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Introduction: In this study we explored brainstem reflex excitability changes, blink reflex recovery cycles (BRRCs), and masseter inhibitory reflexes (MIRs) in patients with amyotrophic lateral sclerosis (ALS). Methods: Fourteen ALS patients and 14 healthy control subjects were recruited. The BRRC was examined at interstimulus intervals (ISIs) of 100, 200, 300, 400, 500, and 600 ms. The latencies and durations of silent period 1 (SP1) and silent period 2 (SP2) of the MIR were measured. Results: Decreased R2 area suppression was prominent in the ALS group at ISIs of 200, 300, and 400 ms (P < 0.02), whereas no significant differences between groups at 100, 500, and 600 ms ISIs (P > 0.05) were observed. SP2 duration was significantly prolonged in the ALS group compared with controls (P = 0.01). Conclusions: Brainstem inhibitory and excitatory interneuronal activity is altered in ALS, possibly brought about by physiological and morphological changes at the cortical or bulbar levels.

Introduction In severely affected inherited polyneuropathy patients, primary demyelination can be difficult to determine by routine extremity limb nerve conduction studies (NCS). Blink reflexes may help classify severe polyneuropathies as either axonal or demyelinating. However, blink reflex studies have not been studied systematically in any genetically confirmed cohort. Methods Patients with a genetic diagnosis who had undergone blink reflex testing and extremity NCS were identified retrospectively. Blink reflex R1 latency, extremity NCS, and severity were compared. Results We identified 26 demyelinating and 23 axonal, genetically confirmed cases, including 20 with PMP22 duplications. In 12 (25%), the ulnar CMAP amplitude was ≤0.5 mV making electrophysiological classification difficult. However, the R1-latency cutoff of >13 ms (demyelinating) robustly classified all patients regardless of severity. Conclusions We show that blink reflex studies are reliable for identification of inherited demyelinating polyneuropathy regardless of severity and can facilitate algorithmic decisions in genetic testing. Muscle Nerve 55: 316-322, 2017.

Introduction: Variegate porphyria (VP) is a rare metabolic disorder that may present as an acute predominantly motor neuropathy. Cranial nerves and brainstem functions have been only scarcely studied. Methods: Brainstem reflexes were examined in symptomatic and non-symptomatic VP mutation carriers of a single family. Results: Similar results were found in the 2 patients with a history of porphyric crises. The blink reflex showed an absence of late responses (R2 and R2c) to stimulation of both sides. The masseter inhibitory reflex showed reduced inhibition of the second phase. The jaw jerk was normal. The asymptomatic carriers did not show any of the abnormalities just noted. Conclusions: Our results are compatible with a central lower pons–upper medulla disorder in the brainstem. We hypothesize that brainstem dysfunction in VP patients with a history of porphyric crises may be due to neurotoxic effects of porphyrin precursors as well as subclinical osmolarity changes due to hyponatremia. Muscle Nerve 46: 426–433, 2012

Introduction: In this study we assessed the effect of paired stimuli on the latencies and amplitudes of the blink reflex. Methods: Blink reflexes were performed with single and paired (5-ms interstimulus interval) stimuli in 47 patients. The changes in latencies between paired and single stimuli were calculated. Results: Paired stimulation produced two types of R1 waveform morphologies: single- and double-peaked waveforms. Increases in R1 and contralateral R2 latencies with paired stimulation were significantly higher in those with single-peaked R1 responses compared to those with double-peaked R1 responses. Conclusions: Interpreting the blink reflex latencies using paired stimulation requires visualization of the R1 waveform morphology. A double-peaked R1 response requires no change in normal latency values, but the latency of a single-peaked R1 should be interpreted from the second shock artifact. The effect on the R2 latency is variable. Muscle Nerve, 2011

The brainstem pathways that mediate the somatosensory blink reflex (SBR) are not completely understood. We hypothesized that the circuits of the SBR might be affected separately from those of the trigeminal blink reflex (TBR). We examined 7 patients with mesencephalic lesions and 8 patients with medullary lesions. The SBR was elicited by median nerve stimulation. The TBR was elicited by supraorbital nerve stimulation. In patients with upper brainstem lesions, the TBR was normal, whereas the SBR was generally abnormal. The SBR was either absent or small and was significantly delayed with respect to control subjects. The opposite was the rule in patients with lower brainstem lesions who had delayed or absent TBR and no abnormal findings in the SBR. The SBR is mediated through circuits in the upper brainstem. Study of the SBR can be helpful in the neurophysiological assessment of patients with mesencephalic lesions.

Until now, there have been no reports on eliciting the blink reflex (BR) during anesthesia at a depth compatible with surgery. We introduce a novel method for eliciting the R1 component of the BR under inhalation or total intravenous anesthesia by using a short train of four to seven stimuli applied over the supraorbital nerve. Recording is done from the ipsilateral orbicularis oculi muscle. We set out to record the BR in 27 patients (age 1-78 years) without involvement of the facial nerve, trigeminal nerve, or brainstem. The BR could not be recorded in only 4 patients (recordability: 86.2%). All patients received at least one bolus of propofol while in surgery. Using this method, the BR was recorded on 4 awake healthy subjects. Boluses of propofol and muscle relaxants should be avoided in order to successfully record the responses. BR recording is feasible in patients under general anesthesia by using this novel technique. Muscle Nerve 39: 642-646, 2009.

An overview is provided on the physiological aspects of the brainstem reflexes as they can be examined by use of clinically applicable neurophysiological tests. Brainstem reflex studies provide important information about the afferent and efferent pathways and are excellent physiological tools for the assessment of cranial nerve nuclei and the functional integrity of suprasegmental structures. In this review, the blink reflex after trigeminal and nontrigeminal inputs, corneal reflex, levator palpebrae inhibitory reflex, jaw jerk, masseter inhibitory reflex, and corneomandibular reflex are discussed. Following description of the recording technique, physiology, central pathways, and normative data of these reflexes, including an account of the recording of recovery curves, the application of these reflexes is reviewed in patients with various neurological abnormalities, including trigeminal pain and neuralgia, facial neuropathy, and brainstem and hemispherical lesions. Finally, simultaneous electromyographic recording from the orbicularis oculi and the levator palpebrae muscles is discussed briefly in different eyelid movement disorders.

In humans, high-intensity electrical stimuli delivered to the fingers induce an inhibitory effect on C7–T1 motoneurons. This inhibitory reflex, called the cutaneous silent period (CSP) is considered a defense response specific for the human upper limbs. It is not clear whether the CSP—like other defense responses such as the corneal reflex and the R III reflex—is an opiate-sensitive nociceptive reflex. Because opiates suppress some, but not all, nociceptive reflexes, we studied the effect of the narcotic-analgesic drug fentanyl on the CSP and the R III reflex. The CSP was recorded from the first dorsal interosseous (FDI) muscle in seven normal subjects during voluntary contraction, before and 10 and 20 min after fentanyl injection. To assess possible fentanyl-induced changes, we also tested the effect of finger stimulation on motor evoked potentials (MEPs) elicited in the FDI muscle by transcranial magnetic stimulation before and after fentanyl injection. Fentanyl-induced changes were also studied on the R III reflex recorded from the biceps femoris muscle. Fentanyl, as expected, suppressed the R III reflex but failed to change the inhibitory effect of finger stimulation on FDI motoneurons. Finger stimulation reduced the size of MEPs in the FDI, and fentanyl injection left this inhibitory effect unchanged. The differential fentanyl-induced modulation of the CSP and R III reflex provides evidence that the CSP circuit is devoid of μ-opiate receptors and is therefore an opiate-insensitive nociceptive reflex, which may be useful in the assessment of central-acting, non-opioid drugs. © 2002 Wiley Periodicals, Inc. Muscle Nerve 25: 000–000, 2002

The aim of the study was to correlate the features of the blink reflex (BR) with the genetic abnormalities and the clinical findings in patients with Huntington's disease (HD) and asymptomatic gene carriers. Twenty patients with HD and 20 relatives were studied. Mutation analysis was performed for the CAG expansion within the HD gene using HD 333-HD 447 as oligonucleotide primers. The BR was elicited transcutaneously by electrical stimulation of the right supraorbital nerve. The recovery curve of the R2 and R3 responses after a conditioning stimulus was evaluated. R2 latency and duration and R3 duration were significantly increased in HD patients and in presymptomatic carriers in comparison with controls; reduced R2 recovery was also clear in both HD and gene-carrier relatives. In HD patients, the R2 latency increase correlated significantly with the severity of facial chorea. The R2 abnormalities are probably caused by impaired suprasegmental control by the basal ganglia over brainstem interneurons, which may precede the onset of involuntary movements, probably conditioning the severity of facial chorea during development of the disease.

Abnormalities of the silent period (SP) and blink reflexes occur in diseases that interfere with inhibitory pathways, such as tetanus and stiff-person syndrome (SPS). The SP is abnormal in tetanus but not in SPS. Studies of the blink reflex in tetanus are limited. In this report, a patient with generalized tetanus is described. The masseteric-and mixed-nerve SP was absent or truncated. In contrast to SPS, blink reflex studies revealed no bilateral R1 component, and a discrete R3 was only present ipsilateral to right supraorbital stimulation. This reflects the distinct inhibitory pathways underlying these disorders.

We studied 18 patients with complete unilateral denervation of the facial muscles after idiopathic facial nerve palsy to determine whether motoneuronal excitability is enhanced in the few motor units that are active at onset of muscle reinnervation. The study was carried out between 75 and 90 days after the facial nerve lesion. We used two needle electrodes to record simultaneously the spontaneous and voluntary activity of the orbicularis oris (OOris) and orbicularis oculi (OOculi) muscles, as well as the responses to ipsilateral and contralateral facial and supraorbital nerve stimuli. All patients showed involuntary firing of motor unit action potentials (MUAPs) in at least one of the muscles. Synkinetic activation of motor units in the OOris was induced by spontaneous blinking in all patients, and by inhalation and swallowing in some. Electrical stimulation of the ipsilateral facial nerve induced a direct M response in only 4 patients. In contrast, long-latency reflex responses were induced in both muscles by electrical stimulation of ipsilateral and contralateral facial and supraorbital nerves in all patients, at latencies ranging between 44 and 132 ms. The shape of such MUAP reflex responses was the same as that of the MUAPs seen to fire at rest. These findings provide evidence of enhanced excitability of facial motoneurons in our patients. Such hyperexcitability may be partly responsible for the postparalytic motor dysfunction syndrome that occurs after facial palsy with severe axonal damage.

Laser pulses selectively excite mechano-thermal nociceptors and evoke brain potentials that may reveal small-fiber dysfunction. We applied CO2-laser pulses to the perioral and supraorbital regions and recorded the scalp laser-evoked potentials (LEPs) and reflex responses in the orbicularis oculi, masticatory, and neck muscles in 30 controls and 10 patients with facial sensory disturbances. Low-intensity pulses readily evoked scalp potentials consisting of a negative component with a latency of 165 ms followed by a positive component at 250 ms. In vertex recordings, the amplitude of LEPs exceeded 30 microV. Although only high-intensity pulses evoked reflex responses, some subjects showed--even to low-intensity pulses--an orbicularis oculi (blink-like) response that markedly contaminated the scalp recording. Scalp LEPs were abnormal in patients with hypalgesia and normal trigeminal reflexes and normal in patients with normal pain sensitivity and abnormal trigeminal reflexes. Possibly because of the high receptor density in this area and the short conduction distance, laser stimulation of the trigeminal territory yields low-threshold and large LEPs, which are useful for detecting dysfunction in peripheral and central pain pathways.

The blink reflex was induced by a defined mechanical impact covering the range from light touch to a hard, painful stroke, and by an electrical current. In both modes of stimulation, the R3—but not the R2—thresholds were correlated with subjective pain thresholds, suggesting a connection between R3 and nociceptor activation. However, R3 magnitude did not increase systematically with increasing levels of subjectively felt pain. The R3, induced by painful impacts, habituated quickly and was strongly affected by attention. The functional significance of the R3 component is discussed. © 1999 John Wiley & Sons, Inc. Muscle Nerve 22: 443–448, 1999.

The electrically evoked blink reflex (BR) consists of an ipsilateral R1 component (R1) at 11 ms and two bilateral components R2 at 33 ms and R3 at 83 ms. It is still unclear whether the R2 is mediated by activation of tactile or nociceptive afferents. For testing the nociceptive hypothesis, nociceptors of the supraorbital nerve were selectively activated by infrared laser stimuli in 10 subjects. Only painful laser stimuli evoked a bilateral early polyphasic BR response (LR2) at 71 ms. Stimulation of infraorbital and mental nerve dermatomes was equally effective. A late bilateral reflex response at 130 ms was occasionally observed. Regarding the nociceptor activation time of about 40 ms, onset latencies were within the range of the electrically evoked R2 and R3, respectively. The good accordance of R2 and LR2 may be due to activation of identical nociceptive fibers or to convergence of electrically evoked tactile and laser-elicited nociceptive input onto common multireceptive neurons.

Blink reflex (BR) was studied in 17 patients with histochemically and genetically confirmed mitochondrial myopathy (MM). Fourteen patients had chronic progressive external ophthalmoplegia (CPEO) associated with a mild to moderate craniosomatic myopathy without any symptoms or signs of central nervous system (CNS) involvement, 2 myoclonic epilepsy with ragged red fibers syndrome, and 1 Kearns-Sayre syndrome. The mean latencies of the early (R1) and late (R2) responses were prolonged (P < 0.01 and P < 0.001, respectively), and the corresponding amplitudes decreased (P < 0.001). Increased habituation of the reflex was clearly observed in 10 out of 14 patients tested (71.4%), 9 of whom presented CPEO. These findings suggest that the brain stem reticular network is in a state of basal inhibition which is presumably due to a subclinical impairment of the cerebral cellular metabolism. Multimodal evoked potentials revealed abnormalities suggestive of CNS involvement in 7 out of 17 patients (41.2%), 4 of whom had CPEO. These observations document the validity of BR in detecting clinically silent brain stem impairment in patients with apparently pure MM and provide important clues for a further understanding of the underlying pathophysiology.

Mobius syndrome is characterized by congenital facial diplegia, frequent impairment of gaze, variable involvement of other cranial muscles, and various musculoskeletal anomalies. The site of dysfunction remains debatable. We performed detailed electrophysiologic studies in 5 children and 2 adults with Mobius syndrome to better delineate the pathophysiology of this disorder. Sensory and motor conduction studies were normal in the extremities. Facial compound muscle action potential amplitudes were reduced in all patients. The blink reflex R 1 responses were unobtainable unilaterally in 2 patients and unobtainable bilaterally in 3 patients. Otherwise, R 1 and R 2 latencies were variably prolonged. The jaw jerk and masseter silent periods, tested in 2 patients, were normal. Detailed electromyographic studies of facial muscles revealed multifocal, chronic neurogenic changes. The findings indicate a brain stem process predominantly affecting the facial nuclei and their internuclear connections rather than a supranuclear or muscular site of involvement.

It has been claimed that functional recovery of the blink reflex occurs after hypoglossal-facial nerve anastomosis. This has been explained through central nervous system plasticity and reorganization of neuronal connections. In 5 patients with reinnervated facial muscles after hypoglossal-facial nerve anastomosis we observed "R1-like" responses that fulfilled criteria for facial nerve axon reflexes or ephapses. First, displacement of the stimulating electrode from the supraorbital to zygomatic area shortened the latency of the evoked response. Second, these responses were stable (jitter mean consecutive difference < 25 microsec) and they had complex potential shapes unmodified by high-frequency stimulation. Finally, collision techniques demonstrated antidromic conduction of impulses in the facial nerve from supraorbital to zygomatic points. Therefore, these "R1-like" responses are not the early component of a functionally recovered blink reflex but motor axon reflexes or ephaptic responses similar to the short latency responses observed following facial nerve regeneration or from sutured nerves in human forearms.

R1 and R2 blink reflex responses to single and paired stimuli were investigated in 23 control subjects, 21 patients with blepharospasm (BSP), 20 patients with torticollis spasmodica (TS), and 23 with hemifacial spasm (HFS). For paired stimuli, we compared measurements of area and peak responses at two and three times R2 threshold. R1 and R2 indices were calculated as the average of the recovery values at 0.5-, 0.3-, and 0.21-s interstimulus intervals to test individual patients. Peak amplitude measurements at three times R2 threshold were optimal. The R2 index was abnormal in 67% of BSP patients, 37% of TS patients, and 50% of HFS patients on the affected side and 20% on the unaffected side. A normal R2 index in one third of patients with BSP may indicate that different pathophysiological mechanisms are involved in this type of focal dystonia.

In 4 patients with familial olivopontocerebellar atrophy (OPCA) we have recently described an abnormal movement of facial muscles characterized by rhythmic muscle twitching during voluntary activation (facial action myoclonus). In the present article, we present the results of a neurophysiologicel study of brainstem reflexes in those 4 patients, in 4 other patients with OPCA but without facial action myoclonus, in 3 patients with pure cerebellar cortical atrophy, and in 6 normal volunteers used as control subjects. All patients had similar clinical features, but only the patients with facial action myoclonus and only one of the other patients with OPCA had brainstem atrophy detected on magnetic resonance imaging. Electrophysiological abnormalities were found in all patients with facial action myoclonus and consisted of myokymia in perioral muscles at rest, spread of spontaneous and reflex blinking to the orbicularis oris, and enhanced long-latency facial reflex responses to stimuli applied to the facial or trigeminal nerve. Other relevant electrophysiological abnormalities were the absence of jaw jerk in 2 patients, the absence of an R1 response of the blink reflex in 1 patient, and a markedly reduced compound muscle action potential of the facial nerve in another patient. Comparable electrophysiological abnormalities were found in only 1 of the patients with OPCA but without facial action myoclonus, and in none of the patients with pure cerebellar cortical atrophy. Facial action myoclonus is a clinical manifestation of a global brainstem functional derangement that may characterize a subgroup of patients with OPCA or constitute a distinctive step in the natural evolution of some forms of the disease. © 1994 John Wiley & Sons, Inc.

Of 45 patients with acoustic neuromas (0.3-5.0 cm), 73% had facial nerve impairment on electrophysiologic testing, but only 16% had facial weakness. Cranial nerve conduction was the most sensitive measurement, especially prolongation of the ipsilateral R1 latency of the blink reflex compared with that of the contralateral reflex. The severity of nerve conduction abnormality was highly correlated with tumor size. Our results confirm and quantitate the sensitivity of nerve action potential latency in response to chronic nerve compression.

We report, for the first time, electrophysiological findings in the Finnish type of familial amyloidosis (FAF), a gelsolin-related form of systemic amyloidosis. Electromyography, nerve conduction studies, and blink reflex examinations were performed in 30 patients (age range 27-74 years). Cranial nerve involvement was detected in all, and peripheral nerve involvement in the majority of patients. Carpal tunnel syndrome was a characteristic feature of FAF, previously unrecognized. Myokymia-type short spontaneous bursts in frontal muscles were found in 3 younger patients. In addition to signs of axonal degeneration we found slow nerve conduction, prolonged distal motor latencies, and conduction blocks suggestive of demyelination. Most nerve conduction velocities correlated remarkably with age. We conclude that FAF is characterized not only by distinct clinical and molecular biological features but also by electrophysiological findings, which enable differentiation from other hereditary amyloidoses.

We studied the effect of the inhibitory phenomenon following transcranial magnetic stimulation (TMS) on brainstem motor neuron excitability and on the cortical control of brainstem reflexes in 5 normal subjects. The R1 component of the blink reflex assessed excitability of the facial nucleus during the period of post-TMS inhibition (experiment 1). TMS effect on the cortical control of brainstem reflexes was assessed by delivery of a stimulus that was less than or equal to the threshold for the R1 with the subject relaxed, yet elicited a potentiated reflex during maneuvers requiring cortical input (i.e., voluntary eye-closure and anticipation, experiment 2). In experiment 1, a suprathreshold electric stimulus applied during post-TMS inhibition elicited an R1 response that was preserved in amplitude (mean 476 ± 44 μV; 123%) compared to control responses not preceded by TMS (mean 386 ± 31 μV). Conversely, in experiment 2, when the R1 was dependent on cortical drive, the mean R1 amplitude during post-TMS inhibition was only 15% (P < 0.01) and 8% (P < 0.01) of control values obtained during eye-closure and anticipation, respectively. These findings imply that the inhibition following TMS originates rostral to the facial nucleus, at a cortical level. © 1993 John Wiley & Sons, Inc.

A 25-year-old man with acute, bilateral facial palsies is presented. He had a lymphocytic meningitis, history of tick bites, and lived in an area endemic for Lyme disease, which was ultimately confirmed by serology. Electrodiagnostic investigation included facial motor nerve study, blink reflex and electromyography of facial muscles, which were indicative of a neurapraxic lesion on the right and an axonopathic lesion on the left. The clinical course was consistent with these findings as the right side fully recovered and the left remained plegic. The clinical features of Lyme associated facial neuritis are reviewed, as is the electrodiagnostic evaluation of facial palsy.

In order to assess the clinical utility of trigemino-facial reflexes in lower facial muscles, we studied perioral reflexes to mechanical and electrical stimulation in 13 patients with spasmodic dysphonia and orofacial dyskinesia and in 7 healthy subjects. Mechanical stimulation of the upper lip of all patients and electrical stimulation of the infraorbital nerve of patients with orofacial dyskinesia elicited larger perioral reflexes than in controls. In the majority of patients, hyperexcitable perioral reflexes were accompanied by increased gain of the blink reflex. In 4 patients, however, trigemino-facial reflexes were enhanced selectively in either the perioral muscles or orbicularis oculi. Our findings suggest that the quantitative assessment of perioral reflexes may provide information about the excitability of brainstem interneurons in cranial dystonia that is complementary to blink reflex studies.

Trichloroethylene (TCE) exposure is known to have specific toxic effects on cranial nerves, the trigeminal nerve (V) in particular. The electrophysiological measurement of the blink reflex (BR) can quantify latency changes in the Vth and VIIth cranial nerve reflex arc. Prior study looked at the blink reflex measurement in a community group exposed to TCE in their drinking water. This study evaluated the use of the electrophysiologic blink reflex as an indicator of neurotoxic effects of TCE in occupationally exposed workers. The BR was tested in individual cases with documented histories of exposure to known chemical neurotoxins including TCE (n = 18). When compared with the nonexposed laboratory control values (n = 30), the subjects with a significant history of TCE exposure demonstrated the most prolonged latencies (greater than or equal to 3.0 SD above the nonexposed group mean) in the R1 component of the blink reflex measurement. The electrophysiological study of the blink reflex has application in assessing TCE exposure and in documenting the neurotoxic effects of that exposure on trigeminal nerve functions in humans.

Masseter (MR) and blink reflexes (BL) were investigated in 51 patients with internuclear ophthalmoplegia (INO) due to multiple sclerosis (28) and lacunar infarction (23). The MR was abnormal in 20 of 23 cases with bilateral INO and in 21 of 28 with unilateral INO. The R1 component of the BL (BL-R1) was abnormal in 7 of 23 patients with bilateral INO and 10 of 28 with unilateral INO. Combined MR and BL-R1 changes occurred in 8 of 28 cases with unilateral INO and 7 of 23 with bilateral INO. The findings provide evidence for a rostral/caudal localization of lesions within the medial longitudinal fasciculus causing INO on the basis of MR and BL-R1 abnormalities. An abnormality limited to MR suggests a midbrain location in 58.8% of patients while abnormal BL-R1 with or without an associated MR change suggests a rostral pontine location in 35.3%.

In 3 patients with a severe pure sensory neuropathy of subacute onset, the masseter reflex remained normal despite absent blink reflex responses and absent stretch reflexes in the extremities. In 20 patients with primary disorders of peripheral nerve axons or myelin, the masseter reflex was abnormal. This study suggests that a normal masseter reflex in patients presenting with a pure sensory neuropathy favors a polyganglionopathy rather than a primary axonal sensory neuropathy, particularly if the blink reflex is abnormal.

We studied the rate of appearance and mechanism of contralateral R1 responses in normal subjects. Contralateral R1 could be produced by facilitating maneuvers such as a gentle contraction of the orbicularis oculi and conditioning stimulus of the median nerve. In addition, changing the position of the stimulating anode to the midline evoked these responses that were abolished by blocking the contralateral supraorbital nerve, confirming its peperipheral origin. We conclude that crossed trigeminofacial pathways probably exist in normal subjects, but in some instances contralateral peripheral trigeminal ophthalmic sensory fibers may be stimulated, giving rise to a contralateral R1 response.