Magnitude Of Startle Response Research Articles

A Systematic Review on Sex Differences in Prepulse Inhibition of Startle

Abstract: Prepulse inhibition of the startle response is defined as the inhibition of the startle reflex to an intense contextual stimulus (named pulse) when a weaker stimulus (named prepulse) precedes it and is considered a measure of sensorimotor gating. Consistent with recent research, it has been observed that this measure might exhibit sex differences in studies of both humans and rodents, although the results in the literature appear to be inconsistent. Therefore, this systematic review aims to analyze the sexual differences observed in human and nonhuman animal studies from a comparative perspective. A comprehensive search was conducted from the inception to the present in the Web of Science, PubMed, and PsycInfo databases. Following the search, 58 studies were included in the review. The average age in human studies ( n = 32) was 31.45 years (range = 4–69), while among nonhuman animal studies ( n = 26), the average age was 75.5 postnatal days (range = 7–360). The results indicated no clear sexual differences in the startle response magnitude. However, consistent sex differences in prepulse inhibition were found, revealing that males exhibited higher levels of sensorimotor gating compared to females in both humans (78.79% of the studies) and nonhuman animal studies (69.23% of the studies). Therefore, the findings corroborate the sex differences of prepulse inhibition and underscore the value of this paradigm in comparative science, emphasizing the importance of considering sex as an independent variable when studying this phenomenon.

Reduced amplitude and slowed latency of the acoustic startle response in adolescents and adults with 22q11.2 deletion syndrome

Background22q11.2 deletion syndrome (22q11DS) is one of the most robust genetic predictors of psychosis and other psychiatric illnesses. In this study, we examined 22q11DS subjects' acoustic startle responses (ASRs), which putatively index psychosis risk. Latency of the ASR is a presumptive marker of neural processing speed and is prolonged (slower) in schizophrenia. ASR measures correlate with increased psychosis risk, depend on glutamate and dopamine receptor signaling, and could serve as translational biomarkers in interventions for groups at high psychosis risk. MethodsStartle magnitude, latency, and prepulse inhibition were assessed with a standard acoustic startle paradigm in 31 individuals with 22q11.2DS and 32 healthy comparison (HC) subjects. Surface electrodes placed on participants' orbicularis oculi recorded the electromyographic signal in ASR eyeblinks. Individuals without measurable startle blinks in the initial habituation block were classified as non-startlers. ResultsAcross the startle session, the ASR magnitude was significantly lower in 22q11DS subjects than HCs because a significantly higher proportion of 22q11DS subjects were non-startlers. Latency of the ASR to pulse-alone stimuli was significantly slower in 22q11DS than HC subjects. Due to the overall lower 22q11DS startle response frequency and magnitudes prepulse inhibition could not be analyzed. ConclusionsReduced magnitude and slow latency of 22q11DS subjects' responses suggest reduced central nervous system and neuronal responsiveness. These findings are consistent with significant cognitive impairments observed in 22q11DS subjects. Further research is needed to untangle the connections among basic neurotransmission dysfunction, psychophysiological responsiveness, and cognitive impairment.

Properties of the Caudal Pontine Reticular Nucleus Neurons Determine the Acoustic Startle Response in Cntnap2 KO Rats.

Rats with a loss-of-function mutation in the contactin-associated protein-like 2 (Cntnap2) gene have been validated as an animal model of autism spectrum disorder (ASD). Similar to many autistic individuals, Cntnap2 knock-out rats (Cntnap2-⁣/-) are hyperreactive to sound as measured through the acoustic startle response. The brainstem region that mediates the acoustic startle response is the caudal pontine reticular nucleus (PnC), specifically giant neurons in the PnC. We previously reported a sex-dependent genotypic effect in the sound-evoked neuronal activity recorded from the PnC, whereby female Cntnap2-⁣/- rats had a dramatic increase in sound-evoked responses compared with wildtype counterparts, but male Cntnap2-⁣/- rats showed only a modest increase in PnC activity that cannot fully explain the largely increased startle in male Cntnap2-⁣/- rats. The present study therefore investigates activation and histological properties of PnC giant neurons in Cntnap2-⁣/- rats and wildtype littermates. The acoustic startle response was elicited by presenting rats with 95 dB startle pulses before rats were euthanized. PnC brain sections were stained and analyzed for the total number of PnC giant neurons and the percentage of giant neurons that expressed phosphorylated cAMP response element binding protein (pCREB) in response to startle stimuli. Additionally, in vitro electrophysiology was conducted to assess the resting state activity and intrinsic properties of PnC giant neurons. Wildtype and Cntnap2-⁣/- rats had similar total numbers of PnC giant neurons and similar levels of baseline pCREB expression, as well as similar numbers of giant neurons that were firing at rest. Increased startle magnitudes in Cntnap2-⁣/- rats were associated with increased percentages of pCREB-expressing PnC giant neurons in response to startle stimuli. Male rats had increased pCREB-expressing PnC giant neurons compared with female rats, and the recruited giant neurons in males were also larger in soma size. Recruitment and size of PnC giant neurons are important factors for regulating the magnitude of the acoustic startle response in Cntnap2-⁣/- rats, particularly in males. These findings allow for a better understanding of increased reactivity to sound in Cntnap2-⁣/- rats and in CNTNAP2-associated disorders such as ASD.

Mice prone to tinnitus after acoustic trauma show increased pre-exposure sensitivity to background noise.

Noise-induced tinnitus is generally associated with hearing impairment caused by traumatic acoustic overexposure. Previous studies in laboratory animals and human subjects, however, have observed differences in tinnitus susceptibility, even among individuals with similar hearing loss. The mechanisms underlying increased sensitivity or, conversely, resistance to tinnitus are still incompletely understood. Here, we used behavioral tests and ABR audiometry to compare the sound-evoked responses of mice that differed in the presence of noise-induced tinnitus. The aim was to find a specific pre-exposure neurophysiological marker that would predict the development of tinnitus after acoustic trauma. Noise-exposed mice were screened for tinnitus-like behavior with the GPIAS paradigm and subsequently divided into tinnitus (+T) and non-tinnitus (-T) groups. Both groups showed hearing loss after exposure, manifested by elevated audiometric thresholds along with reduced amplitudes and prolonged latencies of ABR waves. Prior to exposure, except for a slightly increased slope of growth function for ABR amplitudes in +T mice, the two groups did not show significant audiometric differences. Behavioral measures, such as the magnitude of the acoustic startle response and its inhibition by gap pre-pulse, were also similar before exposure in both groups. However, +T mice showed significantly increased suppression of the acoustic startle response in the presence of background noise of moderate intensity. Thus, increased modulation of startle by background sounds may represent a behavioral correlate of susceptibility to noise-induced tinnitus, and its measurement may form the basis of a simple non-invasive method for predicting tinnitus development in laboratory rodents.

"The mere imagination scares me"-evidence for fear responses during mental imagery of pain-associated interoceptive sensations in adolescents with chronic pain.

According to the bio-informational theory of emotion by Lang, mental imagery of fearful stimuli activates physiological and behavioural response systems, even in the absence of sensory input. We investigated whether instructed mental imagery of pain-associated (not painful) interoceptive sensations entails a threat value and elicits increased startle response, skin conductance level (SCL), and heart rate (HR) indicative of defensive mobilization in adolescents with chronic pain. Additionally, self-reported measures (fear, fear of pain, desire to avoid) were assessed. Adolescents (11-18 years) with chronic headache (CH, n = 46) or chronic abdominal pain (CAP, n = 29) and a control group (n = 28) were asked to imagine individualized pain-associated, neutral and standardized fear scripts. During pain-associated compared with neutral imagery, both pain groups showed higher mean HR, with CH also showing higher HR reactivity, while HR acceleration was not observed within control group. In contrast, during pain-associated compared with neutral imagery, startle response magnitude and SCL remained unchanged in all groups. Additionally, overall levels in self-reports were higher during pain-associated compared with neutral imagery, but significantly more pronounced in the pain groups compared with the control group. Results suggest that the mere imagination of pain-associated sensations elicits specific autonomic fear responses accompanied by increased self-reported fear in adolescents with chronic pain. The specific modulation of heart rate shed new light on our understanding of multimodal fear responses in adolescents with chronic pain and may help to refine paradigms to decrease fear of interoceptive sensations in chronic pain.

Gene expression underlying variation in the survival skills of red drum larvae (Sciaenops ocellatus).

Mortality rates of marine fish larvae are incredibly high and can determine year-class strength. The major causes of larval mortality are predation and starvation, and the performance of larvae in survival skills that can mitigate this mortality (predator evasion, foraging) varies among individuals and cohorts, but the causes of the variation are not known. Transcriptomics can link gene expression variation to phenotypic variation at the whole-system level to investigate the molecular basis of behavioural variation. We used tag-based RNA-sequencing to examine the molecular basis of variation in predator evasion and routine swimming (trait related to foraging efficiency) in the larval red drum, Sciaenops ocellatus. We looked for functional gene networks in which interindividual variation would explain variation in larval behavioural performance. We identified co-expressed gene groups ("modules") associated with predator evasion traits and found enrichment of motor, neural and energy metabolism pathways. These functional associations and pattern of correlations between modules and traits suggest that energy availability and allocation were responsible for the magnitude of startle responses, while differential neural and motor activation were associated with differences in response latency.

Behavior and brain size of larval zebrafish exposed to environmentally relevant concentrations of beta-methylamino-l-alanine.

Harmful algal blooms (HABs) release toxic compounds in water and are increasing in frequency worldwide. The neurotoxin β-methylamino-l-alanine (BMAA) is released by HABs and has garnered much attention over the past 20 years due to its association with human neurodegenerative disorders, but its effects on wildlife are still largely unknown. This study characterized the effects of chronic exposure to environmentally relevant concentrations of BMAA on the behavior and brain size of developing zebrafish (Danio rerio). Zebrafish were continuously exposed to 0, 1, 10, or 100 µg/l waterborne BMAA between 0- and 5-days postfertilization (dpf) before the onset of exogenous feeding. At 5 dpf, locomotion and responses to vibrational and visual stimuli were assessed. Following behavioral testing, larvae body and brain size were measured. Survival between 0 and 5 dpf did not differ between treatments. Moreover, BMAA exposure did not affect thigmotaxis, startle response magnitude, habituation to repeated presentation of vibrational startling stimuli, or relative brain size. A moderate increase in overall activity was observed in larvae exposed to 10 μg/l BMAA under light, but this effect was not seen in dark conditions, indicating that visual processing may have been affected by chronic BMAA exposure. Thus, passive continuous exposure to environmentally relevant concentrations of BMAA prior to first feeding in zebrafish did not affect survival or selected measures used to represent brain development, anxiety, and motor reflexes, but a limited light-dependent effect on locomotion suggests targeted neurotoxicity within the visual system.

Among-individual variation in the swimming behaviour of the amphipod Gammarus pulex under dark and light conditions

In recent years, considerable computational advancements have been made allowing automated analysis of behavioural endpoints using video cameras. However, the results of such analyses are often confounded by a large variation among individuals, making it problematic to derive endpoints that allow distinguishing treatment effects in behavioural studies. In this study, we quantitatively analysed the effects of light conditions on the swimming behaviour of the freshwater amphipod Gammarus pulex by high-throughput tracking, and attempted to unravel among individual variation using size and sex. For this, we developed the R-package Kinematics, allowing for the rapid and reproducible analysis of the swimming behaviour (speed, acceleration, thigmotaxis, curvature and startle response) of G. pulex, as well as any other organism. Our results show a considerable amount of variation among individuals (standard deviation ranging between 5 and 115 % of the average swimming behaviour). The factors size and sex and the interaction between the two only explained a minor part of this found variation. Additionally, our study is the first to quantify the startle response in G. pulex after the light is switched on, and study the variability of this response between individuals. To analyse this startle response, we established two metrics: 1) startle response magnitude (the drop in swimming velocity directly after the light switches on), and 2) startle response duration (the time it takes to recover from the drop in swimming velocity to average swimming speed). Almost 80 % of the individuals showed a clear startle response and, therefore, these metrics demonstrate a great potential for usage in behavioural studies. The findings of this study are important for the development of appropriate experimental set-ups for behavioural experiments with G. pulex.

STREStrogen: The Dichotomous Role of Estrous Cycle on Anxiety‐like Behavior is Dependent upon Stress History

Stress‐induced psychiatric disorders are some of the most debilitating conditions worldwide and occur more often in women than men. Increased risk coincides with the reproductive years when circulating estrogen (E) levels peak, alluding to a critical role of ovarian hormones in susceptibility. Human stress studies support this association as E is linked to negative mood and anxiety during social stressors. However, preclinical research often reports opposing findings of protective effects of E in non‐stressed subjects, indicating reduced anxiety‐like behavioral responses. Yet, rodent studies often neglect to acknowledge the latent effects of stress on E‐induced behavioral differences, like the negative impact of a traumatic experience that perpetuates future interactions. Thus, this divergence between clinical and preclinical findings limits the capability of identifying adequate pharmacological targets for use in naturally cycling females. Therefore, we investigated if prior exposure to stress in intact adult female rats sensitized behavioral outcomes during anxiogenic tasks and whether this was contingent upon the current phase of estrous. Rats were exposed for 15 mins/day over 5 consecutive days to either control handling (CON) or witness stress (WS), a modified social defeat paradigm whereby a female observes social defeat from within a protected compartment of the aggressive resident’s cage. Forty‐eight hours after the 5th and final CON/WS exposure, rats underwent elevated plus maze (EPM) testing, and then acoustic startle response (ASR) testing the next day. Vaginal lavage was obtained immediately following EPM and ASR to confirm estrous phase. Analyses were conducted in a 2 x 2 fashion: stress exposure x estrous phase, in which metestrus/diestrus (M/D) signified putatively low levels of E, and proestrus/estrus (P/E) signified high levels. Results revealed a prominent stress exposure x estrous phase interaction for percentage of time spent in the closed and open arms of EPM. First, CON rats demonstrated reduced avoidance of the open arms when tested during P/E vs M/D. This is in line with studies reporting an anxiolytic effect of E. However, our findings in WS rats supports the notion that E is a critical component of sensitizing anxiety‐like responses in females with a history of stress. Specifically, WS rats demonstrated greater avoidance of open arms in the EPM during P/E vs M/D. Importantly, we also found that not all tests are impacted by cycle stage. Females with a history of stress demonstrated a sensitized startle amplitude compared with CON rats, independent of estrous phase, when tested for magnitude of the innate startle response. Further investigations into E receptor expression and subsequent signaling mechanisms in stress‐sensitive brain regions are necessary to determine how a history of stress modifies behavioral outcomes in the presence of high circulating E. These data can then elucidate novel therapeutic targets important for decreasing the high incidence of psychological disorders in this susceptible population.

Movement analysis of upper limbs during motor task in down syndrome immediately after TDCS combined with non-immersive virtual reality

Startle is a fast response elicited by sudden acoustic, tactile or visual stimuli in a variety of animal species and in humans. The magnitude of startle response can be modulated by external and internal variables and can be a useful tool to study the sensory-motor integration in animals. Different stimuli have been used to induce startle in horses, which makes it difficult to compare the responses to these different approaches. The present study uses ultra-short-term heart rate variability (HRV) analysis to characterize the cardiac autonomic modulation, reactivity assessment and blood cortisol measurements to describe the behavioural and endocrine responses to a simple, easy to replicate, effective and safe method of startle (an umbrella is abruptly opened near the horse). The ultra-short-term (64 s) heart rate (HR) series were interpolated (4 Hz) and divided into 256 points segments then the spectra calculated (Fast Fourier Transform). The spectra were then integrated into low (LF; 0.01–0.07 Hz; Index of Cardiac Sympathetic Modulation) and high (HF; 0.07–0.50 Hz; Index of Cardiac Parasympathetic Modulation) frequency bands. Following the startle test, the HR (p = 0.0101), the power of the LF band of the cardiac interval spectrum (p = 0.0002) and the LF/HF ratio (p = 0.0066) were found to be higher, whereas the power of the HF band of the cardiac interval spectrum was found to be lower (p = 0.0002). Also, the horses showed a noticeable escape response, with latency of reaction varying from 0.28 to 1.28 s, duration of reaction ranging from 1.52 to 7.92 s and escape distance covered varying from 3.43 to 9.97 m. However, the endocrine measurements failed to reveal significant changes in the cortisol levels after the startle test. We conclude that the startle test used in the current study was effective to produce changes in behavioural parameters and cardiac autonomic modulation of the horses and can therefore be an appropriate tool for neurobiological studies. Furthermore, the use of ultra-short segments (64 s) for HRV analysis appears to be effective and promising for the detection of mental stress in horses.

Development of Tinnitus and Hyperacusis in a Mouse Model of Tobramycin Cochleotoxicity.

Aminoglycosides (AG) antibiotics are a common treatment for recurrent infections in cystic fibrosis (CF) patients. AGs are highly ototoxic, resulting in a range of auditory dysfunctions. It was recently shown that the acoustic startle reflex (ASR) can assess behavioral evidence of hyperacusis and tinnitus in an amikacin cochleotoxicity mouse model. The goal of this study was to establish if tobramycin treatment led to similar changes in ASR behavior and to establish whether ebselen can prevent the development of these maladaptive neuroplastic symptoms. CBA/Ca mice were divided into three groups: Group 1 served as a control and did not receive tobramycin or ebselen, Group 2 received tobramycin (200 mg/kg/s.c.) and the vehicle (DMSO/saline/i.p.) daily for 14 continuous days, and Group 3 received the same dose/schedule of tobramycin as Group 2 and ebselen at (20 mg/kg/i.p.). Auditory brainstem response (ABR) and ASR hearing assessments were collected at baseline and 2, 6, 10, 14, and 18 weeks from the start of treatment. ASR tests included input/output (I/O) functions which assess general hearing and hyperacusis, and Gap-induced prepulse inhibition of the acoustic startle (GPIAS) to assess tinnitus. At 18 weeks, histologic analysis showed predominantly normal appearing hair cells and spiral ganglion neuron (SGN) synapses. Following 14 days of tobramycin injections, 16 kHz thresholds increased from baseline and fluctuated over the 18-week recovery period. I/O functions revealed exaggerated startle response magnitudes in 50% of mice over the same period. Gap detection deficits, representing behavioral evidence of tinnitus, were observed in a smaller subset (36%) of animals. Interestingly, increases in ABR wave III/wave I amplitude ratios were observed. These tobramycin data corroborate previous findings that AGs can result in hearing dysfunctions. We show that a 14-day course of tobramycin treatment can cause similar levels of hearing loss and tinnitus, when compared to a 14-day course of amikacin, but less hyperacusis. Evidence suggests that tinnitus and hyperacusis might be common side effects of AG antibiotics.

Cardiac cycle phases affect auditory-evoked potentials, startle eye blink and pre-motor reaction times in response to acoustic startle stimuli

Startle stimuli evoke lower responses when presented during the early as compared to the late cardiac cycle phase, an effect that has been called ‘cardiac modulation of startle’ (CMS). The CMS effect may be associated with visceral-afferent neural traffic, as it is reduced in individuals with degeneration of afferent autonomic nerves. The aim of this study was to investigate whether the CMS effect is due a modulation of only early, automatic stages of stimulus processing by baro-afferent neural traffic, or if late stages are also affected. We, therefore, investigated early and late components of auditory-evoked potentials (AEPs) to acoustic startle stimuli (105, 100, 95 dB), which were presented during the early (R-wave +230 ms) or the late cardiac cycle phase (R +530 ms) in two studies. In Study 1, participants were requested to ignore (n = 25) or to respond to the stimuli with button-presses (n = 24). In Study 2 (n = 23), participants were asked to rate the intensity of the stimuli. We found lower EMG startle response magnitudes (both studies) and slower pre-motor reaction times in the early as compared to the late cardiac cycle phase (Study 1). We also observed lower N1 negativity (both studies), but higher P2 (Study 1) and P3 positivity (both studies) in response to stimuli presented in the early cardiac cycle phase. This AEP modulation pattern appears to be specific to the CMS effect, suggesting that early stages of startle stimulus processing are attenuated, whereas late stages are enhanced by baro-afferent neural traffic.

Can startle response magnitudes be used as a tool to predict sportive capacities? A comparative study between healthy young adults and athletes.

The acoustic startle reflex (ASR) is an intense reaction that involves the contraction of muscle groups in response to an unexpected stimulus. We proposed that an ASR measurement may be used to select physical characteristics among healthy people, including athletes. To find the relationship between the ASR and physical conditioning level, we designed a study to perform ASR measurements, anthropometric measurements, neuromuscular conjugation exercises, strength test, and flexibility test. We studied young adults into 4 groups: male-control, male-athlete, female-control, and female-athlete. Our results showed how the startle amplitude was decreased in athletes compared with controls. In most of the anthropometric parameters, there were differences attending to gender in control groups, but these differences diminished in athletes. In addition, some fitness values were correlated with the latency of the muscle response and with the prepulse inhibition. This study demonstrates that regular practice of a sport, aside from causing changes in common fitness variables, also promotes changes in ASR parameters. In some way, the intense body training stimulates the brain reorganization to enhance some responses related to adapt the ASR. With this study, we are opening a field for those interested in finding out new instruments to discriminate athletes.

Lipopolysaccharide (LPS) induced sickness in early adolescence alters the behavioral effects of the short-chain fatty acid, propionic acid, in late adolescence and adulthood: Examining anxiety and startle reactivity

Early life immune challenges are risk factors for neurodevelopmental disorders. In adolescence, they elicit behavioral symptoms that resemble clinical disorders. Stressors during this time may alter signaling from the gut microbiome, which increases the risk for psychiatric disorders. It was hypothesized that adolescent immune challenges may interact with a gut bacterial product, the short-chain fatty acid, propionic acid (PPA), to potentiate symptoms of anxiety and sensory abnormality. The present study investigated the effects of repeated lipopolysaccharide (LPS) exposure during early adolescence, on the behavioral effects of PPA in late adolescence and adulthood. Male adolescent rats were injected with LPS (0.2 mg/kg i.p.) or the vehicle on postnatal days (P) 28, P30, P32, and P34. They were later administered either PPA (500 mg/kg i.p.) or the vehicle during late adolescence on P40 and P43, and were subsequently tested on the light-dark anxiety test and acoustic startle response, respectively. In adulthood, the rats were again injected with PPA or the vehicle and tested on the light-dark and acoustic startle tasks on P74 and P77. The results of this study showed that LPS and PPA both decreased locomotor activity. PPA reduced vertical activity, percent prepulse inhibition, and acoustic startle response magnitude. LPS increased anxiogenic behaviors and induced a delayed increase in acoustic startle response magnitude in adulthood. Although no LPS and PPA interactions were found, the results of this study suggest that early adolescent immune activation can induce long-term behavioral changes that resemble the complex phenotypes of clinical disorders.

Systemic Treatment with the Enteric Bacterial Fermentation Product, Propionic Acid, Reduces Acoustic Startle Response Magnitude in Rats in a Dose-Dependent Fashion: Contribution to a Rodent Model of ASD.

Autism spectrum disorder (ASD) is a neurodevelopmental disorder, characterized by cognitive and sensorimotor deficits, among others. Hypo-sensitivity and hyper-sensitivity to different stimuli within the same sensory modality, a prominent symptom of ASD, can be assessed by acoustic startle response (ASR) and prepulse inhibition (PPI). Propionic acid (PPA) is a short-chain fatty acid and a by-product of the human gut microbiome. Rodents treated with PPA has been found to produce ASD-related behavioral abnormalities, gastrointestinal discomfort, and conditioned aversions. The present study examined ASR and PPI in adult male rats treated systemically (intraperitoneal injections) with two different doses of PPA. A single injection of PPA produced significant dose-dependent reductions in startle response magnitude relative to control rats. However, PPA-treated rats did not show significant sensorimotor gating abnormalities relative to controls, based on the PPI measures. These findings add to the growing body of evidence supporting the validity of the PPA rodent model of ASD.

Relationship between physiological and parent-observed auditory over-responsiveness in children with typical development and those with autism spectrum disorders.

The objective of this study was to investigate relationships between caregiver-reported sensory processing abnormalities, and the physiological index of auditory over-responsiveness evaluated using acoustic startle response measures, in children with autism spectrum disorders and typical development. Mean acoustic startle response magnitudes in response to 65–105 dB stimuli, in increments of 10 dB, were analyzed in children with autism spectrum disorders and with typical development. Average peak startle latency was also examined. We examined the relationship of these acoustic startle response measures to parent-reported behavioral sensory processing patterns in everyday situations, assessed using the Sensory Profile for all participants. Low-threshold scores on the Sensory Profile auditory section were related to acoustic startle response magnitudes at 75 and 85 dB, but not to the lower intensities of 65 dB. The peak startle latency and acoustic startle response magnitudes at low-stimuli intensities of 65 and 75 dB were significantly related to the low-threshold quadrants (sensory sensitivity and sensation avoiding) scores and to the high-threshold quadrant of sensation seeking. Our results suggest that physiological assessment provides further information regarding auditory over-responsiveness to less-intense stimuli and its relationship to caregiver-observed sensory processing abnormalities in everyday situations.

Effect of stress and attention on startle response and prepulse inhibition

The startle reflex magnitude can be modulated when a weak stimulus is presented before the onset of the startle stimulus, a phenomenon termed prepulse inhibition (PPI). Previous research has demonstrated that emotional processes can modulate PPI and startle intensity, but the available evidence is inconclusive. In order to obtain additional evidence in this domain, we conducted two experiments intended to analyze the effect of induced stress and attentional load on PPI and startle magnitude. Specifically, in Experiment 1 we used a between subject strategy to evaluate the effect on startle response and PPI magnitude of performing a difficult task intended to induce stress in the participants, as compared to a group exposed to a control task. In Experiment 2 we evaluated the effect of diverting attention from the acoustic stimulus on startle and PPI intensity. The results seem to indicate that induced stress can reduce PPI, and that startle reflex intensity is reduced when attention is directed away from the auditory stimulus that induces the reflex.

Individual differences in behavioral activation and cardiac vagal control influence affective startle modification

The startle response (SR) has a close relationship with stress responses. Startle modification (SRM) has been widely used to study stress disorders (e.g., posttraumatic stress disorder). The framework of the behavioral inhibition and activation systems (BIS/BAS) has been thought to correspond with withdrawal and approach motivational processes underlying affective SRM and can influence stress reactivity. Vagally-mediated cardiac activity as indexed by heart rate variability (HRV) has been associated with SRM and regulatory processes during stress. In the present study, the influence of individual differences in the BIS/BAS and resting HRV on affective SRM were examined. Eighty-six subjects viewed affective pictures while acoustic SR stimuli were delivered. Individual differences in motivation were measured by the BIS/BAS scales. The magnitude of SR was assessed as electromyographic activity of the SR eyeblink during pictures of different valences. Resting HRV was derived from electrocardiography. In contrast to previous studies, the present results showed that startle inhibition and potentiation were related to BAS and HRV, but not to BIS. There was also an interaction of BAS and HRV, indicating that the relationship between HRV and SRM strengthened as BAS scores decreased. The present findings suggest that BAS may relate to both withdrawal and approach, and trait stress reactivity is influenced by BAS and cardiac vagal activity. In addition, BAS moderates the relationship between cardiac vagal activity and SRM. These findings have both theoretical and practical implications for the study of SRM, stress disorders, and health.

Cardiac modulation of startle is altered in depersonalization-/derealization disorder: Evidence for impaired brainstem representation of baro-afferent neural traffic

Patients with depersonalization-/derealization disorder (DPD) show altered heartbeat-evoked brain potentials, which are considered psychophysiological indicators of cortical representation of visceral-afferent neural signals. The aim of the current investigation was to clarify whether the impaired CNS representation of visceral-afferent neural signals in DPD is restricted to the cortical level or is also present in sub-cortical structures. We used cardiac modulation of startle (CMS) to assess baro-afferent signal transmission at brainstem level in 22 DPD and 23 healthy control individuals. The CMS paradigm involved acoustic startle stimuli (105dB(A), 50ms) elicited 0, 100, 200, 300, 400 and 500ms after a cardiac R-wave. In healthy control individuals, we observed lower startle responses at 100 and 300ms than at 0 and 400ms after an R-wave. In DPD patients, no effect of the cardiac cycle on startle response magnitude was found. We conclude that the representation of visceral-afferent neural signals at brainstem level may be deficient in DPD. This effect may be due to increased peripheral sympathetic tone or to dysregulated signal processing at brainstem level.

Behavioural, endocrine and cardiac autonomic responses to a model of startle in horses

Startle is a fast response elicited by sudden acoustic, tactile or visual stimuli in a variety of animal species and in humans. The magnitude of startle response can be modulated by external and internal variables and can be a useful tool to study the sensory-motor integration in animals. Different stimuli have been used to induce startle in horses, which makes it difficult to compare the responses to these different approaches. The present study uses ultra-short-term heart rate variability (HRV) analysis to characterize the cardiac autonomic modulation, reactivity assessment and blood cortisol measurements to describe the behavioural and endocrine responses to a simple, easy to replicate, effective and safe method of startle (an umbrella is abruptly opened near the horse). The ultra-short-term (64s) heart rate (HR) series were interpolated (4Hz) and divided into 256 points segments then the spectra calculated (Fast Fourier Transform). The spectra were then integrated into low (LF; 0.01–0.07Hz; Index of Cardiac Sympathetic Modulation) and high (HF; 0.07–0.50Hz; Index of Cardiac Parasympathetic Modulation) frequency bands. Following the startle test, the HR (p=0.0101), the power of the LF band of the cardiac interval spectrum (p=0.0002) and the LF/HF ratio (p=0.0066) were found to be higher, whereas the power of the HF band of the cardiac interval spectrum was found to be lower (p=0.0002). Also, the horses showed a noticeable escape response, with latency of reaction varying from 0.28 to 1.28s, duration of reaction ranging from 1.52 to 7.92s and escape distance covered varying from 3.43 to 9.97m. However, the endocrine measurements failed to reveal significant changes in the cortisol levels after the startle test. We conclude that the startle test used in the current study was effective to produce changes in behavioural parameters and cardiac autonomic modulation of the horses and can therefore be an appropriate tool for neurobiological studies. Furthermore, the use of ultra-short segments (64 s) for HRV analysis appears to be effective and promising for the detection of mental stress in horses.