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PubMed1990

The effects of levodopa and haloperidol on flash and pattern ERGs and VEPs in normal humans.

We investigated the effects of single doses of the dopamine agonist levodopa and the dopamine antagonist haloperidol on pattern and flash electroretinograms (ERGs) and visual evoked potentials (VEPs) in normal subjects. A placebo and two treatment regimens were administered in a randomized double-masked design. No significant intertreatment differences in the pattern ERGs and VEPs were noted. Although not statistically significant, a clearly discernible tendency was found for increased flash ERG b-wave amplitudes after levodopa administration compared with placebo. In comparison with placebo and levodopa, haloperidol was associated with significantly prolonged flash ERG b-wave implicit times, including each oscillatory potential, which also showed increased duration, particularly in the O1-O3 interpeak implicit time. The failure of pattern ERGs and VEPs to show changes after haloperidol may have been related to the timing of the recordings, which took place during the presumed phase of rising blood levels and before the flash ERG and VEP recordings. Our findings further demonstrated the reliability of the flash ERG in revealing changes in dopaminergic status in the visual system and suggest that steady-state (flicker) ERGs, cone ERGs, and oscillatory potentials have particular use in this regard.

Adult↗
PubMed1985

The kinetics of the flash-induced P515 response in relation to the H+-permeability of the membrane bound ATPase in spinach chloroplasts.

The effect of dicyclohexylcarbodiimide (DCCD) on the kinetics of the flash-induced P515 response and on the activity of the ATPase was investigated in isolated spinach chloroplasts. It was found that after the addition of 5 X 10(-8)mol DCCD the rate of ATP hydrolysis induced by a period of 60 sec illumination was decreased to less than 5% of its original value. At this concentration, hardly any effect, if at all, could be detected on the kinetics of the flash-induced P515 response, neither in dark-adapted nor in light-activated chloroplasts. It was concluded that the presence of concentrations of DCCD, sufficiently high to affect the ATPase activity, does not affect the kinetics of the flash-induced P515 response. Since DCCD decreases the H+ permeability of the membrane-bound ATPase, it was concluded that this permeability coefficient for protons is not an important factor in the regulation of the flash-induced membrane potential and, therefore, does not affect the kinetics of the flash-induced P515 response.

Adenosine Triphosphatases↗
PubMed2005

Utility of contrast-enhanced 3D turbo-flash MR angiography in evaluating the intracranial venous system.

The objective of this study was to compare the effectiveness of contrast-enhanced 3D turbo-flash and 2D time-of-flight (TOF) magnetic resonance angiography (MRA) sequences in the visualization and evaluation of the intracranial venous system. A prospective study was carried out on 41 patients referred to our Magnetic Resonance Imaging (MRI) unit with clinical findings suggestive of dural sinus thrombosis. Contrast-enhanced 3D turbo-flash and 2D TOF MRA sequences were performed, and the dural sinuses and cerebral veins were classified into five grades according to the quality of visualization and presence of thrombosis. We found the dural sinuses and cerebral veins to be normal in all sequences in 31 patients. Thrombosis of dural sinuses was detected in ten patients, with four of these ten cases found only in the contrast-enhanced 3D turbo-flash sequence. In general, complete visualization of cerebral veins and dural sinuses was significantly better accomplished with contrast-enhanced 3D turbo-flash MRA than with 2D TOF in either coronal or sagittal/oblique planes. Although 2D TOF MRA may be superior in detecting chronic dural sinus thrombosis, contrast-enhanced 3D turbo-flash MRA sequences may offer advantages for the early diagnosis and management of acute and subacute dural sinus thrombosis.

Adolescent↗
PubMed2003

The value of water-excitation 3D FLASH and fat-saturated PDw TSE MR imaging for detecting and grading articular cartilage lesions of the knee.

OBJECTIVE: To evaluate the diagnostic accuracy of water-excitation (WE) 3D FLASH and fat-saturated (FS) proton density-weighted (PDw) TSE MR imaging for detecting, grading, and sizing articular cartilage lesions of the knee. DESIGN AND PATIENTS: A total of 26 patients underwent MR imaging prior to arthroscopy with the following sequences: (1) WE 3D FLASH: 28/11 ms, scan time: 4 min 58 s, flip angle: 40 degrees; (2) FS PDw TSE: 3433/15 ms, scan time: 6 min 15 s, flip angle: 180 degrees. Grade and size of the detected lesions were quantified and compared with the results of arthroscopy for each compartment. RESULTS: The sensitivity, specificity, positive and negative predictive values, and accuracy for detecting cartilage lesions were 46%, 92%, 81%, 71% and 74% for WE 3D FLASH and 91%, 98%, 96%, 94% and 95% for FS PDw TSE MR imaging. WE 3D FLASH correlated significantly with arthroscopy for grading on the patella ( P<0.0001) and the femoral trochlea ( P=0.02) and for sizing on the femoral trochlea ( P=0.03). FS PDw correlated significantly ( P<0.0001) with arthroscopy for grading and sizing on all compartments. CONCLUSION: FS PDw TSE is an accurate method for detecting, grading and sizing articular cartilage lesions of the knee and yielded superior results relative to WE 3D FLASH MR imaging.

Adult↗
PubMed2001

MR enteroclysis protocol optimization: comparison between 3D FLASH with fat saturation after intravenous gadolinium injection and true FISP sequences.

The aim of this study was to introduce the true fast imaging with steady-state precession (FISP) sequence for MR enteroclysis and compare it with the already used T1-weighted fast low-angle shot (FLASH) sequence. Twenty-one patients underwent both MR and conventional enteroclysis. The MR enteroclysis examination was performed after administration of an iso-osmotic water solution through a nasojejunal catheter and the following sequences were included: (a) true FISP; and (b) 3D FLASH with fat saturation after intravenous injection of 20 mg Buscopan or 1 mg glucagon and 0.1 mmol/kg gadolinium chelates. The true FISP sequence provided images with significantly fewer motion artifacts, whereas 3D FLASH was less sensitive to susceptibility and chemical shift artifacts. The homogeneity of endoluminal opacification, wall conspicuity, and distention of the small bowel were very good to excellent and the two sequences presented no statistically significant differences here. True FISP provided significantly better overall image quality than did 3D FLASH. The true FISP sequence can provide good anatomic demonstration of the small bowel on T2-like images and could be combined with T1-weighted FLASH images for an integrated protocol of MR enteroclysis.

Adolescent↗
PubMed2006

The brain computer interface using flash visual evoked potential and independent component analysis.

In this study flashing stimuli, such as digits or letters, are displayed on a LCD screen to induce flash visual evoked potentials (FVEPs). The aim of the proposed interface is to generate desired strings while one stares at target stimulus one after one. To effectively extract visually-induced neural activities with superior signal-to-noise ratio, independent component analysis (ICA) is employed to decompose the measured EEG and task-related components are subsequently selected for data reconstruction. In addition, all the flickering sequences are designed to be mutually independent in order to remove the contamination induced by surrounding non-target stimuli from the ICA-recovered signals. Since FVEPs are time-locked and phase-locked to flash onsets of gazed stimulus, segmented epochs from ICA-recovered signals based on flash onsets of gazed stimulus will be sharpen after averaging whereas those based on flash onsets of non-gazed stimuli will be suppressed after averaging. The stimulus inducing the largest averaged FVEPs is identified as the gazed target and corresponding digit or letter is sent out. Five subjects were asked to gaze at each stimulus. The mean detection accuracy resulted from averaging 15 epochs was 99.7%. Another experiment was to generate a specified string '0287513694E'. The mean accuracy and information transfer rates were 83% and 23.06 bits/min, respectively.

Adult↗
PubMed1979

A rapid vectorial back reaction at the reaction centers of photosystem II in tris-washed chloroplasts induced by repetitive flash excitation.

In Tris-washed chloroplasts, completely lacking the oxygen-evolving capacity, absorption changes in the range of 420--560 nm induced by repetitive flash excitation have been measured in the presence and absence of electron donors. It was found: (1) At 520 nm flash-induced absorption changes are observed, which predominantly decay via a 100--200-mus exponential kinetics corresponding to that of the back reaction between the primary electron donor and acceptor of Photosystem II (Haveman, J. and Mathis, P. (1976) Biochim. Biophys. Acta 440, 346--355; Renger, G. and Wolff, Ch. (1976) Biochim. Biophys. Acta 423, 610--614). In the presence of hydroquinone/ascorbate as donor couple the amplitude is nearly doubled and the decay becomes significantly slowed down. (2) The difference spectrum of the absorption changes obtained in the presence of hydroquinone/ascorbate, which are sensitive to ionophores, is nearly identical with that of normal chloroplasts in the range of 460--560 nm (Emrich, H.M., Junge, W. and Witt, H.T. (1969) Z. Naturforsch. 24b, 114--1146). In the absence of hydroquinone/ascorbate the difference spectrum of the absorption changes, characterized by a 100--200-mus decay kinetics, differs in the range of 460--500 nm and by a hump in the range of 530--560 nm. The hump is shown to be attributable to the socalled C550 absorption change, which reflects the turnover of the primary acceptor of Photosystem II (van Gorkom, H.J.(1976) Thesis, Leiden), while the deviations in the range of 460--500 nm are understandable as to be due to the overlapping absorption changes of chlorphyll alpha II+. The problems arising with the latter explanation are discussed. (3) The electron transfer due to the rapid turnover at Photosystem II, which can be induced by flash groups with a short dark time between the flashes, is not able to energize the ATPase and to drive photophosphorylation. On the basis of the present results it is inferred, that in Tris-washed chloroplasts under repetitive flash excitation a rapid transmembrane vectorial electron shuttle takes place between the primary acceptor (X320) and donor (Chl alpha II) of Photosystem II, which is not able to energize the photophosphorylation. Furthermore, the data are shown to confirm the localization of X320 and Chl alpha II within the thylakoid membrane at the outer and inner side, respectively.

Adenosine Diphosphate↗
PubMed1981

Investigation of double turnovers in photosystem II charge separation and oxygen evolution with excitation flashes of different duration.

The characteristics of double hitting in Photosystem II charge separation and oxygen evolution in algae and chloroplasts were investigated with saturating excitation flashes of 3 microseconds, 300 ns and 5 ns duration. Two types of double hitting or advancement in S-states were found to occur in oxygen evolution: a non-photochemical type found even with 5 ns flashes and a photochemical type seen only with microsecond-long flashes, which have extensive tails. The non-photochemical type, occurring with a probability of about 3%, is sensitive to the physiological condition of the sample, and is only present in algae or chloroplast samples that have been freshly prepared. In chloroplasts incubated with ferricyanide, a 3-fold increase in double advancement of S-states is observed with xenon-flash illumination but not with 300 ns or 5 ns laser illumination. However, double turnovers in Photosystem II reaction center charge separation are large with xenon flash or 300 ns laser illumination but not with 5 ns laser illumination. This indicates that quite different kinetic processes are involved in double advancement in S-states for oxygen evolution and double turnovers in charge separation. Various models of the Photosystem II reaction center are discussed. Also, based on experiments with chloroplasts incubated with ferricyanide, an unique solution to the oxygen S-state distribution in the dark suggested by Thibault (Thibault, P. (1978) C.R. Acad. Sci. Paris 287, 725-728) can be rejected.

Chlorella↗
PubMed1989

Timing and distribution of flash-evoked activity in the lateral geniculate nucleus of the alert monkey.

Simultaneous recording of activity from multiple cortical laminae in alert monkeys, using multichannel electrodes, has been used to identify the intracranial generators of surface-recorded, visually evoked potentials (VEP) to stroboscopic flash. Beyond their clinical implications, these results offer an unique view of the timing and sequence of cortical visual processing in the alert monkey, including the somewhat surprising findings of an extremely short-latency response in lamina IVA, a contra- over ipsilateral latency advantage throughout lamina IV, and the lack of a consistent flash-evoked response in the major cortical recipient of the magnocellular system, lamina IVCa. The present study used similar techniques to examine flash-evoked activity in LGN and in optic tract, both to elucidate the role of the subcortical pathways in establishing this pattern, and to provide a parallel, detailed view of the timing of visual activity in LGN and optic tract in the alert monkey. Flash-evoked responses are robust in both parvo- and magnocellular laminae, but these responses differ along several dimensions: (1) parvocellular multiunit activity (MUA) is 1/4 to 1/2 the amplitude of magnocellular MUA; (2) oscillatory activity is higher in frequency and shorter in duration in parvo- than in magnocellular responses; (3) inhibitory processes appear less prominent and diverse in parvo- than in magnocellular activity; (4) mean onset latencies of MUA are longer in parvo- than in magnocellular laminae, but there is extensive overlap in these distributions. Latencies encountered in ipsilateral lamina 3, and at laminar borders dorsal to 3, group more clearly with those of the magnocellular laminae than with those of the other parvocellular laminae. As a result, in the parvocellular division as a whole, the average latency to ipsilateral stimulation is shorter than that to contralateral stimulation. The optic tract exhibits a dorsal-to-ventral progression of onset latency and oscillation frequency consistent with a dorsal/ventral segregation of the inputs to parvo- and magnocellular layers. Comparison of optic tract and LGN data reveals that while many LGN response characteristics are initiated in the retina, significant modification of retinal output occurs at LGN. The techniques used here permit a particularly sensitive and reliable assessment of the timing and distribution of visual responses in the optic tract and LGN of alert monkeys. Our data support the view that in the alert monkey, the surface-VEP to passive, binocular flash primarily reflects activation of parvocellular thalamorecipient laminae of Area 17.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Human flash-VEP and quantitative EEG are independently affected by acute scopolamine.

Scopolamine in acute intramuscular doses of 0.25-0.75 mg reduced the P2-N3 flash-VEP amplitude and, in the quantitative EEG, the 8.5-12.0 Hz power and total power in 8 healthy young male volunteers. The effects on flash-VEP and EEG total power were dose dependent and were evident 30 min and 90 min respectively after drug administration, regardless of dose. The reduction in 8.5-12.0 Hz power was limited to the 0.50 and 0.75 mg doses. No systematic effects on the pattern-VEP were observed. Possible interferences with flash- or pattern-VEP amplitude of the scopolamine-induced EEG changes were identified and removed by regression analysis and computation of VEP residuals from the regression function. The P2-N3 flash-VEP residuals proved EEG independent and showed relationships with dose and time after drug administration that were superimposable on those of the original data, with comparable significance levels at the drug/placebo and pre/postdrug statistical comparisons. The results indicate that VEP estimates of drug effects which are independent from EEG changes can be identified in human studies and allow some inference on the cholinergic specificity of the systems affecting late flash-VEP components. The statistical approach used in this study is suitable for application in VEP studies when effects of interacting factors are to be expected.

Adult↗
PubMed1989

Two pulses seen as three flashes: a superposition analysis.

If a single brief light pulse follows the offset of a light field by 0.1-0.3 sec, the pulse is seen as a double flash. This "double flash effect" is a suprathreshold phenomenon: the pulse must exceed detection threshold by 10 times or more for this temporal illusion to occur. A special case of this effect is demonstrated here: two brief, high-luminance pulses separated by 0.1 sec appear as three flashes. In a superposition analysis, hypothetical impulse response functions were added together with various delays to model flash perception. A biphasic impulse response (congruent with threshold flicker and pulse sensitivity) fails to predict perception of three flashes from two pulses. The analysis instead suggests that the visual response to a suprathreshold pulse has several alternating phases of excitation and inhibition.

Humans↗
PubMed1990

Detection of briefly flashed sine-gratings in dark-adapted vision.

Scotopic contrast sensitivity was measured near 20 deg retinal eccentricity for briefly flashed (10 or 20 msec) sine-wave gratings presented in darkness to dark-adapted subjects. For very low spatial frequencies (0.2-0.5 c/deg), curves of contrast sensitivity vs luminous energy show evidence of a low rod plateau and a high scotopic region, with an intervening transition at around -2 to -2.5 log scot td sec. Similar measurements made using long flashed or flickering gratings do not show a plateau. The results suggest that vision in the low rod region is impaired for brief flashes. For the briefly flashed stimuli, curves of contrast sensitivity versus spatial frequency in the low region were best fit by simple Gaussian functions with a variable centre size (sigma c = 0.5----0.25 deg), size decreasing with increasing flash energy. Difference-of-Gaussian functions with constant centre size (sigma c = 0.25 deg) provided the best fit in the high region. Overt input from the cones and grating area artefacts are excluded by appropriate tests. Calculation of photon flux into the receptive field centres suggests that signal compression in P alpha ganglion cells contributes to the low rod plateau.

Contrast Sensitivity↗
PubMed2006

Pigeons' memory for sequences of light flashes: reliance on temporal properties and evidence for delay interval/gap confusion.

In Experiment 1, pigeons were trained to discriminate between sequences of two and four light flashes (illumination of the feeder). Retention functions obtained with dark delays exhibited a choose-many bias at a 1-s delay and a choose-few bias at delays of 4 and 8s. Retention functions obtained with illuminated delays only displayed a slight choose-few bias. In Experiment 2, additional birds were trained with the same sample sequences. However, the intertrial interval was illuminated by the houselight for Group Light, and it was dark for Group Dark. The acquisition data suggested that multiple temporal features of the light flash sequences controlled choice responding. For both groups, the retention functions were similar to those obtained in Experiment 1. In Experiment 3, baseline training with a 1-s dark delay eliminated the choose-many bias, but a significant choose-few bias at extended dark delays was still observed. Pigeons discriminate light flash sequences by relying on temporal properties of the sequence rather than using an event switch to count flashes. The biased-forgetting effects obtained in these studies appear to be primarily due to confusion between the delay interval and the gap between light flashes.

Animals↗
PubMedDate not supplied

A spiking neuron model for synchronous flashing of fireflies.

Certain species of fireflies show a group behavior of synchronous flashing. Their synchronized and rhythmic flashing has received much attention among many researchers, and there has been a study of biological models for their entrainment of flashing. The synchronous behavior of fireflies resembles the firing synchrony of integrate-and-fire neurons with excitatory or inhibitory connections. This paper shows an analysis of spiking neurons specialized for a firefly flashing model, and provides simulation results of multiple neurons with various transmission delays and coupling strengths. It also explains flashing patterns of some firefly species and examines the synchrony conditions depending on transmission delays and coupling strengths.

Action Potentials↗
PubMed2006

Flashing liquid jets and two-phase droplet dispersion I. Experiments for derivation of droplet atomisation correlations.

The large-scale release of a liquid contained at upstream conditions above its local atmospheric boiling point is a scenario often given consideration in process industry risk analysis. Current-hazard quantification software often employs simplistic equilibrium two-phase approaches. Scaled water experiments have been carried out measuring droplet velocity and droplet size distributions for a range of exit orifice aspect ratios (L/d) and conditions representing low to high superheat. 2D Phase-Doppler Anemometry has been utilised to characterise droplet kinematics and spray quality. Droplet size correlations have been developed for non-flashing, the transition between non-flashing and flashing, and fully flashing jets. Using high-speed shadowography, transition between regimes is defined in terms of criteria identified in the external flow structure. An overview companion paper provides a wider overview of the problem and reports implementation of these correlations into consequence models and subsequent validation. The fluid utilised throughout is water, hence droplet correlations are developed in non-dimensional form to allow extrapolation to other fluids through similarity scaling, although verification of model performance for other fluids is required in future studies. Data is reduced via non-dimensionalisation in terms of the Weber number and Jakob number, essentially representing the fluid mechanics and thermodynamics of the system, respectively. A droplet-size distribution correlation has also been developed, conveniently presented as a volume undersize distribution based on the Rosin-Rammler distribution. Separate correlations are provided for sub-cooled mechanical break-up and fully flashing jets. This form of correlation facilitates rapid estimates of likely mass rainout quantities, as well as full distribution information for more rigorous two-phase thermodynamic modelling in the future.

Aerosol Propellants↗
PubMed2005

Increasing the sensitivity of time-resolved photo-CIDNP experiments by multiple laser flashes and temporary storage in the rotating frame.

Pulse sequences have been developed that add up time-resolved photo-CIDNP signals from n successive laser flashes not in the acquisition computer of the NMR spectrometer but in the experiment itself, resulting in a greatly improved signal-to-noise ratio. For this accumulation, CIDNP is first stored in the transverse plane and then on the z axis, and finally superimposed on CIDNP produced by the next flash. These storage cycles also result in a very efficient background suppression. Because only one free induction decay is acquired for n flashes, the noise is digitized only once. The signal gain is demonstrated experimentally and analyzed theoretically. Losses are mostly due to nuclear spin relaxation, and to a small extent to instrument imperfections. With 10 laser flashes, a signal increase by a factor of about 7.5 was realized. As their main advantage compared to signal averaging in the usual way, these sequences yield the same signal-to-noise ratio with fewer laser flashes; the theoretical improvement is by a factor of n.

Journal Article↗
PubMed2004

3D flash lag illusion.

Objective of this research is to study the presence of 3D flash lag illusion created by a moving object that has a motion-in-depth and a flash object. An object consisting of two thin sticks was simulated to approach the subject who observed it with a stereoscope. In the process of approaching, another stick was briefly presented in the middle of the moving sticks. Five human subjects took part in our experiments and all perceived 3D flash lag illusion. The perceived depth created by 3D flash lag illusion was measured by two different psychophysical experiments, by use of a vernier caliper and by a method of nulling with another depth cue. We studied relation between the perceived depth and the presentation distance. The experimental results indicate that the perceived gap by 3D flash lag illusion is independent from the presentation distance.

Adult↗
PubMed2004

Models of the mechanism underlying perceived location of a perisaccadic flash.

A variety of experiments have shown that subjects tend to perceive a target flash as mislocalized when the flash is presented just before, during or shortly after the occurrence of a saccade. The characteristics of this mislocalization suggest that it arises from an anticipatory, slow extraretinal signal, i.e., the signal starts to change before a saccade and continues to change during and after the saccade. However, a target flash creates a visual signal that can persist for as long as 300 ms. Interaction of this visual persistence with the extraretinal signal could have a significant influence on the perceived location of the target flash, and thus on features of the extraretinal signal as inferred from the perceived location. In this study, several different types of models were used to explore how retinal signal persistence together with an extraretinal signal might affect perception. According to these models, the anticipatory, slow extraretinal signal may be an artifact of using a target flash, and the actual extraretinal signal may begin to change only after saccade onset and relatively quickly.

Computer Simulation↗