Magnitude Of Reflex Research Articles

Light-Induced Trigeminal Sensitization without Central Visual Pathways: Another Mechanism for Photophobia

The authors investigated whether trigeminal sensitization occurs in response to bright light with the retina disconnected from the rest of the central nervous system by optic nerve section. In urethane-anesthetized rats, trigeminal reflex blinks were evoked with air puff stimuli directed at the cornea in darkness and at three different light intensities. After normative data were collected, the optic nerve was lesioned and the rats were retested. In an alert rat, reflex blinks were evoked by stimulation of the supraorbital branch of the trigeminal nerve in the dark and in the light. A 9.1 × 10(3) μW/cm(2) and a 15.1 × 10(3) μW/cm(2) light significantly enhanced the magnitude of reflex blinks relative to blinks evoked by the same trigeminal stimulus when the rats were in the dark. In addition, rats exhibited a significant increase in spontaneous blinking in the light relative to the blink rate in darkness. After lesioning of the optic nerve, the 15.1 × 10(3) μW/cm(2) light still significantly increased the magnitude of trigeminal reflex blinks. Bright lights increase trigeminal reflex blink amplitude and the rate of spontaneous blinking in rodents. Light can modify trigeminal activity without involving the central visual system.

Changes in the H Reflex Preceding Voluntary Movements of the Contralateral Lower Limb in Humans

In electromyographic studies on healthy subjects, we recorded the H reflex from the right m. soleus and measured changes in the magnitude of this reflex response related to voluntary movements of the contralateral lower limb performed according to a visual signal. The effects of back and plantar flexions of the contralateral foot of the tested subject in the lying and standing positions were examined. Changes in the H reflex magnitude began to be recorded 60 to 90 msec prior to voluntary movements of the contralateral limb. When the subject was in the lying position, these changes looked like facilitation of the H reflex at both types of movement of the contralateral foot. When the subject stood, facilitation preceded back flexion of the foot of this extremity, while plantar flexion was preceded by inhibition of the tested H reflex. Our results show that the pattern of preliminary changes in the muscle tone of one of the lower limbs is determined by the type of future movement of another limb and peculiarities of the support function realized by this limb.

The role of context in the processing of alcohol‐relevant cues

In line with learning theories of drug addiction, drug-related cues may be viewed as important motivators of continued drug use. They may be differentially effective depending on the context and motivational significance. The present study aimed to test the significance of different contexts in modulating alcohol-related cue reactivity. Pictures depicting alcohol intake or its paraphernalia and pictures without any relation to alcohol intake were varied to depict physical and social contexts or different consumptive contexts associated with full/half-full/empty alcohol beverage containers. We obtained ratings of craving, valence and arousal of the cues as well as skin conductance responses (SCRs) and startle reflex modulation measures from 21 abstinent alcohol-dependent patients, recruited from an addiction treatment center, and 21 matched healthy controls. Social scenes and full glasses or bottles were rated as more pleasant and arousing compared with neutral drinking situations and empty glasses or bottles in patients. Furthermore, we found a decreased startle reflex magnitude to social compared with neutral drinking situations, and both higher SCRs and decreased startle reflex magnitude to full compared with empty glasses or bottles in patients versus controls. These results show that both physical and social and consumptive contexts differentially influence cue reactivity in abstinent alcohol-dependent patients with both social and pub-related physical contexts, and the initial consumptive context eliciting the most appetitive and arousing responses. These data have not only important implications for our understanding of the role of learning in drug dependence but also for treatment, which needs to take these factors into account.

Nocturnal hyperactivity, increased social novelty preference and delayed extinction of fear responses in post-weaning socially isolated mice

When rodents are reared in isolation from young age onwards, they manifest a number of behavioural alterations in adulthood. Since some of these alterations resemble symptoms of psychiatric disorders, the post-weaning social isolation (ISO) manipulation is often applied to create rodent models of these disorders. In rats, ISO effects have been thoroughly characterised, but in mice they are less well documented. Therefore, we further evaluated behaviour of adult ISO mice with a test battery that focussed on abnormalities relevant to schizophrenia. We found that ISO mice were hyperactive during the dark phase. Also, ISO mice showed alterations in magnitude, habituation and prepulse-inhibition of the acoustic startle reflex, increased anxiety, increased social preference and changes in extinction of fear responses. We did not observe increased sensitivity to locomotor-activating effects of amphetamine. It is concluded that ISO of mice might serve as a useful model to test further hypotheses regarding pathogenesis occurring at specific developmental timeframes.

Prediction of Natural History of Neuromuscular Properties After Stroke Using Fugl-Meyer Scores at 1 Month

Background. The link between spasticity and impaired voluntary movement after stroke remains unclear because of the lack of suitable tools characterizing properties of spastic muscles. Describing this relationship early poststroke can potentially help predict the extent and time course of recovery. Objective. To describe the time course of changes in neuromuscular properties after stroke using the upper extremity Fugl-Meyer Assessment (FMA) at 1 month to predict recovery patterns over 1 year. Methods.Using a parallel cascade system identification technique, this study characterized intrinsic and reflex behaviors for different mean elbow joint angles, at specified times poststroke. Then the “growth mixture” model was used to characterize recovery patterns over 1 year. Logistic regression analyses were applied to predict these patterns. The impact of patient characteristics was also investigated. Results. In 21 stroke survivors, 14 had sustained hemorrhage and 7 had thromboses. The study observed several recovery classes, relating intrinsic and reflex stiffness magnitudes with changing elbow angle at different time points. The largest group (48%) showed progressive increase in reflex stiffness over time, but 33% showed declining reflex stiffness over the same period. A third class (19%) showed invariant reflex properties. These differences were linked to the initial reflex magnitudes. The FMA at 1 month showed an inverse relationship with key reflex patterns and proved to be a strong predictor of class membership. Stroke type was also influential. Conclusions. The logistical regression class may enable us to accurately predict reflex responses during the first year, allowing us to apportion impairment between central and peripheral mechanisms.

Versatility of Fear-Potentiated Startle Paradigms for Assessing Human Conditioned Fear Extinction and Return of Fear

Fear conditioning methodologies have often been employed as testable models for assessing learned fear responses in individuals with anxiety disorders such as post-traumatic stress disorder (PTSD) and specific phobia. One frequently used paradigm is measurement of the acoustic startle reflex under conditions that mimic anxiogenic and fear-related conditions. For example, fear-potentiated startle is the relative increase in the frequency or magnitude of the acoustic startle reflex in the presence of a previously neutral cue (e.g., colored shape; termed the conditioned stimulus or CS+) that has been repeatedly paired with an aversive unconditioned stimulus (e.g., airblast to the larynx). Our group has recently used fear-potentiated startle paradigms to demonstrate impaired fear extinction in civilian and combat populations with PTSD. In the current study, we examined the use of either auditory or visual CSs in a fear extinction protocol that we have validated and applied to human clinical conditions. This represents an important translational bridge in that numerous animal studies of fear extinction, upon which much of the human work is based, have employed the use of auditory CSs as opposed to visual CSs. Participants in both the auditory and visual groups displayed robust fear-potentiated startle to the CS+, clear discrimination between the reinforced CS+ and non-reinforced CS−, significant extinction to the previously reinforced CS+, and marked spontaneous recovery. We discuss the current results as they relate to future investigations of PTSD-related impairments in fear processing in populations with diverse medical and psychiatric histories.

Anesthesia Literature Review

Anesthesia Literature Review

Contrastive breathiness on consonants and vowels.

While numerous languages exhibit contrastive breathy phonation either on consonants (e.g., Indic languages) or on vowels (e.g., Zapotec languages); very few languages preserve this contrast across both consonants and vowels. Two such languages are Gujarati and White Hmong. Given that breathiness on consonants is typically realized as a breathy-voiced release into the following vowel, how are the two types of breathiness distinguished in CV sequences, if at all? We examine acoustic and electroglottographic data collected from speakers of Gujarati and White Hmong to determine what properties reliably distinguish breathy and modal voice in potentially ambiguous CV sequences, and to explore the phonetic and phonological properties shared between these two genetically unrelated languages. Preliminary results from both languages are strikingly similar; modal vowels adjacent to breathy consonant releases strongly resemble phonemically breathy vowels, and only the exact timing and magnitude of the acoustic reflexes of breathiness phonetically distinguish the two sequences. Phonological evidence in the form of distributional constraints, however, can aid listeners of both languages in determining the source of breathiness: both languages prohibit the co-occurrence of breathy consonants and breathy vowels, and in White Hmong, tonal cues can also reveal the underlying phonation of an ambiguous CV sequence.

Lack of startle blink potentiation to mutilation pictures irrespective of fearfulness

Previous research has shown that in healthy individuals blood-related stimuli elicit a distinctive autonomic response pattern and heightened processing as compared with other unpleasant and arousing visual stimuli. In addition, growing evidence suggests that information processing of disorder-related stimuli is also different in blood phobia as compared with other specific phobias. In the present study, the magnitude of the startle eyeblink reflex elicited during the viewing of mutilation, human attack, erotica and neutral pictures was recorded in 22 blood phobics and 25 healthy controls. Startle eyeblink responses were measured at 300, 1500, 3500 and 4500-ms time intervals after picture onset in order to assess the attentional/affective modulation and its temporal course. Reliable startle inhibition to erotic pictures and startle potentiation to human attack scenes were found relative to neutral pictures. However, while both groups rated mutilations as the most unpleasant and arousing content, no blink facilitation relative to neutral contents was found at either early or late probe times. Crucially, such effect occurred independently of fear levels, as no difference between phobics and controls was found in the size of the startle blinks elicited throughout the viewing of blood pictures.

Opioid Blockade and Inflammation Reveal Estrous Cycle Effects on Visceromotor Reflexes Evoked by Bladder Distention

Painful bladder disorders vary in intensity with the menstrual cycle in women. We evaluated the influence of the correlate in rats (the estrous cycle) on the nociceptive visceromotor reflex to bladder distention in the presence/absence of inflammation and of spinal opioid blockade. We recorded visceromotor reflexes as electromyogram responses of the abdominal musculature to graded (10 to 60 mm Hg) bladder distention in anesthetized female rats in the presence of intrathecal saline or naloxone (10 μg) 1 day after receiving intravesical zymosan or anesthesia alone. In saline treated rats visceromotor reflexes to bladder distention were significantly greater in those with an inflamed vs a noninflamed bladder when examined together. When separated into phases, rats with bladder inflammation showed complex estrous cycle effects with significantly greater visceromotor reflexes to bladder distention during metestrus and proestrus than diestrus. In naloxone treated rats visceromotor reflexes to bladder distention were significantly greater in those with an inflamed vs a noninflamed bladder when examined together. Naloxone enhanced the overall magnitude of visceromotor reflexes to bladder distention in the inflamed and noninflamed conditions. The magnitude of visceromotor reflexes to bladder distention in noninflamed and inflamed conditions in the presence of naloxone was estrous phase dependent in the order, estrus >metestrus >diestrus >proestrus. Similar findings were apparent on analysis of data on responses at threshold intensity (30 mm Hg). Data suggest that circulating hormones present during the estrous cycle alter bladder reactivity and opioid modulatory systems to maintain constancy of input from the bladder to the central nervous system.

Absence of equifinality of hand position in a double-step unloading task

Equifinality, during arm reaching movements, relates to the capacity of the neuromuscular system to attain the same final position in the presence or absence of transient perturbations. There have been several controversies regarding equifinality in the literature. A brief elastic perturbation, applied during a fast arm movement or just before its initiation, typically does not affect final arm position. On the other hand, several experiments have shown that velocity-dependent perturbations, such as Coriolis force or negative damping, while transient in nature, have a significant effect on final arm position when compared to unperturbed movements. In this study, an unloading paradigm was used to study the role of reflexes with respect to equifinality. The effects on final arm position of suddenly decreasing a static load maintained by fourteen subjects were analyzed. Subjects maintained an initial load produced by a double-joint manipulandum moving in the horizontal plane. The load was suddenly decreased, either in one or in two successive steps with different time intervals, resulting in a rapid reflex-mediated change in arm position. Unloading led to short-latency changes in the activity of shoulder and elbow muscles and significant variations in tonic activity. It was found that the final hand position was shorter for double- versus single-step unloading if the time between two successive changes in load was greater than 100 ms. With a shorter time interval, the final hand positions were the same. This difference in final hand positions was inversely proportional to the hand velocity at the time of the second change in load. Further, agonist/antagonist co-activation increased in double-step unloading. Thus, the change in both the load and the movement velocity may influence the magnitude of the unloading reflex. This may be indicative of a dependence of stretch reflexes on velocity. Perturbation may cause a reflex-mediated increase in joint stiffness, which could explain why equifinality is not preserved after some perturbations, such as velocity-dependant external forces.

Investigation of threshold and magnitude criteria of the nociceptive blink reflex

The nociceptive blink reflex is a trigeminofacial brain-stem reflex which is used in pain research to evaluate the modulation of pain processing. To standardize the analysis of the reflex we investigated which electromyographic parameters show the best correlation with subjective pain ratings and should therefore be used for scoring blink reflex magnitude. Furthermore we investigated which parameters show the highest accuracy and reliability to define the blink reflex threshold. Forty-six subjects each received 54 electrical stimuli to the supraorbital nerve at nine different stimulus intensities, which corresponded to pain ratings between 0 and 70 (scale 0-100). Multilevel modeling was performed to determine which electromyographic blink reflex parameter showed the best correlation with subjective pain ratings. To define the blink reflex threshold ROC analyses were performed, comparing different electromyographic blink reflex parameters with the judgment of expert raters for 2500 blink reflex recordings from this study and 1400 from another. The baseline-adjusted area under the curve showed the best correlation with subjective pain ratings. Seventy-six percent of the residual variance of the pain ratings could be explained by this parameter. The peak z score showed the highest accuracy in defining the blink reflex threshold and also the highest cut-point stability. We recommend the baseline-adjusted area under the curve for scoring the magnitude of the nociceptive blink reflex and the peak z score to define the nociceptive blink reflex threshold. The here defined standardized criteria to score blink reflex magnitude and threshold improve the comparability and validity of blink reflex studies.

Carbachol injection into the pontine reticular formation depresses laryngeal muscle activities and airway reflexes in decerebrate cats

To understand the role of cholinoceptive, medial pontine reticular formation (mPRF) neurons in the control of upper airway, pharyngolaryngeal reflexes, we measured activities of intrinsic laryngeal muscles (posterior cricoarytenoid, PCA; thyroarytenoid, TA), diaphragm (DIA), genioglossus (GG) and a neck muscle (trapezius) in unanesthetized, decerebrated, spontaneously breathing cats with and without mPRF carbachol injections. The ethimoidal nerve was electrically stimulated to evoke sneezing, and the superior laryngeal nerve to evoke the laryngeal reflex, swallowing, and coughing. Carbachol reduced the amplitudes of the spontaneous electromyographic activities in the neck, TA, PCA, GG, and DIA to 7%, 30%, 54%, 45% and 71% of control, respectively, reduced the respiratory rate to 53% without changes in expiratory CO 2 concentration; the magnitude of the laryngeal reflex in the TA muscle to 56%; increased its latency by 13%; and reduced the probability of stimulus-induced sneezing, swallowing, and coughing to less than 40%. These changes lasted more than 1 h. These data demonstrate that important upper airway reflexes are suppressed by increasing cholinergic neurotransmission in the mPRF. Because acetylcholine release in the mPRF changes in accordance with sleep–wake cycles, the present findings are relevant to the control of upper airway reflexes during various vigilance states.

Ocular Vestibular Evoked Myogenic Potentials Via Bone-Conducted Vibrations Applied to Various Midsagittal Cranial Sites

This study applied bone-conducted vibration (BCV) stimulation to various midsagittal sites on the cranium to optimize stimulation conditions for ocular vestibular evoked myogenic potentials (oVEMPs). Ten healthy subjects (7 men and 3 women, aged 25-32 yr) without previous ear disorders were enrolled in this study. Each subject underwent oVEMP test using BCV applied to 4 cranial sites on the midsagittal plane, namely, the Fpz (above the glabella), Fz (the midline forehead at the hairline), Cz (vertex), and inion. In addition, the linear distances from the vestibule to the 4 sites were measured via multiplanar reconstruction of computed tomographic scans. Tertiary referral university hospital. All 10 subjects showed 100% clear oVEMPs at the Fpz, Fz, inion, and Cz sites. The mean +/- SD nI latencies of these 4 sites were 8.9 +/- 0.8, 9.8 +/- 2.4, 11.2 +/- 1.5, and 14.0 +/- 2.0 milliseconds, respectively, exhibiting significant differences among the 4 sites. The median (range) nI-pI amplitudes of oVEMPs stimulated via the Fpz, Fz, inion, and Cz sites were 15.8 microV (4.2-55.8 microV), 9.9 microV (3.8-29.0 microV), 11.5 microV (5.5-58.0 microV), and 6.1 microV (2.5-21.4 microV), respectively, indicating significant differences among the 4 sites. Of them, the oVEMPs elicited by BCV mode at the Fpz represented the largest nI-pI amplitude, when compared with the other 3 sites. Furthermore, the linear distances from the vestibule to the Fpz, Fz, inion, and Cz sites were 10.7 +/- 0.4, 11.5 +/- 0.5, 8.6 +/- 0.4, and 12.0 +/- 0.5 cm, respectively. The inion site had the shortest distance to the vestibule, but it did not show the earliest nI latency. The Fpz may be the optimal site for BCV stimulation for screening oVEMPs in reflex magnitude.

BARORECEPTOR REFLEX ROLE IN BLOOD PRESSURE LONG-TERM REGULATION

Less than 50 % Wistar male rats with intact baroreceptor reflex developed arterial hypertension 8 weeks after renal artery clipping in the model «two kidneys - one clip». Blood pressure level negatively correlated with initial magnitude of the baroreceptor reflex. At the same time all rats (100 %) with the damaged baroreceptor reflex developed hypertension after renal artery clipping. Thus, we conclude that baroreceptor reflex counteracts the development of vasorenal hypertension and it can take part in blood pressure long-term regulation.

Psychophysiological responses to pain: Further validation of the nociceptive flexion reflex (NFR) as a measure of nociception using multilevel modeling

Physiological reactions to noxious stimuli are often used to make inferences about pain, but few studies have thoroughly examined the intra- and interindividual relationships between them. In the present study (N=104), multilevel analyses was used to assess relations between physiological (nociceptive flexion reflex magnitude [NFR], blink reflex magnitude, skin conductance response [SCR], heart rate [HR]) and subjective reactions to electrocutaneous stimuli. All physiological reactions were significant predictors of ratings when entered alone, explaining 1% (SCR) to 29% (NFR) of the variance; but only NFR, blink, and HR were significant in a multivariate predictor model. Significant interindividual variability in slopes was found for blink and HR, but not NFR. A final trimmed model that included NFR, blink, and the blink random slope explained 35% of the variance in ratings.

Distinct Profiles of Anxiety and Dysphoria during Spontaneous Withdrawal from Acute Morphine Exposure

The negative motivational aspects of withdrawal include symptoms of both anxiety and depression, and emerge following termination of chronic drug use as well as after acute drug exposure. States of acute withdrawal are an inherent part of intermittent drug use in humans, but the contribution of acute withdrawal to the development of addiction has received limited systematic investigation, due to a lack of preclinical models for withdrawal states that emerge spontaneously after acute drug exposure. Here, we have characterized a spontaneous increase in the magnitude of the acoustic startle reflex (i.e., spontaneous withdrawal-potentiated startle) that emerges following acute morphine administration in rats, and compared the time course of startle potentiation and place conditioning. We find that startle potentiation appears related to a decrease in opiate receptor occupancy and reflects an anxiety-like state with a pharmacological profile similar to other signs of opiate withdrawal. Spontaneous startle potentiation emerges before the rewarding effects of morphine have subsided, even though naloxone administration after a single morphine exposure causes both startle potentiation and conditioned place aversion (CPA). These results demonstrate that negative emotional signs of withdrawal develop following just one exposure to morphine, and are likely a recurrent aspect of intermittent drug use that may contribute to the earliest adaptations underlying the development of addiction. Furthermore, the dissociation between spontaneous startle potentiation and CPA suggests anxiogenic and dysphoric manifestations of opiate withdrawal may be mediated by distinct neural mechanisms that are progressively engaged as withdrawal unfolds.

Startle Response in Behaviorally Inhibited Adolescents With a Lifetime Occurrence of Anxiety Disorders

ObjectiveBehaviorally inhibited children face increased risk for anxiety disorders, although factors that predict which children develop a disorder remain poorly specified. The current study examines whether the startle reflex response may be used to differentiate between behaviorally inhibited adolescents with and without a history of anxiety. MethodParticipants were assessed for behavioral inhibition during toddlerhood and early childhood. They returned to the laboratory as adolescents and completed a fear-potentiated startle paradigm and a clinical diagnostic interview (Schedule for Affective Disorders and Schizophrenia for School-Age Children-Present and Lifetime Version). Magnitude of the startle reflex was examined at baseline and during cues associated with safety and threat. ResultsOnly adolescents who showed high levels of behavioral inhibition and had a lifetime occurrence of anxiety disorders showed increased startle reactivity in the presence of safety cues. Neither behavioral inhibition nor diagnosis was related to startle reactivity during threat cues. ConclusionsThese results suggest that neurobiological measures, such as the startle reflex, may be a potential risk marker for the development of anxiety disorders among behaviorally inhibited adolescents. These methods may enhance our ability to identify vulnerable individuals before the development of anxious psychopathology. J. Am. Acad. Child Adolesc. Psychiatry, 2009;48(6):610–617.

Location-specific modulations of plantar cutaneous reflexes in human (peroneus longus muscle) are dependent on co-activation of ankle muscles

Cutaneous reflexes induced in lower leg muscles by non-noxious electrical stimulation to the foot sole are strongly modified depending on the stimulated location. Little is known, however, about the functional importance of this location-specificity. We examined modulation of cutaneous reflexes in the peroneus longus muscle during co-activation of the peroneus longus (PL), soleus, and tibialis anterior muscles in ten healthy volunteers. We successfully recorded 121 intramuscular single motor units (MU) of cutaneous reflexes in PL elicited by stimulating either fore-medial, fore-lateral, or heel regions of the plantar foot while performing plantarflexion and eversion (PF + EV), dorsiflexion and eversion (DF + EV), or isolated eversion (EV). Firing probability increased following fore-lateral stimulation during the PF + EV and EV tasks, but not during the DF + EV. Fore-medial stimulation, irrespective of the task, suppressed the reflex. Heel stimulation facilitated the reflex only during the PF + EV and DF + EV tasks. In general, cutaneous reflex magnitudes were larger during the PF + EV task than during the others, irrespective of whether the effects were facilitatory or suppressive. These results suggest that the magnitude of the reflex effects on the PL motoneurons strongly depends on activation of plantarflexors and dorsiflexors.

Specificity of Reflex Adaptation for Task-Relevant Variability

The motor system responds to perturbations with reflexes, such as the vestibulo-ocular reflex or stretch reflex, whose gains adapt in response to novel and fixed changes in the environment, such as magnifying spectacles or standing on a tilting platform. Here we demonstrate a reflex response to shifts in the hand's visual location during reaching, which occurs before the onset of voluntary reaction time, and investigate how its magnitude depends on statistical properties of the environment. We examine the change in reflex response to two different distributions of visuomotor discrepancies, both of which have zero mean and equal variance across trials. Critically one distribution is task relevant and the other task irrelevant. The task-relevant discrepancies are maintained to the end of the movement, whereas the task-irrelevant discrepancies are transient such that no discrepancy exists at the end of the movement. The reflex magnitude was assessed using identical probe trials under both distributions. We find opposite directions of adaptation of the reflex response under these two distributions, with increased reflex magnitudes for task-relevant variability and decreased reflex magnitudes for task-irrelevant variability. This demonstrates modulation of reflex magnitudes in the absence of a fixed change in the environment, and shows that reflexes are sensitive to the statistics of tasks with modulation depending on whether the variability is task relevant or task irrelevant.