Physiological Habituation Research Articles

Normative values of the nociceptive blink reflex habituation

Introduction: Habituation is a physiological phenomenon, characterized by response reduction to repeated stimulus presentation. In headache disorders, habituation studies have involved different paradigms with several stimulation parameters and sensory modalities, and consistently showed impaired habituation in primary headaches in the interictal phase. The nociceptive blink reflex (nBR) and its related R2 response, modulated by a polysynaptic network in the trigeminocervical complex, is one of the most studied in the field. The lack of nBR habituation normative data hampered the possibility to draw conclusions regarding the functional status of individual patients. The present study aims to define normative values for the nBR habituation process in healthy subjects without a personal diagnosis and family history of migraine, or other headache disorders.Methods: We enrolled 40 healthy subjects (24 females, 32.7±11.6 years) for nBR recording and nBR habituation assessment. To assess the habituation of nBR, 26 consecutive stimuli were administered at three different and randomized stimulus frequencies (0.2, 0.3, 0.5 Hz). After excluding the first response, the remaining 25 area under the curve (AUC) were divided in 5 blocks, and the average values of the AUC was calculated for each block. The percentage reduction in the AUC of the fifth block, compared to the first, represents the habituation index (HI) value. We considered a one-tailed 10th percentile threshold as the lower threshold of normative values for nBR HI.Results: The habituation phenomenon was confirmed for all study frequencies. The absolute AUC of the R2 component across the five blocks of stimulation was higher in female subjects when compared to male for 0.5 Hz (p=0.021) and 0.2 Hz (p=0.007). We found a frequency-dependent habituation pattern, being lower at the 0.2 Hz stimulation when compared to 0.5 Hz (p=0.001), and 0.3 Hz (p=0.008). The average HIs were 73.1±13.6 at 0.5 Hz, 69.2±15.0 at 0.3 Hz, and 61.1±21.4 at 0.2 Hz. HIs were comparable between male and female subjects, without correlations with age, intensity of stimulation, and latency of the R2 component. The 10th percentile of the HIs was 43.5% for 0.5 Hz, 55.8% for 0.3 Hz, and 28.6% for 0.2 Hz.Conclusions: We investigated the nBR habituation in a population of healthy subjects for normative data collection. We described a frequency- dependent degree of habituation, being more pronounced at higher frequencies of stimulation. Moreover, we described gender-related features of response behaviour, which is extremely important in the migraine field. Our study further characterized the physiological habituation phenomenon in healthy controls exposed to a nociceptive stimulation. The definition of a normative habituation value will open novel possibilities in the study of migraine, as well as other headache and pain disorders.

Repeated hypoxic episodes allow hematological and physiological habituation in rainbow trout.

Introduction: Under climate change, the increase in temperature in aquatic environments may induce oxygen depletion. In extreme cases, low oxygen may become a limiting factor for fish, thus generating stress. In addition, consecutive hypoxic episodes may complicate the recovery of individuals and hinder their ability to modulate physiological and biochemical responses to maintain homeostasis. Thus, the aim of this study was to determine the hematological and physiological responses of rainbow trout under a condition of repeated hypoxic and manipulation stresses at three different time points. Methods: Every hypoxic episode consisted of exposing the fish to low dissolved oxygen concentrations (2 mgO2/L for 1 h). Following the exposure, the fish were allowed to recover for 1 h, after which they were sampled to investigate hematological and physiological parameters. Results and discussion: The results showed a pattern of habituation reflected by values of hematocrit, hemoglobin, and mean corpuscular volume, indicating a certain ability of rainbow trout to resist this type of repeated hypoxic events, provided that the fish can have some recovery time between the exposures.

Immersive Virtual Reality Exposures for the Treatment of Childhood Anxiety.

Exposure-based cognitive behavior therapy (CBT) has demonstrated efficacy and is recommended as a front-line treatment for childhood anxiety. Unfortunately, challenges exist that impact the effective implementation of exposure-based CBT in clinical practice. One of the primary challenges is the accessibility and availability of exposure stimuli (e.g., spiders, storms, heights) in CBT sessions. Immersive virtual reality (VR) has shown promise as a scalable and sustainable solution to address this clinical need, but remains largely untested in youth with anxiety disorders. Here, we examine the use of VR exposures in the treatment of youth with an anxiety disorder (i.e., specific phobias). We aimed to investigate: (1) the feasibility and clinical benefit of VR exposures; (2) whether VR exposures elicit changes in physiological arousal and/or subjective distress; and (3) whether habituation serves as a mechanism across physiological and subjective outcomes for VR exposures. Three youth and their parents completed a clinical evaluation, which was followed by a one session treatment (OST) with VR exposures. Afterward, youth and parents completed clinical assessments one-week and 1-month after treatment. Immersive VR exposures were found to be feasible and demonstrated clinical benefit for reducing anxiety severity. Additionally, VR exposures elicited changes in both physiological and subjective outcomes. Finally, physiological habituation to VR exposures was observed among participants who exhibited treatment response at follow-up. Collectively, these findings demonstrate preliminary evidence that VR exposures are feasible, tolerable, and show some therapeutic benefit for treating youth with anxiety.

Native species exhibit physiological habituation to invaders: a reason for hope.

Animals cope with environmental perturbations through the stress response, a set of behavioural and physiological responses aimed to maintain and/or return to homeostasis and enhance fitness. Vertebrate neuroendocrine axis activation in response to environmental stressors can result in the secretion of glucocorticoids (GCs), whose acute increases may be adaptive, while chronic elevation may be detrimental. Invasive grey squirrels (Sciurus carolinensis) act as a stressor eliciting elevation of GCs in native red squirrels (Sciurus vulgaris). Here we used 6-year data of variation in faecal glucocorticoid metabolite (FGM) concentrations following invasion by grey squirrels in three red squirrel populations, to identify if red squirrels showed physiological habituation to this stressor. The decrease in FGMs over time was more pronounced shortly after invasion and at high densities of grey squirrels while it decreased less strongly and was no longer influenced by the invader density as time since invasion elapsed. At the individual level, FGMs also decreased more markedly as each red squirrel experienced prolonged contact with the invader. Our study provides compelling new data suggesting that native species in the wild can habituate to prolonged contact with invasive species, showing that they may avoid the potentially harmful effects of chronic elevations in GCs.

Computer Based Body Exposure in Adolescents With Anorexia Nervosa: A Study Protocol.

Body dissatisfaction is a core feature of eating disorders (EDs) and plays an essential role in the development and maintenance of anorexia nervosa (AN). In the current study, a computer based body exposure intervention is conducted and evaluated regarding short-term effects on body dissatisfaction, psychopathology, viewing patterns, and stress reactivity. Within a randomized controlled trial (RCT) female adolescents and young women with AN are either receiving the intervention or treatment as usual (TAU). Furthermore, in a transdiagnostic approach, a highly body-dissatisfied group of clinical control participants obtaining the intervention will be surveyed to identify AN-specific processes. The standardized four-session body exposure intervention using photographs of the own body is adapted from a manualized body image treatment program for computer use. Psychopathology (body dissatisfaction, body image avoidance, body checking, depression, anxiety) is assessed via standardized questionnaires before and after the intervention. During each session, attentional biases regarding one's own body are measured via eye tracking, stress levels are measured via subjective ratings, heart rate variability, as well as salivary cortisol and alpha amylase. Between- and within-subject effects will be assessed. The pilot study aims to identify short-term effects of the intervention on body dissatisfaction and attentional bias, as well as to investigate the potential underlying mechanism of physiological habituation.

Exposure to violence and nonassociative learning capability confer risk for violent behavior.

A substantial body of research demonstrates that experiences of trauma are associated with disruptions in learning processes. Specifically, research shows altered nonassociative and associative learning in individuals who report traumatic experiences. The combination of trauma and altered learning also confers risk for negative health and mental health outcomes. One subtype of trauma that receives less attention in terms of its association with learning processes is exposure to violence (ETV)-witnessing violence, hearing gunfire, and/or being the victim of violence. Preliminary evidence shows that ETV is related to disruptions in nonassociative and associative learning processes, but these studies did not use direct and objective measures of learning. Additionally, research documents a robust relationship between ETV and violent behavior, but there has been no work examining whether it is the combination of elevated levels of ETV and learning patterns that poses a risk for engagement in violent behavior. In the present study, 164 participants completed two auditory basic learning tasks, one measuring nonassociative learning (habituation) and another measuring associative learning acquisition (classical conditioning), while skin conductance was recorded. Results indicate that individuals with higher ETV display a decreased likelihood of physiological habituation, but ETV is unrelated to associative learning acquisition. Further, the combination of higher ETV and nonhabituation predicts a greater number of violent crimes. These findings suggest that, for those with higher ETV, variations in capability for nonassociative learning may confer risk for violent behavior. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

The use of whole-body cryotherapy: time- and dose-response investigation on circulating blood catecholamines and heart rate variability

PurposeA predominance of parasympathetic drive is observed following cold exposure. Such modulation of the autonomic nervous system (ANS) is associated with faster post-exercise recovery. Within this context, whole-body cryotherapy (WBC) has been spreading in sport medicine, though the optimal temperature and frequency are unclear. The aim of this study was to examine the effects of different cryotherapy conditions on the sympathovagal balance.MethodsForty healthy males were randomly assigned into five different groups (− 110 °C, − 60 °C, − 10 °C, control temperature [≃ 24 °C]) and undertook 5 WBC sessions over 5 consecutive days. Cardiac autonomic activity was assessed through heart rate variability (HRV) using power density of high frequency (HF), root-mean square difference of successive R–R intervals (RMSSD) and sympathovagal balance (LF/HF). Systemic sympathetic activity was assessed via circulating blood catecholamines.ResultsMean weekly RMSSD (pre: 48 ± 22 ms, post: 68 ± 29 ms) and HF (pre: 607 ± 692 ms2, post: 1271 ± 1180 ms2) increased (p < 0.05) from pre to post WBC, only in the − 110 °C condition. A rise in plasma norepinephrine was found after the first − 110 °C WBC session only (pre: 173 ± 98, post: 352 ± 231 ng L−1, p < 0.01); whereas, it was not significant after the 5th session (pre: 161 ± 120, post: 293 ± 245 ng L−1, p = 0.15).ConclusionThese results suggest that one − 110 °C WBC exposure is required to stimulate the ANS. After five daily exposures, a lower autonomic response was recorded compared to day one, therefore suggesting the development of physiological habituation to WBC.

Short-term neurophysiological effects of sensory pathway neurorehabilitation strategies on chronic poststroke oropharyngeal dysphagia.

Neurorehabilitation strategies for chronic poststroke (PS) oropharyngeal dysphagia (OD) have been mainly focused on the neurostimulation of the pharyngeal motor cortex with only marginal effects. In contrast, treatments targeting the PS oropharyngeal sensory pathway dysfunction offer very promising results, but there is little knowledge on the underlying mechanisms. We aimed to explore the neurophysiological mechanisms behind the effect of three sensory neurostimulation strategies. We carried out a randomized two-blinded parallel group's crossover sham-controlled clinical trial in 36 patients with unilateral stroke and chronic unsafe swallow to investigate the effect of repetitive transcranial magnetic stimulation (rTMS) of the primary sensory cortex (A), oral capsaicin (B) and intra-pharyngeal electrical stimulation (IPES; C). The effect was evaluated immediately after the interventions with videofluoroscopy (VFS) and motor/sensory evoked potentials (MEP/SEP). Interventions induced no changes in the biomechanics of the swallow response during VFS. However, an enhancement of motor cortex excitability (latency shortening and increased size of thenar MEP) was found with active interventions (A+B+C, and B/C alone; P<.05 for all) but not with sham. Active but not sham interventions shortened pharyngeal SEP latency in the ipsilesional hemisphere (A+B+C: P2-peak, P=.039; A: N2-peak, P=.034) and antagonized the physiological habituation in pharyngeal MEP (A+B+C and A alone, P<.05 for both). Sensory pathway neurostimulation strategies caused immediate enhancement of motor cortex excitability with peripheral strategies (capsaicin and IPES) and of pharyngeal sensory conduction with rTMS. These changes support the use of sensory neurorehabilitation strategies in promoting swallow recovery in chronic PS-OD.

Sensory Habituation as a Shared Mechanism for Sensory Over-Responsivity and Obsessive-Compulsive Symptoms.

BackgroundSome individuals who suffer from obsessive–compulsive (OC) disorder (OCD), report disturbing sensory preoccupations. The inability to stop obsessing over stimuli resonates with a difficulty in sensory habituation. Impaired sensory habituation, to a degree that clearly dysregulates response to sensory stimuli, and impairs participation in everyday activities, can be part of a disorder known as sensory over-responsivity (SOR). Although previous studies indicated a correlation between OCD and SOR, physiological experiments show that individuals with OCD are not more sensitive to sensory stimuli than controls. In the current study, we (1) validated a sensory habituation psycho-physiological protocol and (2) tested whether a “slow to habituate” mechanism can explain the occurrence of elevated SOR and OC symptoms.MethodsWe designed a protocol to test auditory sensory habituation through electrodermal activity (EDA) recording. The protocol included two randomly ordered aversive and neutral sound conditions; each set of six everyday life sounds was presented as a continuous stimulus. During the presentation of sounds, EDA was measured and participants could press a button to shorten the stimuli. Participants also completed sensory and OC symptom questionnaires. Participants included 100 typically developing adults that were divided into high versus low OC symptom groups. Mixed models analysis was used throughout to meet the need for capturing the temporal nature of habituation.ResultsDistinct physiological indices were computed to measure sensitivity versus habituation. Habituation was slower in the aversive versus neutral condition. Sensitivity was higher for the aversive stimuli. Self-report of sensory habituation and sensitivity partially correlated with the physiological habituation indices. A comparison of the physiological pattern between those with high versus low OC symptoms revealed significant differences in the habituation and sensitivity indices, across conditions.ConclusionThe interplay between SOR and OC symptoms can be explained by a “slow to habituate” mechanism. Identifying behavioral and physiological markers of sensory problems in OCD is important for assessment, intervention and the discovery of underlying mechanisms.

The time course of responding to aversiveness in females with a history of non-suicidal self-injury

Non-suicidal self-injury is a risk factor for suicidal behavior, particularly in females. Two prominent theories of suicide suggest that habituation to the psychophysiological aversiveness of NSSI is a mechanism by which NSSI exposure may lead to increased risk for suicide. Several laboratory studies examining the relationship between physiological habituation and suicide attempt history have yielded mixed results, potentially due to their use of broad measures of physiological arousal and/or focus on specific psychopathologies. However, no studies have examined the association between the time course (e.g., habituation, initial reactivity) of responding to aversiveness and NSSI, which may help to elucidate psychophysiological mechanisms of NSSI. Therefore, we examined habituation and initial reactivity to aversiveness (indexed by the time course of acoustic startle reflex, a well-validated measure of defensive responding) in three groups of young adult females – those with a history of NSSI, psychiatric controls matched on potential confounds (e.g., psychopathology, trauma history, demographics), and healthy controls. Results indicated that individuals with a history of NSSI exhibited blunted initial reactivity and marginally slower habituation to aversiveness relative to the two control groups. The NSSI group's insensitivity to aversiveness may reflect prior psychophysiological habituation, and may be a mechanism through which prior NSSI exposure leads to increased risk for suicidal behavior.

Stop Making Noise! Auditory Sensitivity in Adults with an Autism Spectrum Disorder Diagnosis: Physiological Habituation and Subjective Detection Thresholds

Auditory sensitivities are common among people with autism spectrum disorder diagnoses (ASD). As underlying factors are unknown, we examined whether ASD adults (NASD = 33; NTypically Developing = 31; 25–45 years; IQ > 70): (1) habituated slower to auditory stimuli; (2) had lower auditory detection thresholds; and (3) whether these mechanisms related to self-reported auditory sensitivities. Two auditory stimuli (tone, siren) were repeated, whilst skin conductance responses were recorded to measure habituation. Detection thresholds were measured by stepwise reductions in tone volume. We found no evidence in favor of our hypotheses, but ASD adults did rate the auditory stimuli as more arousing. Based on explorative analyses, we argue that studying the strength of physiological responses to auditory stimuli is needed to understand auditory sensitivities.

Measuring the conditioned response: A comparison of pupillometry, skin conductance, and startle electromyography

In human fear conditioning studies, different physiological readouts can be used to track conditioned responding during fear learning. Commonly employed readouts such as skin conductance responses (SCR) or startle responses have in recent years been complemented by pupillary readouts, but to date it is unknown how pupillary readouts relate to other measures of the conditioned response. To examine differences and communalities among pupil responses, SCR, and startle responses, we simultaneously recorded pupil diameter, skin conductance, and startle electromyography in 47 healthy subjects during fear acquisition, extinction, and a recall test on 2 consecutive days. The different measures correlated only weakly, displaying most prominent differences in their response patterns during fear acquisition. Whereas SCR and startle responses habituated, pupillary measures did not. Instead, they increased in response to fear conditioned stimuli and most closely followed ratings of unconditioned stimulus (US) expectancy. Moreover, we observed that startle-induced pupil responses showed stimulus discrimination during fear acquisition, suggesting a fear potentiation of the auditory pupil reflex. We conclude that different physiological outcome measures of the conditioned response inform about different cognitive-affective processes during fear learning, with pupil responses being least affected by physiological habituation and most closely following US expectancy.

Integrating Mindfulness and Biofeedback in the Treatment of Posttraumatic Stress Disorder

Teaching mindfulness skills as part of psychological rehabilitation for PTSD patients can be highly beneficial. However, certain factors must be considered such as determining at what stage of therapy to introduce mindfulness training, the length of the practices, and the focal point of the training (e.g., attention, open focus, loving kindness). This article will address these considerations and outline ways in which psychophysiological monitoring and biofeedback can assist therapists in guiding their clients through the process. Specifically, it will highlight how the elevated arousal levels typical of PTSD and the lack of physiological habituation result in rigid and negatively biased attention, which in turn propels the elevated arousal levels into a vicious cycle. Mindfulness practices and approach may help achieve increased flexibility; however, the process must be tailored for each client in accordance with the severity of his or her PTSD symptoms.

Special Issue: More Mindful, More Accepting, More Compassionate, and More Self-Regulation

The cover of this special issue of Biofeedback shows a nature image evocative of mindfulness (Thanks to Shutterstock for the image.)This special issue on “More Mindful, More Accepting, More Compassionate, and More Self-Regulation” is a continuation of the themes presented in several previous special issues of the Biofeedback magazine on mindfulness. The guest editors are Inna Khazan and Donald Moss. The editors have once again gathered a variety of authors contributing articles on the theme that becoming more mindful, more accepting, and more compassionate leads naturally to better self-regulation, and adds a dimension to clinical biofeedback and neurofeedback.In the lead article, Leah Lagos presents a protocol for integrating mindfulness and heart rate variability biofeedback, with the goal of fostering courage, confidence, and resilience. She applies this protocol in optimal performance work in athletics as well as in corporate consulting work. Her article includes a case narrative of a 42-year-old corporate executive seeking assistance with work stress and negative emotions. The combination of mindfulness and heart rate variability biofeedback enabled him to tune out negative thoughts, improve his confidence, and gain trust in his ability to perform optimally.Nimrod Tom Oren, Dror Gronich, and Arnon Rolnick introduce an innovative “Stairway to Togetherness” model for working with couples and families. Their model uses mindfulness interventions and biofeedback to de-escalate conflicts, reduce emotional and physiological reactivity, and enhance psychophysiological mutual-regulation patterns. Their stairway model emphasizes moving upward from a relational basement of reactivity and suspicion, through a ground floor of cognitive and physiological calming, through an acceptance floor of increased mindfulness and mutual compassion, to a top floor of high hopes and togetherness.Yuval Oded provides an article exploring the integration of mindfulness and biofeedback into the psychotherapeutic treatment of posttraumatic stress disorder (PTSD). Oded examines research on the psychophysiological, perceptual, and cognitive features of PTSD. He highlights how the elevated arousal levels typical of PTSD and the lack of physiological habituation result in rigid and negatively biased attention, which in turn propels the elevated arousal levels in a vicious cycle of posttraumatic experiencing. Oded then introduces a detailed approach combining mindfulness practices, psychophysiological monitoring, and biofeedback to assist therapists in guiding their clients through the psychotherapeutic process.

Physiological responses to repeated stress in individuals with high and low trait resilience

This study examined individual differences in trait resilience in physiological recovery from, and physiological habituation to, repeated stress (i.e. public speaking). Eighty-two college students were categorized as either high (n=40) or low (n=42) on trait resilience, based on the scores of the Connor-Davidson Resilience Scale (CD-RISC). Subjective and physiological data were collected from participants across seven laboratory stages: baseline, stress anticipation 1, stress 1, post-stress 1, stress anticipation 2, stress 2, and post-stress 2. Results indicated that high-trait-resilient participants exhibited more complete heart rate (HR), systolic and diastolic blood pressure (SBP, DBP) recovery from the first and second stress anticipation exposures as compared to low-trait-resilient participants. High-trait-resilient participants demonstrated higher resting respiratory sinus arrhythmia (RSA) coupled with more complete RSA recovery from the first and second stress anticipation exposures as compared to their low-trait-resilient counterparts. Moreover, high-trait-resilient participants exhibited pronounced SBP and DBP habituation across two successive stress anticipation exposures, with greater decreases in SBP and DBP reactivity to recurrent stress anticipation as compared to the low-trait-resilient participants. These findings suggest an adaptive physiological response pattern to recurrent stress in high-trait-resilient individuals.

Expectation to feel more pain disrupts the habituation of laser-pain rating and laser-evoked potential amplitudes

Increased pain perception due to the expectation to feel more pain is called nocebo effect. The present study aimed at investigating whether: (1) the mere expectation to feel more pain after the administration of an inert drug can affect the laser-pain rating and the laser-evoked potential (LEP) amplitude, and (2) the learning potentiates the nocebo effect. Eighteen healthy volunteers were told that an inert cream, applied on the right hand, would increase the laser pain and LEP amplitude to right hand stimulation. They were randomly assigned to either “verbal session” or “conditioning session”. In the “verbal session”, LEPs to both right and left hand stimulation were recorded at the same intensity before (baseline) and after cream application. In the “conditioning session”, after an initial cream application the laser stimulus intensity was increased surreptitiously to make the subjects believe that the treatment really increased the pain sensation. Then, the cream was reapplied, and LEPs were recorded at the same stimulus intensity as at the baseline. It was found that the verbal suggestion to feel more pain disrupted the physiological habituation of the laser-pain rating and LEP amplitude to treated (right) hand stimulation. Unlike previously demonstrated for the placebo effect, the learning did not potentiate the nocebo effect.

Peripheral sensitization reduces laser-evoked potential habituation

Laser-evoked potential (LEP) habituation was investigated under the influence of capsaicin-induced peripheral and central sensitization. Fifteen subjects received 100 repetitive painful laser stimuli at the right hand dorsum at primary (application area; condition I) and secondary areas (beyond application area; condition II) in two different sessions after applying capsaicin topically. Conditions I and II were compared to a control condition without capsaicin application. N1, N2, and P2 latencies and N1 and N2/P2 amplitudes were recorded by EEG. Quantitative sensory testing (QST) and the Liewald Diary reaction time experiment were used as control tests. QST documented heat hyperalgesia as a sign of peripheral sensitization in the primary area and pinprick hyperalgesia in the primary and secondary area as a sign of central sensitization, after applying capsaicin. The N2/P2 amplitude habituation was significantly reduced in the primary area compared to controls (the primary area represents peripheral sensitization). The LEPs of the secondary area (the secondary area represents central sensitization) showed no significant N2/P2 amplitude habituation compared to controls. The comparison between conditions I vs. II showed no significant difference regarding N2/P2 amplitude and laser pain rating. Capsaicin-induced central sensitization does not alter LEP habituation. The physiological habituation of LEP amplitudes is reduced due to peripheral mechanisms after applying capsaicin topically. These findings form a basis for future studies, which use the habituation paradigm to investigate pain conditions promoted by sensitization phenomena.

An exploratory analysis of the relations between the rate of physiological habituation, the acquired capability for suicide, and acute risk factors for suicide

Purpose – The interpersonal theory of suicide proposes that an individual must acquire the capability for suicide to carry out a near-lethal or lethal suicide attempt. This capability develops via habituation in response to painful and provocative life events. Some individuals might be more vulnerable to developing the capability for suicide because they habituate more quickly to stimuli. The purpose of this paper is to examine the relations between the rate of physiological habituation and acquired capability, proxies for acquired capability, and acute risk factors for suicide. Design/methodology/approach – Depressed, suicidal individuals completed self-report assessments and a startle reflex task assessing the rate or speed of physiological habituation in response to repeated bursts of white noise. Findings – Slower habituation was associated with hopelessness and negative stressors. The rate of habituation was not associated with acquired capability. Originality/value – The current study informs the understanding of how physiological habituation is related to suicide risk factors.

Experience, cortisol reactivity, and the coordination of emotional responses to skydiving.

Physiological habituation to laboratory stressors has previously been demonstrated, although the literature remains equivocal. Previous studies have found skydiving to be a salient naturalistic stressor that elicits a robust subjective and physiological stress response. However, it is uncertain whether (or how) stress reactivity habituates to this stressor given that skydiving remains a risky, life-threatening challenge with every jump despite experience. While multiple components of the stress response have been documented, it is unclear whether an individual’s subjective emotions are related to their physiological responses. Documenting coordinated responsivity would lend insight into shared underlying mechanisms for the nature of habituation of both subjective (emotion) and objective (cortisol) stress responses. Therefore, we examined subjective emotion and cortisol responses in first-time compared to experienced skydivers in a predominantly male sample (total n = 44; males = 32, females = 12). Hierarchical linear modeling (HLM) revealed that experienced skydivers showed less reactivity and faster recovery compared to first-time skydivers. Subjective emotions were coordinated with physiological responses primarily within first-time skydivers. Pre-jump anxiety predicted cortisol reactivity within first-time, but not experienced, skydivers. Higher post-jump happiness predicted faster cortisol recovery after jumping although this effect overlapped somewhat with the effect of experience. Results suggest that experience may modulate the coordination of emotional response with cortisol reactivity to skydiving. Prior experience does not appear to extinguish the stress response but rather alters the individual’s engagement of the HPA axis.

Sleep Dissolves Illusion: Sleep Withstands Learning of Visuo-Tactile-Proprioceptive Integration Induced by Repeated Days of Rubber Hand Illusion Training

Multisensory integration is a key factor in establishing bodily self-consciousness and in adapting humans to novel environments. The rubber hand illusion paradigm, in which humans can immediately perceive illusory ownership to an artificial hand, is a traditional technique for investigating multisensory integration and the feeling of illusory ownership. However, the long-term learning properties of the rubber hand illusion have not been previously investigated. Moreover, although sleep contributes to various aspects of cognition, including learning and memory, its influence on illusory learning of the artificial hand has not yet been assessed. We determined the effects of daily repetitive training and sleep on learning visuo-tactile-proprioceptive sensory integration and illusory ownership in healthy adult participants by using the traditional rubber hand illusion paradigm. Subjective ownership of the rubber hand, proprioceptive drift, and galvanic skin response were measured to assess learning indexes. Subjective ownership was maintained and proprioceptive drift increased with daily training. Proprioceptive drift, but not subjective ownership, was significantly attenuated after sleep. A significantly greater reduction in galvanic skin response was observed after wakefulness compared to after sleep. Our results suggest that although repetitive rubber hand illusion training facilitates multisensory integration and physiological habituation of a multisensory incongruent environment, sleep corrects illusional integration and habituation based on experiences in a multisensory incongruent environment. These findings may increase our understanding of adaptive neural processes to novel environments, specifically, bodily self-consciousness and sleep-dependent neuroplasticity.