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PubMed1977

Carbon monoxide and flash evoked potentials from rat cortex and superior colliculus.

In view of the conflict between qualitative reports that flash evoked potentials from superior colliculus (SC) and visual cortex (VC) of rats are uniquely sensitive to low levels of carbon monoxide (CO), and a more quantitative report that the visual cortex evoked potential is not sensitive to low levels of CO, the present report documents the effects of different concentrations of CO upon flash evoked potentials from these areas. The amplitude of the P3-N4 component from the SC evoked potential demonstrated the best dose/effect relationship, increasing up to levels of 38% carboxyhemoglobin (COHb). Latencies were affected only when COHb levels reached 55%. The use of the visual system to determine effects of toxic agents upon the central nervous system in discussed.

Animals↗
PubMed1982

Covariation between two-flash threshold and skin conductance level in first-breakdown schizophrenics: relationships in drug-free patients and effects of treatment.

Earlier research suggested that, compared with other individuals, schizophrenics show a different form of covariation between electrodermal level and perceptual discrimination, as indexed by the two-flash threshold. However, dispute has arisen as to whether previous contradictory results obtained on patient samples can be explained by a conventional inverted-U function or whether the relationship takes on an entirely different form, i.e., a U function. The latter alternative was confirmed here in a study of first-breakdown drug-free schizophrenics, tested on 3 consecutive days after hospital admission and before treatment began. However, the U function was evident only in the larger of two subgroups of schizophrenics, identified as patients whose treatment was delayed longer after admission, who were clinically less emotionally responsive and who, in basic personality, were more introverted. When the patients were subsequently tested during treatment, no systematic relationship between two-flash threshold and skin conductance could be discerned. The latter presumably reflected the fact that, during this phase of the experiment, there were marked and complex changes in the individual measures, the effects of treatment on which were briefly examined.

Adolescent↗
PubMed1994

Improved target volume definition for precision radiotherapy planning of meningiomas by correlation of CT and dynamic, Gd-DTPA-enhanced FLASH MR imaging.

In this methodological paper the authors report a fast, T1-weighted gradient-echo sequence (FLASH) for dynamic, Gd-DTPA-enhanced magnetic resonance (MR) imaging of meningiomas and its application in precision radiotherapy planning. Indications for radiotherapy included unresected tumors, tumor remaining after surgery, and recurrences. The patient's head was fixed in a stereotactic localization system which is usable at the CT, MR and the linear accelerator installations. By phantom measurements different materials (steel, aluminum, titanium, plastic, wood, ceramics) used for the stereotactic system were tested for mechanical stability and geometric MR image distortion. All metallic stereotactic rings (closed rings made of massive metal) led to a more or less dramatic geometric distortion and signal cancellation in the MR images. The best properties--nearly no distortion and high mechanic stability--are provided by a ceramic ring. If necessary, the remaining geometric MR image distortion can be 'corrected' (reducing displacements to the size of a pixel) by calculations based on modeling the distortion as a fourth order two-dimensional polynomial. The target volume was defined in dynamic, T1-weighted FLASH MR images, which were measured before, during, and after the controlled intravenous infusion of 0.1 mmol/kg body weight Gd-DTPA. The stereotactic localization technique allows the precise transfer of the target volume information from MR onto CT data to provide a map of the radiation attenuation coefficient for dose calculation. In genera, the superior soft tissue contrast of MR showed an excellent tumor delineation, especially in regions, such as the base of the skull, where the target often was obscured in CT images.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1993

Acute effects of ethanol on pattern reversal and flash-evoked potentials in rats and the relationship to body temperature.

The effects of acute ethanol treatment on flash and pattern reversal visual evoked potentials (FEPs and PREPs, respectively) were examined in three experiments using Long-Evans rats. The relationships of evoked potential parameters with blood ethanol concentration and body temperature were examined. In Experiment 1, rats were treated i.p. with vehicle or 0.5, 1.0 or 2.0 g ethanol/kg body weight, and tested 30 min later. The 2.0 g/kg group had prolonged latencies of PREP peaks, no changes in PREP peak-to-peak amplitudes, and lower body temperatures than saline-treated controls. The peak latency shifts were significantly correlated with both blood ethanol concentration and body temperature, and were of a magnitude to be expected from similar changes in body temperature alone. Experiment 2 measured both PREPs and paired-flash FEPs in rats 30 min after injection of either 0, 0.5 or 2.0 g/kg ethanol. PREP changes were found following treatment with the high dose which were similar to those of Experiment 1. Some FEP peak latencies were prolonged and peak-to-peak amplitudes were reduced by both doses of ethanol, despite the fact that body temperatures were reduced at only the high dose. At 2.0 g/kg ethanol, the FEP changes in latency, but not amplitude, were in accordance with what would be expected from body temperature changes alone. The third study attempted to investigate the role of reduced body temperature in producing the visual evoked potential changes by testing at room temperatures of 22 or 30 degrees C. Contrary to expectations, the rats receiving 2 g/kg ethanol were approx. 1 degree C cooler than controls at both room temperatures. Evoked potential latencies were greater in ethanol-treated rats than controls at both room temperatures. There were no significant effects of ethanol on FEP amplitudes. Overall, the effects of low doses of ethanol were independent of temperature changes, but the effects of higher doses of ethanol (2.0 g/kg) could not be distinguished from those produced by differences in body temperature alone.

Analysis of Variance↗
PubMed1994

Critical processes which characterize the photocurrent of retinal rod outer segments to flash stimuli.

The chemical reactions of retinal rod outer segments (ROS) were modeled aimed at finding the critical process for the reconstruction of the photocurrent to flash stimuli. The differential equations, which were derived from the chemical reactions, were numerically integrated. According to the present model, it was found that the most critical process for the recovery of the photocurrent was the synthesis of cGMP by guanylate cyclase in the [Ca2+]i-dependent manner. The other recovery processes, such as rhodopsin phosphorylation, transducin and phosphodiesterase inactivation seemed not to be involved in the recovery of the photocurrent to flash stimuli. Finally, a recently proposed scheme in which transducin remained bound to phosphodiesterase after its activation was examined. The simulation for this scheme showed that the ROS sensitivity was greatly reduced because of the limited amplification in the transduction cascades.

Calcium↗
PubMedDate not supplied

Effects of chlorpromazine on pattern and flash ERGs and VEPs compared to oxazepam and to placebo in normal subjects.

Antidopaminergic drugs delay the pattern-reversal VEP (P-VEP) and the flash VEP (F-VEP) and, in separate studies, reductions in the amplitude and increases in the latencies of scotopic ERGs have been reported. This study investigated the effects of chlorpromazine (CPZ) on the pattern ERG (P-ERG), P-VEP, flash ERGs and VEPs and oscillatory potentials (OPs). Normal volunteers (N = 15) were administered a placebo, or a single dose of CPZ 100 mg or oxazepam (OZP) 15 mg at weekly intervals, in a double-blind crossover design. A gold foil-ipsilateral ear derivation and an Oz'-Fz derivation were used for the ERG and VEP recordings, respectively. The latencies of 'mixed' and cone ERGs were significantly prolonged after CPZ compared to both placebo and to OZP. Amplitudes of rod- and cone-dominated ERGs were reduced following CPZ administration. All components of the OPs were significantly delayed after CPZ administration. No significant intertreatment differences were found in the F-VEP results. The P-ERG P50 peak and the P-VEP N70 and P100 peaks were significantly delayed after CPZ in the case of 28' checks but not 55' checks. Retinocortical times and P-ERG and P-VEP amplitudes were not significantly affected. In contrast to CPZ, the administration of OZP had virtually no significant effects compared to placebo. These findings suggest that the antidopaminergic CPZ has a primary effect on retinal electrophysiology. Similar findings have been reported in Parkinson's disease and in animal models.

Adult↗
PubMed1992

Alterations in rat flash and pattern reversal evoked potentials after acute or repeated administration of carbon disulfide (CS2).

Because solvents may selectively alter portions of visual evoked potentials, we examined the effects of carbon disulfide (CS2) on flash (FEPs) and pattern reversal (PREPs) evoked potentials. Long-Evans rats were administered ip carbon disulfide either acutely or for 30 days. FEPs or PREPs were recorded prior to and 1, 2, 4, 8, or 24 hr after a single dose of CS2 (0, 100, 200, 400, or 500 mg/kg). Flash evoked potentials were also recorded 1, 2, 6, and 24 hr after the last of 30 doses of 200 mg CS2/kg/day. Acute exposure to CS2 consistently decreased the amplitude of FEP peak N160 at 1 hr, depressed peak N30 amplitude over 2-4 hr, and increased the latency of peaks P21, N30, P46, N56, and N160 for up to 4 hr after treatment. Carbon disulfide decreased the amplitude of PREP peaks P65, N83, P88, and N122 4 hr after treatment. Colonic temperature was depressed up to 8 hr after treatment. Administration of 200 mg CS2/kg/day decreased the amplitude of FEP peak N30 and increased the latencies of peaks P21, N30, P46, N56, and N160 up to 24 hr after the last dose. The differential effects of CS2 on portions of FEPs indicate that FEP peaks can be independently modulated. Changes in PREPs were temporally correlated with alterations in early FEP peaks, but FEP peak N160 was depressed at an earlier time point. Repeated CS2 exposure affected FEPs at lower doses and for a longer time than an acute exposure, similar to the reported greater severity of neurological disturbances following repeated CS2 exposures in humans.

Animals↗
PubMed1979

Inhibition of aspartate release from the retina of the anaesthetised rabbit by stimulation with light flashes.

Rabbits were anaesthetised and the cornea, iris, lens and vitreous were removed from eyes to form an eye-cup which was filled with Krebs-bicarbonate Ringer. The medium in the eye-cup was replaced at 10-min intervals and the amino acids in each resulting sample were assayed. Exposure of the dark-adapted retina to flashes of light (3 Hz) did not alter the efflux of glutamate glutamine, alanine, glycine or GABA. The efflux of taurine and ACh was greatly increased by light flashes, but in contrast, the release of aspartate was reduced by more than 50%, a result consistent with the suggestion that aspartate may be a photoreceptor transmitter substance.

Anesthesia, General↗
PubMed1994

Impairment of place navigation of rats in the Morris water maze by intermittent light is inversely related to the duration of the flash.

The relative contribution of allocentric and egocentric orientation to place navigation was studied in Long-Evans rats trained in the Morris water maze in permanent light, permanent darkness or flickering light (1 Hz, flash durations 25, 100, 300, 500 and 800 ms). After 3 days of training (nine blocks of four trials), escape latencies were 38 and 7 s in the dark- and light-trained groups, respectively, and corresponded to the light-dark ratio in the flicker-trained groups. Shorter-than-predicted latencies in the 25- and 100-ms groups reflected visual persistence of approximately 200 ms. The difference between flickering light (100 ms) and permanent light performance during acquisition of place navigation to a new target was significantly smaller in rats previously trained in light than in naive animals. It is concluded that longer flash duration gives the animals more opportunities to locate relevant landmarks and to estimate their distance.

Animals↗
PubMed1987

ECG-triggered arterial FLASH-MR flow measurement using an external standard.

In ECG-triggered FLASH-MR images, the inflow of unsaturated spins into the imaging plane results in the reproducible delineation of time variant flow in the arterial system. With the additional acquisition of an external reference image upstream the arterial vessel under investigation, the quantification of flow is possible with the FLASH-MR sequence in one measurement. The method allows the rapid measurement of arterial flow at least in great vessels.

Aorta, Abdominal↗
PubMed1996

Functional MR imaging of visual and motor cortex stimulation at high temporal resolution using a FLASH technique on a standard 1.5 Tesla scanner.

Functional magnetic resonance imaging (fMRI) was performed on a conventional 1.5 T scanner by means of a modified FLASH-technique at temporal resolutions of 80 and 320 ms. The method's stability was assessed by phantom measurements and by investigation of three volunteers resulting in a low amplitude (3%) periodic (4 s) signal modulation for the in vivo measurements, which was not observable in the phantom experiments. fMRI activation studies of motor and visual cortices of four adjacent slices were carried out on 12 healthy right-handed volunteers. Stimulation was performed by a triggered single white light flash or single finger-to-thumb opposition movement, respectively. Event-related response of visual and motor activation was traced over 10.24 s with a temporal resolution of 320 ms for the four slice measurements. Brain activation maps were calculated by correlation of measured signal time course with a time-shifted boxcar function. Activation was quantified by calculation of percentual signal change in relation to the baseline. Observed signal magnitudes were about 5-7% in visual and about 8-12% in primary motor cortex. While photic response was delayed by about 2 s, motor stimulation showed an instantaneous increase of the MR signal. MR signal responses for both stimuli had decayed completely after about 5 s. Our results show that event-related fMRI enables mapping of brain function at sufficient spatial resolution with a temporal resolution of up to 80 ms on a conventional scanner.

Adult↗
PubMed2006

Fast structural brain imaging using an MDEFT sequence with a FLASH-EPI hybrid readout.

A sequence for the fast acquisition of T1 weighted structural brain images with whole brain coverage and isotropic resolution of 1mm is presented. It is based on MDEFT with a FLASH-EPI hybrid readout. Several techniques for artefact suppression are implemented, like echo time shifting, asymmetric k-space sampling, and navigator echo acquisition. It is shown experimentally that the hybrid MDEFT sequence with a total duration of 8min yields approximately the same signal-to-noise and contrast-to-noise ratios as a 12min standard MDEFT sequence based on a FLASH readout. Further experiments show that echo time shifting suppresses artefacts in the vicinity of the scalp and in areas suffering from field inhomogeneities and that the concept of asymmetric k-space sampling reduces the susceptibility to head movement.

Adult↗
PubMed2006

Brainstem auditory evoked potentials and flash visual evoked potentials in Vietnamese miniature pot-bellied pigs.

Brainstem auditory evoked potentials (BAEP) and flash visual evoked potentials (VEP) were recorded from juvenile (5-7 weeks of age) and adult Vietnamese miniature pot-bellied pigs to provide normative data for clinical applications. BAEP responses were collected in response to stimulus intensities of 85, 95, and 105 dB nHL. VEP responses were collected in response to flashes of white light in a darkened room. Left-right ear and left-right eye responses did not differ significantly, and were combined for analysis, with each animal providing two data points for each response. BAEP responses in juvenile subjects were mature, and in all subjects showed the typical pattern of decreasing peak latencies and increasing peak amplitudes with increasing stimulus intensity. VEP responses in juvenile subjects were near to mature values, but the latencies still exceeded those of adults. Differences in response maturation between precocial and altricial species are discussed.

Aging↗
PubMed2005

Computational neurobiology of the flash-lag effect.

In the flash-lag effect (FLE) a moving object is perceived ahead of a stationary stimulus flashed in spatial alignment. Several explanations have been proposed to account for the FLE and its dependence on a variety of psychophysical attributes. Here, we show that a simple feed-forward network reproduces the standard FLE and several related manifestations, such as its modulation by stimulus luminance, trajectory, priming, and spatial predictability. A minimal set of elements, based on plausible neuronal mechanisms, yields a unified account of these visual illusions and possibly other perceptual phenomena.

Humans↗
PubMed2004

FLASH, a component of the FAS-CAPSASE8 apoptotic pathway, is directly regulated by Hoxb4 in the notochord.

The Hox genes are a family of homeodomain-containing transcription factors that confer positional identity during development. Although their regulation and function have been extensively studied, very little is known of their downstream target genes. Here we show that Hoxb4 directly induces the expression of FLASH in the notochord of embryos after neurulation. FLASH is a component of the FAS-CAPSASE8 apoptotic pathway, and blocking its activity, or that of Hoxb4, prevents apoptosis in the notochord.

Amino Acid Sequence↗
PubMed2004

Driver behaviour during flashing green before amber: a comparative study.

The paper discusses the results of extensive measurements of drivers' stopping behaviour during signal programmes with and without flashing green before amber. Ten locations in Switzerland, Austria, and Germany were recorded with a video camera and analysed using an image-processing system. About 5000 cycles were documented. The analysis shows that the flashing green increases the number of early stops, as drivers tend to underestimate the duration of the time to the end of amber. Discrete choice models of the stopping behaviour are estimated for inclusion in suitable microsimulation models of traffic flow. The model results show that speed and distance to stop line, and their interaction (potential time to the stop line with unchanged speed) explain the stopping process.

Austria↗
PubMed2002

Flash-induced turnover of the cytochrome bc1 complex in chromatophores of Rhodobacter capsulatus: binding of Zn2+ decelerates likewise the oxidation of cytochrome b, the reduction of cytochrome c1 and the voltage generation.

The effect of Zn2+ on the rates of electron transfer and of voltage generation in the cytochrome bc1 complex (bc1) was investigated under excitation of Rhodobacter capsulatus chromatophores with flashing light. When added, Zn2+ retarded the oxidation of cytochrome b and allowed to monitor (at 561-570 nm) the reduction of its high potential heme b(h) (in the absence of Zn2+ this reaction was masked by the fast re-oxidation of the heme). The effect was accompanied by the deceleration of both the cytochrome c(1) reduction (as monitored at 552-570 nm) and the generation of transmembrane voltage (monitored by electrochromism at 522 nm). At Zn2+ <100 microM the reduction of heme b(h) remained 10 times faster than other reactions. The kinetic discrepancy was observed even after an attenuated flash, when bc1 turned over only once. These observations (1) raise doubt on the notion that the transmembrane electron transfer towards heme b(h) is the main electrogenic reaction in the cytochrome bc1 complex, (2) imply an allosteric link between the site of heme b(h) oxidation and the site of cytochrome c1 reduction at the opposite side of the membrane, and (3) indicate that the internal redistribution of protons might account for the voltage generation by the cytochrome bc1 complex.

Bacterial Chromatophores↗
PubMed1986

Flash spectrophotometric identification of a fourth rhodopsin-like pigment in Halobacterium halobium.

A fourth retinal-containing pigment in Halobacterium halobium cell membrane was examined by flash spectrophotometry. The absorption maximum of this pigment was at about 480 nm. Flash light caused a photoreaction cycle with a half recovery time of about 300 ms at room temperature. The photoreaction cycle involved at least two photo-intermediates. The absorption maximum of the first one was at about 350 nm and that of the second was at around 530 nm. The spectral properties of this pigment and the content of the cells correlate with the sensitivity of photo-repellent response to the light around 480 nm. We suggest a name 'phoborhodopsin' for this new pigment.

Halobacterium↗