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At least 379 records · Page 21Linked to original sources
PubMed2000

Involvement of the noradrenergic system in modulating the blink reflex in humans.

Several researches have shown that the spinal reflex transmission in animals, as well as humans, was inhibited by alpha(2)-agonists, due to a disfacilitation of tonic noradrenergic control on motoneuronal output. To understand better the mechanisms regulating certain aspects of motor activity, here we reinvestigated the possible role of noradrenergic systems in modulating reflex activity of the brainstem in humans. To this aim, blink reflex responses (R1 and R2) evoked by electrical stimulation of the supraorbital nerve were electromyographically recorded in healthy volunteers. Both R1 and R2 areas were measured at 10-min intervals before and after i.v. injection of alpha(2)-agonist clonidine (0.5 microg/kg). The substance induced consistent depression of R1, which reached its maximum 40 min after drug administration (-43% of the control values). Ipsilateral R2 area resulted little affected by clonidine (-15% at 50 min), whereas no effects were observed in contralateral R2. Blood pressure values were never altered by drug injections. These results, taken together with previous observations, support the hypothesis that alpha(2)-agonist substances may cause a transient inactivation of noradrenergic neurons, thus releasing neurons involved in the circuitry of the blink reflex from a facilitatory drive. Since clonidine differentially modulated blink reflex responses, it is likely to assume that such a disfacilitation concerns mostly pontine units mediating the R1. However, the complexity of clonidine's effects at multiple pre- and postsynaptic sites does not allow us to exclude that other systems are involved in the alpha(2)-mediated control of facial motoneurons.

Adult↗
PubMed1997

Bilateral coupling in learned blinking: side superiority, synchrony and temporal coordination in normal cats.

In order to study interocular temporal coupling in the initiation of learned symmetrical blinking, experiments were carried out on cats trained to blink in response to a 500-ms tone paired with 100-ms airpuffs randomly delivered to either eye (alternate airpuff; 6 animals) or simultaneously directed to both eyes (bilateral airpuff; 4 animals) 400 ms after tone onset. In spite of the fact that differences in conditioned response (CR) latencies of the right and left eye varied in a wide range between positive and negative values in all subjects, a statistically significant difference between the mean CR latencies of the two eyes (further called side superiority) was found in 6 animals, of which 4 were trained by alternate airpuff and 2 by bilateral airpuff. Superiority of the right eye was found in 3 animals and the opposite was observed in the other 3. Analysis of the differences between CR latencies of the two eyes showed that side superiority was not due to the ability of one eye to give CRs consistently shorter than those of the other eye, but it crucially depended on the higher proportion of trials in which the superior eye led. The ability to give simultaneous CRs by the two eyes was found inversely related to the mean CR latency per session and subject. Regression analysis showed that power equations best described these relationships. In all animals, the frequency distribution of simultaneous CRs paralleled the frequency distribution of all CRs. In spite of a considerable trial-by-trial variability in the temporal relationships between CR latencies of the two eyes, clear-cut linear correlations were found by plotting the mean CR latencies of the right and left eye per both session and subject. The results reviewed in this paper are best accounted for by suggesting that blink onset of the two eyes is independently controlled by two distinct command signals and is modulated by bilaterally-balanced and lateralized influences.

Air Pressure↗
PubMed1997

Bilateral coupling in learned blinking: effects of lesion aimed at callosal disconnection of the cat motor cortex.

The effects of selective transection of the rostralmost portion of the corpus callosum, which contains fibers interconnecting the motor cortices of the two hemispheres, on interocular temporal coupling in the initiation of learned symmetrical blinking were examined in 5 cats trained to blink in response to a 500-ms tone paired with 100-ms airpuffs randomly delivered to either eye (alternate airpuff; 3 animals) or simultaneously directed to both eyes (bilateral airpuff; 2 animals) 400 ms after tone onset. Lesioning had no effect on ability to respond, but did cause a significant increase in the mean conditioned response (CR) latencies of both eyes in all subjects. In the intact cats, a statistically significant difference between the mean CR latencies of the two eyes (hereafter called side superiority) was found in three animals, two of which exhibited superiority of the left eye. After lesioning, it was found that the right eye proved superior to the left eye in four subjects. Both before and after lesioning, side superiority was not due to the ability of one eye to give CRs consistently shorter than those of the other eye, but it crucially depended on the higher proportion of trials in which the superior eye led. A linear correlation between CR latencies of the right and left eye was found in all animals both before and after lesioning. It is suggested that subsequent to lesioning aimed at callosal disconnection of the motor cortex, the effects on initiation of learned symmetrical blinking are the consequences of withdrawal of both bilaterally balanced modulatory influences to both eyes and lateralized modulatory influences to the left eye.

Animals↗
PubMed1998

Characterization of blink reflex interneurons by activation of diffuse noxious inhibitory controls in man.

The blink reflex consists of an early, pontine R1-component and a late, medullary R2-component. R1 and R2 can be evoked by innocuous stimuli, but only the R2 also by painful heat, suggesting that the R2 is mediated by wide dynamic range neurons (WDR) of the spinal trigeminal nucleus. Remote noxious stimuli suppress the activity in WDR neurons via activation of diffuse noxious inhibitory controls (DNIC), whereas low-threshold mechanoreceptive neurons (LTM) are unaffected. In order to characterize the trigeminal interneurons of R1 and R2 we investigated the modulation of the blink reflex by remote painful heat. The blink reflex was elicited in 11 healthy subjects by innocuous electrical pulses applied to the left supraorbital nerve. The remote, painful heat stimuli were applied by a Peltier type thermode to the left volar forearm. Remote painful heat of 44 to 46 degreesC significantly suppressed the R2 by 15% (p<0.01), while the R1 remained unchanged. These results provide further evidence that the R2 is mediated by medullary WDR neurons and the R1 by pontine LTM neurons.

Adult↗
PubMed1981

Blinking and the mechanics of the lacrimal drainage system.

High-speed photography, using picture rates up to 500/sec, has confirmed many key aspects of the tear drainage process reported over the years by various investigators. The punctal openings are seen to elevate themselves from the lid margin at the start of the closing phase of the blink, allowing their forceful meeting and occlusion by the time the closing lid is halfway down. Completion of lid closure then compresses the canaliculi and lacrimal sac, forcing contained fluid through the drainage system. The elastic expansion of the channels during the opening phase of the blink forms a suction, holding the lid margins at the punctal region together as the lids open. During the latter part of this opening, the punctal areas are seen to "pop' apart suddenly as the vacuum is broken, and tear fluid from the marginal tear strips is drawn into the puncta in the first few seconds following the blink.

Biomechanical Phenomena↗
PubMed1992

Muscle activity during unconditioned and conditioned eye blinks in the rabbit.

EMGs were recorded from the orbicularis oculi, retractor bulbi and superior rectus muscles in rabbits to investigate the time course of muscle activation during unconditioned and conditioned eye blinks. EMGs from the three muscles showed two responses, with the responses of the orbicularis oculi and retractor bulbi showing the same latency, and the responses of the superior rectus lagging. The latency of responses to periorbital electrostimulation was about 5 ms, and to air puff stimulation about 10 ms. Results showed a tight coupling of activity between muscles, with cross-correlograms peaking at 0.65 to 0.85 and showing little time shift. Stimulus-response curves showed clear non-linearities in the response of the muscle to changes in stimulus strength. Local anesthesia of the cornea had little effect on unconditionally evoked responses. The form of unconditionally evoked responses was similar with periorbital electrostimulation and air puff stimuli but differed in latency. These results show the form of the eye blink reflex response and will be of importance in interpreting electrophysiological studies of the classically conditioned eye blink of rabbits.

Animals↗
PubMed1984

Sites in the rabbit flocculus specifically related to eye blinking and neck muscle contraction.

In alert rabbits, the cerebellar flocculus was mapped for effects of local stimuli delivered through glass microelectrodes. Triple-barreled glass microelectrodes were used, each barrel of which was filled with solution containing one of three different dyes (Fast Green FCF, Pontamine Sky Blue and Nigrosine) for differentially labeling the sites exhibiting different stimulus effects. In addition to eye movements reported earlier, eye blinking and contraction of dorsal neck muscles were elicited from limited areas of the flocculus. Eye blinking sites were concentrated rostroventrally and neck muscle contraction sites caudoventrally within the flocculus. The present results suggest that the rabbit flocculus contains specific sites devoted to the control of eye blinking and neck posture.

Animals↗
PubMed2000

Prepulse inhibition of the blink reflex by laser stimuli in normal humans.

The subcortical integrative effects of laser-induced activation of pain ascending tracts were examined in 11 healthy volunteers, aged 22-52 years. Subjects underwent either CO2 laser stimulation at the dorsum of the hand, electrical stimulation of digital nerves at the 3rd finger, or mechanical taps to the first dorsal interosseous space, preceding a blink reflex elicited by a supraorbital nerve electrical stimulus. The percentage inhibition induced in the R2 response of the blink reflex was similar for the three different stimulus modalities, but occurred at a different time interval. Compared to control trials, the R2 response of the test trials was a mean of 23.1% at the interval of 250 ms with laser stimuli, 17.4% at the interval of 100 ms with electrical stimuli to the 3rd finger, and 20.6% at the interval of 90 ms with a mechanical tap to the 1st interosseous space. Activation of pain receptors induces prepulse inhibition of the blink reflex at a delay corresponding to a slowly conducting pathway. The percentage inhibition is similar to that observed with other somatosensory inputs.

Adult↗
PubMed2001

Is the R3 component of the human blink reflex nociceptive in origin?

The R3 component of the blink reflex can reproducibly be evoked by noxious stimulation but can probably also be elicited by innocuous stimuli. This study was conducted to investigate the contribution of nociceptive A delta and C fibers to the generation of the electrically evoked R3 blink reflex. Electrical thresholds for detection, pain and all blink reflex components were determined and the modulatory effects of local anesthesia were investigated. The electrical R3 threshold of 4.6 +/- 0.5 mA (mean +/- SE) corresponded to 2.9 times the detection threshold and to 0.35 times the pain threshold. The R3 threshold was significantly below the pain threshold. Under local anesthesia of the supraorbital skin with a complete loss of warm and cold sensation, a loss of pinprick sensation, but a normal detection of tactile stimuli, the electrical pain threshold increased, all other thresholds remained unchanged. Under local anesthesia none of the reflex components were significantly reduced. Cutaneous A beta fibers and nociceptive A delta fibers, but not unmyelinated C fibers, contribute to the generation of the electrically evoked R3 component. According to the recruitment order in peripheral sensory nerves the electrical threshold of the R3 is mainly determined by activation of A beta fibers. Thus, it can not be assumed that the electrically evoked R3 is an adequate model to investigate nociceptive processing.

Adult↗
PubMedDate not supplied

[Eye blink: electrophysiological behavioral index (author's transl)].

Eye movements of 15 subjects were recorded through EEG derivation (nasion to first quarter of mid-line) during 17 different precisely controlled psychophysiological situations of 2'30 each. These situation were supposed to trigger the various sensory modalities--visual, auditory, gustato--olfactory, and subjects having to be either passive or active. The relationship between the Number of Eye Blinks per minute (NEB) and each psychophysiological situation were studied. An average oculographic profile was obtained across situations.--The average value of NEP was approximately 25/mn.--In order to control serial effects the situation order was reversed for 7 of the 15 subjects: no serial effect was noticed.--As regards the influence of the various sensory modalities, it appeared that blinking rate was minimal during visual situations, and maximal during tactile, olfactory and taste situations.--The changes in blinking rate were discussed in terms of visual and oculor factors, variations in selective attention or cognitive process and also in terms of emotional factors as they appear in some stressing situations in which the task demand was particularly important.

Behavior↗
PubMed1985

[The blink reflex and the diagnosis of multiple sclerosis. Clinical correlations in 66 patients].

The blink reflex obtained from 66 patients with multiple sclerosis (MS) shows 73% pathologic responses with MS considered as definite, 50% with MS considered as probable and only 18% with possible MS. These findings are of great diagnostical help, particularly in the absence of clinical evidence of involvement of the brain-stem. Among 8 electrological syndromes of alteration of the blink reflex, those due to large lesions of the brain-stem are often associated with definite MS, but small alterations of the blink reflex are more valuable for multifocal characterisation of the illness.

Blinking↗
PubMed1992

[Idiopathic peripheral facial paralysis. Prognostic value of the combined study of the blink reflex with stimulation of the facial nerve. 91 cases].

The blink reflex and stimulodetection of the facial nerve was studied during the first ten days, the 30th and 60th day and at the end of the sixth month in 91 patients with Bell's palsy. In patients with present R1 during the first ten days, there was a remarkable tendency towards a satisfactory recovery without complications. On the contrary using this single test, it is impossible to determine with 100% accuracy, which Bell's palsy will have an unsatisfactory recovery with severe dysfunction. The blink reflex seems to be a useful test for predicting the prognosis in an early stage of the paralysis. The association of the blink reflex and stimulodetection of the facial nerve allows to evaluate the risk of sequelae by the means of different electrophysiological patterns.

Blinking↗
PubMed2004

Blink reflex abnormalities in Tourette syndrome.

OBJECTIVE: Tourette syndrome (TS) is a not uncommon disorder which represents the most complex manifestation of the spectrum of tic disorders, with onset during childhood or early adolescence. There are no definitive tests for diagnosis of TS. The objective of this study has been to demonstrate whether neurophysiological abnormalities of the blink reflex can be observed in patients affected with TS and correlate with the severity of TS. METHODS: We enrolled 17 patients with Tourette syndrome, diagnosed according to DSM IV Diagnostic Criteria, and 10 healthy volunteers. Tic severity was assessed using a self rating scale (Tourette Syndrome Symptom List, TSSL) and examiner ratings (Yale Global Tic Severity Scale (YGTSS), and Tourette-Syndrome Global Scale (TSGS)). The blink reflex was elicited by stimulating the supraorbital nerve in order to measure the early response (R1), homolateral and contralateral R2 (late) responses, amplitude of R1 and duration of R2. RESULTS: We observed a mean duration of R2 significantly longer in the patient group than in the control group (P<0.01, Student t test), without any statistically significant differences of R1 and R2 latencies and of R1 amplitude between the patient group and the control group. Correlations between changes in clinical rating scores and R2 duration were tested by simple linear regression analysis, which has not demonstrated a significant correlation between TSSL scores, clinical rating scores (measured by TSGS and YGTSS) and duration of R2. CONCLUSIONS: A pattern as to excitability of the blink reflex can be a frequent abnormality in TS patients, not correlated with its severity.

Adult↗
PubMed2005

Sex hormonal modulation of hemispheric asymmetries in the attentional blink.

The present study examines differences in functional cerebral asymmetries modulated by gonadal steroid hormones during the menstrual cycle in women. Twenty-one right-handed women with regular menstrual cycles performed a double-stream rapid serial visual presentation (RSVP) task, with one stream in each visual field, during the low steroid menses and the high steroid midluteal phase. They were required to detect a target item, and then a probe item, each of which could appear in either stream. If the probe item appeared 200 ms after the target, detection of the probe was impaired-a phenomenon known as the "attentional blink." This occurred in both streams in the midluteal phase, but only in the right visual field during menses. Thus low steroid levels appeared to restrict the attentional blink to the left hemisphere, while high levels of estradiol and progesterone in the midluteal phase appeared to reduce functional asymmetries by selectively increasing the attentional blink in the right hemisphere. This effect appears to be mediated by estradiol rather than progesterone, and it is compatible with the assumption of a hormone-related suppression of right hemisphere functions during the midluteal phase.

Adult↗
PubMed1998

Electrophysiological evidence for a postperceptual locus of suppression during the attentional blink.

When an observer detects a target in a rapid stream of visual stimuli, there is a brief period of time during which the detection of subsequent targets is impaired. In this study, event-related potentials (ERPs) were recorded from normal adult observers to determine whether this "attentional blink" reflects a suppression of perceptual processes or an impairment in postperceptual processes. No suppression was observed during the attentional blink interval for ERP components corresponding to sensory processing (the P1 and N1 components) or semantic analysis (the N400 component). However, complete suppression was observed for an ERP component that has been hypothesized to reflect the updating of working memory (the P3 component). Results indicate that the attentional blink reflects an impairment in a postperceptual stage of processing.

Adolescent↗
PubMed2003

Blink-related microtrauma: when the ocular surface harms itself.

Superior limbic keratoconjunctivitis results mechanically from blinking under prolonged unphysiological conditions. The pathogenic process is known as blink-related microtrauma. This review aimed to explore the validity of a general theory that besides superior limbic keratoconjunctivitis, there may be other diseases of the ocular surface arising from mechanical microtrauma. A review of relevant clinical and microscopic lesions in a range of ocular surface disorders with possible mechanical aetiology was conducted. New terms were selected to facilitate understanding of such new aetiology. Besides superior limbic keratoconjunctivitis, other ocular surface disorders regarded as primarily derived from blink microtrauma are: other filamentary keratitides; blepharospasm and severe ptosis; canthal/palpebral froth; affections from disordered eyelid lining; and contact lens related damage. A group of secondarily microtraumatic disorders was identified, including the example of microtrauma impacting upon interpalpebral bulbar prominences. Superior limbic keratoconjunctivitis is the archetype of diseases affecting a unique combination; namely, the ocular surface conjoined with its lacrimal fluid. It is only one among many diseases actively generated within the confines of 'a self-harming surface'.

Blinking↗
PubMed2002

Prognostic value of the blink reflex in acoustic neuroma surgery.

OBJECTIVE: The study goal was to demonstrate that blink reflex analysis can predict postoperative facial nerve outcome in cerebellopontine angle tumor surgery. STUDY DESIGN, SETTING, AND PATIENTS: In an open and prospective study conducted at a single tertiary care center over 3 years, 91 subjects with a vestibular schwannoma filling the internal auditory meatus were enrolled and operated on via a translabyrinthine approach. The difference in latency of the early response (DeltaR1) of the blink reflex between the pathologic side and the healthy side was calculated in every patient during a complete electrophysiologic examination of the facial nerve performed on the day before surgery. MIN OUTCOME MEASURES: DeltaR1 was compared with the other preoperative data (tumor volume, facial function), with the perioperative observations (difficulties with the dissection of the facial nerve), and especially with the postoperative status after 1 year. The statistical study was conducted using polynomial regression. RESULTS: Patients with a negative or zero DeltaR1 have normal facial function at 1 year. For those with a positive DeltaR1 the outcome is not favorable unless the tumor is small. For patients presenting with an immediate complete facial paralysis, the value of DeltaR1 is also indicative of facial function outcome. CONCLUSION: Statistical analysis shows that the blink reflex, through DeltaR1, has an excellent prognostic value in anticipating the difficulties with facial nerve dissection and postoperative facial function after 1 year.

Adult↗
PubMed2006

Single subthalamic nucleus deep brain stimuli inhibit the blink reflex in Parkinson's disease patients.

The disordered output from the basal ganglia to the pontine tegmentum nuclei is considered responsible for a number of abnormalities in brainstem reflexes in patients with Parkinson's disease. One of the most conspicuous of these abnormalities is the reduced inhibition of the blink reflex by a prepulse stimulus. The circuit of prepulse inhibition involves structures and fibre groups that can be reached by stimuli applied through the electrodes implanted in the subthalamic nucleus for deep brain stimulation (STNDBS). In seven Parkinson's disease patients we examined whether single STNDBS induced prepulse effects on the blink reflex and how they compared with the effects induced by single auditory and somatosensory stimuli. Prepulse inhibition was determined by measuring the percentage inhibition induced in the R2 component of the orbicularis oculi response to supraorbital nerve stimuli. The inter-stimuli intervals (ISI) between the prepulse and the supraorbital nerve stimuli were 0 to 30 ms and 100 ms for single STNDBS and 100 ms for auditory and somatosensory modalities. The results obtained with acoustic and somatosensory stimuli were compared with those obtained from a group of 20 age-matched healthy subjects. Single STNDBS induced significant inhibition of the R2 in all patients at ISIs between 10 and 30 ms, with a mean percentage inhibition of 94% at the ISI of 30 ms. On the contrary, significant inhibition by auditory or somatosensory stimuli was induced in only two out of the seven patients. The mean percentage inhibition at the ISI of 100 ms was 37% for auditory and 40% for somatosensory stimuli, well below reference limits for prepulse inhibition in control subjects (61%). Single STNDBS induces significant prepulse inhibition of the blink reflex in Parkinson's disease patients who have abnormally reduced auditory and somatosensory prepulse effects. This finding helps define the prepulse circuit in humans and the eventual site of its dysfunction in Parkinson's disease.

Acoustic Stimulation↗