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At least 865 records · Page 48Linked to original sources
PubMed1988

Lesions of the substantia nigra retard Pavlovian eye-blink but not heart rate conditioning in the rabbit.

Bilateral radio-frequency (RF) lesions of the substantia nigra retarded Pavlovian eye-blink (EB) conditioning without affecting concurrent heart rate (HR) conditioning. Dopamine (DA) depletion occurred only in the caudate nucleus, whereas norepinephrine (NE) depletion was limited to the hypothalamus. Bilateral 6-hydroxydopamine (6-OHDA) lesions of substantia nigra retarded acquisition of both EB and HR responses. Six-OHDA lesions produced significant NE depletion in the nucleus acumbens/septi, frontal cortices, and hypothalamus, as well as DA depletion in the caudate nucleus. Trials required to reach EB conditioning criterion was significantly correlated with caudate DA levels. The magnitude of conditioned bradycardia was on the other hand significantly correlated with hypothalamic NE levels. These results suggest that interruption of the nigro-striatal dopaminergic pathway retards Pavlovian somatomotor learning without affecting concurrent autonomic learning, although the latter may depend on an intact ascending NE pathway to the hypothalamus, which passes through the tegmentum and thus is also destroyed in some cases by substantia nigra lesions.

Animals↗
PubMed1989

Hippocampal lesions impair memory of short-delay conditioned eye blink in rabbits.

Involvement of hippocampus in short-delay eye blink conditioning was reexamined during conditioned response (CR) consolidation. Rabbits received bilateral hippocampectomy, removal of overlying neocortex, or sham lesions and were trained with tone/puff pairings to early acquisition (consolidation) or well trained (overtraining); retention was tested. Two effects were observed: 1) Rabbits with hippocampal lesions showed less retention in the consolidation experiment than controls. Previous studies may not have found this because initial training was more complete. Overtrained hippocampal rabbits showed more retention, which agrees with this suggestion. 2) Hippocampectomized rabbits showed larger CR amplitudes in the overtraining experiment. The complementary roles of hippocampus in the consolidation process during early learning and in modulating the expression of the amplitude/time course of behavioral conditioned responses after associations are well learned are discussed.

Animals↗
PubMed1985

Intraseptal scopolamine has differential effects on Pavlovian eye blink and heart rate conditioning.

The effects of intraseptal scopolamine hydrobromide injections on Pavlovian (classical) conditioning were evaluated, with tones used as the conditioned stimulus (CS) and a periorbital electric shock train as the unconditioned stimulus (UCS). Eye blink (EB) and heart rate (HR) conditioned responses were concomitantly recorded. Although injections of scopolamine into the medial septum impaired the acquisition of the Pavlovian conditioned eyelid reflex, these injections enhanced the magnitude of accompanying Pavlovian conditioned HR decelerations. However, scopolamine applied to the lateral septal area had no effect on EB conditioning, relative to the vehicle, but, like medial injections, enhanced the magnitude of the accompanying HR decelerations. These results are compatible with those of previous investigations: Medial septal dysfunction impairs somatomotor conditioning but leaves autonomic conditioning intact, and septal dysfunction produces a parasympathetic bias of the cardiovascular system.

Animals↗
PubMed2006

Top-down controlled, delayed selection in the attentional blink.

In a previous study, it was shown that the attentional blink (AB)--the failure to recall the 2nd of 2 visual targets (T1 and T2) presented within 500 ms in rapid serial visual presentation--is reduced when T2 is preceded by a distractor that shares a feature with T2 (e.g., color; Nieuwenstein, Chun, van der Lubbe & Hooge, 2005). Here, this cuing effect is shown to be contingent on attentional set. For example, a red distractor letter preceding a green digit T2 is an effective cue when the task is to look for red and green digits, but the same red cue is relatively ineffective when the task is to look for only green digits or when the color of T2 is not specified. It is also shown that cuing is not interrupted by a distractor intervening between the cue and T2. These findings provide evidence for a contingent, delayed selection account of the AB.

Attention↗
PubMed2005

Auditory attentional blink: masking the second target is necessary, delayed masking is sufficient.

When two target items (T1 and T2) are presented in rapid succession among fillers, processing T2 is often impaired. This phenomenon is known as the attentional blink (AB). Within the visual modality, this second-target deficit generally occurs only if T2 is masked by a trailing item. The current study was designed to examine whether masking of T2 also plays a critical role in the auditory AB. Results showed a reliable AB effect even when the item following T2 was replaced by silence. However, the AB deficit was abolished when T2 was the last presented stimulus. Our results suggest that, as in vision, T2 masking is necessary for the AB to take place in audition, but that masking is effective even when delayed, providing evidence that the phenomenon shares some functional mechanisms across sensory modalities.

Adult↗
PubMed1997

On/off blinking and switching behaviour of single molecules of green fluorescent protein.

Optical studies of individual molecules at low and room temperature can provide information about the dynamics of local environments in solids, liquids and biological systems unobscured by ensemble averaging. Here we present a study of the photophysical behaviour of single molecules of the green fluorescent protein (GFP) derived from the jellyfish Aequorea victoria. Wild-type GFP and its mutant have attracted interest as fluorescent biological labels because the fluorophore may be formed in vivo. GFP mutants immobilized in aereated aqueous polymer gels and excited by 488-nm light undergo repeated cycles of fluorescent emission ('blinking') on a timescale of several seconds-behaviour that would be unobservable in bulk studies. Eventually the individual GFP molecules reach a long-lasting dark state, from which they can be switched back to the original emissive state by irradiation at 405 nm. This suggests the possibility of using these GFPs as fluorescent markers for time-dependent cell processes, and as molecular photonic switches or optical storage elements, addressable on the single-molecule level.

Animals↗
PubMed2006

Blinking fluorophores: what do they tell us about protein dynamics?

The ability to detect emission from a single fluorophore presents a powerful tool to probe the dynamic properties of protein molecules during their interactions with ligands. Here, different classes of experiments are reviewed and a distinction is drawn between experiments that monitor signals from a large number of proteins, one molecule at a time, from those that follow a single protein molecule over many individual cycles. The latter approach is potentially capable of resolving dynamic heterogeneity, such as that displayed by enzymes that fluctuate between high and low activity states. Other factors that need to be considered are the origin of the fluctuations in the emission signal and the extent to which this represents the properties of the protein under investigation, as opposed to the probe itself. Most fluorophores show fluctuations in their emission rates, termed flickering, blinking or intermittency, which may occur on a similar time-scale as the event under investigation.

Enzymes↗
PubMed2004

Aging correlation functions for blinking nanocrystals, and other on-off stochastic processes.

Following recent experiments on power law blinking behavior of single nanocrystals, we calculate two-time intensity correlation functions I(t)I(t+t') for these systems. We use a simple two state (on and off) stochastic model to describe the dynamics. We classify possible behaviors of the correlation function and show that aging, e.g., dependence of the correlation function on age of process t, is obtained for classes of the on time and off time distributions relevant to experimental situation. Analytical asymptotic scaling behaviors of the intensity correlation in the double time t and t' domain are obtained. In the scaling limit I(t)I(t+t('))-->h(x), where four classes of behaviors are found: (i) finite averaged on and off times x=t' (standard behavior); (ii) on and off times with identical power law behaviors x=t/t' (case relevant for capped nanocrystals); (iii) exponential on times and power law off times x=tt' (case relevant for uncapped nanocrystals); (iv) for defected off time distribution we also find x=t+t'. Origin of aging behavior is explained based on simple diffusion model. We argue that the diffusion controlled reaction A+B <==>AB, when followed on a single particle level exhibits aging behavior.

Journal Article↗
PubMed2005

Fluorescence intermittency in blinking quantum dots: renewal or slow modulation?

We study the time series produced by blinking quantum dots, by means of an aging experiment, and we examine the results of this experiment in the light of two distinct approaches to complexity, renewal and slow modulation. We find that the renewal approach fits the result of the aging experiment, while the slow modulation perspective does not. We make also an attempt at establishing the existence of an intermediate condition.

Journal Article↗
PubMed2005

Lag-1 sparing in the attentional blink: benefits and costs of integrating two events into a single episode.

When people monitor a visual stream of rapidly presented stimuli for two targets (T1 and T2), they often miss T2 if it falls into a time window of about half a second after T1 onset--the attentional blink. However, if T2 immediately follows T1, performance is often reported being as good as that at long lags--the so-called Lag-1 sparing effect. Two experiments investigated the mechanisms underlying this effect. Experiment 1 showed that, at Lag 1, requiring subjects to correctly report both identity and temporal order of targets produces relatively good performance on T2 but relatively bad performance on T1. Experiment 2 confirmed that subjects often confuse target order at short lags, especially if the two targets are equally easy to discriminate. Results suggest that, if two targets appear in close succession, they compete for attentional resources. If the two competitors are of unequal strength the stronger one is more likely to win and be reported at the expense of the other. If the two are equally strong, however, they will often be integrated into the same attentional episode and thus get both access to attentional resources. But this comes with a cost, as it eliminates information about the targets' temporal order.

Adult↗
PubMed1975

Electrically elicited blink reflex in diagnosis of multiple sclerosis. Review of 260 patients over a seven-year period.

The blink reflex obtained from 260 patients with suspected multiple sclerosis was analysed according to clinical criteria for diagnosis. The R1 component was dealyed on one or both sides in 96 of 145 patients with definite diagnosis (66 per cent), 32 of 57 with probable diagnosis (56 per cent), and 17 of 58 with possible diagnosis (29 per cent). The incidence of abnormal R1 rose with increasing duration of illness in each category. When the reflex was analysed according to the clinical localization of the lesion in the 260 patients, R1 was abnormal in 49 of 63 patients with pontine signs (78 per cent), 59 of 104 with other brain-stem signs (57 per cent), and 37 of 93 with no clinical brain-stem signs (40 per cent). Alteration of R2 was less specific but, when seen in the face of a normal R1, was usually associated with clinical signs suggesting lateral medullary lesions. These fingings offer direct evidence that conduction through demyelinated zones in the central nervous system is indeed slowed and that the degree of slowing can be measured objectively by means of this simple technique in man. The high inicdence of delayed R1 in patients with no clinical pontine signs suggests that the test may be used to document a clinically silent pontine lesion in multiple sclerosis and help to establish the anatomical dissemination of pathology.

Adolescent↗
PubMed1998

Random dots blinking: a new approach to elucidate the activities of the extrastriate cortex in humans.

To investigate cortical activities related to the visual recognition of characters, we recorded the magnetoencephalography (MEG) in six normal subjects who were encouraged to discriminate capital English letters displayed for a brief period. To reduce the primary responses evoked by the luminance change in the striate cortex (V1), we used a novel stimulus method, random dots blinking (RDB), by means of the temporal changes of patterns using a large number of small random dots. Along with the MEG recording, we also measured the discrimination accuracy rate (%) to know how well the subjects recognized the letters. One clear component, about 300 ms in peak latency, was identified in all six subjects. Its peak amplitude and the discrimination accuracy rate increased similarly as the character display duration became longer. Its signal source was estimated in the extrastriate cortex, around the fusiform gyrus, in the right hemisphere. We suspect that the activity in these cortical areas has strong relation to the conscious perception of characters.

Adult↗
PubMed1999

The attentional blink and P300.

The attentional blink (AB) is a brief impairment of visual processing occurring 200-500 ms after a target in a rapid stream of visual stimuli. At issue here is the relationship between AB and the P300 ERP component, as both are maximal at about 300 ms and have been hypothesised to reflect inhibitory processes. Two experiments revealed that AB and P300 follow a similar time course at the individual and group level, that reducing task difficulty has similar effects on AB and P300 magnitude at the group level, but that there is no relationship between the magnitude of AB and P300 within observers. These findings suggest a moderate association between the two phenomena, which may mirror transient inhibition of cortical networks to facilitate processing of target events.

Adult↗
PubMed2006

Description of the fluorescence intensity time trace of collections of CdSe nanocrystal quantum dots based on single quantum dot fluorescence blinking statistics.

This paper analyzes the observed phenomenology of the fluorescence time trace of collections of quantum dots (QDs) in terms of the model parameters that characterize the fluorescence blinking statistics of single QDs. We demonstrate that the non-universal dynamics that appear in fluorescence time traces of collections of QDs at short time scales are related to the universal dynamics that appear at longer time scales. We explore how the extent of time separation between the short and long dynamics affects the transition region and the dynamics at longer time scales. We suggest a methodology to extract single QD statistical model parameters from experimental fluorescence time traces of collections of QDs. We explore theoretical time traces and their experimental analogs for three different cases that span the diverse nonuniversal dynamics that appear at short time scales.

Journal Article↗
PubMed2002

Objects and events in the attentional blink.

When two visual targets, T1 and T2, are presented in rapid succession, detection or identification of T2 is almost universally degraded by the requirement to attend to T1 (the attentional blink, or AB). One interesting exception occurs when T1 is a brief gap in a continuous letter stream and the task is to discriminate its duration. One hypothesized explanation for this exception is that an AB is triggered only by attention to a patterned object. The results reported here eliminate this hypothesis. Duration judgments produced no AB whether the judged duration concerned a short gap in the letter stream (Experiment 1) or a letter presentedfor slightly longer than others (Experiment 2). When identification of an identical longer letter T1 was required (Experiment 3), rather than a duration judgment, the AB was reestablished Direct perceptual judgments of letter streams with gaps embedded showed that whereas brief gaps result in the percept of a single, briefly hesitating stream, longer gaps result in the percept of two separate streams with a separating pause. Correspondingly, an AB was produced in Experiment 4, when participants were required to judge the duration of longer T1 gaps. We propose that, like spatially separated objects, temporal events are parsed into discrete, hierarchically organized events. An AB is triggered only when a new attended event is defined, either when a long pause creates a new perceived stream (Experiment 4) or when attention shifts from the stream to the letter level (Experiment 3).

Adult↗
PubMed1974

Electromyographic and reflex study in idiopathic and symptomatic trigeminal neuralgias: latency of the jaw and blink reflexes.

Recorded jaw reflexes were studied in 51 normal subjects. In addition, the blink and jaw reflexes combined with masseteric electromyography were recorded in 17 unselected patients with facial pain. Six of these patients, including two without neurological anomalies, showed electrodiagnostic anomalies. The method proved valuable for differentiation between idiopathic and symptomatic trigeminal neuralgia.

Adult↗
PubMed1977

Blink reflexes and the state of arousal.

Blink reflexes were studied in 40 subjects at rest and during the performance of a task. The early reflex (R1) showed an increase of amplitude of action potential during the task, the late reflex (R2) did not. The latency of R1 did not change within the 45 minutes test period; R2 showed an increase of latency during task. R1 showed a systematic decrease in amplitude within rest and task periods, presumably because of habituation. R2 amplitudes decreased throughout the whole experiment, independent of task or rest.

Action Potentials↗
PubMed1978

Disturbances of ocular movements and blinking in schizophrenia.

Neurological examination and electroencephalograms and electro-oculograms, recorded by telemetry, from unmedicated patients with acute and chronic schizophrenia demonstrate a number of abnormalities of extraocular movement including staring, abnormal blink rate, absent glabellar reflex, and increase in horizontal eye movements. As potential clues to the pathophysiology of schizophrenia, these disturbances are analysed in relation to anatomical substrate and dopamine modulation of ocular movement, rapid eye movement sleep, and the neurological disorders in which similar disturbances of ocular movement occur.

Adolescent↗