A model system for motor learning: adaptive gain control of the blink reflex

Summary An important aspect of the control of movement is how the nervous system produces adaptive gain modification. To investigate this problem in a simple motor system, we studied lid movement and orbicularis oculis muscle activity in human and rabbit subjects during adaptation of reflex eye blinks. The gain of the reflex could be increased or decreased, depending upon the nature of the adaptive stimulus. Since these gain changes could persist upon removal of the adapting stimulus, adaptation appears to result from a modification of the neural program subserving the blink reflex. The orbicularis oculis electromyogram revealed that the neural modifications producing adaptive gain changes predominantly altered the longer latency components of the reflex, while the short latency components remained unchanged. Moreover, in two other paradigms that modulate the gain of reflexes, habituation and reflex modification, similar changes also occured primarily in the longer latency components of the blink reflex. This result suggests that modification of neurons in longer latency, indirect pathways, may underlie different forms of motor learning.     

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 1.5×R2 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 2×threshold. In this paradigm, OOemg area and MA of both R1 and R2 were linearly related to stimulus magnitude. Neither the systemically administered centrally acting α₂-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. Received: 18 June 1996 / Accepted: 21 February 1997     

Long-term depression of the human blink reflex

Long-term depression (LTD) of synaptic transmission is reliably induced by low-frequency stimulation (LFS) of presynaptic nerve fibers in vitro. Many experiments suggest that LTD of basal transmission is not readily induced either in awake or anesthetized animals in vivo. In order to fill the gap between the in vitro cell studies and the in vivo situation, the effect of LFS on trigeminal somatosensory processing in healthy volunteers was investigated. Excitability of trigeminal sensory neurons was tested by applying the blink reflex (BR) elicited by electric stimulation of supraorbital nerve afferents. LFS of these afferents induced a significant reduction of the BR integral, a significant increase of the BR onset latency and a significant decrease of the stimulus intensity ratings. This depressive effect on the BR lasted for at least 1 h after the end of LFS. Thus, this study documented for the first time a long-term depression of trigeminal somatosensory processing in healthy volunteers. Electronic Publication     

Attentional blink reflex modulation in a continuous performance task is modality specific

Four experiments investigated the attentional modulation of acoustic blinks during continuous spatial tracking tasks. Experiment 1 found blink magnitude inhibition in a visual tracking task. Experiment 2 replicated this finding and also found blink latency slowing. Experiment 3 varied the difficulty of the task and found larger blink inhibition in the easy condition. Blink latency slowing did not differ and was significant at both difficulty levels. Experiment 4 employed less difficult visual and acoustic tracking tasks at two levels of task load. Blink magnitude inhibition during the visual and facilitation during the acoustic task was significant during high load in both modality groups. Blink latency was slowed in all visual task conditions and shortened in the difficult acoustic task. These results indicate that attentional blink modulation in a continuous spatial tracking task is modality specific.     

Somatosensory eye blink reflex in peripheral facial palsy

To investigate the association between somatosensory blink reflex (SBR) and peripheral facial palsy (PFP) severity and trigeminal blink reflex (BR) changes in cases with PFP and subsequent postparalytic facial syndrome development (PFS). One hundred and twenty subjects with peripheral facial palsy and post-facial syndrome and 44 age and gender matched healthy volunteers were enrolled to this study. Blink reflexes and somatosensory blink reflex were studied in all. The association between R1 and R2 responses of the BR and SBR positivity was investigated. SBR was elicited in 36.3% of normal subjects, in 18.3% of PFP and in 65.3% of PFS patients. In the paralytic side, the frequency of SBR positivity was significantly lower in PFP group compared to controls and SBR was most frequently observed in patients with PFS. Compared to PFP and control groups, SBR positivity on the non-paralytic side significantly revealed a higher rate in PFS patients. SBR positivity of patients in whom R1 or R2 were absent, was significantly lower than those subjects with prolonged or normal R1 or R2 responses. PFP and successive PFS are good models for the sensory motor gate mechanisms and/or excitability enhancement of brainstem neurons responsible for SBR.     

Nicotinamide prevents the long-term effects of perinatal asphyxia on basal ganglia monoamine systems in the rat

Asphyxia during birth can cause gross brain damage, but also subtle perturbations expressed as biochemical or motor deficits with late onset in life. Thus, it has been shown that brain dopamine levels can be increased or decreased depending upon the severity of the insult, and the region where the levels are determined. In this study, perinatal asphyxia was evoked by immersing pup-containing uterus horns removed by hysterectomy in a water bath at 37°C for various periods of time from 0 to 20 min. After the insult, the pups were delivered, given to surrogate mothers, treated with nicotinamide, further observed and finally, 4 weeks later, killed for monoamine biochemistry of tissue samples taken from substantia nigra, neostriatum and nucleus accumbens. The main effect of perinatal asphyxia was a decrease in dopamine and metabolite levels in nucleus accumbens, and a paradoxical increase in the substantia nigra. Nicotinamide (100 mg/kg i.p., once a day for 3 days, beginning 24 h after the perinatal asphyctic insult) prevented the effect of asphyxia in nucleus accumbens. Furthermore, striatal dopamine levels were increased by nicotinamide in asphyctic animals. No apparent changes were observed in substantia nigra. A prominent unexpected effect of perinatal asphyxia alone was on the levels of the metabolite of 5-hydroxytryptamine, 5-hydroxyindoleacetic acid (5-HIAA), which were increased in substantia nigra and decreased in both neostriatum and accumbens. However, nicotinamide increased 5-HIAA levels in all regions, which appeared to be related to the extent of the asphyctic insult. These results suggest that nicotinamide is a useful treatment against the long-term consequences produced by perinatal asphyxia on brain monoamine systems, and that there is a therapeutic window following the insult, providing a therapeutic opportunity to protect the brain. Electronic Publication     

A pharmacological distinction between the long and short latency pathways of the human blink reflex revealed with tobacco

Summary In three, normal, human subjects, tobacco smoking was used as a pharmacological probe to modify differentially the direct and indirect pathways underlying the blink reflex. The latency of the indirect R2 component of the orbicularis oculis electromyogram evoked by electrical stimulation of the trigeminal supraorbital nerve transiently increased 20–80% after smoking, while the latency of the shorter latency, direct R1 component remained constant. The magnitude of both components of the blink reflex transiently decreased. The data demonstrate that tobacco smoking can differentially alter the long and short latency components of the blink reflex, and suggest that these effects result from modifications of central pathways sensitive to nicotine.     

Midbrain 6-hydroxydopamine lesions modulate blink reflex excitability

The blink reflex abnormalities present in the 6 hydroxydopamine (6-OHDA) lesioned rat model of parkinsonism mimicked those of the human with Parkinon's disease. In alert rats, we monitored the long and short latency components of the orbicularis oculi electromyographic (OOemg) response evoked by electrical stimulation of the supraorbital branch of the trigeminal nerve (SO). Two paradigms, habituation and double pulse, provided a measure of blink reflex excitability. In normal rats, repeated stimulation of the SO produced habituation of the R2 component of the blink. In the double pulse paradigm, presentation of two identical SO stimuli resulted in a reduced or suppressed OOemg response to the second stimulus relative to the first. In rats with complete, unilateral lesions of midbrain dopamine neurons, repeated SO stimulation produced facilitation rather than habituation of the R2 component of the blink reflex. This facilitation occurred only with the eyelid contralateral to the lesion. In the double pulse paradigm, the lesioned rats showed increased excitability rather than suppression. This effect occurred bilaterally, although the increased excitability was strongest contralateral to the lesion. Rats with partial lesions of midbrain dopamine neurons exhibited qualitatively similar, but less pronounced blink reflex abnormalities. The R1 component of the blink reflex was unaffected by either the complete or partial lesions. Thus, modification of the blink reflex by 6-OHDA lesions provides a reproducible parkinsonian-like symptom which is amenable to investigations of increases in reflex excitability.     

Pattern of extraocular muscle activation during reflex blinking

Summary 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.     

三叉神经分布区带状疱疹患者瞬目反射检测结果分析

目的：观察三叉神经分布区带状疱疹患者瞬目反射(BR)检测结果并分析与预后的关系。方法：对18例临床确诊为三叉神经分布区带状疱疹的患者进行BR检测．刺激病侧及对侧眶上神经，在眼轮匝肌进行记录。结果：急性期11例患者BR潜伏期及波幅无明显异常，6例患者R1、R2及R2′潜伏期延长，波幅降低，另1例患者R1及R2、R2′波形消失。上述7例患者中有部分在恢复期遗留有三叉神经分布区感觉减退及神经痛。结论：部分三叉神经带状疱疹患者可出现BR异常，对预后有一定判断作用。     

面瘫患者面神经电图和瞬目反射的应用比较

目的:比较面瘫患者瞬目反射和面神经电图的应用价值。方法:这些面瘫患者经过四周基础治疗和(或)针灸治疗后,进行健、患侧瞬目反射(207例)和面神经电图(205例)检查比较。结果:瞬目反射治疗前健、患侧R1值的差异有极显著意义(P<0．01);治疗后健、患侧R1值的差异无显著意义 (P>0．05)。面神经电图患侧潜伏期延长者于治疗后均有所好转(P<0．05),波幅降低者治疗后无明显改善(P>0．05)。结论:面瘫患者治疗后瞬目反射改善非常明显,而面神经电图恢复存在明显的滞后现象,早期诊断(发病第一周)瞬目反射检查优于面神经电图,中后期面神经电图检查优于瞬目反射。     

Prepulse modulation of the startle reaction and the blink reflex in normal human subjects

Blink reflexes are usually considered the most representative and consistent response of the auditory startle reaction (ASR), and they are often the only response evaluated in human psychophysiological studies. However, auditory stimuli also induce an auditory blink reflex (ABR), the physiological characteristics and brainstem circuitry of which may be different from those of the ASR. This study aimed to investigate whether there were differences between the orbicularis oculi (OOc) responses elicited with the ABR (OOcABR) and those elicited with the ASR (OOcASR) regarding their behavior to prepulse modulation. For comparison, we also examined the OOc responses to supraorbital nerve stimulation (OOcEBR). Electromyographic responses were simultaneously recorded from the OOc, masseter (MAS) and sternocleidomastoid (SCM) muscles. ABRs were considered when auditory stimuli induced responses limited to the OOc, and ASRs were considered when responses were induced in all muscles recorded from. Prepulse stimuli were either a weak electrical stimulation at the third finger (somatosensory prepulse) or a weak acoustic tone (auditory prepulse) that preceded the response-eliciting stimuli by intervals ranging from 0 to 200 ms. Prepulse effects differed according to prepulse modality, but the OOcABR and the OOcASR were always modulated in the same way. In both responses, somatosensory prepulses induced facilitation from 20 to 50 ms, followed by inhibition beyond 75 ms, and auditory prepulses induced no facilitation but a significant inhibition beyond 30 ms. In the OOcEBR, both somatosensory and acoustic prepulses induced facilitation of R1 and inhibition of R2 beyond 30 ms. Our results suggest that the OOcABR and the OOcASR exhibit the same physiological behavior regarding prepulse modulation. It is hypothesized that prepulse facilitation is due to direct impingement of subthreshold excitatory inputs onto the facial motoneurons while prepulse inhibition results from the engagement of a presynaptic inhibitory circuit in the brainstem. Received: 9 October 1998 / Accepted: 29 April 1999     

椎基底动脉供血不足和脑干梗死患者的瞬目反射检测

目的：探讨瞬目反射(BR)对椎基底动脉供血不足(VBI)及脑干梗死的临床应用价值。方法：用表面电极刺激三叉神经眶上支，在双侧眼轮匝肌进行记录。对BR异常者治疗1、3、6个月后复查。结果：VBI组80例治疗前BR异常者58例(72．5％)，治疗一个月后复查BR恢复正常者39例，BR正常或治疗后恢复正常者近期都能获得基本痊愈，而BR持续异常者则预后较差。脑干梗死组26例，：BR全部异常且异常程度重于VBI组。结论：在对VBI及脑干梗死诊断、疗效观察及预后评价中，BR是一项极为客观有用的指标。     

Modulation of electrically elicited blink reflex components by visual and acoustic prestimuli in man

The effects of a prestimulus on the electrically elicited blink reflex components were investigated in 20 healthy subjects. In the first group of 10 subjects (warned group), electric shocks were delivered in isolation or preceded, at an interstimulus interval (ISI) of 0.1 s, 1 s, or 10 s, by a visual or acoustic warning stimulus. In the second group of 10 subjects (unwarned group), the electric shocks were delivered either in isolation or preceded, at the same ISI, by visual or acoustic stimuli having no warning value. The modulation of the three blink reflex components was then analysed. Compared to the baseline condition, the R1 oligosynaptic component was enhanced at 0.1 s and 1 s ISI, in the warned group with the visual prestimulus, but only at 0.1 s after a visual and acoustic prestimulus in the unwarned group. On the contrary, the polysynaptic responses showed a different course: R2 was significantly reduced at the 0.1 s interval in the warned group with both the prestimuli, and only with the visual prestimulus in the unwarned group. The R3 was inhibited at all three intervals with the visual prestimulus, and at the 0.1 s and 1 s with the acoustic one in the warned group, and only at 0.1 s in the unwarned group, both after visual and acoustic prestimuli. The decrement in R2 and R3 observed with the shortest interval was probably related to the prepulse inhibition of startle reflex. Furthermore, only R3 was still inhibited at longer intervals, when the sustained processes of attention may have influenced this component. Perhaps this combination of events represents, in the warned group, the best preparation for voluntary reflex reaction.     

偏头痛患者发作期脑干听觉诱发电位和瞬目反射检测

目的：观察偏头痛患者发作期脑干听觉诱发电位(BAEP)和瞬目反射(BR)改变。方法：对45例偏头痛发作期患者进行BAEP、BR检测。结果：BR和BAEP联合检测提示脑干病变者31例，占69％；BAEP、BR检测提示听神经、三叉神经传入通路功能障碍和面神经传出通路功能障碍共26例，占58％，其中三叉神经传入通路障碍21例，占81％。结论：偏头痛发作期存在着以脑干和三叉神经为主的神经功能障碍．与血管舒缩功能障碍很可能互为因果、相互影响。     

The effect of stimulus modality and task difficulty on attentional modulation of blink startle

The effects of the sensory modality of the lead stimulus and of task difficulty on attentional modulation of the electrical and acoustic blink reflex were examined. Participants performed a discrimination and counting task with either two acoustic, two visual, or two tactile lead stimuli. In Experiment 1, facilitation of the electrically elicited blink was greater during task-relevant than during task-irrelevant lead stimuli. Increasing task difficulty enhanced magnitude facilitation for acoustic lead stimuli. In Experiment 2, acoustic blink facilitation was greater during task-relevant lead stimuli, but was unaffected by task difficulty. Experiment 3 showed that a further increase in task difficulty did not affect acoustic blink facilitation during visual lead stimuli. The observation that blink reflexes are facilitated by attention in the present task domain is consistent across a range of stimulus modality and task difficulty conditions.     

瞬目反射正常值测定及临床应用价值

目的 :研究瞬目反射 (BR)的正常值及其临床应用价值。方法 :采用Keypoint神经电生理仪 ,表面电极刺激眶上神经 ,分别在同侧眼轮匝肌记录出R1 波和R2 ′波 ,在对侧眼轮匝肌记录出R2 ′波。对 30例健康成人和 5 6例患者 (主要包括面神经麻痹 ,三叉神经痛 ,脑干损伤以及脑出血 )进行BR检测。结果 :正常组BR各潜伏期平均值分别是R1 为 10 7ms,R2 和R2 ′为 30 8ms和 30 6ms;患者组根据损伤部位分为传入型、传出型以及脑干型损伤 ,其R1 、R2 和R2 ′异常规律组合不同。结论 :BR检测不仅能早期反映颅神经损伤 ,还能区分颅神经损伤的类型。     

不同年龄抑郁症患者瞬目反射的研究

目的:探讨抑郁症与瞬目反射(BR)的关系。方法:对90例抑郁症(青年和老年各45例)患者及60例正常对照组(青年和老年各30例)进行BR检测。结果:与青年对照组和老年对照组比较,青年抑郁症患者和老年抑郁症患者BR的R2、R2′潜伏期分别显著延长(P<0.001),老年抑郁症患者的波幅与老年对照组、青年抑郁症患者的波幅相比显著升高,差异存在极显著意义(P<0.001)。结论:抑郁症患者存在BR的异常,提示抑郁症患者可能存在脑干功能障碍。     

The effects of change in lead stimulus modality on the modulation of acoustic blink startle

In two experiments we investigated the effect of generalized orienting induced by changing the modality of the lead stimulus on the modulation of blink reflexes elicited by acoustic stimuli. In Experiment 1 (n = 32), participants were presented with acoustic or visual change stimuli after habituation training with tactile lead stimuli. In Experiment 2 (n = 64), modality of the lead stimulus (acoustic vs. visual) was crossed with experimental condition (change vs. no change). Lead stimulus change resulted in increased electrodermal orienting in both experiments. Blink latency shortening and blink magnitude facilitation increased from habituation to change trials regardless of whether the change stimulus was presented in the same or in a different modality as the reflex-eliciting stimulus. These results are not consistent with modality-specific accounts of attentional startle modulation.     

Distinct early and late subcomponents of the photic blink reflex: Response characteristics in patients with retrogeniculate lesions

To assess cortical contributions to the photic blink reflex, signal averaged electromyograms (EMG) were compared for responses to strobe flashes presented within the blind and sighted hemifields of 13 patients with occipital lobe lesions. Reflexes evoked by flashes within the scotoma were virtually identical to those evoked by flashes within the intact visual field. This suggests that both the early and late components of this reflex (R50 and R80, respectively) are mediated by subcortical structures that do not require, or benefit from, conscious visual processing. Additional findings included larger R80s at the eyelid contralateral to the lesion, regardless of stimulated hemifield. This presumably reflects the loss of a tonic descending influence of visual cortex onto the motor limb of the reflex arc. The R80 was also larger for stimuli activating the crossed (temporal hemifield) rather than the uncrossed (nasal hemifield) afferent pathway.