Blink reflex prepulse inhibition and excitability recovery: Influence of age and sex

ObjectiveAge and sex affect various reflexes in healthy humans. Their respective influence on prepulse inhibition (PPI) of the trigeminofacial blink reflex (BR) and BR excitability recovery has not as yet been investigated in detail.MethodsWe studied the trigeminofacial BR bilaterally in 62 healthy volunteers (31 males, age 41.0 ± 13.2 years, mean ± SD, 31 females, 39.2 ± 11.7 years) following right supraorbital nerve stimulation. Single sweeps were recorded either alone (n = 8) or conditioned by a prepulse applied 100 ms earlier to the dominant index finger though ring electrodes (n = 8). Latency and amplitude of the ipsilateral R1 component, as well as latency and area-under-the-curve of the ipsilateral R2 and contralateral R2c components were measured in single traces and then averaged per subject. BR excitability recovery was established bilaterally following right supraorbital nerve stimulation with paired pulses. Six responses were averaged on-line per interstimulus interval (ISI 160, 300, and 500 ms).ResultsUnconditioned BR did not differ significantly between males and females, but R2 and R2c latencies increased with age. Prepulse stimulation caused significant facilitation of R1 (latency and amplitude), and inhibition of R2 and R2c (latency and area), irrespective of age. PPI of R2 and R2c area was significantly more pronounced in men. BR excitability recovery was significantly influenced by age, but not by sex. Multiple regression showed inverse correlation of age with conditioned R2 and R2c area at ISI 300 ms and 500 ms (P < 0.01 each), indicating reduced excitability recovery. No parameter showed significant interaction of age × sex.ConclusionThese data indicate less pronounced PPI of the trigeminofacial BR in females, concurring with previous reports of sex differences in protective reflexes, but also suggesting less rigorous filtering of information flow to the brain in females. Reduced BR excitability to paired-pulse stimulation may counteract age-related disinhibition of brainstem interneuronal circuitry.SignificanceThe present findings allow new insight into human brainstem physiology.     

The role of blink reflex R1 latency as an electrophysiological marker in diabetic distal symmetrical polyneuropathy

ObjectiveStudies showed a relatively prolonged blink R1 latency in patients with diabetic distal symmetrical polyneuropathy (DSPN) compared to that without DSPN. We tested the hypothesis that blink R1 latency would provide a diagnostic alternative to nerve conduction studies (NCS) in DSPN and act as a marker of the severity of NCS abnormalities in DSPN.MethodA total of 109 patients with type 2 diabetes underwent blink reflex studies and NCS. We used the composite amplitude scores of nerve conductions (CAS), which consisted of motor (tibial, peroneal and ulnar) and sensory (sural and ulnar) amplitudes for estimating the severity of NCS.ResultsPatients with DSPN had longer blink R1, R2, and contralateral R2 latencies (P < 0.0001, P = 0.001, and P = 0.031, respectively) and higher CAS (P < 0.0001). Area under curve on receiver operating characteristic curve analysis in diagnosing occurrence of DSPN in blink R1 latency was 0.772 (P < 0.0001). Multiple linear regression analysis showed that blink R1 latency was independently associated with CAS.ConclusionBlink R1 latency may be valuable in auxiliary diagnosis and in determining the severity of NCS abnormalities in DSPN.SignificanceBlink R1 latency can be added as a supplemental marker of severity of NCS in DSPN, especially if the patient’s sural amplitudes has a floor effect.     

Pedunculopontine tegmental Nucleus-evoked prepulse inhibition of the blink reflex in Parkinson’s disease

ObjectiveTo investigate the effects on the blink reflex (BR) of single stimuli applied to the pedunculopontine tegmental nucleus (PPTg).MethodsThe BR was evoked by stimulating the supraorbital nerve (SON) in fifteen patients suffering from idiopathic Parkinson’s disease (PD) who had electrodes monolaterally or bilaterally implanted in the PPTg for deep brain stimulation (DBS). Single stimuli were delivered to the PPTg through externalized electrode connection wires 3–4 days following PPTg implantation.ResultsPPTg stimuli increased the latency and reduced duration, amplitude and area of the R2 component of the BR in comparison to the response recorded in the absence of PPTg stimulation. These effects were independent of the side of SON stimulation and were stable for interstimulus interval (ISI) between PPTg prepulse and SON stimulus from 0 to 110 ms. The PPTg-induced prepulse inhibition of the BR was bilaterally present in the brainstem. The R1 component was unaffected.ConclusionsThe prepulse inhibition of the R2 component may be modulated by the PPTg.SignificanceThese findings suggest that abnormalities of BR occurring in PD may be ascribed to a reduction of basal ganglia-mediated inhibition of brainstem excitability.     

Blink reflexes in chronic tension-type headache patients and healthy controls

ObjectiveTo use the R2 component of nociceptive-specific blink reflex (nBR) to probe the trigeminal nociceptive system and compare chronic tension-type headache (CTTH) patients and healthy controls.MethodsThirty patients with CTTH and 30 age- and sex-matched healthy control subjects were included. nBR were evoked by painful electrical pulses (0.5 ms duration), delivered by a concentric electrode placed on the left lower forehead close to the supraorbital foramen. The EMG activity in the orbicularis oculi muscles was recorded bilaterally. The electrical stimulus intensities to evoke individual sensory threshold (Is) and pin-prick pain sensation (Ip) were assessed. A fixed stimulation intensity of 1.5× Ip was used to evoke the nBR. The perceived pain intensity of the electrical stimulus (I_BR) was assessed by the subjects on a 0–10 cm visual analogue scale (VAS).ResultsIs did not differ between CTTH patients and controls (P = 0.687) but were lower in females than in males (P = 0.020). CTTH patients had higher scores on I_BR than controls (P = 0.026). ANOVA showed significantly higher pre-stimulus EMG values in CTTH patients on the left (stimulated) side (P < 0.001), whereas there were no differences between males and females (P > 0.168). There were no significant differences in the absolute values of the nBR, however CTTH patients had significantly lower values of the normalized root mean square (RMS) (P = 0.035) and area under the curve (AUC) (P = 0.042) of the nBR on the left side compared with control subjects with no sex-related differences (P > 0.070). The onset latencies and duration were not significantly different between CTTH and control subjects or between female and male subjects (P > 0.270). There was no significant correlation between any of the BR parameters (RMS, AUC) and clinical characteristics of CTTH (headache intensity and duration) (P > 0.163).ConclusionsThe results of the present study did not detect a significantly different blink reflex response in CTTH patients, but suggested that painful electrical stimulation was associated with consistent increases in eye muscle activity on the same side.SignificanceThese findings add further information to central nociceptive pathways in CTTH patients.     

Effect of slow rTMS of motor cortex on the excitability of the Blink Reflex: A study in healthy humans

ObjectiveTo evaluate the after-effects of low frequency, sub-threshold repetitive Transcranial Magnetic Stimulation (rTMS) of primary motor cortex, on the excitability of Blink Reflex (BR) in healthy subjects.MethodsThe BR recovery cycle was carried out in 10 healthy volunteers in basal conditions, immediately after rTMS (30 s), 15 and 60 min later. A paired electric supraorbital stimulus paradigm with inter-stimulus intervals (ISI) of 100–600–1000–1500 ms was used. The “real” rTMS consisted of a 200 stimuli long train delivered at 1 Hz and intensity 80% of rest Motor Threshold of the FDI muscle, using a focal coil applied over the primary motor cortex region. The basal BR recovery cycle was also compared with that obtained after a “sham” rTMS.ResultsThe recovery of the R2 component of the BR was significantly suppressed 30 s after rTMS. This effect was also observed at 15 min, though of lower magnitude and only at long ISIs (1000-1500 ms). No significant effect on R2 recovery was observed 60 min after real rTMS as well as after sham rTMS.ConclusionsrTMS of motor cortex modulates the excitability of BR through its action on cortical excitability and on the cortical facilitatory drive to the brainstem reflex pathways.SignificanceSlow (1 Hz), sub-threshold rTMS of motor cortex determines a long-lasting reduction of excitability of BR.     

The role of pedunculopontine nucleus in isolated REM sleep behavior disorder and REM sleep without atonia

IntroductionThe aim of this study was to analyze the functions of pedunculopontine nucleus (PPN) in isolated REM sleep behavior disorder (iRBD) and REM sleep without atonia (RSWA) to investigate the role of PPN in dream-enacting motor behaviors in RBD. We evaluated the activity of PPN through the prepulse modulation (PPM) together with other brainstem reflexes to investigate the differences in changes at brainstem.MethodsWe included nine patients with isolated RSWA and 10 patients with iRBD. For diagnosis, all patients underwent polysomnography. None of the patients had parkinsonism or dementia. We also included 17 healthy participants with similar age and sex. Blink reflex (BR), PPM of BR, recovery excitability of BR, and auditory startle reflex (ASR) were recorded in all participants.ResultsThere was a prepulse inhibition deficit in iRBD and RSWA groups compared to healthy subjects. The BR-R2 recovery at 200 ms interval was also higher in patients with iRBD and RSWA. In ASR recordings, the response probabilities were higher in the RBD group compared to RSWA and control groups.ConclusionThe PPM was abnormal in both iRBD and RSWA whereas ASR was enhanced in iRBD. We suggest that there are certain similarities and differences in the pathophysiologies of iRBD and RSWA.     

Blink reflex in patients with postparalytic facial syndrome and blepharospasm: Trigeminal and auditory stimulation

ObjectiveThe enhancement of blink reflex (BR) excitability was shown in patients with postparalytic facial syndrome (PFS) and essential blepharospasm (EB). We prospectively investigated patients with PFS and EB whether BR alterations demonstrated by trigeminal stimulation will similarly be observed upon auditory stimulation.MethodsFifteen patients with PFS, 15 patients with EB, and 30 healthy volunteers were involved. Electrically stimulated trigeminal BR and auditory BR were studied bilaterally.ResultsThe mean R2 amplitude and duration values were highest in EB patients, being significantly higher than PFS patients (p < 0.05) and control group (p < 0.01). The mean R2 duration in PFS patients were also significantly longer in compared to control group (p = 0.025). EB patients showed a higher mean R (auditory) amplitude and duration than PFS patients (p < 0.05) and controls (p < 0.04). The mean R (auditory) duration was longer on symptomatic side of PFS patients in compared to controls (p = 0.05).ConclusionsWe observed that there is an enhanced excitability of BR circuit in postparalytic facial syndrome and essential blepharospasm, which could be evoked by auditory stimulation in addition to trigeminal stimulation.SignificanceThe enhanced excitability in patients with EB and PFS probably originates from the final common pathway of BR circuit, namely facial motor or premotor neurons.     

Reorganization of sensorimotor gating after peripheral facial palsy starts at brainstem*

Background and objective We aimed to analyze the alterations in sensorimotor gating at brainstem after peripheral facial palsy (PFP). To examine sensorimotor gating, we used prepulse modulation (PPM) of blink reflex (BR). We also recorded BR recovery to identify excitability changes in the facial nucleus.

Patients and method We included 33 patients and 39 recordings. Control group was composed of 16 healthy subjects. Simultaneous bilateral baseline BR, BR recovery at ISI of 300-ms and BR-PPM at ISI of 100-ms recordings were performed after stimulation of trigeminal nerve on right sides of healthy subjects and on both sides of patients. Severity of PFP and time lapse from the onset was noted.

Results Mean R1 amplitude was increased, whereas mean R2 and R2c magnitude were reduced in all groups after prepulse stimulation. However, multivariate ANOVA showed significance at group level (patients and healthy subjects), at prepulse level (no prepulse and 100-ms prepulse) and group and prepulse level. Suppression of R2 or R2c was lower on both sides of patients compared to healthy subjects and the deficit first started on the symptomatic side.

Conclusion Suppression of R2 and R2c after prepulse stimulation is reduced in PFP suggesting decreased filtering of facial sensory input at brainstem level. Trigeminal sensitization at brainstem develops early after PFP.     

Sensorimotor gating deficits in multiple system atrophy: Comparison with Parkinson's disease and idiopathic REM sleep behavior disorder

BackgroundPrepulse inhibition (PPI) of the auditory blink reflex is a measure of sensorimotor gating, which reflects an organism's ability to filter out irrelevant sensory information. PPI has never been studied in patients with multiple system atrophy (MSA), although sensorimotor deficits are frequently associated with synucleinopathies. We investigated whether alterations in PPI were more pronounced in MSA compared with Parkinson's disease (PD), idiopathic rapid eye movement sleep behavior disorder (iRBD) and healthy controls.Methods10 patients with MSA, 12 patients with iRBD, 40 patients with PD, and 20 healthy controls completed the study. A passive acoustic prepulse inhibition paradigm was applied with prepulses 5 dB and 15 dB above background noise at 30-, 60-, 120- and 300-ms intervals.ResultsNon-parametric analyses showed that MSA patients had significantly lower prepulse inhibition, as measured with max-amplitude, than PD patients and iRBD patients on the 60 ms–85 dB and 120 ms–85 dB inter-stimulus intervals. The same relation was found when using area under the curve. No differences were found between groups for the 30 ms–85 dB and 300 ms–85 dB. Furthermore, blink reflex characteristics such as habituation did not differ between patients and controls.ConclusionsThe present study showed that sensorimotor gating, as measured with PPI, is markedly reduced in MSA. This may be due to the pronounced severity of striatal and brainstem dysfunction, as well as the degeneration of other structures related to the PPI modulating pathways in MSA. PPI may be a non-invasive neurophysiological measure that can aid in the differential diagnosis between PD and MSA.     

Blink reflex alterations in recently diagnosed diabetic patients

Objective. The aim of the present study was to determine the frequency of blink reflex alterations and to examine the influence of hyperglycemia in inducing the alterations in recently diagnosed Type 2 diabetes mellitus patients.Methods. A cross-sectional study was carried out on patients having asymptomatic diabetes with a period of evolution under 10 years. In all 47 patients (26 women and 21 men), serum glycemia levels were determined and the latency onset of the blink reflex components were measured.Results. The average patient age was 44.5±11.0 (mean ± SD) years with a diabetes evolution period of 4.3±2.9 (mean ± SD) years. After a fasting serum glucose test, the diabetic patients were catalogued as normoglycemic (⩽126 mg/dl) or as hyperglycemic (>26 mg/dl) and subjected to a blink reflex test. The results obtained from the diabetic patients were compared with those from a non-diabetic control group. 14.8–31.9% of the diabetic patients showed alterations in blink reflex component latencies. The differences compared with the control group were significant (p<0.05).Conclusions. Diabetes, as is well-known, can affect the central and peripheral nervous system and there does not appear to be a link between glycemic levels and blink reflex components. However, blink reflex alterations were present even in diabetic patients with a relatively short period of disease evolution.     

Variability of the blink reflex in patients with migraine

Background and purposeSensitization of brainstem trigeminal nuclei and activation of the trigeminovascular system are thought to play an important role in migraine. The blink reflex has become a valuable tool for investigating trigeminal nerve function. The aim of the study was to assess the differences in electrophysiological examinations of the trigeminal nerve (blink reflex) in a group of patients with migraine in comparison with a healthy control group.Material and methodsThe examination was conducted among 58 patients. Patients were diagnosed in the Polyclinic or hospitalized in the Department of Neurology of Warsaw Medical University in Bielański Hospital. The study group included 29 patients suffering from migraine (diagnosed according to the International Classification of Headache Disorders, 2^nd edition) and 29 patients without headaches served as controls. All patients underwent neurological examination and magnetic resonance imaging to identify organic disorders. The blink reflex was tested among all patients in accordance with electrophysiological laboratory standards.ResultsThe latency of the R1 response was significantly shorter among patients with migraine. The latency of R2 and R2’ responses was similar in patients and controls. A significant inverse correlation was observed between latency of R2 and R2’ responses and frequency of migraine attacks.ConclusionsThe inverse correlation between the frequency of attacks and the latency of R2 and R2’ responses of the blink reflex confirms the abnormal eaxcitability induced by the high frequency of migraine attacks.     

Central pain processing in chronic tension-type headache

ObjectiveChronic tension-type headache (CTTH) affects 3% of the population. Directly and indirectly it causes high costs and considerable loss of quality of life. The mechanisms of this disorder are poorly understood and the treatment possibilities are therefore limited. The blink reflex (BR) reflects neuronal excitability due to nociceptive input in the brainstem. The aim of this study was to investigate nociceptive processing at the level of the brainstem in an experimental pain model of CTTH symptoms.MethodsThe effect of conditioning pain, 5 min infusion of hypertonic saline into the neck muscles, was investigated in 20 patients with CTTH and 20 healthy controls. In addition, a pilot study with isotonic saline was performed with 5 subjects in each group. The BR was elicited by electrical stimuli with an intensity of four times the pain threshold, with a superficial concentric electrode. We measured the BR, sensibility to pressure and electrical pain scores before, during and 25 min after the saline infusion.ResultsThe pain rating of the electrical stimuli and the pain score of the hypertonic saline infusion were significantly higher in CTTH patients than in healthy volunteers. The primary endpoint was the relative change of the blink reflex integral immediately after hypertonic saline infusion. It was significantly smaller in CTTH patients on the contralateral side (−24.5% ±7.0 (sem)) compared to healthy volunteers (0.4% ±6.8), (p < 0.05, Holm–Sidak), while there was no significant difference on the ipsilateral side (−5.9% ±3.2 vs. −3.4% ±3.0, n.s., Holm–Sidak).ConclusionThere was no robust difference in BR integral after conditioning tonic neck pain between CTTH patients and healthy volunteers, but CTTH patients were more sensitive to nociceptive stimuli.SignificanceA combined homotopic and heterotopic effect of the conditioning pain onto the blink reflex could account for this finding.     

Central nervous system abnormalities in vaginismus

ObjectiveTo investigate possible altered CNS excitability in vaginismus.MethodsIn 10 patients with primary idiopathic lifelong vaginismus, 10 with vulvar vestibulitis syndrome accompanied by vaginismus and healthy controls we recorded EMG activity from the levator ani (LA) and external anal sphincter (EAS) muscles and tested bulbocavernosus reflex (BCR). Pudendal-nerve somatosensory evoked potentials (SEPs) were tested after a single stimulus. Pudendal-nerve SEP recovery functions were assessed using a paired conditioning-test paradigm at interstimulus intervals (ISIs) of 5, 20 and 40 ms.ResultsEMG in patients showed muscular hyperactivity at rest and reduced inhibition during straining. The BCR polysynaptic R2 had larger amplitude (p < 0.01) and longer duration (p < 0.01) in patients from both groups than in controls. In controls, paired-pulse SEPs were suppressed at the 5 ms ISI for N35–P40 (p < 0.05) and P40–N50 ms (p < 0.001) and facilitated at the 20 ms ISI for N35–P40 (p < 0.05) and P40–N50 (p < 0.05). No significant differences were found in the paired-pulse N35–P40 in patients and controls but the cortical P40–N50 at 20 ISI was facilitated in patients (p < 0.05).ConclusionsEMG activity is enhanced and the cortical SEP recovery cycle and BCR are hyperexcitable in vaginismus.SignificanceThe neurophysiological abnormalities in patients with vaginismus indicate concomitant CNS changes in this disorder.     

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.     

Quantification of the auditory startle reflex in children

ObjectiveTo find an adequate tool to assess the auditory startle reflex (ASR) in children.MethodsWe investigated the effect of stimulus repetition, gender and age on several quantifications of the ASR. ASR’s were elicited by eight consecutive auditory stimuli in 27 healthy children. Electromyographic activity of orbicularis oculi, masseter, sternocleidomastoid, deltoid, abductor pollicis brevis, quadriceps muscles and the sympathetic skin response were recorded. ASR parameters (response probability in % and magnitude in area-under-the-curve) were: (1) combined response of all six muscles (2) blink response.ResultsResponse probabilities were 78% in orbicularis oculi (median latency 41 ms), 17% in sternocleidomastoid (median latency 66 ms), 10% in masseter (median latency 66 ms) and lower in other muscles. The ASR combined response probability and the sympathetic skin response significantly decreased with the repetitive stimuli, but the blink response probability did not. The magnitude (area-under-the-curve) of both the blink response and the combined response did not decrease with the repetitive stimuli. There were no gender or age effects.ConclusionAs in adults, the blink response and the combined response of multiple muscles show different habituation patterns in children.SignificanceInvestigation of multiple muscles seems appropriate to quantify the ASR in children.     

Cutaneous silent period changes in Type 2 diabetes mellitus patients with small fiber neuropathy

ObjectiveSmall myelinated (A-δ) and unmyelinated (C) somatic sensory fibers are initially affected and may be the earliest exhibited sign of neuropathy in glucose dysmetabolism. Cutaneous silent period (CSP) is an inhibitory spinal reflex and its afferents consist of A-δ nerve fibers. The aim of this study was to evaluate CSP changes in Type 2 diabetic patients with small fiber neuropathy.MethodsForty-three patients and 41 healthy volunteers were included. CSP latency and duration, as well as CSP latency difference of the upper and lower extremities, were examined.ResultsNerve conduction studies were within normal limits in both groups. Lower extremity CSP latency was longer (122.1 ± 15.5 vs. 96.4 ± 6.4 ms; p < 0.001), CSP duration was shorter (29.5 ± 8.9 vs. 43.1 ± 5.0 ms; p < 0.001), and latency difference was longer (48.1 ± 12.6 vs. 22.7 ± 3.7; p < 0.001) in patients than controls. The difference was more significant in patients with neuropathic pain. No significant difference existed in upper extremity on CSP evaluation.ConclusionThe CSP evaluation together with nerve conduction study, has been demonstrated to be beneficial and performance of latency difference in addition to CSP latency and duration may be a valuable parameter in electrophysiological assessment of diabetic patients with small fiber neuropathy.SignificanceAn additional CSP evaluation may be considered in cases which nerve conduction studies do not provide sufficient information.     

The stimulus intensity modifies the blink reflex recovery cycle in healthy subjects and in blepharospasm

OBJECTIVE: The excitability of human brainstem interneurons is measured by the blink reflex recovery cycle and is abnormal in blepharospasm. We wondered whether the results of this paradigm depend on the stimulus intensity. METHODS: We investigated the blink reflex recovery cycle in 13 healthy control subjects and in 13 patients with blepharospasm (7 of them treated with botulinum toxin) using 4 levels of stimulus intensity (5, 12, 19 and 26 mA) and two interstimulus intervals (ISIs, 150 or 250 ms). RESULTS: In all groups the inhibition of the second R2 response was reduced with strong stimulus intensities: In controls, the inhibition of the second R2 decreased significantly (e.g. young controls, ISI 150 ms, from 89.6+/-15.6% at 5 mA to 21.9+/-49.7% at 26 mA, mean+/-standard deviation). In patients the R2 inhibition found at 5 mA was converted in an R2 facilitation at 26 mA, irrespective of the status of treatment. In addition, the patients' results at 5 mA did not differ significantly from the controls' results at 26 mA. CONCLUSIONS: The R2 inhibition and its sensitivity to detect abnormal interneuronal excitability depend on the stimulus intensity, which may act by modifying the excitability of the R2 interneurons.     

Gain modulation of the middle latency cutaneous reflex in patients with chronic joint instability after ankle sprain

ObjectiveTo investigate the neural alteration of reflex pathways arising from cutaneous afferents in patients with chronic ankle instability.MethodsCutaneous reflexes were elicited by applying non-noxious electrical stimulation to the sural nerve of subjects with chronic ankle instability (n = 17) and control subjects (n = 17) while sitting. Electromyographic (EMG) signals were recorded from each ankle and thigh muscle. The middle latency response (MLR; latency: 70–120 ms) component was analyzed.ResultsIn the peroneus longus (PL) and vastus lateralis (VL) muscles, linear regression analyses between the magnitude of the inhibitory MLR and background EMG activity showed that, compared to the uninjured side and the control subjects, the gain of the suppressive MLR was increased in the injured side. This was also confirmed by the pooled data for both groups. The degree of MLR alteration was significantly correlated to that of chronic ankle instability in the PL.ConclusionsThe excitability of middle latency cutaneous reflexes in the PL and VL is modulated in subjects with chronic ankle instability.SignificanceCutaneous reflexes may be potential tools to investigate the pathological state of the neural system that controls the lower limbs in subjects with chronic ankle instability.     

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.     

The effect of paired stimuli on blink reflex latencies in normal subjects

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