Measurement of muscle reflex time in radicular disorders of the lumbosacral region]

The results of studies performed by the authors show that time measurements of proprioceptive muscular reflexes (triceps surae and tibialis posterior reflexes) may be considered a valuable addition to methods of topical diagnosis of radicular disturbances in the lumbosacral region. The reflexes were tested in twenty normal subjects. There were found an intraindividual constancy of the respective reflex time with a maximum deviation of 2 ms as well as a lateral variability up to 1.3 ms. Radicular compressions resulted in an increase in reflex time by 2 to 66 ms or failure of the reflex potential to be recorded. The pathological cases were compared with clinical and neurological studies, positive myelographies using radiopaque substances, and results of surgical operations. Compared with the results of surgical operations, changes in reflex time indicated damage to the reflex arc in ninety percent of the cases.     

Use of the conditional reflex to assess the temporal characteristics of curarization effects on heart rate responding

A Pavlovian methodological counterpart to the use of druginduced changes in operant rates of responding was used to assess the temporal characteristics of d-tubocurarine chloride effects on the heart rate conditional reflex in rats. After a stable conditional reflex had been established, the base heart rate, as well as the unconditional and conditional reflex, was monitored during administration of the drug. A sizable behavioral effect was reflected in all three measures, including a temporary abolition of the conditional and unconditional reflexes. An interpretation of these results was discussed, and further development and application of this specific methodology was explored.     

Development of selective attention in young infants: Enhancement and attenuation of startle reflex by attention

This study examined the effect of level of attention engagement on the modification of the blink reflex in young infants. Infants at 8, 14, 20, or 26 weeks of age were presented with interesting visual or auditory stimuli. At delays defined by changes in heart rate known to be associated with sustained attention or attention disengagement, blink reflexes were elicited by visual or auditory blink reflex stimuli. Blink amplitude varied according to the level of attention, and the match between the foreground and blink reflex stimulus. If the infant was attending to the foreground stimulus, a blink reflex stimulus in the same modality resulted in enhanced blink reflex magnitude. A blink reflex stimulus in the other modality resulted in an attenuated blink reflex magnitude. If attention was not engaged with the foreground stimulus, this modulation of the blink reflex did not occur. This ‘selective modality effect’ showed an increasing tendency to occur between 8 and 26 weeks of age. These results show that selective attention to modalities increases over this age range.     

Influence of delayed muscle reflexes on spinal stability: Model-based predictions allow alternative interpretations of experimental data

Model-based calculations indicate that reflex delay and reflex gain are both important for spinal stability. Experimental results demonstrate that chronic low back pain is associated with delayed muscle reflex responses of trunk muscles. The aim of the present study was to analyze the influence of such time-delayed reflexes on the stability using a simple biomechanical model. Additionally, we compared the model-based predictions with experimental data from chronic low back pain patients and healthy controls using surface-electromyography. Linear stability methods were applied to the musculoskeletal model, which was extended with a time-delayed reflex model. Lateral external perturbations were simulated around equilibrium to investigate the effects of reflex delay and gain on the stability of the human lumbar spine. The model simulations predicted that increased reflex delays require a reduction of the reflex gain to avoid spinal instability. The experimental data support this dependence for the investigated abdominal muscles in chronic low back pain patients and healthy control subjects. Reflex time-delay and gain dependence showed that a delayed reflex latency could have relevant influence on spinal stability, if subjects do not adapt their reflex amplitudes. Based on the model and the experimental results, the relationship between muscle reflex response latency and the maximum of the reflex amplitude should be considered for evaluation of (patho) physiological data. We recommend that training procedures should focus on speeding up the delayed reflex response as well as on increasing the amplitude of these reflexes.     

Psychophysiological mechanisms involved in the affective regulation and food restriction of women at risk of suffering from bulimia nervosa

The aim of the study was to explore the effect of visualizing food images under different mood states and food restriction conditions on the emotional modulation of two defense reflexes (startle reflex and cardiac defense). 72 women at risk of suffering from bulimia nervosa were assigned to two groups: 1) a group under induced positive, neutral, or negative mood state and, 2) a 6-hour-food-deprived group or a non-deprived group. Second-by-second heart rate and electromyogram activity from the orbiculari oculi region were recorded after the auditory stimulus. The results showed that, while viewing food images, non-deprived women under negative mood state potentiated the cardiac defense response and the startle motor reflex. Results are discussed in the context of emotional eating theories and Peter Lang's motivational priming model.     

The effect of motor preparation on changes in h reflex amplitude during the response latency of a warned reaction time task

Monosynaptic Hoffman reflexes (H reflexes) were recorded from the soleus muscle during the response latency of a warned reaction time (RT) task that required plantarflexion of the foot. The task was done under four conditions of predictability of the response signal (RS), created by the factorial combination of foreperiod duration (1 and 4 s) and variability (fixed and variable). RT varied systematically with RS predictability and was facilitated in conditions that favored prediction of the RS. The response latency was divided into two successive phases by the onset of reflex augmentation: a premotor phase of constant reflex amplitude and a succeeding motor phase marked by progressively increasing reflex amplitude. Reflex augmentation during the motor phase was coupled more closely to the imminent movement than to the preceding signal to respond. The duration of the premotor phase was unaffected by RS predictability, but the duration of the motor phase (like RT) was shorter when the RS was more predictable. The maximum H reflex amplitude reached during the motor phase was greater when the RS was more predictable. The tonic level of H reflex amplitude during the premotor phase was greater in conditions that made prediction of the RS difficult. A second experiment showed that this difference was present throughout the foreperiod. These results suggest that conditions that favor prediction of the RS enhance motor preparation. changes in motor preparation (which affect RT) affect the processes underlying reflex amplitudes in the premotor phase and throughout the preceding foreperiod, in conditions that make prediction of the RS difficult, appear to reflect heightened general arousal.     

The Effect of Motor Preparation on Changes in H Reflex Amplitude During the Response Latency of a Warned Reaction Time Task

Monosynaptic Hoffman reflexes (H reflexes) were recorded from the soleus muscle during the response latency of a warned reaction time (RT) task that required plantarflexion of the foot. The task was done under four conditions of predictability of the response signal (RS), created by the factorial combination of foreperiod duration (1 and 4 s) and variability (fixed and variable). RT varied systematically with RS predictability and was facilitated in conditions that favored prediction of the RS. The response latency was divided into two successive phases by the onset of reflex augmentation: a premotor phase of constant reflex amplitude and a succeeding motor phase marked by progressively increasing reflex amplitude. Reflex augmentation during the motor phase was coupled more closely to the imminent movement than to the preceding signal to respond. The duration of the premotor phase was unaffected by RS predictability, but the duration of the motor phase (like RT) was shorter when the RS was more predictable. The maximum H reflex amplitude reached during the motor phase was greater when the RS was more predictable. The tonic level of H reflex amplitude during the premotor phase was greater in conditions that made prediction of the RS difficult. A second experiment showed that this difference was present throughout the foreperiod.

These results suggest that conditions that favor prediction of the RS enhance motor preparation. Changes in motor preparation (which affect RT) affect the processes underlying reflex augmentation in the motor phase. Enhanced preparation may allow more efficient organization of the descending commands to move, causing higher levels of spinal excitability to be reached in a briefer time. The higher tonic reflex amplitudes in the premotor phase and throughout the preceding foreperiod, in conditions that make prediction of the RS difficult, appear to reflect heightened general arousal.     

The role of the perioral reflex in lip motor control for speech.

The analysis of spinal and brainstem reflexes has been shown to be a useful method of quantifying the various inputs to motoneuron pools involved in voluntary motor control. This work is selectively reviewed as a background to a discussion of the role of the perioral reflex in lip motor control for speech. Data on the sensorimotor innervation of the lips and the static and dynamic properties of the perioral reflex are presented in support of the notions that (1) perioral reflex analysis provides a viable technique for analyzing brainstem excitability changes underlying lip muscle contraction for speech, and (2) the perioral reflex loop is an important functional element in lip motor control for speech.     

Effects of subchronic administration of gammahydroxybutyrate (GHB) on spatial working memory in rats

GHB, a popularly known drug as "liquid ecstasy", is a substance with abuse potential. Among the possible described side-effects after the continued consumption of GHB are amnesia and deterioration of memory. Likewise, recent studies indicate the existence of neurotoxicity in certain brain regions after its prolonged treatment. The aim of this study was to examine the effect of the subchronic administration of GHB (10 and 100 mg/kg) on spatial memory and sensoriomotor reflexes in male rats, using the Morris water maze and a battery of sensoriomotor tests, respectively. The results indicated that animals treated with GHB (10 mg/kg) showed a greater latency of escape during the phase of acquisition in the days first and third of tests, as compared with the control group (p<0.05), as well as a deterioration of grasping reflex with the two doses of GHB (p<0.01). Numerous studies indicated that the medial prefrontal cortex is a crucial neuronal substrate in the working memory and grasping reflex modulation. These results suggest that prolonged administration of GHB could alter structure and/or function of the medial prefrontal cortex, as well as its interconnections with other brain regions involved in the evaluated cognitive and neurological processes.     

Stretch reflexes in the human masticatory muscles: a brief review and a new functional role

Stretch reflexes play a vital role in fine-tuning movements and in automatically maintaining posture. This article briefly reviews the operation of the stretch reflex in the human masticatory system. The conventional approach of stretching muscles in an open-loop manner has yielded much valuable information on the operation of this reflex. In particular, it has revealed that stretching the jaw-closing muscles evokes a reflex response with two major components. The short-latency reflex is favoured when stretches are brisk, but slower stretches evoke an additional long-latency component. In the hand muscles, the long-latency response is transcortical: in the masticatory muscles, it is not. In addition to its role in servo-control of muscle length during chewing, the stretch reflex in the jaw-closing muscles maintains the vertical position of the mandible during vigorous head movements such as those that occur during running, jumping, hopping and other vigorous whole-body movements in which the head moves briskly up and down. This is an interesting model system in which to investigate stretch reflexes with natural stimuli under unrestrained, physiological conditions.     

Training-specific adaptations of H- and stretch reflexes in human soleus muscle

The authors investigated the effect of physical exercise on reflex excitability in a controlled intervention study. Healthy participants (N = 21) performed 4 weeks of either power training (ballistic strength training) or balance training (sensorimotor training [SMT]). Both training regimens enhanced balance control and rate of force development, whereas reductions in peak-to-peak amplitudes of stretch reflexes and in the ratio of the maximum Hoffman reflex to the maximum efferent motor response (Hmax:Mmax) measured at rest were limited to SMT. The differences in reflex excitability between the training regimens indicated different underlying neural mechanisms of adaptation. The reduced reflex excitability following SMT was most likely induced by supraspinal influence. The authors discuss an overall increase in presynaptic inhibition of Ia afferent fibers as a possible mechanism.     

Adaptation to visual rearrangement: Role of sensory discordance

The relative contributions of proprioceptive and efferent information in eliciting adaptation to visual rearrangement were studied under two conditions of visual stimulation. Subjects permitted sight of their forearm under normal room illumination showed significant adaptation when the forearm was (a) moved up and down under the action of tonic vibration reflexes, (b) voluntarily moved through the same trajectory at the same pace, (c) viewed while still, and (d) viewed while the margins of the elbow were vibrated. The reflex movement condition elicited significantly greater adaptation than the other conditions. Subjects allowed only sight of a point source of light attached to their hand showed significant adaptation when the forearm was (a) reflexly moved, (b) voluntarily moved through the same trajectory at the same rate, (c) passively moved, (d) still, and (e) vibrated while still. Less adaptation occurred as the amount of proprioceptive information about limb position was decreased. The adaptation elicited by voluntary movements of the forearm and by reflex movements did not differ significantly. It is concluded that corollary-discharge signals may not be crucial in adaptation to visual rearrangement; a more important factor appears to be discordance between proprioceptive and visual information.     

A quantitative assessment of the effects of malnutrition on behavioral development in laboratory mice

The aim of this study was to compare the effects of malnutrition on behavioral development in mice with those due to heredity obtained in a previous study. To this end behavioral development was assessed using a developmental time scale which allowed comparison of the two studies. Pregnant B6D2F1/J mice were maintained on either a protein restricted or normal protein diet from Day 7 to Day 24 postconception, at which time the low protein group was returned to the normal diet until behavioral testing at Day 32. Behavioral development in the control group replicated the values obtained in previous studies, whereas the malnourished pups were retarded by 1.4 days. This was of the same order of magnitude as that reported previously for maternal inbreeding. Measures of maternal and pup body weight at birth, Day 24 and Day 32 indicated that although the malnourished animals were initially significantly lighter in weight they had recovered by Day 32. Litter size however, declined between birth and time of behavioral testing in the malnourished group.     

Effects of caffeine on the trigeminal blink reflex

The acoustic startle and trigeminal blink reflexes share the same motor output. Since caffeine has been shown to augment the startle reflex, it was proposed that caffeine would also increase the trigeminal blink reflex. In 6 humans, the effects of caffeine (100 mg) on the trigeminal blink reflex were investigated. Reflex blinks were elicited by stimulation of the supraorbital branch of the trigeminal nerve. Following ingestion of caffeinated coffee, reflex blinks increased in amplitude and duration and occurred at a shorter latency than reflex blinks following ingestion of decaffeinated coffee. Since the blink reflex is a brainstem reflex, these results suggest that the psychomotor effects of caffeine facilitate brainstem processing.     

Dentist phobia

This study analyzes so-called hopeless gaggers,i.e., patients in whom dental treatment and wearing of a prosthesis produced a retching or vomiting reaction, in order to investigate the sources and properties of this pathologic reaction. In 35 patients, an anamnestic inquiry, a determination of the reflexogenic zone, a recording of the peripheral pattern of the pathologic reflex, and extinction training were performed. A group of six normal persons served as a comparison group. It was shown that patients, in comparison with normals, had an enlarged receptive field, were sensitive to a broader population of stimuli, and showed precursors and aftereffects of the retching-vomiting not found in normals. This pathologic reaction was the symptom of different Psychopathologie processes, such as specific fear, repugnance-fear-based disturbances, diffuse anxiety, goal-directed behavior, depressive states and, at least in one case, visceral pathology. The various patients differed with respect to properties of the reaction as well as in the sensitivity to the extinction procedure. It is discussed that different integrative nervous processes play a role in the origin and development of the syndrome: activation of unconditional reflexes, activation of classic and instrumental conditional reflexes, activation of such reflexes by an increase of the reactivity level of specific and unspecific structures of the brain, generalization of stimuli,etc.     

Hydrocortisone infusion exerts dose- and sex-dependent effects on attention to emotional stimuli

Glucocorticoid administration has been shown to exert complex effects on cognitive and emotional processing. In the current study we investigated the effects of glucocorticoid administration on attention towards emotional words, using an Affective Go/No-go task on which healthy humans have shown an attentional bias towards positive as compared to negative words. Healthy volunteers received placebo and either low-dose (0.15 mg/kg) or high-dose (0.45 mg/kg) hydrocortisone intravenously during two separate visits in a double-blind, randomized design. Seventy-five minutes post-infusion, the subjects performed tests of attention (Rapid Visual Information Processing [RVIP]), spatial working memory (Spatial Span) and emotional processing (Affective Go/No-go task [AGNG]). On the attention task, performance was impaired under both hydrocortisone doses relative to placebo, though the effect on error rate was not significant after controlling for age; Spatial Span performance was unaffected by hydrocortisone administration. On the AGNG task, relative to the placebo condition the low-dose hydrocortisone infusion decreased response time to emotional words while high-dose hydrocortisone increased response time. In the females specifically, both high and low dose hydrocortisone administration attenuated the normal attentional bias toward positively valenced words. These data suggest that, in healthy women, the modulation of attention by the emotional salience of stimuli is influenced by glucocorticoid hormone concentrations.     

惊跳反射的生理心理机制

惊跳反射作为动物及人类在应对意外刺激或遇到险情时的一种避险保护反应,具有重要的生物学意义。以往的研究较多关注听觉惊跳反射,在反应指标上多采用眼部及面部表情肌的反应,如眨眼反射。惊跳反射的生理机制为突发性强刺激直接传向杏仁核的直接通路所致。惊跳反射增强的心理机制可能为致敏作用或恐惧性条件作用,而惊跳反射衰减的心理机制可能是适应、前脉冲抑制或愉快衰减。未来的研究应关注视觉惊跳反射,观察全身躯体姿势维持肌肉群的反应模式,并以先进设备对惊跳反射的信息加工脑机制进行深入的研究     

Developmental changes in the responses of preterm infants to a painful stressor

The purpose of this investigation was to examine longitudinally gestational age and developmental differences in preterm infants' self-regulatory abilities in response to a painful stressor, as well as associations between behavioral and cardiovascular responses. Participants included 49 healthy premature infants. Behavioral and cardiovascular responses to a heel stick blood draw were compared between infants of 28-31 and 32-34 weeks' gestation age at birth. Both gestational age groups displayed behavioral and cardiovascular indications of stress in response to the blood draw. However, both shortly after birth and several weeks later, infants born at younger gestational ages (28-31 weeks) were more physiologically reactive. Evidence that the behavioral stress responses of 28-31 weeks' gestation age group preterm infants do not reflect their physiological responses suggests that evaluation of preterm infants' experiences and risk require assessments of both physiology and behavior. The greater stress vulnerability of the 28-31 weeks' gestation group relative to the 32-34 weeks' gestation group and the implications of this for subsequent development are discussed.     

Startle reflex inhibition in the rat: its persistence after extended repetition of the inhibitory stimulus

Startle reflexes to intense sound bursts are inhibited by weak stimuli that briefly precede their elicitation. In three experiments the startle stimulus (a 110-dB SPL tone burst) was presented 100 ms after the final link in a train of stimuli, the length of the train varying from 1 to 1,000, its repetition rate varying from 1 per s to 10 per s, and its constituents being 40 dB or 50 dB white noise bursts of 25 ms duration. Inhibition was invariant across train length and repetition rate. In a final experiment the startle stimulus was presented a variable interval after the final link, from 40 ms to 1280 ms, with 1 or 100 noise bursts (50 dB) in the train. Inhibition developed more rapidly following the last member of the 100-stimulus train, suggestive of a "priming" or sensitization effect of stimulus repetition, but its overall strength and subsequent rate of decay were not different in the two conditions. The general persistence of inhibition following these extended series of stimuli reveals that reflex inhibition must be the outcome of a fixed and obligatory process associated with sensory input.     

The anxiety disorder spectrum: Fear imagery,physiological reactivity,and differential diagnosis∗

Abstract

This review considers recent research assessing psychophysiological reactivity to fear imagery in anxiety disorder patients. As in animal subjects, fear cues prompt in humans a state of defensive motivation in which autonomic and somatic survival reflexes are markedly enhanced. Thus, a startle stimulus presented in a fear context yields a stronger (potentiated) reflex, providing a quantitative measure of fearful arousal. This fear potentiation is further exaggerated in specific or social phobia individuals when viewing pictures or imagining the phobic object. Paradoxically, fear imagery studies with more severe anxiety disorder patients – panic disorder with agoraphobia, generalized anxiety disorder, or anxious patients with comorbid depression – show a blunted, less robust fear potentiated response. Furthermore, this reflex blunting appears to systematically be more pronounced over the anxiety disorder spectrum, coincident with lengthier chronicity, worsening clinician-based judgments of severity and prognosis, and increased questionnaire-based indices of negative affectivity, suggesting that normal defensive reactivity may be compromised by an experience of long-term stress.