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At least 1,153 records · Page 64Linked to original sources
PubMed1986

A flashing-light method for recording centric relation.

A flashing-light system has been described which provides a simple method for ensuring equalized pressure in recording the relationship of the mandible to the maxillae. The wires that protrude from the mouth do not appear to create any discomfort or distraction during the procedures. This method tends to be more comfortable than extraoral or intraoral tracing techniques. The method may create patient fear because an electrical device is used in the oral cavity. In addition, if the metal surfaces (pins and cups) are not fully coated with wax, there may be contact with adjacent soft tissue, which creates an electric sensation.

Dental Instruments↗
PubMed1994

Image quality of direct digital intraoral x-ray sensors in assessing root canal length. The RadioVisioGraphy, Visualix/VIXA, Sens-A-Ray, and Flash Dent systems compared with Ektaspeed films.

The Trophy RadioVisioGraphy model 32000 system in Normal Mode, the Trophy RVG-PC in Normal and Archive Mode, the Gendex VIXA/Visualix, the Regam Sens-A-Ray, and the Villa Flash Dent in High-Resolution Mode and Normal Mode were compared with respect to the visibility of endodontic files. Kodak Ektaspeed film served as the reference. An acrylic embedded human skull was prepared for taking radiographs with endodontic files (Kerr files size 10 and size 15) on full root length and 1.5 mm short in upper and lower premolars and molars. Possibilities for enhancement of the digital images were not studied. Receiver operating characteristics curves were derived and the areas under the curves were averaged and compared using Student's t test statistic (p < 0.05). Kodak Ektaspeed film gave acceptable results for both file sizes. Both Trophy RVG units in Normal Mode and the Regam Sens-A-Ray system gave results above the areas under the curves equals 0.95 for the size 15 files. For the size 10 files the values of the areas under the curves of all sensors systems were below this threshold. It is concluded that both RVG units in Normal Mode and the Sens-A-Ray system render a comparable result with conventional radiography in determining root canal length with the use of a size 15 files. All sensor systems were unacceptably inferior to film images when size 10 files were used.

Dental Pulp Cavity↗
PubMed1991

Posttraining presentation of a flashing light alters retrieval of a two-way active avoidance task in rats.

Rats were trained and tested in a two-way active avoidance task (30 trials, 0.4-mA footshock, 24-h training-test interval). Exposure to an open field with flashing light (60-W lamp, 30 Hz, for 7 min, OFL) 2 h after training caused a retrieval impairment for the avoidance task, a phenomenon called retroactive interference. Animals familiarized with the OFL 24 h before training showed no retrieval impairment when exposed to the OFL 2 h after training. Both adrenal medullectomy (performed 7 to 14 days before training) and dexamethasone treatment (2 mg/kg, injected IP 24 h and 12 h before training) prevented the OFL interfering effect. Time-course experiments revealed that OFL presented either 1 or 4 h after training caused no retrieval deficit, and that animals exposed to the OFL 2 h after training and receiving another OFL presentation 1 or 2 h, but not 4 h, prior to testing had normal retrieval performance. These results suggest: 1) that the retroactive interference caused by presentation of OFL 2 h after training is due to failure of retrieval of the avoidance task since it is counteracted by the pretest presentation to the OFL, 2) that the OFL-induced retrieval interfering effect partly depends on the novelty of the OFL situation, and on the functional integrity of pituitary ACTH and adrenomedullar-dependent mechanisms and 3) that there are different mechanisms involved in posttraining and pretest OFL effects since they present distinct time-courses.

Adrenal Medulla↗
PubMed1994

Within-session changes in peak N160 amplitude of flash evoked potentials in rats.

The negative peak occurring approximately 160 ms after stimulation (peak N160) of flash evoked potentials (FEPs) of rats changes with repeated testing. Habituation, sensitization, and arousal have all been invoked to explain these changes, but few studies have directly tested these explanations. We examined within-session changes in peak N160 amplitude with repeated testing, and the modulatory effects of stimulus intensity and auditory white noise. Peak N160 amplitude increased with daily testing (between-session changes), and was larger at greater stimulus intensities. In contrast, peak N160 amplitude underwent within-session increases on early days and within-session decreases on later days. The within-session changes were not affected by stimulus intensity. In rats previously tested in a quiet environment, exposure to acoustic white noise increased motor activity and transiently decreased peak N160 amplitude, which then increased and subsequently decreased with continued photic and acoustic stimulation. Repeated testing in the presence of noise did not alter the within-session changes in peak N160 amplitude. Heart rate showed both within- and between-session decreases, but was unaffected by noise. The data suggest that the within-session changes in peak N160 amplitude may reflect a habituation-like response to the test environment.

Acoustic Stimulation↗
PubMed1996

Possible confounding effects of strobe "clicks" on flash evoked potentials in rats.

Flash evoked potentials (FEPs) undergo within- and between-session changes and are modified by auditory white noise (26). We examined whether an auditory potential produced by the "click" associated with the strobe discharge could be recorded, and if alterations in an auditory response could explain the within- and between-session changes in FEPs. We also examined differences between a frontal cortex or a nasal reference electrode location on FEPs and auditory potentials. An auditory potential associated with the strobe discharge could be clearly recorded. This response was eliminated by the presence of 80 dB SPL masking white noise. However, the within- and between-session changes in FEPs could not be explained by modifications of the auditory potential. Animals whose ear drums were ruptured did not exhibit an auditory response, and their FEPs were similar to those of controls tested in the presence of masking white noise. A nasal reference electrode decreased the impact of auditory potentials on FEPs, but allow visual potentials (electroretinogram and optic tract activity) to influence FEPs. The data show that auditory potentials associated with the strobe discharge can be recorded from the visual cortex of rats, and that these auditory responses represent a possible confounding factor in the interpretation of toxicological studies employing FEPs.

Acoustic Stimulation↗
PubMed1983

Recovery at short intervals between masking flashes.

Recovery of a masked target (T + M) by a homogeneous flash (B) appears to follow a different rule at T-M intervals (t1) greater than 60 msec (Tenkink and Werner, 1981) than at shorter intervals (Purcell et al., 1982). The first study is now extended to shorter t1 and confirms the other study. Recovery peaks at a constant T-B interval (t2) of 60 msec (20 msec less than or equal to t1 less than or equal to 60 msec). Also a U-shaped curve relating correct performance to t1 was found (t2 greater than 120 msec). Two alternative explanations for the recovery phenomenon are presented. In both the important assumption is that the main effect of B is to suppress T and M activity at an early stage in the visual system.

Adult↗
PubMed1985

Two temporal phases, brightness-dependent and -independent, in the chromatic response elicited by a briefly-flashed monochromatic light: a preliminary report.

The strength of chromatic response elicited by a briefly-flashed monochromatic light, which varied in its exposure duration, was measured with the "transient cancellation method" in Experiment 1. It was found that the chromatic response of a test color depended on brightness of the test field, up to the exposures of 100-200 msec. But it began to decrease, independent of brightness of the field, at the longer durations. The above results were confirmed by Experiment 2, in which the perceived saturation of a colored light was estimated with the two alternative forced choice method. Those results were tentatively interpreted as indicating the two kinds of chromatic responses presumably originating at the different stages in the visual system. Some other psychophysical dada on color vision were briefly referred to in relation to the present results.

Color Perception↗
PubMed1987

Effect of surround configuration on increment thresholds of a tiny violet flash.

Increment thresholds were measured for a 5', 435-nm test flash (50 or 200 msec) on background fields of various wavelengths and spatial configurations. As the field diameter was increased, the detection threshold for the 50-msec test decreased rapidly and leveled off when the field diameter exceeded 20'. For short-to-middle wavelength fields (much less than or equal to 503 nm), the detection threshold for the 200-msec test varied with field diameter in a similar manner to those observed for the 50-msec tests, while for middle-to-long wavelength fields (much greater than or equal to 544 nm), the detection threshold continued to decrease even when the field diameter exceeded 20'. The temporal-integration properties and the threshold vs intensity curves were determined for 465-nm and 579-nm fields to specify the mechanisms responsible for the detection. It was shown that the detection thresholds of the test upon the large 579-nm field were characterized by the short-wavelength mechanism isolated by an intense yellow adapting field, whereas the detection thresholds of the test upon the small 579-nm or the 465-nm field showed an intrusion of a more sensitive alternate mechanism, presumably the middle-wavelength mechanism. It was suggested that the sensitivity of the S cone signals might be affected by spatially distributed signals from the longer-wavelength mechanisms.

Adaptation, Ocular↗
PubMedDate not supplied

Saccade-contingent displacement of the apparent position of visual stimuli flashed on a dimly illuminated structured background.

Subjects were required to perceptually judge the location of flash targets presented at the time of a saccade at various positions scattered two-dimensionally on a dimly illuminated structured background. The saccade-contingent mislocalization was shown only in the direction parallel to the saccade, and not in the direction perpendicular to the saccade. In addition, the mislocalization under the "illuminated background" condition was different in several respects from that observed when targets were presented in the dark. It was suggested that the mislocalization is successfully explained by assuming three physiological and cognitive processes: a sluggish activity of the extraretinal eye position signal, visual cues from the visible background, and selective inattention to image displacements.

Humans↗
PubMed1995

Nature of the pupillary responses evoked by chromatic flashes on a white background.

Color flashes on a steady-white background are classically used to isolate the response of the chromatic (color-opponent), as opposed to achromatic (luminance), channel in psychophysical investigations. The present study shows that pupillary responses evoked by such stimuli behave as if they are composed of functionally separable components. One component has a temporally transient waveform and has an action spectrum that is similar to the spectral sensitivity curve of the psychophysical chromatic channel. The present study discusses the possibility that the pupillary response is mediated by phasic (M-like) neurons and/or by tonic (P-like) neurons.

Color Perception↗
PubMed1994

Contribution of extrastriate area V4 to the surface-recorded flash VEP in the awake macaque.

This study compared striate and extrastriate contributions to the surface-recorded flash VEP. Laminar visual evoked potential, current source density and multiunit activity profiles were obtained with multicontact electrodes from areas V1 and V4 in three awake macaques. As found earlier, the major striate contribution is to early (N40, P55-80) components. Major contributions to the later (N95, P120, Late Negativity) components arise from V4. Early, afferent-triggered inhibition in V4 also produces a small contribution to N40. Response latencies in V4 vs V1 suggest an input to V4, bypassing V1, emphasizing a parallel processing component of visual system organization.

Action Potentials↗
PubMed1989

Effects of ketamine, naloxone, and physostigmine on flash evoked potentials in rat superior colliculus.

Flash evoked potentials were recorded from the superior colliculus of chronically implanted hooded rats at 5 and 20 min following IP injections of saline, ketamine (75 mg/kg), naloxone (10 mg/kg), or physostigmine (0.4 mg/kg) on separate days. Components in an early positive complex were unaffected by ketamine and naloxone, but were reduced in amplitude by physostigmine. A positive spike emerged from the middle of a later negative wave following ketamine administration, but the amplitude of the negative wave was unaltered by naloxone or physostigmine. A succeeding positive component was enhanced by both ketamine and physostigmine. Physostigmine produced the most consistent alterations in latency, with most components increasing in latency. Naloxone pretreatment did not alter ketamine's influence on evoked potential amplitudes. Pretreatment with physostigmine briefly decreased the amplitude of the ketamine-induced positive spike, augmented the amplitude of the succeeding positive component, and also increased most peak latencies. Ketamine, naloxone and physostigmine all produced approximately equivalent hypothermia. Physostigmine, but not naloxone, pretreatment augmented the ketamine-induced hypothermia. The body temperature data suggest that some of the observed latency alterations are secondary to hypothermia. The amplitude data indicate that ketamine and physostigmine produce a combination of similar, distinct, and antagonistic effects on evoked potentials.

Animals↗
PubMedDate not supplied

Flow-flash, time-resolved resonance Raman spectroscopy of the oxidation of reduced and of mixed valence cytochrome oxidase by dioxygen.

Time-resolved resonance Raman spectroscopy has been used to study the reduction of oxygen by both reduced and mixed valence cytochrome oxidase. Laser flash photodissociation of CO from the carbon monoxy complex of the enzyme, after this species had been rapidly mixed with oxygenated buffer, was used to initiate the reaction for both forms of the enzyme. The CO photolysis product of the mixed valence enzyme contains cytochrome a3+ and cytochrome a3(2+) in its unligated form. This species reacts with O2 in the first few microseconds to form a photolabile intermediate which has Raman frequencies characteristic of oxygenated heme. This indicates that an oxyhemoglobinlike complex of oxygen with a3(2+) is the precursor to oxygen reduction. A similar intermediate is detected in the fully reduced enzyme reaction. In the mixed valence oxidase system, the oxy intermediate is replaced by a nonphotolabile species in which a3 is oxidized with t1/2 approximately equal to 200 musec. These results demonstrate the feasibility of applying time-resolved vibrational techniques to irreversible electron transfer reactions and, in particular, elucidate some of the transient species in the cytochrome oxidase/O2 system.

Carbon Monoxide↗
PubMedDate not supplied

Evidence for a photoactivation of CO rebinding to fully reduced cytochrome c oxidase after low-temperature flash photolysis.

Carbon monoxide rebinding to isolated fully reduced cytochrome c oxidase has been investigated by low-temperature, flash photolysis, dual-wavelength spectrometry. By using separately different wavelength pairs to monitor the liganding of CO to Fe a3 and by keeping all other experimental conditions identical, there has been singled out a photoactivation effect on CO rebinding. For instance, at 187 K, the rate constant of CO rebinding observed at 425-475 nm was twice that derived from the kinetic at 444-475 nm despite a rate constant of photodissociation about 10 times larger at 425-475 nm than at 444-475 nm. This new finding is discussed with respect to previous investigations under similar conditions.

Animals↗
PubMed1985

Separation and characterisation of light scattering transients from rod outer segments of vertebrate photoreceptors: design and performance of a Multi Angle Flash Photolysis Apparatus (MAFPA).

A device was built for the simple computer-controlled routine determination of the angular dependence of light scattering transients obtained from biological material. It was called Multi Angle Flash Photolysis Apparatus (MAFPA). The MAFPA allows the simultaneous registration of rapid, light-induced light scattering transients at eight scattering angles between 0 degree and 28 degrees. In typical applications changes in scattered light intensity as small as delta I/I = 4 X 10(-5) can be resolved at scattering angles less than 24 degrees, while at 28 degrees the resolution drops to delta I/I = 2 X 10(-4). The time resolution is 32 microseconds. The MAFPA was designed for high accuracy, ease of use and ruggedness. It is made from relatively inexpensive parts and can be copied fairly easily by a good machine/electronics shop. In this communication we describe the design of the MAFPA and how it was used for the characterisation of four structurally distinct light-induced light scattering signals from photoreceptor rod outer segments. These signals are known as P (or binding) signal, G- (or dissociation) signal, N (or rhodopsin) signal and as the ATP-dependent signal AL. The signals have been separated by means of their different angular dependence, their different saturation behavior and nucleotide requirement. A great number of detailed studies will have to be carried out before one can fully understand the physical and biochemical origin of these signals. At this point, however, it can be stated that the so-called 'dissociation signal', showing an angular dependence indicative of a change in refractive index or scattering mass, is not merely an inversion of the preceding 'binding signal', the latter clearly reflecting a gross structural change, i.e. a shrinkage of the disks. Moreover, there are conditions where P signals are observed to persist even after the completion of the subsequent dissociation signals. The two remaining signals N and AL show a pronounced angular dependence which is not easily interpreted. The fact that both exhibit a maximal amplitude at relatively small angles seems to indicate the participation of rather large structural domains.

Adenosine Triphosphate↗
PubMed1992

The effects of low-pass filtering on the flash visual evoked potential of the albino rat.

Flash visual evoked potentials (FVEPs) were recorded from the rat in order to determine the effects of low-pass filtering on the wave form. The low-frequency (high pass) filter remained fixed at 3.2 Hz while the setting of the high-frequency (low-pass) filter was progressively raised from 32 Hz to 3.2 kHz. The amplitude of the primary cortical potential (P30) steadily increased while its latency decreased until asymptotic values were recorded with a low-pass cut-off of 320 Hz. Thereafter, there was little additional change in wave form. It is concluded that a bandpass of 3.2-320 Hz is optimal to record the primary cortical response of the FVEP, and this is consistent with the theory that the P30 potential is generated by comparatively slow post-synaptic activity. In a second experiment the effects of low-pass filtering were examined on the later and more labile secondary components of the FVEP wave form. These were found to be less responsive to low-pass filtering than the early components and assumed a near optimal configuration when the high-frequency cut-off was raised to 80 Hz. The high-frequency filter setting which is most appropriate to record the primary component of the FVEP therefore appears to be more than adequate also to record the secondary responses. It is also shown that the same principles of low-pass filtering on the FVEP will apply irrespective of whether the subject is awake or anaesthetised.

Anesthesia↗
PubMed1996

A low-cost UV laser for flash photolysis of caged compounds.

Photolysis of caged compounds has become a standard tool for the rapid application of bioactive molecules. In principle this technique also allows to apply substances in a spatially very restricted manner. An important practical limitation for such experiments, however, is the high cost of UV lasers. Here we describe the assembly of an inexpensive pulsed nitrogen laser which is suitable for photolysis experiments. The laser which can be constructed in less than 1 week and for less than US$ 500 emits light pulses with a duration of approximately 5 ns, an energy of up to 200 microJ (= 40 kW) and a wavelength of 337 nm. Its beam can be focused to roughly 30 microns, a firing frequency of up to 50 Hz can be achieved, and electrical artifacts are minimal. These specifications make the laser optimally suited for most photolysis experiments. Its low price and ease of use should make the technique of spatially restricted flash photolysis amenable to many laboratories.

Animals↗
PubMed1987

The intra-individual reproducibility of flash-evoked potentials in a sample of children.

Visual evoked potentials (VEPs) to flash stimuli were recorded twice from 26 children aged 10-13 years, with an intersession interval of about 10 months. Test-retest reliability was poor for recordings taken from scalp locations overlying non-specific cortex and somewhat better for specific cortex. The size of consistency coefficients (i.e. correlations within session) showed that noise and artefacts were not the decisive factors which lower reliability. A comparison with retest correlations of broad band parameters of the EEG at rest for the same sample showed, to our surprise, smaller retest reliability for VEP parameters. Variability of the VEP in children over time seems to be a substantial as its well-known inter-individual variability.

Adolescent↗