Blink reflex in hemiplegia

Analysis of the corneal reflex with air puff: normal controls and patient groups

Though there are several reports published about the corneal reflex elicited by different methods, a standardized electrophysiologic study with air puff in man has not been published. The aim of this study is to standardize the corneal reflex elicited by air puff to cornea. The authors studied the corneal reflex with air puff and direct touch by using a standardized method in patients with thalamic hemorrhage (n = 15), hemispheric infarction (n = 9), brainstem infarction (n = 9), multiple sclerosis (n = 12), and Bell's palsy (n = 12) and in normal control subjects (n = 21). The conventional blink reflex (BR) was also studied. The reflex responses were recorded from both orbicularis oculi muscles by air puff and direct touch to cornea in addition to the electrical stimulation of the supraorbital nerve. No statistical difference could be detected between the responses elicited by air puff or direct touch to cornea (P > 0.05). Corneal reflex responses were statistically different from the R2 response of the BR (P < 0.005). Because the responses elicited by direct touch and air puff to cornea are identical, air puff to cornea can be used confidently to study the corneal reflex.

Reduced brain stem excitability in mitochondrial myopathy: evidence for early detection with blink reflex habituation studies

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.

Effect of the inhibitory phenomenon following magnetic stimulation of cortex on brainstem motor neuron excitability and on the cortical control of brainstem reflexes

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 microV; 123%) compared to control responses not preceded by TMS (mean 386 +/- 31 microV). 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.

Abnormalities of the blink reflex in Gilles de la Tourette syndrome

The blink reflex and it's recovery cycle were studied in 26 patients with Gilles de la Tourette syndrome and 10 controls. There was a significant increase in the mean duration of the R2 response. The amplitude of the R2 response following paired shocks (mean R2[T]/R2[C]%) was 11%, 40% and 52% of the conditioning stimulus with intervals of 200 ms, 500 ms and 1 second in the patients, compared with 10%, 17% and 32% respectively in the controls. Half the patients, however, had normal recovery cycles and voluntary suppression of tics and blinks reduced the amplitude of R2 in all patients. These results suggest increased excitability of brainstem interneurons in Gilles de la Tourette syndrome.

Effects of general anesthesia on the human blink reflex

The blink reflex was studied in 10 patients undergoing elective procedures under general anesthesia. Anesthetic agents were isoflurane, halothane, nitrous oxide, methohexital, and thiopental in various combinations. At induction, blink reflexes were diminished by low-dose thiopental (1-1.5 mg/kg) and abolished by high-dose thiopental (4-8 mg/kg) and methohexital (1.5 mg/kg). Blink reflexes were absent during halogenated volitile inhalational anesthesia and did not return until patients were in the recovery room, well after end-tidal anesthetic levels were zero by mass spectroscopy. Recovery of consciousness and the ability to blink on command often preceded return of any blink reflex activity, indicating that the blink reflex is not useful as a postoperative test of facial nerve function in the operating room after anesthesia. In six patients, blink reflexes were still diminished 2-3 hours after cessation of anesthesia, at a time when patients were fully oriented and corneal and eyelid reflexes were clinically normal. This finding suggests that the blink reflex might be a sensitive test of subtle CNS dysfunction after inhalational anesthesia and potentially could serve as a useful objective indicator of recovery from anesthesia for outpatient surgery.

Maturation of blink reflex in children

The blink reflex was examined in 57 subjects aged from neonate to adult in the alert state. The ipsilateral late response (R2) was elicited in all subjects and considered most suitable to evaluate maturational changes of the blink reflex. In a few subjects older than 3 years and of adults, the ipsilateral early response (R1) was difficult to observe. The contralateral late response (R2') could not be obtained in 32% of neonates and infants. From the observation about developmental change of an interference pattern, a latency shortening of R2 and a latency difference between R2' and R2, the blink reflex in children may be considered as mature at no later than 5 years of age. In addition, the R2 latency tended to increase temporarily through 1 or 2 years from late infancy. The reflex circuit evaluated by the blink reflex in children may partially change its makeup after the early infantile period and is almost fully mature at no later than 5 years.

Electrically elicited blink reflex and early acoustic evoked potentials in circumscribed and diffuse brain stem lesions

In the present paper, the function of the brain stem in patients with brain stem lesions of various aetiology is investigated with electrophysiological methods. The clinical observations are supplemented by experimental investigations on cats, in which the blink reflex and the early acoustic evoked potentials were registered during the acute elevation of intracranial pressure. The findings in patients with circumscribed space-occupying lesions in the posterior fossa document that the registration of the BR and the BAEP have a functional diagnostic significance above and beyond the neurological and radiological investigation. In the case of the cerebellar space occupations, specific alterations could not be observed. On the contrary, the alterations of BR and BAEP indicate a general disturbance of brain stem function, possibly as a result of a general increase of intracranial pressure. In cerebellopontine angle tumours, both BR and BAEP showed specific alterations which were usually asymmetrical. The BR changes ipsilateral to the tumour are of major topodiagnostic significance, whereas the alterations of the contralateral potential are especially informative in the registration of BAEP. The alterations of BR and BAEP also allow an appraisal of the localization and extent of the lesion in primary space occupations in the brain stem: A pathological R1 indicates a pontine lesion, whereas pathological R2 responses are found in medullary and in oral pontine and mesencephalic lesions. In contrast to cerebellopontine angle tumours, the BAEP tends to show symmetrical alterations in primary brain stem lesions. The prolongations of interpeak latencies correspond to the brain stem segment concerned, and the same also applies to pathological amplitude reduction and deformations of individual potentials. In patients with localized brain stem damage, the reflex pathway of R2 is discussed on the basis of the BR findings. In contrast to the view held up to now that only structures situated caudal of the facial nucleus area are responsible for the genesis of the R2 response, it is assumed on the basis of our own observations that pontomesencephalic structures rostral to the facial nuclei are also important for the genesis of R2. Registration of BR and BAEP in patients with acute diffuse brain stem damage shows that both methods have a high diagnostic and prognostic value. Isolated damage and combined brain stem lesion can be demonstrated and the course can be followed up. Normalization of pathological findings reflects clinical recovery, and conversely a secondary deterioration indicates the presence of complications.(ABSTRACT TRUNCATED AT 400 WORDS)

Trigeminal dysfunction in patients with Bell's palsy

The trigeminal function was investigated in 30 consecutive patients with acute unilateral peripheral facial palsy. The patients were tested with electrophysiological methods within 5 weeks after onset of the disease. Trigeminus-evoked potential test (TEP) disclosed trigeminal dysfunction in 47%, while the blink reflex test (BR) showed trigeminal pathology in 60% of the patients. A topographical analysis of the trigeminal system showed that 24% of the patients had BR patterns that were consistent with brainstem involvement. In 2 cases (7%), TEP was pathological though the BR test proved normal. These findings suggest a more central trigeminal affection and may demonstrate multifocal lesions. This was further underlined by the investigation of the auditory brainstem response (ABR) which indicated brainstem involvement in 28%. It is concluded that acute facial palsy is frequently a symptom of a central nervous affection.

Changes in the recruitment pattern of single motor units in the blink reflex of patients with parkinsonism and hemiplegia

The recruitment pattern of single motor units (SMUs) was studied in the early (R1) and late (R2) blink reflex components in normal subjects (15), patients with parkinsonism (10) and with hemiplegia due to hemispheral lesions (5). Reflexes were evoked by constant current stimuli applied to the supraorbital nerve. SMU discharges were recorded in the preseptal part of the lower eyelid using a bipolar needle electrode. Thresholds of R1 and R2, latencies at the thresholds and the number of discharges in R2 were determined. In parkinsonism, the recruitment of SMUs in R1 was impaired, suggesting that the malfunction of the basal ganglia in this disorder is associated with a reduced excitability of neurons in the pontine brain-stem. In hemiplegia, the recruitment in both R1 and R2 could be impaired. The orderly function of neurones in the pontine and medullary pathways of these components appears to require facilitatory hemispheral influences. Signs of disinhibition occasionally found in R1 may point to an imbalance between facilitatory and inhibitory hemispheral influences upon the pontine pathway.

Habituation of the blink reflex: computer assisted quantitative analysis

The electrically evoked blink reflex (BR) was elicited in 20 healthy volunteers, varying the stimulus interval by a computer JN 110. Latencies, amplitudes, reflex duration and reflex areas of early and late components of the BR were analysed by a computer program testing the signal-to-noise ratio, the response configuration and frequency distribution. Changes in habituation related to the stimulus interval can be illustrated best by the progressive diminution of R2 areas. Computing the habituation in relation to the stimulation frequency by a standardized program seems to be a quantitative method to assess habituation in various diseases and during treatment studies.

Blink reflex in patients with hemispheric cerebrovascular accident (CVA). Blink reflex in CVA

A blink reflex consists of an early unilateral component, R1, and a late bilateral component, R2. During an acute phase of hemispheric cerebrovascular accident, R1 and R2 were abnormal in 30 and 50 of 66 patients, respectively. Paired stimuli usually corrected R1 but not R2, which was profoundly suppressed. The discrepancy between polysynaptic R2 and oligosynaptic R1 indicates a greater disfacilitation at the level of interneurons than at the motoneuron, which serves as the final common path. Abnormality of R2 occurred bilaterally with stimulation on the affected side of face and contralaterally after stimulation on the normal side in 31 patients. This finding suggests a diffuse loss of internuncial excitability, contralateral to the hemispheric lesion. Changes of R2 implicated the brainstem pathways forming the afferent and efferent arc of the reflex in 7 and 8 patients, respectively. The remaining 4 comatose patients had no R2 irrespective of stimulus sites. Clinical localization of the hemispheric lesion showed no consistent correlation with the type of blink reflex abnormalities. The CT scans revealed widely scattered changes in 29 patients with abnormal blink reflex but with a tendency to overlap in the inferior Rolandic area. This contrasted with conspicuous sparing of the inferior post-central region in 10 patients with normal blink reflex. These findings suggest the presence of crossed facilitation to this reflex from wide areas of the cortex but most prominently from the sensory representation of the face.

Effect of increased intracranial pressure on the blink reflex in cats

During an acute increase in ICP produced by balloon inflation three different phases could be observed. In the first phase (ICP 40-50 mm Hg) the latencies of R 1 and R 2 showed an initial decrease followed by increase in latency. In the second phase (ICP 50-70 mm Hg) R 2 disappeared, whereas R 1 showed marked alterations, prolongation of the latency and duration, and a decreasing amplitude. In the third phase no response could be evoked. The pathophysiological observations correlated with the morphological alterations. Two ischaemic zones with BBB damage which "transsected" the mesodiencephalic and pontomesencephalic border were found. The results suggest that the disappearance of R 2 depends on rostral damage, whereas alteration of R 1 is caused by a pontomesencephalic lesion.

Unilateral reduction of the early and late blink reflex component in hemiparkinson syndrome

Electrically evoked blink reflexes were recorded in 10 patients with unilateral tremor and/or rigor, mostly diagnosed as hemiparkinson syndrome. Five of the patients could be investigated before and after stereotaxic thalamo-subthalamotomy. The EMG activity of the early and late components was quantified by means of averaging and integrations techniques. In addition, the latencies of the reflex components were determined. The major finding was a unilateral decrease of the EMG activity of both the early and late components confined to the clinically affected side. This pattern points to a lowered state of excitability of neurons in or close to the facial nucleus, probably due to a dysfunction of contralateral EPMS structures. A loss of facilitatory influences from EPMS centers, e.g. the nigro-striatal system, on brain stem neurons in the area of the facial nucleus appears most probable. The latencies of the early and late components were mostly normal. After stereotaxic surgery, the BR activity was decreased bilaterally. The difference between the affected and unaffected sides, however, was nearly unchanged. At present an unspecific postoperative effect cannot be excluded.

Quantitative analysis of blink reflexes in patients with hemiplegic disorders

Electrically evoked blink reflexes were investigated in 18 patients with hemiplegia and in 15 control subjects, using common electromyographic techniques. The EMG activities of the early and late components were quantitatively and integration. In addition, the latencies of the single components were determined. Regarding the EMG activity of the late components two major types of BR alteration could be distinguished. In type I stimulation of the clinically affected side evoked significantly decreased late components on both the affected and the unaffected sides. This pattern points to a lowered excitability of the brain stem trigeminal systems and may be associated with predominantly sensory disorders. In type II the decrease of the late components was confined to the affected side independent of the side of stimulation. This pattern may indicate a lowered excitability of the brain stem facial systems and/or of the lateral bulbar reticular formation and may be correlated with predominantly motor deficits. Both types are presumably due to a loss of facilitatory influences associated with the hemispheral lesion. Although the early component was frequently decreased on the affected side there was no consistent pattern and no relation to the alterations of the late components. The latencies of both responses, predominantly of the late ones were frequently prolonged, in particular following stimulation of the affected side. Comparison of the seemingly normal components in the patients with the corresponding control values pointed to a generally lowered blink reflex excitability in hemiplegic patients.

[Abolition by naloxone of the inhibitory effect of peripheral electrical stimulation on the blink reflex]

The effects of a low frequency (2 c/sec) peripheral stimulation (electro-acupuncture, EA) on the nociceptive (R2) response of the blink reflex elicited by supra-orbital nerve stimulation (0.1 msec, 1 shock/8 sec) were studied in 10 healthy subjects. EA stimulation produced a very significant inhibition of the reflex in 8 subjects. Double-blind injection of naloxone (0.8 mg) reversed this inhibition while no signiificant change was observed with placebo. These results suggest that EA stimulation induces the release of endogenous opiates.