stimulation]

In alert curarized rats the influence of an electric stimulation of the tail skin on the flash-evoked activity of single units of the dorsal part of the lateral geniculate body (CGLd) was investigated. The light flashes were applied 400 msec prior to the electric shocks. 50% of the units showed a change of the response pattern to flash. In the majority of cases the response shifts consisted in a facilitation, which developed gradually and persisted in most of the units examined, even when the electrical stimulus was no longer given in combination with the light. The results are discussed taking into consideration the possibility of an altered emotional or motivational status of the animal, which could play a role in the development of plasticity at the unitary level.     

INTENSITY AND CRITICAL FREQUENCY FOR VISUAL FLICKER

Using the rotating striped cylinder device previously employed for determination of the flicker response function with lower animals, corresponding measurements have been made with human observers. The curves based upon the relation between critical flash frequency and critical intensity for the signalling of the recognition of flicker have the properties of human flicker fusion data as obtained by other methods. They also have the quantitative properties of the flicker curves provided by the motor responses of insects and fishes to the seen movement of flashes. This applies to the variation found in repeated measurements as well as to the nature of the analytical function describing the connection between flash frequency and intensity. The data for human visual flicker and those for the responses of lower animals are therefore essentially homologous.     

Interval-specific event related potentials to omitted stimuli in the electrosensory pathway in elasmobranchs: an elementary form of expectation

Multiunit activity and slow local field potentials show Omitted Stimulus Potentials (OSP) in the electrosensory system in rays (Platyrhinoidis triseriata, Urolophus halleri) after a missing stimulus in a 3 to >20 Hz train of V pulses in the bath, at levels from the primary medullary nucleus to the telencephalon. A precursor can be seen in the afferent nerve. The OSP follows the due-time of the first omitted stimulus with a, usually, constant main peak latency, 30–50 ms in medullary dorsal nucleus, 60–100 ms in midbrain, 120–190 ms in telencephalon — as though the brain has an expectation specific to the interstimulus interval (ISI). The latency, form and components vary between nerve, medulla, mid-brain and forebrain. They include early fast waves, later slow waves and labile induced rhythms. Responsive loci are quite local. Besides ISI, which exerts a strong influence, many factors affect the OSP slightly, including train parameters and intensity, duration and polarity of the single stimulus pulses. Jitter of ISI does not reduce the OSP substantially, if the last interval equals the mean; the mean and the last interval have the main effect on both amplitude and latency.Taken together with our recent findings on visually evoked OSPs, we conclude that OSPs do not require higher brain levels or even the complexities of the retina. They appear in primary sensory nuclei and are then modified at midbrain and telencephalic levels. We propose that the initial processes are partly in the receptors and partly in the first central relay including a rapid increase of some depressing influence contributed by each stimulus. This influence comes to an ISI-specific equilibrium with the excitatory influence; withholding a stimulus and hence its depressing influence causes a rebound excitation with a specific latency.Abbreviations DN dorsal nucleus of medullary lateral line lobe - EEG electroencephalogram - EP evoked potential - ERP event related potential - IR induced rhythm - ISI interstimulus interval - OSP omitted stimulus potential - MLN mesencephalic lateral nucleus - P75 positive peak at 75 ms     

Flicker alternating potentials in the ERGs of insects in response to two different stimuli

Summary A special pattern of the flicker is studied in insects belonging to four Orders, i. e. the differential electrical synchronised response of the eye periodically stimulated by two slightly different alternating illuminations.After having checked that the flicker in response to a regular periodical stimulation at every frequency is made up of successive equal potentials, we use two slightly different alternate flickering flashes. It is established that the alternation of two periodical stimulations of a different duration, as well as the alternation of two periodical stimulations of a different intensity, results, over a certain frequency which depends on the insect studied, in the appearance of a flicker marked with the alternation of two potentials whose difference increases at the same time as the frequency of stimulation.The dependence of this phenomenon on modulation of the light flux is described. At a given frequency of stimulation, the alternation of a high and low potential is more obvious when the modulation is lower.A particular experiment allows us to admit that the differential threshold of electrical response to two different stimulations is under 0.25%, at the frequency 100 Hz, inCalliphora erythrocephala.All the phenomena observed can be explained by a mathematical theory which considers the characteristics of the amplitude of the response to sinusoidal stimulations of various frequencies, i. e. the characteristics of the transfer function of the frequencies.