Evoking blinks with natural stimulation and detecting them with a noninvasive optical device: a simple, inexpensive method for use with freely moving animals

Many laboratories studying eyeblinks in unanesthetized rodents use a periorbital shock to evoke the blink. The stimulus is typically delivered via a tether and usually obliterates detection of a full unconditioned response with electromyographic (EMG) recording. Here we describe the adapter we have used successfully for several years to deliver puffs of air to the cornea of freely moving rats during our studies of eyeblink conditioning. The stimulus evokes an unconditioned response that can be recorded without affecting the EMG signal. This allows a complete analysis of the unconditioned response which is important for studies examining reflex modification or the effect of drugs, genetic manipulations, or aging on the unconditioned blink reflex. We also describe an infrared reflective sensor that can be added to the tether to minimize the number of wires that need to be implanted around the eye, and which is relatively immune to electrical artifacts associated with a periorbital shock stimulus or other devices powered by alternating current. The responses recorded simultaneously by EMG wires and the optical sensor appear highly correlated and demonstrate that the optical sensor can measure responses that might otherwise be lost due to electrical interference from a shock stimulus.     

Pathophysiology of pain in postherpetic neuralgia: a clinical and neurophysiological study

Postherpetic neuralgia is an exceptionally drug-resistant neuropathic pain. To investigate the pathophysiological mechanisms underlying postherpetic neuralgia we clinically investigated sensory disturbances, pains and itching, with an 11-point numerical rating scale in 41 patients with ophthalmic postherpetic neuralgia. In all the patients we recorded the blink reflex, mediated by non-nociceptive myelinated Aβ-fibers, and trigeminal laser evoked potentials (LEPs) related to nociceptive myelinated Aδ- and unmyelinated C-fiber activation. We also sought possible correlations between clinical sensory disturbances and neurophysiological data. Neurophysiological testing yielded significantly abnormal responses on the affected side compared with the normal side (P < 0.001). The blink reflex delay correlated with the intensity of paroxysmal pain, whereas the Aδ- and C-LEP amplitude reduction correlated with the intensity of constant pain (P < 0.01). Allodynia correlated with none of the neurophysiological data. Our study shows that postherpetic neuralgia impairs all sensory fiber groups. The neurophysiological-clinical correlations suggest that constant pain arises from a marked loss of nociceptive afferents, whereas paroxysmal pain is related to Aβ-fiber demyelination. These findings might be useful for a better understanding of pain mechanisms in postherpetic neuralgia.     

Effect of spinal cord injury and of intrathecal baclofen on brainstem reflexes

Reorganization of neural circuits within the central nervous system following injury appears to be a means of compensatory mechanism for loss of function. Reorganization following spinal cord injury is known to evoke changes at the cortical and spinal cord levels. Recent studies, however, provide evidence of enhanced brainstem reflexes and alterations in excitatory and inhibitory interneuronal brainstem circuits, suggesting that reorganization following spinal cord injury occurs also at the brainstem level. Reversal of these changes by continuous intrathecal baclofen infusion to normal levels or beyond indicates strong GABAergic involvement. Rapid changes in the blink reflex and its prepulse inhibition following intrathecal baclofen bolus application that parallel clinical changes in muscle hypertonia suggest a muscle tone regulating effect of baclofen at the brainstem level. Enhanced brainstem reflexes in spinal cord injury patients may be the consequence of decreased GABA-mediated inhibition and/or strengthening of facilitatory connections due to either direct or indirect plastic changes occurring at the brainstem level. Modulation of brainstem reflexes by baclofen may foster the understanding of pathophysiological mechanisms underlying diseases with increased brainstem activity. Rehabilitation after central nervous system injury will always be a challenge, but understanding the mechanisms of reorganization of undamaged neural pathways may help to develop better strategies for enhancing neuronal plasticity and for implementing neuronal reorganization into carefully planned therapy.     

Assessment of excitability in brainstem circuits mediating the blink reflex and the startle reaction

Excitability is probably the concept that fits better with the definition of the role of neurophysiology in the study of brainstem functions and circuits. Neurophysiological techniques are likely the best suited of all paraclinical tests for documenting the eventual excitability changes that may occur in certain physiological states and in many neurological disorders. The best known test of brainstem excitability is the blink reflex. While a single stimulus can already indicate the readiness of the interneuronal path and the facial motoneurons to fire, pairs of stimuli (conditioning and test) are suited to analyze the degree of excitability recovery after a single discharge. Another brainstem reflex circuit, which excitability testing can be of interest for physiological and clinical exams is the one involved in the startle reaction. The size of the responses and their habituation are the typical measures of excitability of the startle reflex circuit. Prepulse inhibition is a method to modulate both, the blink reflex and the startle reaction. It is defined as the inhibitory effect caused by a stimulus of an intensity low enough not to induce a response by itself on the response elicited by a subsequent stimulus. The circuits of the blink reflex, startle reaction and prepulse inhibition share some commonalities but they are different enough for the three techniques to provide unique, clinically relevant, information in certain conditions. The role of neurophysiology is not limited to testing those functions. It is important also for the assessment of many other circuits, such as those implicated in eye movements, vestibular reflexes, arousal, sleep, breathing, or autonomic reactions, which are not considered in this review.     

后循环梗死患者的BAEP、BR、TSEP检测

目的：探讨后循环脑梗死（PCI）患者脑干听觉诱发电位（BAEP）、瞬目反射（BR）、三叉神经诱发电位（TSEP）三种电生理变化。方法：选择60例经头颅MRI检查证实为PCI患者（病例组）,分别于入院一周之内行BAEP、BR、TSEP检查,观察BAEP波形及I、Ⅲ、V波潜伏期（PL）、峰间期（IPL）,计算BR既R1、R2、R2波平均PI。、波幅及TSEP各成分PL,并与40例健康体检者作对照。结果：病例组60例中BAEP异常35例（58％）,异常主要表现为I、V波的PL、I—V波的IPL延长和I／V波幅比〉1。BR异常33例（55％）,异常主要表现为R2波的PL延长,R2、R2’波幅下降。TSEP检查病例组与对照组PL比较未见明显差异。结论：BAEP、BR两种电生理检查方法能够较好地检测出PCI患者神经功能异常,联合应用BAEP及BR能够为PCI患者的神经功能的判断提供重要参考。     

眨眼反射在面瘫诊断中的应用

目的：进一步研究眨眼反射（ＢＲ）检查在面瘫诊断中的临床意义。方法：对４０名正常人，不同原因周围性面瘫３０例及腮腺肿瘤３２例进行ＢＲ检查及随访观察。结果：获得ＢＲ潜伏期正常值范围。发现面瘫患者ＢＲ结果与临床面瘫评分有非常显著联系。面瘫早期ＢＲ反应存在者预后良好。Ｂｅｌ麻痹患者在起病２～７２ｈ内ＢＲ检查均出现异常改变。腮腺肿瘤术前ＢＲ异常者均为恶性肿瘤。结论：ＢＲ检查对周围性面瘫程度评估及预后判断有相当意义，对起病７２ｈ内的面瘫诊断优于其它常规面神经电诊断方法，对腮腺肿瘤的良恶性判断有一定参考价值。     

Neurophysiological assessment of trigeminal nerve reflexes in disorders of central and peripheral nervous system.

The trigeminal nerve and nuclei (the trigeminal complex) are unique in the human body with regard to their anatomical and physiological characteristics. They are also special regarding the lesions in which they are involved, both at the peripheral level because of the susceptibility of some terminal branches, and at the nuclei because of their large size and the large amount of connections with other centers. Conventional magnetic resonance imaging studies are often not sufficiently informative to demonstrate very tiny lesions that could be responsible for an important damage in the brainstem. Therefore, clinical neurophysiology and specifically, the techniques used in the study of the trigeminal functions, remain as convenient diagnostic and research tools to document clinically evident lesions or uncover subclinical abnormalities. This review is focussed on the clinical applicability of the study of trigeminal reflexes, including methods employed in the documentation of focal lesions of peripheral branches, trigeminal involvement of peripheral neuropathies, specific lesions of the trigeminal ganglia, central nervous dysfunctions causing abnormalities in the excitability of trigeminal neurons, and the possible use of trigeminal nerve reflexes in the study of facial pain syndromes and headache.     

The Effect of an Acoustic Warning Stimulus Upon the Electrically Elicited Blink Reflex in Humans

In a warned Go/No-Go reaction time experiment blink reflexes were elicited electrically immediately before, at, and shortly after the onset of a low intensity acoustic warning stimulus. This provided the opportunity to study the mutual effects of two stimuli of different modalities arriving at the facial nucleus. The warning stimulus was followed after 3 s by an acoustic response stimulus. Sixteen subjects participated in the experiment. They were informed by the response stimulus if a response (a voluntary blink of the right eye) was required. R1 magnitude was increased from 10 ms to 100 ms after warning stimulus onset, with a pronounced peak at 50 ms. The bilateral late component R2 was enhanced when the reflex eliciting stimulus preceded the warning stimulus. Between 20 ms and 30 ms after warning stimulus onset, R2 returned to control level, whereas an eliciting stimulus presented 40 ms or later after warning stimulus onset produced a pronounced inhibition. R2 latency was facilitated immediately after warning stimulus onset. It was concluded that the mutual effects of stimuli of different modalities can be interpreted only if the moment of arrival at the motor nucleus is taken into consideration.     

The n10 component of the ocular vestibular-evoked myogenic potential (oVEMP) is distinct from the R1 component of the blink reflex

ObjectiveBone-conducted vibration (BCV) in the midline at the hairline (Fz), results in short latency potentials recorded by surface electrodes beneath the eyes – the ocular vestibular-evoked myogenic potential (oVEMP). The early negative component of the oVEMP, n10, is due to vestibular stimulation, however it is similar to the early R1 component of the blink reflex. Here we seek to dissociate n10 from R1.MethodsSurface potentials were recorded from the infraorbital electromyogram of 10 healthy subjects, 6 patients with bilateral vestibular loss, 2 with unilateral vestibular loss, 4 with facial palsy and 3 with facial and vestibular nerve lesions on the same side. BCV was delivered at Fz, the inion, the glabella or the supraorbital ridge using a tendon hammer or a bone-conduction vibrator.ResultsOnset latencies of the n10 evoked by taps at Fz or inion were significantly shorter than the R1 components of blink responses to supraorbital and glabellar stimuli. Upward gaze increased the amplitude of n10 but not R1. The n10 was absent bilaterally in patients with bilateral vestibular loss and beneath the contralesional eye in patients with unilateral vestibular loss, but in both these groups of patients R1 was preserved. In severe facial palsy the R1 component was absent or delayed and attenuated ipsilesionally, but n10 was preserved bilaterally. In subjects with unilateral facial and vestibular nerve lesions (Herpes Zoster of the facial and vestibulocochlear nerves) the dissociation was complete – the ipsilesional R1 was absent or attenuated whereas the ipsilesional n10 was preserved.Conclusionsn10 is distinguished from R1 by its earlier onset, laterality, modulation by gaze position and dissociation in patient groups.SignificanceThe n10 component evoked by BCV at Fz is not the R1 component of the blink reflex.     

瞬目反射联合经颅多普勒对后循环缺血的诊断价值

目的:探讨瞬目反射(BR)、经颅多普勒超声(TCD)对后循环缺血(PCI)患者的联合诊断价值。方法:对85例临床确诊为后循环缺血患者行BR、TCD检测。结果:85例患者BR异常率为61%,TCD异常率为76%,同时其相应参数有不同程度改变。结论:BR、TCD分别从神经电生理及血流动力学方面为PCI的诊断提供有价值的客观依据,联合检测互为补充,有助于提高后循环缺血的阳性检出率。