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PubMed1997

Blink reflex to supraorbital nerve stimulation in the cat.

Neurophysiological studies of the blink reflex to supraorbital nerve stimulation were conducted in eight alert, adult male cats. The cat, like other mammals, shows both short-latency (R1) and long-latency (R2) orbicularis oculi electromyographic (OOemg) components. Measures of OOemg latency, duration, integrated area, and maximum amplitude (MA) were obtained at a stimulus magnitude of 1.5xR2 threshold. The mean (+/-SE) minimal latencies for R1 and R2 were 8.26+/-0.85 and 22.97+/-1.53 ms, respectively. On average, R1 MA was larger than R2 MA. R1 and R2 area measures were similar. Three stimulus paradigms were tested. In a paired-stimulus paradigm, the interstimulus interval (ISI) was randomly varied from 100 to 1200 ms. Ratios were constructed for the OOemg area and MA by dividing the test response by the conditioning response. In this paradigm, although a significant linear relationship was observed only between ISI and R2 MA, conditioning effects were noted on both R1 and R2 area and MA test responses at several ISIs. In a habituation paradigm, both R2 and R1 showed habituation at stimulus frequencies from 0.5 to 2 Hz. In a stimulus-response paradigm, stimulus magnitude was randomly varied between threshold and 2xthreshold. In this paradigm, OOemg area and MA of both R1 and R2 were linearly related to stimulus magnitude. Neither the systemically administered centrally acting alpha2-adrenergic antagonist yohimbine nor agonist clonidine had significant effects on blink reflex parameters, habituation, or the paired-stimulus paradigm. Overall, these results suggest that there are important similarities in the control and modulation of the R1 and R2 components of the blink reflex to supraorbital nerve stimulation in cats.

Adrenergic alpha-Agonists↗
PubMed2002

Electromyographical differentiation between the acoustic blink and startle reflex. Implications for studies investigating startle behavior.

Recent evidence suggests that electromyographic activity in the orbicularis oculi muscle occurring in response to sudden acoustic stimuli consists of two overlapping components: the blink and the startle reflex. The aim of the present study was to identify these two components in acoustically elicited eyeblink responses and to analyze their differential modulation by weak acoustic prepulses. The prevalence, latency and amplitude characteristics of double EMG peaks in pulse-alone and prepulse-pulse trials (PP) with 30 ms and 100 ms interstimulus intervals were assessed in 16 healthy volunteers.EMG responses with two peaks were registered in 42.6 % of the pulse-alone trials and in 56.2 % of the PP30 and 48.7 % of the PP100 trials, respectively. Prepulse inhibition of the amplitude was greater for the second peak (14.2 % (P2) vs. -11.5 % (P1) in PP30 trials; 62.6 % (P2) vs. 32.3 % (P1) in PP100 trials), resulting also in higher P1/P2 amplitude ratios in prepulse-pulse trials (P1/P2: 62.9 % in pulse-alone, 92.6 % in PP30 and 100.1 % in PP100 trials). In conclusion, double peaks are a common phenomenon in human studies of acoustically elicited blink responses. It is postulated that the first peak represents the auditory blink reflex, whereas the second peak corresponds to the startle reflex, which may be more susceptible to prepulse inhibition. This complexity should be taken into account in clinical studies of the modulation of the startle reflex.

Acoustic Stimulation↗
PubMed2003

Blink-related sensorimotor anatomy in the rat.

Protection of the eye and maintenance of the precorneal tear film depend on sensory innervation of the cornea and eyelids and motor innervation of muscles involved in closing and opening the eyes. Using a variety of fluorescent and transganglionic tracers, the sensorimotor innervation of blink-related orbital and periorbital structures was studied in Sprague-Dawley rats. The orbicularis oculi muscle surrounded the entire palpebral fissure and was innervated by motoneurons located along the dorsal cap of the ipsilateral facial motor nucleus. Upper and lower eyelid orbicularis oculi motoneurons were strictly ipsilateral and co-extensive, but upper eyelid orbicularis oculi motoneurons were, on average, slightly rostral and lateral to lower eyelid orbicularis oculi motoneurons. Facial motoneurons supplying the frontoscutularis, a muscle that helps to elevate the upper eyelid, were located in the medial division of the ipsilateral facial motor nucleus. Presumptive type Abeta afferents from the cornea terminated most prominently at the junction of the first cervical segment and the spinal trigeminal nucleus, pars caudalis. There was a second concentration of corneal terminations at the junction of pars caudalis and pars interpolaris of the spinal trigeminal nucleus. Sparse projections to the spinal trigeminal nucleus, pars oralis and the principal trigeminal nucleus were also detected. Presumptive type Abeta afferents from the eyelids terminated throughout the rostrocaudal extent of the spinal trigeminal nucleus with a heavy concentration within laminae III and IV of the first cervical segment. Presumptive types Adelta and C terminals from the eyelids were virtually limited to laminae I and II of the first cervical segment. Central terminations from the frontal nerve were present in the principal trigeminal nucleus and throughout the spinal trigeminal nucleus, but were most prominent within the dorsal horn of the first cervical segment. Our comprehensive description of blink-related sensorimotor anatomy in rats will provide a foundation for future physiological studies of blinking.

Animals↗
PubMed1982

Some observations on the blink reflex in posttraumatic coma.

Blink reflex studies were carried out on 51 comatose patients with signs of brain stem impairment due to head injury. Twenty-five patients were studied in acute coma on day 1 or 2 after trauma. Twenty-six patients were studied in prolonged coma during days 3-12 after brain injury. Brain stem involvement was divided clinically and by CT scan into secondary lesions due to supratentorial mass displacement and primary lesions due to direct violence to the brain stem. Further, the comatose states were separated by behavioural and EEG signs of sleep into "sleep' and more "alert' states. The blink reflexes were recorded after mechanical and electrical stimulation. Mechanical stimulation appeared to be more effective in evoking late responses than the electrical stimulus. The elicitability of the late responses was also dependent on the time of stimulation. During "sleep', usually accompanied by a spindle-EEG, the late responses were totally absent after both mechanical and electrical stimulation in acute coma. In more "alert' states, usually accompanied by high voltage delta waves in the EEG, the late responses, especially direct R2, could be frequently elicited by mechanical stimulation. These differences decreased during prolonged coma. All patients with signs of secondary brain stem involvement who had at least one late component in the acute stage of coma recovered well. So did all patients, with one exception, with primary brain stem injuries. Early recovery of the blink reflexes in cases of primary brain stem injury was a further favourable sign. Consistent absence of R2 (and R1) in prolonged coma indicated a bad outcome. The presence of all components in prolonged coma was of less prognostic significance than in the acute stage.

Adult↗
PubMed1985

Magnetic fields produced by eye blinking.

Magnetic signals produced by voluntary eye blinking were recorded. The maximal signals were found over the posterior parts of the orbits. The polarity of the signal reversed over each eye and in the frontal midline. The amplitude increases with light and amplitude decreases with darkness were similar in the electrical and magnetic blink and eye movement signals. Three different simulation models were used in the interpretation of the results. It is concluded that the primary current source of the blink signal is the transretinal current density. Lid movements change the geometry of the volume conductor resulting in changes in the measured electrical and magnetic field patterns.

Adult↗
PubMed1993

Valid identification of blink artefacts: are they larger than 50 microV in EEG records?

Can artefacts, in particular of blink potentials, be validly identified in EEG data by defining EEG amplitudes as artefacts whenever their absolute values exceed 50 microV? Does the performance of this 50 microV criterion change when the data have been high-pass filtered (simulating a low time constant)? These questions were studied in data of an auditory oddball task recorded from young and elderly healthy adults and from Alzheimer patients. The performance of the 50 microV criterion heavily depended on the distance from the eyes: most blinks were detected at Fz, very few at Pz and Oz. This rate further decreased after high-pass filtering. A qualitative effect of the 50 microV criterion occurred in the Alzheimer patients' Pz data: unidentified blink artefacts caused a late positive wave that mimicked a delayed P3. In the high-pass filtered data, this effect occurred not only at Pz but also at Cz. These results lead to the conclusion that the 50 microV criterion does not in general perform well, and in particular may bias results when records are made from Pz or from Cz only using a short time constant.

Adult↗
PubMed1994

Blink reflex far fields mimicking putative cortical trigeminal evoked potentials.

The R1 component of the blink reflex was evoked by stimulation of the left supraorbital and infraorbital nerves in 10 subjects. In addition, an artificial dipole was placed over the left eyebrow, in order to simulate the occurrence of the R1 component of the blink reflex. These electrical events were recorded at scalp locations Fz, F8, F7, C6, C5, referred either to Cv7 (seventh cervical vertebra) or to Fz. It was found that the blink R1 and the field of the artificial dipole had similar behaviour across the scalp; larger amplitudes were recorded ipsilateral to the stimulus from derivations referred to Cv7, but when referred to Fz larger contralateral amplitudes were measured. In the latter condition, the scalp-recorded R1 shows similar amplitude behaviour to electrical events originating from the cortex and hence its appearance may be deceiving.

Blinking↗
PubMed1986

Effects of vibratory stimulation on muscular pain threshold and blink response in human subjects.

The effects of vibratory stimulation on muscular pain threshold were investigated in 28 healthy subjects. Pain sensation was evaluated by the subjects' verbal reports in response to electrical stimulation of the vastus medialis muscle. Concomitant variations of blink response evoked as a component of the startle reaction were also studied. In all the subjects tested, high frequency vibration (110 Hz) induced a marked and long lasting elevation of the muscular pain threshold but only when vibration was applied to the skin overlying the ipsilateral quadriceps tendon or neighbouring areas and not when applied to remote ipsi- or contralateral regions. This effect was prevented either when tonic vibration reflex (TVR) of the quadriceps muscle was elicited or the skin underlying the vibrator was anaesthetized. Vibratory stimulation at low frequency (30 Hz) failed to produce any consistent effect on muscular pain threshold. Variations in threshold for blink response, as a rule, closely followed those of muscular pain threshold. However, a facilitation of the blink response, not accompanied by changes in pain sensation, was observed during the first period of both high and low frequency vibratory stimulation. The effectiveness of high frequency vibration in raising the muscular pain threshold is coherent with previous results showing that vibration is able to affect pain sensation. Present results suggest a role for rapidly adapting receptors (RA) and/or pacinian corpuscles (PC) in this effect and support the hypothesis of an inhibition of nociceptive messages, possibly at spinal segmental levels, by volleys in large myelinated afferent fibres.

Adult↗
PubMed2004

Pre-pulse inhibition of the acoustic startle eye-blink in the Göttingen minipig.

Pre-pulse inhibition (PPI) of the startle response is a measure of sensorimotor gating which has been frequently shown to be deficient in schizophrenic patients. In humans it is typically measured as the attenuation of the startle eye-blink reflex EMG when a startle eliciting noise is preceded by a weak white noise pre-pulse (PP), the interval between the PP and the startle noise stimulus (SNS) determining the degree of inhibition. Aiming at developing a new animal model of schizophrenia, we have investigated the acoustic startle eye-blink and PPI in 10 Göttingen minipigs. The stimuli and the block design of the stimulation were similar to paradigms used in human research. Initially the startle habituation across trials and blocks, secondarily the PPI at PP to SNS intervals of 30, 60, 120, 220, 520, 1020 and 2020 ms was investigated. One pig out of ten did not have a startle response, and three other pigs did not have a startle response of a sufficient magnitude to demonstrate the PPI seen in the other six pigs at the expected PP intervals of 60, 120, and 220 ms. Maximal inhibition was seen at the 220 ms interval (mean PPI 58.6%, range -18.4 to 94.6%, N = 9). Most of the results in the pigs are in accordance with findings in studies of the human startle eye-blink EMG and this initial study promotes further studies and the use of the PPI measure in the validation of minipig models of psychiatric disorders.

Acoustic Stimulation↗
PubMed2005

Spontaneous blinking behaviour in persistent vegetative and minimally conscious states: relationships with evolution and outcome.

There is evidence that spontaneous blinking correlates with cognitive functions. This arises from the observation that blinking rate (BR) is modulated by arousal levels, basic cognitive processes (e.g., attention, information processing, memory, etc.) and more complex cognitive functions (e.g., reading, speaking, etc.). The aim of this work was to test the role of BR evaluation in the assessment of cognitive network functioning in awake patients with consciousness deficits. Thirteen patients were recruited for the study, and were assessed by the Glasgow coma scale (GCS) and Glasgow outcome scale (GOS) on admittance and discharge, respectively. A level of cognitive functioning scale (LCFS) score was assigned at every change in awareness or at least every 2 weeks. At the same time as the clinical tests, the BR was observed for a 5-min period. Ten healthy subjects, observed throughout three non-consecutive days, formed the control group. The BR underwent a different temporal behaviour in the two diagnostic categories. In the persistent vegetative state (PVS) group it remained stable throughout time and linked with the clinical conditions of the patients; whereas in the non-persistent vegetative state (NPVS) group it decreased over time as the cognitive conditions improved. Moreover, a strong inverse correlation was found between overall BR values and LCFS scores. We have concluded that the blinking behaviour changes manifested in PVS and NPVS patients reflect different evolution phases of a cholinergic-dopaminergic imbalance, and that a reduced BR characterizes the early stages of consciousness recovery.

Adult↗
PubMed2004

Abnormalities of prepulse inhibition do not depend on blink reflex excitability: a study in Parkinson's disease and Huntington's disease.

OBJECTIVE: Prepulse inhibition of the blink reflex is a robust phenomenon with an interesting physiology and a large potential for clinical applicability. In the study presented here we investigated whether the blink reflex inhibition by a prepulse (BRIP) is influenced by the blink reflex excitability recovery (BRER). METHODS: The study was undertaken in 20 patients with Parkinson's disease (PD), 20 patients with Huntington's disease (HD) and 20 healthy volunteers. BRER was determined by measuring the size of the response to a test supraorbital nerve stimulus as a percentage of the response to a conditioning stimulus at inter-stimuli intervals of 100-1000 ms. BRIP was determined as the percentage reduction induced in the response to a supraorbital nerve stimulus by either a low intensity auditory click or a weak third finger somatosensory stimulus, applied with a leading interval of 50-110 ms. RESULTS: There was a negative correlation between the percentage BRER and the percentage BRIP (Pearson's correlation coefficient of -0.37). BRER was enhanced in 14 PD patients (70%) and 6 HD patients (30%), while it was depressed in 10 HD patients (50%). BRIP was significantly reduced in 15 PD patients (75%) and 16 HD patients (80%). No significant correlation was found between abnormally enhanced BRER and abnormally reduced BRIP in all patients as a group (chi(2)=2.4;P=0.11). A weak correlation was found in PD patients (P=0.019) and no correlation was observed in HD patients (P=0.8). CONCLUSIONS: Our results indicate that an abnormally reduced BRIP was not always accompanied by an abnormally enhanced BRER in patients with HD. The two tests likely assess specific and distinct brainstem functions, and provide different types of information. While BRIP may be the result of a widespread integrative processing of sensory stimuli, BRER likely reflects the excitability of a chain of brainstem inter-neurons. SIGNIFICANCE: BRER and BRIP provide independent information on the state of functionally separate circuits that converge on trigemino-facial brainstem inter-neurons.

Acoustic Stimulation↗
PubMed2006

Dissociation between pain and the nociceptive blink reflex during psychological arousal.

OBJECTIVE: To investigate the effect of psychological arousal on pain ratings and the R2 component of the electrically evoked blink reflex to a 'pure' noiciceptive stimulus. METHODS: Pain ratings and R2 to a noiciceptive stimulus (pulse width 0.3ms, 2mA, delivered from a concentric electrode attached to the supraorbital region of the forehead) were investigated in 16 healthy participants before and during a serial subtraction task, and in 16 control participants who sat quietly during nociceptive stimulation. RESULTS: Pain ratings decreased whereas R2 amplitude increased during the serial subtraction task. CONCLUSIONS: Supra-spinal rather than spinal mechanisms inhibited pain perception during psychological arousal. Moreover, psychological arousal facilitated the R2 component of the blink reflex to a nociception-specific stimulus. SIGNIFICANCE: Supra-spinal influences need to be considered during clinical evaluation of the trigeminal nociceptive blink reflex.

Adult↗
PubMed2005

Vision: in the blink of an eye.

Although we blink every 4 to 6 seconds, we notice neither the act of blinking nor the mini-blackouts they cause. A new study using imaging techniques identifies the neural structures in humans involved in suppressing vision processing and visual awareness during blinking.

Blinking↗
PubMed2006

Temporal changes in the tear menisci following a blink.

This study investigated tear meniscus formation after a blink. Multiple images of the inferior and superior menisci, viewed en-face, were sequentially captured using a video-slitlamp that permitted the measurement of tear meniscus height (TMH). In a similar manner, tangentially viewed images were obtained of the inferior meniscus so changes in cross-sectional radius of curvature (TMR) with time could be determined. Additionally, the relationship between inferior TMH and tear volume was quantified by the successive instillation of small aliquots of fluid. In this latter experiment the inflow and outflow of tears were controlled by anaesthetizing the ocular surface and inner nose, and use of punctal plugs. The TMH of both menisci rose after a blink (p<0.01) by a similar amount (p=0.59). This suggests that capillarity is dominant over gravity in tear drainage, however, it may simply reflect that these influences are small compared to the large flow resistances that occur in thin films, hydraulic connectivity between the two menisci, or differences in their anterior-posterior width leading to unequal volume-height relationships. TMR increased with time after a blink (p<0.0001); immediately on eye opening the curvature of the inferior meniscus was approximately circular but this soon became eccentric, with the radius of its upper half exceeding that of its lower half. The growth rate of the two menisci slowed with time and this, based on theoretical considerations, is predicted to have occurred primarily because localized thinning of the tear film adjacent to the menisci markedly raised flow resistance. Inferior TMH increased linearly with the cumulative volume of instilled fluid (r2=0.98), supporting its use in the diagnosis and classification of tear anomalies, although the gradient of this relationship varied between subjects.

Adult↗
PubMed2005

Postural and eye-blink indices of the defensive startle reflex.

Postural and eye-blink reactions to acoustic startle probes were examined in 24 volunteers, who completed two blocked conditions (baseline, startle). A postural reaction during the startle condition demonstrated a reflexive movement in the anterior-posterior direction, which was not observed during the baseline condition. This reflexive response was positively associated with the eye-blink reflex, such that larger blink magnitude related to greater posterior movement. These findings were not observed for postural movements in the medial-lateral direction. The results suggest that a measurable postural reaction may be observed following a startling acoustic stimulus, which may reflect generalized bodily flexion associated with a preparatory behavioral response.

Acoustic Stimulation↗
PubMed2006

Comparisons of dorsal and ventral hippocampus cornu ammonis region 1 pyramidal neuron activity during trace eye-blink conditioning in the rabbit.

Previous studies demonstrating a critical role of the hippocampus during trace eye-blink conditioning have focused primarily upon the dorsal portion of the structure. However, evidence suggests that a functional differentiation exists along the septotemporal axis of the hippocampus. In the present study, the activity of 2588 single cornu ammonis region 1 pyramidal neurons of the dorsal hippocampus and ventral hippocampus were recorded during trace and pseudo-eye-blink conditioning of the rabbit. Learning-related increases in dorsal hippocampus neuron firing rates were observed immediately prior to behavioral criterion, and increased over the course of training. Activation of dorsal hippocampus neurons during trace conditioning was also greater than that of ventral hippocampus neurons, including during the trace interval, in well-trained animals. An unexpected difference in the patterns of learning-related activity between hemispheres was also observed. Neurons of the dorsal hippocampus ipsilateral and contralateral to the trained eye, exhibiting significant increases in firing rate [rate increasing neurons], demonstrated the greatest magnitude of activation early and late in training, respectively. Rate increasing neurons of the dorsal hippocampus also exhibited a greater diversity of response profiles, with 69% of dorsal hippocampus rate increasing neurons exhibiting significant increases in firing rate during the conditioned stimulus and/or trace intervals, compared with only 8% of ventral hippocampus rate increasing neurons (the remainder of which were significantly responsive during only the unconditioned stimulus and/or post-unconditioned stimulus intervals). Only modest learning-related activation of ventral hippocampus neurons was observed, reflected as an increase in conditioning stimulus-elicited rate increasing neuron response magnitudes over the course of training. No differences in firing rate between dorsal hippocampus and ventral hippocampus neurons during a 1-day pre-training habituation session were observed. Thus, dorsal hippocampus activation is more robust, suggesting a more substantial role for these neurons in the processing of temporal information during trace eye-blink conditioning.

Action Potentials↗
PubMed2005

Laser evoked potentials and prepulse inhibition of the blink reflex in patients with Wallenberg's syndrome.

Spinothalamic tract lesions in patients with Wallenberg's syndrome can be demonstrated by abnormalities in the laser evoked potentials (LEPs) to stimulation of the affected side. However, before reaching the structures generating LEPs, laser stimuli can induce effects at a subcortical level. We examined LEPs and laser-induced prepulse inhibition of the blink reflex in seven patients with Wallenberg's syndrome within a month after the infarct. All patients had abnormally elevated thresholds for temperature and pain sensation, and for pinprick pain induced by laser stimuli, in the affected vs the non-affected side. LEPs to stimulation of the affected side were abnormal because of absent, reduced or delayed responses. However, the same laser stimuli that were unable to induce LEPs generated normal inhibition of the blink reflex response when applied 250ms before a trigeminal nerve electrical stimulus. The percentage inhibition induced in the R2 response of the blink reflex by laser stimulation of the affected side was not different from that induced by stimulation of the non-affected side, or in control subjects. These results are compatible with either a different pathway for prepulse inhibition and evoked potentials or a reduced energy requirement of the sensory input generating prepulse inhibition in comparison to that generating evoked potentials.

Adult↗
PubMed2005

Spontaneous eye-blinking and stereotyped behavior in older persons with mental retardation.

Previous research indicates that abnormal stereotyped movements are associated with central dopamine dysfunction and that eye-blink rate is a noninvasive, in vivo measure of dopamine function. We measured the spontaneous eye-blinking and stereotyped behavior of older adults with severe/profound mental retardation living in a state mental retardation facility. Analyses revealed that the mean eye-blink rate of the residents that engaged in stereotypy was significantly lower than the rate for residents who did not exhibit stereotypy. Moreover, the stereotypy group also demonstrated greater variability in interblink intervals. These results provide further empirical support for the involvement of dopamine in stereotyped behavior and are consistent with an emerging motor control model of stereotypy.

Adult↗