Influence of age and gender on the jaw-stretch and blink reflexes

The aim of this study is to investigate the influence of age and gender on jaw-stretch and blink reflexes (BR). Thirty “young” (26.5±0.7 years) and thirty “old” (47.8±1.8 years) healthy adults were included. Short-latency stretch reflex responses were evoked in the masseter and temporalis muscles by fast jaw-stretches, and BR in orbicularis oculi muscle 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. For the jaw-stretch reflex, the pre-stimulus EMG activity in the old subjects was significantly lower than that of the young subjects in the right and left masseter and temporalis muscles (P<0.006), whereas there was no difference in the results between males and females. The normalized peak-to-peak amplitude of the EMG in the left masseter and left and right temporalis muscles was significantly lower in the old subjects compared with the young subjects (P<0.02). Females had significantly higher normalized peak-to-peak EMG amplitudes compared with males in the right masseter and left temporalis muscles (P<0.05). The old subjects had significantly lower root mean square (RMS) (P=0.01) and average (P<0.02) BR values in the right and left orbicularis oculi muscles, and lower area under the curve (AUC) (P=0.02) values in the left orbicularis oculi muscle compared with the young subjects. Female subjects had significantly lower AUC (P=0.02) in the left orbicularis oculi muscle compared with males. The old subjects had significantly later offset (P<0.003) and longer duration (P<0.001) in the left orbicularis oculi compared with the young subjects. The results of the present study demonstrated a significant effect of both age and gender on stretch and BR and suggested that these variables should be taken into consideration in the interpretation of brainstem reflexes in basic and clinical studies.     

Tuning the gain of somato-sympathetic reflexes by stimulation of the thoracic spine in humans

In animals, somatic stimulation of the limbs can evoke sympathetic reflexes of supraspinal origin. In addition, spinal reflexes can be elicited by stimulation of somatic tissues of the trunk. However, limited evidence is available concerning the specific modulation of sympathetic reflexes by afferents from the thoracic spine. This has also been largely overlooked in healthy humans. The aim of the present study was to determine whether tonic noxious heat (NH) applied to the skin over T3–T5 could segmentally increase supraspinal sympathetic reflexes (skin conductance responses – SCRs) induced by phasic electrical stimulation of the sural nerve. In addition, the effect of spinal manipulation (SM) on SCR amplitude and SCR amplification by NH was investigated. During the control session, palmar and plantar SCR amplitude was stable, showing no significant modulation. During NH and SM, however, palmar SCR amplitude was respectively increased and decreased in comparison to baseline, leading to a robust difference in SCR amplitude between the 2 conditions (p < 0.001). Moreover, these changes were also significantly and marginally different compared to the control session (p = 0.041 and p = 0.053, respectively). Interestingly, when applied immediately before NH, SM had a preventive effect on palmar SCR amplification induced by NH. In sharp contrast, changes in plantar SCRs were not significantly different between sessions (p = 0.42). Altogether, these results indicate that somatic stimulation of the thoracic spine may modulate somato-sympathetic reflexes segmentally in conscious, healthy volunteers.     

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

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

A hierarchy of neural control of mastication in the rat

In rats anaesthetized with ketamine, rhythmic jaw-opening and jaw-closing movements were induced by palatal stimulation. The two masseter muscles (jaw-closing) and the four digastric muscles (jaw-opening) were fitted with electrodes, which could be used either for electrical stimulation or for recording electromyographic responses. Electrical stimulation of the masseters in the phase when the digastrics were the contracting muscles, caused responses in the digastrics. The amplitude of these responses was dependent on whether the stimulated masseters were active or not. The responses in digastric persisted when contraction of the masseters during stimulation was prevented by dantrolene sodium but they disappeared when the masseteric nerves were blocked with xylocaine. The responses in digastric are thus reflexes from stimulating afferent fibres in the masseteric nerves. Likewise, electrical stimulation of the four digastrics in the phase when the masseters were contracting, caused responses in the masseters. The amplitude of these responses, however, was independent of the state of activity of the stimulated digastrics. Furthermore, the responses in masseter disappeared when contraction of the digastrics was prevented by dantrolene sodium; but they persisted when the digastric nerves were blocked with xylocaine, provided the digastrics continued to twitch to the electric stimuli. The responses in masseter are thus reflexes in masseter caused by mechanical stretch transmitted from the digastric twitches. In the rhythmic preparation, prevention of contraction of the masseters of digastrics by dantrolene sodium or xylocaine leaves the overall frequency and amplitude of the evoked rhythmic activity unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)     

Acoustic startle response in patients with orthostatic tremor

Background and aim

Orthostatic tremor is a high frequency tremor predominantly on calf muscles during standing. Brainstem is the most probable generator in the pathogenesis since it comprises bilaterally projecting centers regulating stance or tone. We aimed to investigate the functional role of brainstem through the evaluation of acoustic startle response in primary orthostatic tremor patients.

Patients and method

We included 7 (2 males) consecutive patients and 13 (5 males) healthy volunteers. Diagnosis was confirmed by polymyographic surface electromyography. All subjects underwent acoustic startle response and blink reflex investigations.

Results

Presence rate (71.4% vs. 100%, p = 0.042) and response rate (27.5% vs. 40.5%, p = 0.047) of total acoustic startle response were lower in patient group. Similarly, probability over orbicularis oculi was lower among patients (p = 0.003). However, blink reflex was observed in all patients and healthy volunteers and latencies of startle and blink reflexes were similar between groups.

Conclusions

In our patient group, normal response rate and latencies of R1 and R2 show structural integrity of at least blink reflex circuit at brainstem. On the other hand, suppressed response rates probably reflect decreased excitability of auditory startle reflex pathway.     

Glutamate receptor blockade in the rostral ventromedial medulla reduces the force of multisegmental motor responses to supramaximal noxious stimuli

The rostral ventromedial medulla (RVM) has been established as part of a descending pain-modulatory pathway. While the RVM has been shown to modulate homosegmental nociceptive reflexes such as tail flick or hindpaw withdrawal, it is not known what role the RVM plays in modulating the magnitude of multisegmental, organized motor responses elicited by noxious stimuli. Using local blockade of glutamate receptors with the non-specific glutamate receptor antagonist kynurenate (known to selectively block nociceptive facilitatory ON-cells), we tested the hypothesis that the RVM facilitates the magnitude of multi-limb movements elicited by intense noxious stimuli. In male Sprague–Dawley rats, we determined the minimum alveolar concentration (MAC) of isoflurane necessary to block multi-limb motor responses to noxious tail clamp. MAC was determined so that all animals were anesthetized at an equipotent isoflurane concentration (0.7 MAC). Supramaximal mechanical stimulation of the hindpaw or electrical stimulation of the tail elicited synchronous, repetitive movements in all four limbs that ceased upon, or shortly after (<5 s) termination of the stimulus. Kynurenate microinjection (2 nmol) into the RVM significantly attenuated, by 40–60%, the peak and integrated limb forces elicited by noxious mechanical stimulation of the hindpaw (p < 0.001; two-way ANOVA; n = 8) or electrical stimulation of the tail (peak force: p < 0.011, two-way ANOVA; n = 8), with significant recovery 40–60 min following injection. The results suggest that glutamatergic excitation of RVM neurons, presumably ON-cells, facilitates organized, multi-limb escape responses to intense noxious stimuli.     

Remote effects of self-paced teeth clenching on the excitability of hand motor area

We studied remote effects of teeth clenching on motor cortical and spinal cord excitability using transcranial magnetic stimulation (TMS), brainstem electrical stimulation (BES), and ulnar nerve stimulation (F-wave) in eight normal volunteers. The TMS, BES, and ulnar nerve stimulation at the wrist were given at different intervals (0–200 ms) after the onset of masseter contraction. Surface electromyographic responses were recorded from the first dorsal interosseous muscle. Responses at different intervals were compared with the response elicited when the subject made no teeth clenching (control response). In TMS, conditioned responses (during teeth clenching) were significantly larger than the control at all intervals. In contrast, in BES and F-waves, conditioned responses were not larger than the control at an early phase (intervals shorter than 50 ms), whereas they were larger than the control at later intervals (longer than 50 ms). These results suggest that facilitation occurs in the hand motor area at the early phase of teeth clenching, and spinal facilitation dominates at its late phase. This time course of facilitation may indicate that the motor cortex must regulate hand muscles finely at the early phase of teeth clenching, and spinal cord may stabilize them firmly at the late phase. The excitability changes of the hand motor area may be in parallel with that of the masseter motor area which reflects the pattern of masseter contraction when the subject activates the masseter muscle phasically at the early phase and sustains that contraction at the late phase. Electronic Publication     

Brainstem evaluation in children with primary nocturnal enuresis

We investigated the brainstem integrity in children with primary nocturnal enuresis (PNE) using auditory brainstem responses (ABR), blink reflex and exteroceptive suppression of the masseter muscle. We examined 23 children with PNE (16 male, 7 female; mean age: 10.4 years) and 19 control subjects (11 male, 8 female; mean age: 11.8 years). ABR parameters such as wave latencies, amplitudes and interpeak latencies and blink reflex parameters such as R1 and R2 amplitude and latencies were not significantly different between the 2 groups. Although S2 parameters of the exteroceptive suppression of the masseter muscle were easily and completely obtained from the control subjects, in the PNE group S2 onset latency and duration were not recorded in 26% of the study children (n = 6) (P = 0.01). S2 duration time was significantly lowered in the enuretic group (left side: P = 0.001 and right side: P = 0.003). S2 duration time changes in the enuretic group supports a possible brainstem dysfunction in children with PNE.     

Somatosensory eye blink reflex in peripheral facial palsy

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

A Short Latency Vestibulomasseteric Reflex Evoked by Electrical Stimulation Over the Mastoid in Healthy Humans

We describe EMG responses recorded in active masseter muscles following unilateral and bilateral electrical vestibular stimulation (EVS, current pulses of 5 mA intensity, 2 ms duration, 3 Hz frequency). Averaged responses in unrectified masseter EMG induced by unilateral EVS were examined in 16 healthy subjects; effects induced by bilateral (transmastoid) stimulation were studied in 10 subjects. Results showed that unilateral as well as bilateral EVS induces bilaterally a clear biphasic response (onset latency ranging from 7.2 to 8.8 ms), that is of equal amplitude and latency contra- and ipsilateral to the stimulation site. In all subjects, unilateral cathodal stimulation induced a positive—negative response termed p11/n15 according to its mean peak latency; the anodal stimulation induced a response of opposite polarity (n11/p15) in 11/16 subjects. Cathodal responses were significantly larger than anodal responses. Bilateral stimulation induced a p11/n15 response significantly larger than that induced by the unilateral cathodal stimulation. Recordings from single motor units showed that responses to cathodal stimulation corresponded to a brief (2–4 ms) silent period in motor unit discharge rate. The magnitude of EVS-induced masseter response was linearly related to current intensity and scaled with the mean level of EMG activity. The size of the p11/n15 response was asymmetrically modulated when subjects were tilted on both sides; in contrast head rotation did not exert any influence. Control experiments excluded a possible role of cutaneous receptors in generating the masseter response. We conclude that transmastoid electrical stimulation evokes vestibulomasseteric reflexes in healthy humans at latencies consistent with a di-trisynaptic pathway.     

Blink reflex in hyperthyroidism

Although there are studies regarding the effects of thyroid hormones on some neurologic reflexes, literature lacks knowledge of the effects of thyroid hormones on blink reflex circuits. To understand the behaviour of excess thyroid hormone on this circuit that involves synapses in brainstem, we studied electrically elicited blink reflexes of 7 patients with hyperthyroidism, 8 patients with hyperthyroidism who were under therapy and 14 volunteers as control by electroneuromyograph. Mean values of the latencies and amplitudes of the R1 and R2 responses were not statistically different between groups, while the duration of R2 response and controlateral R2 response were found shorter in patients with hyperthyroidism comparing to the patients under therapy and controls. We have thought that these findings might reflect the inhibitor effect of the excess thyroid hormone on polysynaptic reflex arc of the blink response.     

Filters for optimal smoothing of acoustic and electric blink reflex EMG responses to determine blink response magnitude

The functional (i.e., kinematic) aspects of the blink reflex depend on the size of the integrated orbicularis oculi EMG response. Peak amplitude of smoothed rectified EMG is often used as an approximation of integrated EMG. A comparison was made between the outputs of 24 different smoothing filters, correlating peak amplitude of acoustic or electric blink reflexes with integrated EMG. The coefficient of determination (R²) was largest (i.e., ≥.95 for acoustic and ≥.90 for electric blink reflexes) when using either (1) a first-order resistor-capacitor filter with a time constant of 50 or 100 ms, (2) a boxcar filter averaging 51 or 101 data points, or (3) an unequal-weight finite impulse response filter with a cutoff frequency of 5 or 10 Hz. These filters are thus recommended when determining peak amplitude. Applying a baseline correction on peak amplitude and integrated EMG produced slightly smaller values of R² compared with uncorrected measures.     

Jaw-opening reflex after CO2 laser stimulation of the perioral region in man

CO₂ laser pulses selectively excite A-δ and C mechano-thermal nociceptors in the superficial layers of the skin. To study the jaw-opening reflex elicited by a purely nociceptive input, we delivered laser pulses to the perioral region in 15 subjects. Sensory threshold was very low (9 mJ/mm²). High-intensity noxious laser pulses (more than 4 × sensory threshold) evoked a single phase of electromyogram suppression (laser silent period, LSP) at an onset latency of 70 ms in the contracted masseter and temporal muscles, bilaterally. Even maximum-intensity laser pulses failed to activate the suprahyoid muscles. The recovery curves to paired laser stimuli showed that at short interstimulus intervals the test LSP was strongly suppressed. At about 380 ms it recovered to 50%, i.e. its recovery curve resembled that of the masseter late silent period after electrical mental nerve stimulation (SP2). In experiments studying the interaction with heterotopic stimuli and non-nociceptive responses, chin-taps or electrical shocks delivered to the supraorbital, infraorbital or mental nerves before laser stimulation strongly suppressed the LSP. A preceding perioral laser pulse strongly suppressed the masseter SP evoked by supraorbital stimulation and the SP2 evoked by mental stimulation, but left SP1 unaffected. We conclude that the perioral A-δ fibre input elicits a jaw-opening reflex simply by inhibiting the jaw-closers. The LSP response is mediated by a multisynaptic chain of brainstem interneurons and shares with the masseter SP2 part of the central circuit in the ponto-medullary region. We also propose that a common centre processes the various inputs for jaw opening. Received: 18 July 1997 / Accepted: 20 October 1997     

Photoperiodic modulation of reproductive physiology and behaviour in the cichlid fish Cichlasoma dimerus

Timing of breeding to an optimal season is a requirement for a successful reproductive outcome in seasonally breeding species. Photoperiodic signals are capable of modifying the reproductive behaviour and reproductive systems in several vertebrate species. The cichlid fish Cichlasoma dimerus shows highly organized breeding activities and different social status. The aim of this study is to test whether C. dimerus reproductive behaviour (male aggressive behaviour and female choice) and reproductive physiology (GnRH3 morphometric parameters, pituitary hormones content and organ-somatic indexes) are modulated by photoperiod. Before spawning, dominant pairs were isolated and kept in opposite tanks of 20 l for one week, so they could see each other but not physically interact. Afterwards, a group was exposed for four weeks to a short photoperiod (8 h light:16 h dark) (short photoperiod exposed animals: SP) while another group was exposed to a long photoperiod (14 h light:10 h dark) (long photoperiod exposed animals: LP). Temperature was maintained constant. Behavioural experiments showed that male aggression related to territory selection and its defence is reduced in SP males. Further, SP females were never chosen. At the brain level we demonstrated that GnRH3 neuronal optical density of staining was reduced. Finally, at the pituitary level we showed that SP males showed low levels of β-LH, PRL and GH in the pituitary, and that SP females showed no significant differences in the pituitary content of any hormone. Taken all together these results suggest that in C. dimerus the photoperiod is a relevant environmental cue related to reproductive behaviour and physiology.     

Acute peripheral facial palsy: Is there a trigeminal nerve involvement?

The aim of this study was to investigate trigeminal nerve involvement in patients with peripheral facial palsy. In total, 25 patients with facial nerve palsy and 19 controls were tested by electrophysiological methods regarding their facial and trigeminal nerve functions within 1 month after disease onset. The presence of an abnormal blink reflex was determined in patients with peripheral facial palsy by comparing paralytic and non-paralytic sides (12.3 ± 1.1 and 10.8 ± 1.3, respectively; p = 0.001). However, the average masseter inhibitory reflex difference between the paretic and non-paralytic sides of patients compared with the corresponding side-to-side comparison for controls was not statistically significant. The masseter inhibitory reflex response was abnormal in some cases. These findings suggest that the masseter inhibitory reflex, a trigemino–trigeminal reflex, was normal in most of our patients with peripheral facial palsy, but may be abnormal in individual cases. Our study showed that subclinical disorders affecting the trigeminal pathways occur in individual patients with idiopathic facial palsy, while the majority of patients have no trigeminal nerve involvement.     

Electrophysiological findings of acute peripheral facial palsy in diabetic and non-diabetic patients

The aim of this study is to investigate the role of diabetes mellitus on the clinical and electrophysiological findings of peripheral facial palsy (PFP), the effect of the diabetes duration and polyneuropathy on the electrophysiological parameters. A total of 32 diabetic and 40 non-diabetic patients with peripheral facial palsy were included. All patients were divided into two subgroups based on the time of electrophysiological examinations: within the first 15 days versus within 16–30 days. Neuropathy symptoms and the results of neurological examinations and electrophysiological findings were recorded. The findings of electroneurography (EnoG), blink reflex (BR) evaluation, and needle electromyography (EMG) indicated statistically significant blink reflex abnormalities in diabetic patients compared to non-diabetics. Delay in the latency was more remarkable in the R2 component than in the R1 (p < 0.001). The delay in the R1 latency was also observed in the non-affected side for diabetic patients. The longer duration of the diabetes caused significant delay on the blink reflex latency on both the affected and non-affected sides for R1 component (p = 0.019, p = 0.041, respectively). In contrary, neither the diabetes duration nor the age of the patients correlated with the clinical severity of facial palsy, fiber loss, fibular nerve compound muscle action potential amplitudes, and the nerve conduction velocities.     

Control of trigeminal motoneurons from the cerebellar interpositus nucleus of the guinea pig.

1. Effects of stimulation of the cerebellar interpositus nucleus (IPN) on jaw reflexes and trigeminal motoneurons were studied along with the route responsible for the effects in ketamine-anesthetized guinea pigs. 2. Stimulation in the IPN evoked a bilateral, ipsilaterally dominant, short-latency reciprocal effect on jaw reflexes: a depression of the jaw-closing masseteric reflex and a facilitation of the jaw-opening digastric reflex. This reciprocal phase was followed by a non-reciprocal facilitatory phase. 3. Stimulation in the IPN evoked a short-latency, strychnine-sensitive inhibitory postsynaptic potential (IPSP) followed by a rebound depolarizing potential in the jaw-closing masseter motoneurons (MAMNs) and an excitatory postsynaptic potential (EPSP) in the jaw-opening anterior digastric motoneurons (ADMNs). The time course of the intracellular response of MAMNs to the IPN stimulation was similar to that of the IPN-induced effects on the jaw-closing reflex. In contrast, the duration of the IPN-induced EPSP in ADMNs was shorter than the IPN-induced facilitation of the jaw-opening reflex. 4. After the IPN neurons were lost by injection of kainic acid into the nucleus, the reciprocal effect of the IPN stimulation on the jaw reflexes could not be seen, even though the projection fibers from the trigeminal sensory nucleus to the IPN remained essentially intact. 5. Stimulation in the superior cerebellar peduncle (SP) induced the same reciprocal effect on the jaw reflexes as the IPN stimulation. A lesion of the SP virtually abolished the reciprocal effect on the jaw reflexes of stimulation in the IPN ipsilateral with reference to the SP lesion. 6. Transection of the brain stem at the level immediately caudal to the red nucleus did not affect the reciprocal effect of the IPN stimulation on the jaw reflexes. 7. We conclude that the IPN output bilaterally induces an inhibition of jaw-closing MAMNs and an excitation of jaw-opening ADMNs, oligosynaptically by way of a direct cerebelloreticular projection system via the SP.     

健康青少年与老年人单音、图像、汉字结构识别的事件相关电位研究

目的了解不同类型刺激对健康老年及青少年的事件相关电位（ＥＲＰ）的影响。方法对６０名青少年及４７名老年健康志愿者做单音、图像及汉字结构识别视觉刺激的ＥＲＰ研究。结果１、外源性成分的比较：（１）单音：男性及女性的Ｐ２ＰＬ均是老年组长于青少年组（Ｐ＜０．０５）；（２）图像：男性Ｆｚ、Ｃｚ部位的Ｎ１ＰＬ和女性Ｐ２ＰＬ均是老年组短于青少年组（Ｐ＜０．０５）；（３）汉字结构：男性Ｐ２ＰＬ和女性Ｎ１、Ｐ２ＰＬ老年组短于青少年组（Ｐ＜０．０５）。２、内源性成分及ＲＴ的比较：（１）单音：男性及女性Ｎ２、Ｐ３ＰＬ及ＲＴ均是老年组长于青少年组（Ｐ＜０．０５）；（２）图像：男性Ｎ２ＰＬ及Ｃ３、Ｐｚ部位的Ｐ３ＰＬ、ＲＴ和女性Ｐ３ＰＬ及ＲＴ，老年组长于青少年组（Ｐ＜０．０５）；（３）汉字结构：男性Ｐ３ＰＬ及ＲＴ，老年组长于青少年组（Ｐ＜０．０５），女性Ｆｚ部位的Ｎ２ＰＬ，老年组短于青少年组（Ｐ＜０．０５）；Ｐ３ＰＬ及ＲＴ，老年组长于青少年组（Ｐ＜０．０５）。结论ＥＲＰ的性别差异及年龄差异随刺激的不同而变化。     

H-reflexes in masseter and temporalis muscles in man

In contrast with limb muscles, studies on H-reflexes in the trigeminal system are scarce. The present report aimed at reevaluating the responses obtained in the masseter and temporalis muscles after electrical stimulation of their nerves. Twenty-four subjects participated in the experiments. The reflexes were elicited in the masseter and temporal muscles by monopolar stimulation and recorded using surface electrodes. Stimulation of the masseteric nerve evoked an M-response in the masseter and an H-reflex in both the masseter and the temporal muscles. In contrast with the masseter muscle, where the homonymous H-reflex disappeared at higher stimulation intensities, the heteronymous temporal H-reflex remained and reached a plateau. Simultaneous stimulation of the masseteric and deep temporal nerves resulted in an M-response and an H-reflex in both the masseter and temporal muscles. Increasing stimulus intensitites led to disappearance of the H-reflex in both muscles. The results were compared with those obtained by others on limb muscles. As in these muscles, the presence of heteronymous H-reflexes in the jaw muscles can be used in future studies of motoneuronal excitability.     

Startle blink facilitation during the go signal of a reaction time task is not affected by movement preparation or attention to the go signal

Startle reflex eliciting stimuli presented at the onset of the go signal in a simple forewarned reaction time (RT) task (at a SOA of 0 ms) elicit larger blink reflexes than do stimuli presented later (e.g., at a SOA of 150 ms) or during inter trial intervals. The present study investigated whether this facilitation is affected by attention to the go signal or motor preparation. Participants performed a forewarned reaction time task that crossed the requirements for a speeded response (Hold versus Move) and for a discrimination task performed with the go signal (Report versus No report). Relative to control reflexes, blinks elicited at a SOA of 0 ms were facilitated and blinks elicited at a SOA of 150 ms were inhibited. RTs were slower on trials that required attention to the go signal and in both attention conditions and at both SOAs shortened in the presence of a blink-eliciting stimulus. However, neither attention to the go signal nor motor preparation affected blink facilitation at the 0 ms SOA. This finding suggests that the blink reflex facilitation observed at a SOA of 0 ms with the onset of a go signal reflects on the summation of sub- and supra-threshold activations of the startle pathway.