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At least 253 records · Page 14Linked to original sources
PubMed2005

Blinking and nonradiant dark fraction of water-soluble quantum dots in aqueous solution.

Water-soluble quantum dots (qdots) are now being used in life sciences research to take advantage of their bright, easily excited fluorescence and high photostability. Although the frequent erratic blinking and substantial dark (never radiant) fractions that occur in all available qdots may interfere with many applications, these properties of individual particles in biological environments had not been fully evaluated. By labeling Qdot-streptavidin with organic dyes, we were able to distinguish individual dark and bright qdots and to observe blinking events as qdots freely diffused in aqueous solution. Bright fractions were measured by confocal fluorescence coincidence analysis (CFCA) and two-photon cross-correlation fluorescence correlation spectroscopy (FCS). The observed bright fractions of various preparations were proportional to the ensemble quantum yields (QYs), but the intrinsic brightness of individual qdots was found to be constant across samples with different QYs but the same emission wavelengths. Increasing qdots' illuminated dwell time by 10-fold during FCS did not change the fraction of apparently dark qdots but did increase the detected fraction of blinking qdots, suggesting that the dark population does not arise from millisecond blinking. Combining CFCA with wide-field imaging of arrays of qdots localized in dilute agarose gel, the blinking of qdots was measured across five orders of magnitude in time: approximately 0.001-100 s. This research characterizes photophysical pathologies of qdots in biologically relevant environments rather than adhered on dielectric surfaces and describes methods that are useful for studying various bioapplicable nanoparticles.

Biophysical Phenomena↗
PubMed1970

The human blink reflex.

A detailed study of the human blink reflex in the different parts of the orbicularis oculi muscle has been carried out. The first component of the blink reflex has been demonstrated in patients with Friedreich's ataxia, who have selective loss of large sensory fibres resulting in loss of proprioceptive input. It has been established that both components of the blink reflex are cutaneous reflexes which represent a highly organized and purposeful mechanism in man. Afferent fibres for the blink reflex have been identified in the human supraorbital nerve and their conduction velocity has been estimated for the first time in man. It has been demonstrated that both components of the blink reflex are mediated by the same group of afferent fibres.

Adolescent↗
PubMed2002

Delayed working memory consolidation during the attentional blink.

After the detection of a target (T1) in a rapid stream of visual stimuli, there is a period of 400-600 msec during which a subsequent target (T2) is missed. This impairment in performance has been labeled the attentional blink. Recent theories propose that the attentional blink reflects a bottleneck in working memory consolidation such that T2 cannot be consolidated until after T1 is consolidated, and T2 is therefore masked by subsequent stimuli if it is presented while T1 is being consolidated. In support of this explanation, Giesbrecht & Di Lollo (1998) found that when T2 is the final item in the stimulus stream, no attentional blink is observed, because there are no subsequent stimuli that might mask T2. To provide a direct test of this explanation of the attentional blink, in the present study we used the P3 component of the event-related potential waveform to track the processing of T2. When T2 was followed by a masking item, we found that the P3 wave was completely suppressed during the attentional blink period, indicating that T2 was not consolidated in working memory. When T2 was the last item in the stimulus stream, however, we found that the P3 wave was delayed but not suppressed, indicating that T2 consolidation was not eliminated but simply delayed. These results are consistent with a fundamental limit on the consolidation of information in working memory.

Adolescent↗
PubMed2002

Blinks of the mind: memory effects of attentional processes.

If 2 words are presented successively within 500 ms, subjects often miss the 2nd word. This attentional blink reflects a limited capacity to attend to incoming information. Memory effects were studied for words that fell within an attentional blink. Unrelated words were presented in a modified rapid serial visual presentation task at varying stimulus-onset asynchronies, and attention was systematically manipulated. Subsequently, recognition, repetition priming, and semantic priming were measured separately in 3 experiments. Unidentified words showed no recognition and no repetition priming. However, blinked (i.e., unidentified) words did produce semantic priming in related words. When, for instance, ring was blinked, it was easier to subsequently identify wedding than apple. In contrast, when the blinked word itself was presented again, it was not easier to identify than an unrelated word. Possible interpretations of this paradoxical finding are discussed.

Attention↗
PubMed1989

Loss of spontaneous blinking in a patient with Balint's syndrome.

A patient with Balint's syndrome caused by bilateral parieto-occipital lesions lost spontaneous blinking, suggesting that humans, like nonhuman primates, have parietal lobe neurons that are important for blinking. Although the functions of spontaneous blinking are not known, they may help initiate some saccades and, like saccades, be involved in the cancellation of thalamic inhibitory postsynaptic potentials, thereby facilitating processing of new foveal targets. Spontaneous blinking may also facilitate sensory relay during sustained attention and, therefore, help prevent fading of a retinal image.

Adult↗
PubMed2000

Increased blink rate in advanced Parkinson's disease: a form of 'off'-period dystonia?

Blink rates were measured in 25 patients with fluctuating Parkinson's disease in the "off' and "on" periods. In 17 patients, the "off"-period blink rate was low and increased after administration of levodopa. In the remaining eight patients, the "off"-period blink rate was high and returned to normal levels after levodopa. It is suggested that increased blink rate in the latter group represents a new form of "off"-period dystonia.

Adult↗
PubMed1989

Prestimulation effects on blink and cardiac reflexes of 15-month human infants.

Reduction of reflex startle by brief changes in prestimulation is a robust phenomenon in adults of several species. Although the phenomenon does not require structures above midbrain, it has a long and uneven developmental course. This study of human infants assessed prestimulus effects at 15 months, within a period which has failed, in past work, to show the usual inhibitory modulation. Magnitude and onset latency of the startle blink and concurrent changes in heart rate were measured under four conditions: 2 single-stimulus conditions, 25-msec, 84-dB, 1000-Hz tone or 50-msec, 109-dB white noise; 2 paired-stimulus conditions, noise bursts preceded by tone at lead times of 125 msec or 225 msec. Compared to noise-alone, paired conditions elicited insignificant increases in blink size, significant shortening of blink onset latency, and significant attenuation of heart rate responses. The findings add to growing evidence of a dissociation between modulating effects on blink magnitude and latency and of a dissociation between modulating effects on somatic and autonomic reflexes.

Arousal↗
PubMed1993

Pattern of extraocular muscle activation during reflex blinking.

Studies in humans and rabbits suggest that cocontraction of extraocular muscles occurs with reflex and voluntary blinks. We determined the pattern of extraocular muscle activity elicited by blink-evoking visual and trigeminal stimuli by electromyographically recording antagonistic pairs of extraocular muscles in alert rabbits. In addition, we recorded the activity of antidromically identified oculomotor motoneurons in response to the same stimuli in alert rabbits. The data demonstrate that all extraocular muscles except the superior oblique transiently increase their activity in response to blink-evoking stimuli. The pattern of extraocular muscle activity with reflex blinks mirrors that occurring in the lid-closing muscle, orbicularis oculi, but the latency of extraocular muscle activation is longer.

Animals↗
PubMed1995

The trigeminally evoked blink reflex. II. Mechanisms of paired-stimulus suppression.

The paired-stimulus paradigm, presentation of a pair of identical reflex-eliciting stimuli to the supraorbital nerve (SO) with an interstimulus interval of less than 2 s, evokes a response to the second, test, stimulus which is less than that elicited by the first, conditioning, stimulus. In this study, we investigated the site of this suppression and its pharmacology in the alert guinea pig. Both the early (R1) and the late (R2) component of the SO-evoked blink reflex exhibited suppression in the paired-stimulus paradigm. Initiation of suppression appeared to be specific to the afferent limb of the reflex rather than the result of motor activity generated by the conditioning stimulus. Neither acoustic conditioning stimuli nor air puffs that elicited blinks via another branch of the trigeminal nerve suppressed the test response. Extremely weak SO shocks, however, that did not directly elicit a reflex, caused suppression of the response to subsequent SO stimuli of normal intensity. Paired stimulus suppression of the R1 component appeared to involve activation of GABAB receptors within the spinal trigeminal nucleus. Both systemic injections and microinjections of baclofen into the spinal trigeminal nucleus enhanced R1 suppression, whereas identical injections of CGP35348, a GABAB antagonist, diminished R1 suppression. Furthermore, single-unit recordings in alert animals revealed that spinal trigeminal neurons exhibited suppression in the paired-stimulus paradigm that resembled that of the R1 component of the blink reflex. These findings showed that sensory gating underlies paired-stimulus suppression of the SO-evoked blink reflex and that activation of GABAB receptors plays an important role in this process.

Acoustic Stimulation↗
PubMed1984

Saccade and blinking evoked by microstimulation of the posterior parietal association cortex of the monkey.

Electrical stimulation with microelectrodes of the posterior parietal association cortex in alert behaving monkeys elicited saccadic eye movements and blinking. The sites in which saccades were elicited by electrical stimulation were concentrated in the anteromedial part of area 7a, especially in the posterior bank of the intraparietal sulcus, in a region which sends efferent projections to the frontal eye field and the superior colliculus, but they were also found in the posterolateral part of area 7a. Compared with the frontal eye fields and the superior colliculus, the threshold current for eliciting saccades was relatively high, on the average 86 microA. Moreover, the elicitation of saccade was inconsistent even with suprathreshold stimulation and suppressed during visual fixation. Latencies of the saccades were relatively long, on the average 50ms; they were longer in the posterolateral part than in the anteromedial part. Direction and amplitude of evoked saccades depended on the site of stimulation, but was independent of eye position in most cases. However, "goal-directed" saccades which depended on initial eye position were elicited in three penetrations in the posterolateral part of area 7a. The threshold of mainly in the lateral part of area 7a. The threshold of blinking was 70 microA and the latency was 50 ms on the average. In contrast to saccades, blinking was elicited constantly with each stimulus even during attentive fixation. We occasionally recorded single unit activity at the site of stimulation with the same electrodes. More than half of the units recorded at the site of blinking responded to approaching visual stimulus.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1997

Influence of the superior colliculus on the primate blink reflex.

In this study we used microstimulation to investigate the influence of the superior colliculus on the trigeminal blink reflex. We report that stimulation in the intermediate to deep layers of the tectum produced inhibition of reflex blinks at a latency of approximately 26 ms. We considered the hypothesis that the blink inhibition was mediated via the omnipause neurons (OPNs) of the eye movement control system in the brainstem. Our results show that the least effective sites for suppression were in the rostral colliculus. This is inconsistent with the prediction that OPNs should be maximally recruited from the rostral tectum near the "fixation zone." From these points and other considerations, we conclude that the reflex blink suppression from the superior colliculus is not directly mediated by the OPNs or the saccadic eye movement circuits.

Animals↗
PubMed2006

Blink amplitude but not saccadic hypometria indicates carriers of Parkin mutations.

We investigated saccades, eyelid blinks, and their interaction in symptomatic (n = 22) and asymptomatic (n = 31) subjects with (n = 19) and without (n = 34) Parkin mutations. Saccadic hypometria was correlated with clinical symptoms of Parkinson's disease, irrespective of mutational status. By contrast, blink amplitude was increased in carriers of Parkin mutations independent of their clinical status. Saccade main sequence and blink effects on saccades were normal. We propose that increased blink amplitude may serve as an endophenotype in carriers of Parkin mutations.

Adult↗
PubMed2005

Spreading the sparing: against a limited-capacity account of the attentional blink.

The identification of the second of two targets presented in close succession is often impaired--a phenomenon referred to as the attentional blink. Extending earlier work (Di Lollo, Kawahara, Ghorashi, and Enns, in Psychological Research 69:191-200, 2005), the present study shows that increasing the number of targets in the stream can lead to remarkable improvements as long as there are no intervening distractors. In addition, items may even recover from an already induced blink whenever they are preceded by another target. It is shown that limited memory resources contribute to overall performance, but independent of the attentional blink. The findings argue against a limited-capacity account of the blink and suggest a strong role for attentional control processes that may be overzealously applied.

Adolescent↗
PubMed2005

Differences of blink-reflex abnormalities in patients suffering from idiopathic and symptomatic trigeminal neuralgia.

We investigated the brainstem blink reflex in patients suffering from idiopathic and symptomatic trigeminal neuralgia to establish possible dysfunction in the reflex cycle and determine eventual differences between the two disease types. The study included 35 patients with idiopathic disease and seven patients with symptomatic disease, their results compared with those of 50 normal controls. We stimulated the forehead afferents of the supraorbital nerve and recorded the response from both orbicularis oculi muscles. We tested latencies of bilateral late components (R2, R2'), irritative R3 component and the incidence of R3 component. The patients with idiopathic trigeminal neuralgia showed normal parameters of blink reflex, except for the greater incidence of R3 component. Patients with symptomatic trigeminal neuralgia showed prolonged latencies of R2, R2' and R3 components when stimulating the afflicted side, but no significant difference in incidence of R3 component compared with the control group. The results indicate that abnormalities of blink reflex are significantly different in the two groups of patients. The high incidence of R3 component seems to be typical of idiopathic disease, whereas the prolonged latencies of late reflex components after stimulation of the afflicted side seem to be typical for symptomatic disease. These results suggest that testing the blink reflex may prove a significant aid in distinguishing the idiopathic and symptomatic disease types.

Adult↗
PubMed1996

Blink rate in children with attention-deficit-hyperactivity disorder.

Spontaneous blink rate, a noninvasive measure of dopamine function, was coded in 28 children with attention-deficit-hyperactivity disorder (ADHD) and in 47 normal children during a listening, a conversation, and a verbal recall task. Unlike the normal children, the children with ADHD did not increase their blink rates significantly across these three tasks. The ADHD subjects were were not on stimulants had significantly lower blink rates than the normal children during verbal recall. The ADHD subjects on stimulants, however, had significantly higher blink rates than the normal subjects during the listening task. These preliminary findings are discussed in light of their potential implications for theories on neurotransmitter dysfunction and arousal in ADHD.

Adolescent↗
PubMed1986

Pathway of the blink reflex in the brainstem of the cat: interneurons between the trigeminal nuclei and the facial nucleus.

Blink reflex responses evoked by electrical stimulation of the supraorbital nerve were examined using cats and the pathway of the blink reflex in the brainstem was elucidated. Both early response (ER) and late response (LR) were mediated by the main sensory trigeminal nucleus and the spinal trigeminal nucleus. However, a lesion of the main sensory trigeminal nucleus had less effect on the blink reflex than a lesion of the spinal trigeminal nucleus. The ER was mediated not only by the shorter disynaptic pathway of 3 neurons through the trigeminal nerve, the trigeminal nuclei and the facial nucleus but also by a polysynaptic pathway of 4 neurons. The interneurons were located between the trigeminal nuclei and the facial nucleus. Some of these interneurons participated in the production of both ER and LR. The area of the brainstem responsible for ER and LR of the blink reflex was the reticular formation from the rostral part of the medulla to the pons except the medial area around the median sulcus. The LR interneurons were distributed more widely than the ER interneurons.

Animals↗
PubMed1994

Central mid-temporal spikes triggered by blinking.

The closed-circuit TV-electroencephalogram (CCTV-EEG) of a 6-year-old boy revealed central mid-temporal spikes (CMTS) triggered by blinking. The spikes occurred spontaneously, as well as reflexly, following the blinks by 100-200 msec. Triggered spikes occurred in the light and dark and also while awake and drowsy. However, spontaneous spikes, not triggered by blinks, also occurred in drowsiness. These findings demonstrate activation of CMTS by an endogenous behavior (blinking).

Blinking↗
PubMed1991

Interaction between the blink reflex and the abnormal muscle response in patients with hemifacial spasm: results of intraoperative recordings.

Patients with hemifacial spasm (HFS) have an abnormal muscle response (AMR) that can be elicited by stimulating one branch of the facial nerve and recording electromyographically from muscles innervated by other branches of the facial nerve. In addition, the R1 component of the blink reflex can be elicited from the affected side in patients with HFS who are undergoing microvascular decompression (MVD) operations under inhalation anesthesia. A synkinetic component of the blink reflex response that corresponds to the R1 component can be recorded from the mentalis muscle. In the present study we show that the blink reflex elicited by electrical stimulation of the supraorbital nerve can suppress the AMR elicited by electrical stimulation of the temporal branch of the facial nerve in patients with HFS when the interval between stimulation of the supraorbital nerve and stimulation of the temporal branch of the facial nerve (interstimulus interval, ISI) is such that the blink reflex response would appear later than the AMR if they had been elicited independently. Within a short range of ISIs the two responses suppress each other partially or totally. We find evidence that the suppression of the AMR is the result of an interaction in the facial motonucleus. We believe that the results of the present study support the hypothesis that the facial motonucleus is hyperactive in patients with HFS, and we suggest that the AMR is a result of backfiring from the facial motonucleus and that it may thus be an exaggerated F-response.

Blinking↗