Optimising a model-based approach to inferring fear learning from skin conductance responses

Dimensionality and optimal combination of autonomic fear-conditioning measures in humans

Fear conditioning, also termed threat conditioning, is a commonly used learning model with clinical relevance. Quantification of threat conditioning in humans often relies on conditioned autonomic responses such as skin conductance responses (SCR), pupil size responses (PSR), heart period responses (HPR), or respiration amplitude responses (RAR), which are usually analyzed separately. Here, we investigate whether inter-individual variability in differential conditioned responses, averaged across acquisition, exhibits a multi-dimensional structure, and the extent to which their linear combination could enhance the precision of inference on whether threat conditioning has occurred. In a mega-analytic approach, we re-analyze nine data sets including 256 individuals, acquired by the group of the last author, using standard routines in the framework of psychophysiological modeling (PsPM). Our analysis revealed systematic differences in effect size between measures across datasets, but no evidence for a multidimensional structure across various combinations of measures. We derive the statistically optimal weights for combining the four measures and subsets thereof, and we provide out-of-sample performance metrics for these weights, accompanied by bias-corrected confidence intervals. We show that to achieve the same statistical power, combining measures allows for a relevant reduction in sample size, which in a common scenario amounts to roughly 24%. To summarize, we demonstrate a one-dimensional structure of threat conditioning measures, systematic differences in effect size between measures, and provide weights for their optimal linear combination in terms of maximal retrodictive validity.

Pain reflects the informational value of nociceptive inputs

ABSTRACT

Pain perception and its modulation are fundamental to human learning and adaptive behavior. This study investigated the hypothesis that pain perception is tied to pain's learning function. Thirty-one participants performed a threat conditioning task where certain cues were associated with a possibility of receiving a painful electric shock. The cues that signaled potential pain or safety were regularly changed, requiring participants to continually establish new associations. Using computational models, we quantified participants' pain expectations and prediction errors throughout the task and assessed their relationship with pain perception and electrophysiological responses. Our findings suggest that subjective pain perception increases with prediction error, that is, when pain was unexpected. Prediction errors were also related to physiological nociceptive responses, including the amplitude of nociceptive flexion reflex and electroencephalography markers of cortical nociceptive processing (N1-P2-evoked potential and gamma-band power). In addition, higher pain expectations were related to increased late event-related potential responses and alpha/beta decreases in amplitude during cue presentation. These results further strengthen the idea of a crucial link between pain and learning and suggest that understanding the influence of learning mechanisms in pain modulation could help us understand when and why pain perception is modulated in health and disease.

The impact of doxycycline on human contextual fear memory

RATIONALE

 Previous work identified an attenuating effect of the matrix metalloproteinase (MMP) inhibitor doxycycline on fear memory consolidation. This may present a new mechanistic approach for the prevention of trauma-related disorders. However, so far, this has only been unambiguously demonstrated in a cued delay fear conditioning paradigm, in which a simple geometric cue predicted a temporally overlapping aversive outcome. This form of learning is mainly amygdala dependent. Psychological trauma often involves the encoding of contextual cues, which putatively necessitates partly different neural circuits including the hippocampus. The role of MMP signalling in the underlying neural pathways in humans is unknown.

METHODS

Here, we investigated the effect of doxycycline on configural fear conditioning in a double-blind placebo-controlled randomised trial with 100 (50 females) healthy human participants.

RESULTS

Our results show that participants successfully learned and retained, after 1 week, the context-shock association in both groups. We find no group difference in fear memory retention in either of our pre-registered outcome measures, startle eye-blink responses and pupil dilation. Contrary to expectations, we identified elevated fear-potentiated startle in the doxycycline group early in the recall test, compared to the placebo group.

CONCLUSION

Our results suggest that doxycycline does not substantially attenuate contextual fear memory. This might limit its potential for clinical application.

Measuring human context fear conditioning and retention after consolidation

Fear conditioning is a laboratory paradigm commonly used to investigate aversive learning and memory. In context fear conditioning, a configuration of elemental cues (conditioned stimulus [CTX]) predicts an aversive event (unconditioned stimulus [US]). To quantify context fear acquisition in humans, previous work has used startle eyeblink responses (SEBRs), skin conductance responses (SCRs), and verbal reports, but different quantification methods have rarely been compared. Moreover, preclinical intervention studies mandate recall tests several days after acquisition, and it is unclear how to induce and measure context fear memory retention over such a time interval. First, we used a semi-immersive virtual reality paradigm. In two experiments (N = 23 and N = 28), we found successful declarative learning and memory retention over 7 d but no evidence of other conditioned responses. Next, we used a configural fear conditioning paradigm with five static room images as CTXs in two experiments (N = 29 and N = 24). Besides successful declarative learning and memory retention after 7 d, SCR and pupil dilation in response to CTX onset differentiated CTX+/CTX- during acquisition training, and SEBR and pupil dilation differentiated CTX+/CTX- during the recall test, with medium to large effect sizes for the most sensitive indices (SEBR: Hedge's g = 0.56 and g = 0.69; pupil dilation: Hedge's g = 0.99 and g = 0.88). Our results demonstrate that with a configural learning paradigm, context fear memory retention can be demonstrated over 7 d, and we provide robust and replicable measurement methods to this end.

Aerobic exercise after extinction learning reduces return of fear and enhances memory of items encoded during extinction learning

Fear conditioning paradigms are widely used in laboratory settings to discover treatments that enhance memory consolidation and various fear processes (extinction learning, limit return of fear) that are relevant targets of exposure-based therapies. However, traditional lab-based paradigms often use the exact same conditioned stimuli for acquisition and extinction (typically differentiated with a context manipulation), whereas the opposite is true in clinical settings, as exposure therapy rarely (if ever) uses precisely the exact same stimuli from an individual's learning history. Accordingly, this study utilized a novel three-day category-based fear conditioning protocol (that uses categories of non-repeating objects [animals and tools] as conditioned stimuli during fear conditioning and extinction) to determine if aerobic exercise enhances the consolidation of extinction learning (reduces return of fear) and memory (for items encoded during extinction) during subsequent tests of extinction recall. Participants (n=40) completed a fear acquisition (day 1), fear extinction (day 2), and extinction recall (day 3) protocol. On day 1, participants completed a fear acquisition task in which they were trained to associate a category of conditioned stimuli (CS+) with the occurrence of an unconditioned stimulus (US). On day 2, participants were administered a fear extinction procedure during which CS+ and CS- categorical stimuli were presented in absence of the occurrence of the US. After completing the task, participants were randomly assigned to either receive moderate-intensity aerobic exercise (EX) or a light-intensity control (CON) condition. On day 3, participants completed fear recall tests (during which day 1, day 2, and novel CS+ and CS- stimuli were presented). Fear responding was assessed via threat expectancy ratings and skin conductance responses (SCR). During the fear recall tests, the EX group reported significantly lower threat expectancy ratings to the CS+ and CS- and exhibited greater memory of CS+ and CS- stimuli that were previously presented during day 2. There were no significant group differences for SCR. These results suggests that administration of moderate-intensity aerobic exercise following extinction learning contributes to reduced threat expectancies during tests of fear recall and enhanced memory of items encoded during extinction.

Effect of the Matrix Metalloproteinase Inhibitor Doxycycline on Human Trace Fear Memory

Learning to predict threat is of adaptive importance, but aversive memory can also become disadvantageous and burdensome in clinical conditions such as posttraumatic stress disorder (PTSD). Pavlovian fear conditioning is a laboratory model of aversive memory and thought to rely on structural synaptic reconfiguration involving matrix metalloproteinase (MMP)9 signaling. It has recently been suggested that the MMP9-inhibiting antibiotic doxycycline, applied before acquisition training in humans, reduces fear memory retention after one week. This previous study used cued delay fear conditioning, in which predictors and outcomes overlap in time. However, temporal separation of predictors and outcomes is common in clinical conditions. Learning the association of temporally separated events requires a partly different neural circuitry, for which the role of MMP9 signaling is not yet known. Here, we investigate the impact of doxycycline on long-interval (15 s) trace fear conditioning in a randomized controlled trial with 101 (50 females) human participants. We find no impact of the drug in our preregistered analyses. Exploratory post hoc analyses of memory retention suggested a serum level-dependent effect of doxycycline on trace fear memory retention. However, effect size to distinguish CS+/CS- in the placebo group turned out to be smaller than in previously used delay fear conditioning protocols, which limits the power of statistical tests. Our results suggest that doxycycline effect on trace fear conditioning in healthy individuals is smaller and less robust than anticipated, potentially limiting its clinical application potential.

Atypical Response to Affective Touch in Children with Autism: Multi-Parametric Exploration of the Autonomic System

This study aimed at evaluating the autonomic response to pleasant affective touch in children with Autism Spectrum Disorders (ASD) and age-matched typically developing (TD) peers, thanks to multiple autonomic nervous system (ANS) parameters and by contrasting CT (C-tactile fibers) high- vs. low-density territory stimulations. We measured pupil diameter, skin conductance, and heart rate during gentle stroking of two skin territories (CT high- and low-density, respectively, forearm and palm of the hand) in thirty 6-12-year-old TD children and twenty ASD children. TD children showed an increase in pupil diameter and skin conductance associated with a heart rate deceleration in response to tactile stimulations at the two locations. Only the pupil was influenced by the stimulated location, with a later dilation peak following CT low-density territory stimulation. Globally, ASD children exhibited reduced autonomic responses, as well as different ANS baseline values compared to TD children. These atypical ANS responses to pleasant touch in ASD children were not specific to CT-fiber stimulation. Overall, these results point towards both basal autonomic dysregulation and lower tactile autonomic evoked responses in ASD, possibly reflecting lower arousal and related to social disengagement.

Measuring human trace fear conditioning

Trace fear conditioning is an important research paradigm to model aversive learning in biological or clinical scenarios, where predictors (conditioned stimuli, CS) and aversive outcomes (unconditioned stimuli, US) are separated in time. The optimal measurement of human trace fear conditioning, and in particular of memory retention after consolidation, is currently unclear. We conducted two identical experiments (N₁  = 28, N₂  = 28) with a 15-s trace interval and a recall test 1 week after acquisition, while recording several psychophysiological observables. In a calibration approach, we explored which learning and memory measures distinguished CS+ and CS- in the first experiment and confirmed the most sensitive measures in the second experiment. We found that in the recall test without reinforcement, only fear-potentiated startle but not skin conductance, pupil size, heart period, or respiration amplitude, differentiated CS+ and CS-. During acquisition without startle probes, skin conductance responses and pupil size responses but not heart period or respiration amplitude differentiated CS+ and CS-. As a side finding, there was no evidence for extinction of fear-potentiated startle over 30 trials without reinforcement. These results may be useful to inform future substantive research using human trace fear conditioning protocols.

Autonomic tone in children and adults: Pupillary, electrodermal and cardiac activity at rest

Considering the suspected involvement of the autonomic nervous system (ANS) in several neurodevelopmental disorders, a description of its tonus in typical populations and of its maturation between childhood and adulthood is necessary. We aimed to arrive at a better understanding of the maturation of the sympathetic (SNS) and parasympathetic (PNS) tonus by comparing children and adults at rest, via recordings of multiple ANS indices. We recorded simultaneously pupil diameter, electrodermal activity (EDA) and cardiac activity (RR interval and HRV: heart rate variability) in 29 children (6-12 years old) and 30 adults (20-42 years old) during a 5-min rest period. Children exhibited lower RR intervals, higher LF peak frequencies, and lower LF/HF (low frequency/high frequency) ratios compared to adults. Children also produced more spontaneous EDA peaks, reflected in a larger EDA AUC (area under the curve), in comparison with adults. Finally, children displayed a larger median pupil diameter and a higher pupillary hippus frequency than adults. Our results converged towards higher SNS and PNS tones in children compared to adults. Childhood would thus be characterized by a high autonomic tone, possibly reflecting a physiological state compatible with developmental acquisitions.

Learning about threat from friends and strangers is equally effective: An fMRI study on observational fear conditioning

Humans often benefit from social cues when learning about the world. For instance, learning about threats from others can save the individual from dangerous first-hand experiences. Familiarity is believed to increase the effectiveness of social learning, but it is not clear whether it plays a role in learning about threats. Using functional magnetic resonance imaging, we undertook a naturalistic approach and investigated whether there was a difference between observational fear learning from friends and strangers. Participants (observers) witnessed either their friends or strangers (demonstrators) receiving aversive (shock) stimuli paired with colored squares (observational learning stage). Subsequently, participants watched the same squares, but without receiving any shocks (direct-expression stage). We observed a similar pattern of brain activity in both groups of observers. Regions related to threat responses (amygdala, anterior insula, anterior cingulate cortex) and social perception (fusiform gyrus, posterior superior temporal sulcus) were activated during the observational phase, possibly reflecting the emotional contagion process. The anterior insula and anterior cingulate cortex were also activated during the subsequent stage, indicating the expression of learned threat. Because there were no differences between participants observing friends and strangers, we argue that social threat learning is independent of the level of familiarity with the demonstrator.

Misophonia: Analysis of the neuroanatomic patterns at the basis of psychiatric symptoms and changes of the orthosympathetic/ parasympathetic balance

Background/Aim

Misophonia is a disorder characterized by reduced tolerance to specific sounds or stimuli known as “triggers,” which tend to evoke negative emotional, physiological, and behavioral responses. In this study, we aimed to better characterize participants with misophonia through the evaluation of the response of the autonomic nervous system to “trigger sounds,” a psychometric assessment, and the analysis of the neurological pathways.

Materials and methods

Participants included 11 adults presenting with misophonic disturbance and 44 sex-matched healthy controls (HCs). Following recently proposed diagnostic criteria, the participants listened to six “trigger sounds” and a “general annoyance” sound (baby crying) during a series of physiological tests. The effects were examined through functional magnetic resonance imaging (fMRI), the analysis of heart rate variability (HRV), and of galvanic skin conductance (GSC). The fMRI was performed on a 3T Scanner. The HRV was obtained through the analysis of electrocardiogram, whereas the GSC was examined through the positioning of silver-chloride electrodes on fingers. Furthermore, the psychometric assessment included questionnaires focused on misophonia, psychopathology, resilience, anger, and motivation.

Results

Participants with misophonia showed patterns of increased sympathetic activation in response to trigger sounds and a general annoyance sound, the low frequency (LF) component of HRV, the sympathetic index, and the number of significant GSC over the threshold, where the amplitude/phasic response of GSC was higher. The fMRI analysis provided evidence for the activation of the temporal cortex, the limbic area, the ventromedial prefrontal/premotor/cingulate cortex, and the cerebellum in participants with misophonia. In addition, the psychometric assessment seemed to differentiate misophonia as a construct independent from general psychopathology.

Conclusion

These results suggest the activation of a specific auditory-insula-limbic pathway at the basis of the sympathetic activation observed in participants with misophonia in response to “trigger and general annoyance sounds.” Further studies should disentangle the complex issue of whether misophonia represents a new clinical disorder or a non-pathological condition. These results could help to build diagnostic tests to recognize and better classify this disorder. The relevance of this question goes beyond purely theoretical issues, as in the first case, participants with misophonia should receive a diagnosis and a targeted treatment, while in the second case, they should not.

Inhibiting Human Aversive Memory by Transcranial Theta-Burst Stimulation to the Primary Sensory Cortex

BACKGROUND

Predicting adverse events from past experience is fundamental for many biological organisms. However, some individuals suffer from maladaptive memories that impair behavioral control and well-being, e.g., after psychological trauma. Inhibiting the formation and maintenance of such memories would have high clinical relevance. Previous preclinical research has focused on systemically administered pharmacological interventions, which cannot be targeted to specific neural circuits in humans. Here, we investigated the potential of noninvasive neural stimulation on the human sensory cortex in inhibiting aversive memory in a laboratory threat conditioning model.

METHODS

We build on an emerging nonhuman literature suggesting that primary sensory cortices may be crucially required for threat memory formation and consolidation. Immediately before conditioning innocuous somatosensory stimuli (conditioned stimuli [CS]) to aversive electric stimulation, healthy human participants received continuous theta-burst transcranial magnetic stimulation (cTBS) to individually localized primary somatosensory cortex in either the CS-contralateral (experimental) or CS-ipsilateral (control) hemisphere. We measured fear-potentiated startle to infer threat memory retention on the next day, as well as skin conductance and pupil size during learning.

RESULTS

After overnight consolidation, threat memory was attenuated in the experimental group compared with the control cTBS group. There was no evidence that this differed between simple and complex CS or that CS identification or initial learning were affected by cTBS.

CONCLUSIONS

Our results suggest that cTBS to the primary sensory cortex inhibits threat memory, likely by an impact on postlearning consolidation. We propose that noninvasive targeted stimulation of the sensory cortex may provide a new avenue for interfering with aversive memories in humans.

Virtual Reality Adaptation Using Electrodermal Activity to Support the User Experience

Virtual reality is increasingly used for tasks such as work and education. Thus, rendering scenarios that do not interfere with such goals and deplete user experience are becoming progressively more relevant. We present a physiologically adaptive system that optimizes the virtual environment based on physiological arousal, i.e., electrodermal activity. We investigated the usability of the adaptive system in a simulated social virtual reality scenario. Participants completed an n-back task (primary) and a visual detection (secondary) task. Here, we adapted the visual complexity of the secondary task in the form of the number of non-player characters of the secondary task to accomplish the primary task. We show that an adaptive virtual reality can improve users’ comfort by adapting to physiological arousal regarding the task complexity. Our findings suggest that physiologically adaptive virtual reality systems can improve users’ experience in a wide range of scenarios.

Navigating the manyverse of skin conductance response quantification approaches - A direct comparison of trough-to-peak, baseline correction, and model-based approaches in Ledalab and PsPM

Raw data are typically required to be processed to be ready for statistical analyses, and processing pipelines are often characterized by substantial heterogeneity. Here, we applied seven different approaches (trough-to-peak scoring by two different raters, script-based baseline correction, Ledalab as well as four different models implemented in the software PsPM) to two fear conditioning data sets. Selection of the approaches included was guided by a systematic literature search by using fear conditioning research as a case example. Our approach can be viewed as a set of robustness analyses (i.e., same data subjected to different processing pipelines) aiming to investigate if and to what extent these different quantification approaches yield comparable results given the same data. To our knowledge, no formal framework for the evaluation of robustness analyses exists to date, but we may borrow some criteria from a framework suggested for the evaluation of "replicability" in general. Our results from seven different SCR quantification approaches applied to two data sets with different paradigms suggest that there may be no single approach that consistently yields larger effect sizes and could be universally considered "best." Yet, at least some of the approaches employed show consistent effect sizes within each data set indicating comparability. Finally, we highlight substantial heterogeneity also within most quantification approaches and discuss implications and potential remedies.

Design and Implementation of an Emergency Undocking Curriculum for Robotic Surgery

INTRODUCTION

Current training for robotic surgery crisis management, specifically emergency robotic undocking protocol (ERUP), remains limited to anecdotal experience. A curriculum to impart the skills and knowledge necessary to recognize and complete a successful ERUP was developed using an education approach then evaluated.

METHODS

Baseline knowledge and confidence regarding ERUP were established for 5 robotic teams before completing 2 full-immersion simulations separated by an online self-paced learning module. In each simulation, teams operated on a perfused hydrogel model and were tasked to dissect a retroperitoneal tumor abutting a major vessel. During vascular pedicle ligation, a major vascular bleed and nonrecoverable robotic fault were remotely induced, necessitating ERUP with open conversion. After the simulation, participants completed surgery task load index (cognitive load assessment) and realism surveys. Weighted checklists scored participants' actions during each simulation. Surgical metrics including estimated blood loss, time to control bleeding, and undocking time were recorded. Curriculum retention was assessed by repeating the exercise at 6 months.

RESULTS

Participants experienced high levels of cognitive demand and agreed that the simulation's realism and stress mimicked live surgery. Longitudinal analysis showed significant knowledge (+37.5 points, p = 0.004) and confidence (+15.3 points, p < 0.001) improvements from baseline to completion. Between simulations, checklist errors, undocking time, and estimated blood loss decreased (38⇾17, -40 seconds, and -500 mL, respectively), whereas action scores increased significantly (+27 points, p = 0.008). At 6 months, insignificant changes from curriculum completion were seen in knowledge (-4.8 points, p = 0.36) and confidence (+3.7 points, p = 0.1).

CONCLUSIONS

This simulation-based curriculum successfully improves operative team's confidence, knowledge, and skills required to manage robotic crisis events.

Current trends and opportunities in the methodology of electrodermal activity measurement

Electrodermal activity (EDA) has been measured in the laboratory since the late 1800s. Although the influence of sudomotor nerve activity and the sympathetic nervous system on EDA is well established, the mechanisms underlying EDA signal generation are not completely understood. Owing to simplicity of instrumentation and modern electronics, these measurements have recently seen a transfer from the laboratory to wearable devices, sparking numerous novel applications while bringing along both challenges and new opportunities. In addition to developments in electronics and miniaturization, current trends in material technology and manufacturing have sparked innovations in electrode technologies, and trends in data science such as machine learning and sensor fusion are expanding the ways that measurement data can be processed and utilized. Although challenges remain for the quality of wearable EDA measurement, ongoing research and developments may shorten the quality gap between wearable EDA and standardized recordings in the laboratory. In this topical review, we provide an overview of the basics of EDA measurement, discuss the challenges and opportunities of wearable EDA, and review recent developments in instrumentation, material technology, signal processing, modeling and data science tools that may advance the field of EDA research and applications over the coming years.

Whole brain correlates of individual differences in skin conductance responses during discriminative fear conditioning to social cues

Understanding the neural basis for individual differences in the skin conductance response (SCR) during discriminative fear conditioning may inform on our understanding of autonomic regulation in fear-related psychopathology. Previous region-of-interest (ROI) analyses have implicated the amygdala in regulating conditioned SCR, but whole brain analyses are lacking. This study examined correlations between individual differences in SCR during discriminative fear conditioning to social stimuli and neural activity throughout the brain, by using data from a large functional magnetic resonance imaging study of twins (N = 285 individuals). Results show that conditioned SCR correlates with activity in the dorsal anterior cingulate cortex/anterior midcingulate cortex, anterior insula, bilateral temporoparietal junction, right frontal operculum, bilateral dorsal premotor cortex, right superior parietal lobe, and midbrain. A ROI analysis additionally showed a positive correlation between amygdala activity and conditioned SCR in line with previous reports. We suggest that the observed whole brain correlates of SCR belong to a large-scale midcingulo-insular network related to salience detection and autonomic-interoceptive processing. Altered activity within this network may underlie individual differences in conditioned SCR and autonomic aspects of psychopathology.

Saccadic scanpath length: an index for human threat conditioning

Threat-conditioned cues are thought to capture overt attention in a bottom-up process. Quantification of this phenomenon typically relies on cue competition paradigms. Here, we sought to exploit gaze patterns during exclusive presentation of a visual conditioned stimulus, in order to quantify human threat conditioning. To this end, we capitalized on a summary statistic of visual search during CS presentation, scanpath length. During a simple delayed threat conditioning paradigm with full-screen monochrome conditioned stimuli (CS), we observed shorter scanpath length during CS+ compared to CS- presentation. Retrodictive validity, i.e., effect size to distinguish CS+ and CS-, was maximized by considering a 2-s time window before US onset. Taking into account the shape of the scan speed response resulted in similar retrodictive validity. The mechanism underlying shorter scanpath length appeared to be longer fixation duration and more fixation on the screen center during CS+ relative to CS- presentation. These findings were replicated in a second experiment with similar setup, and further confirmed in a third experiment using full-screen patterns as CS. This experiment included an extinction session during which scanpath differences appeared to extinguish. In a fourth experiment with auditory CS and instruction to fixate screen center, no scanpath length differences were observed. In conclusion, our study suggests scanpath length as a visual search summary statistic, which may be used as complementary measure to quantify threat conditioning with retrodictive validity similar to that of skin conductance responses.

Theta oscillations synchronize human medial prefrontal cortex and amygdala during fear learning

Numerous animal studies have demonstrated that fear acquisition and expression rely on the coordinated activity of medial prefrontal cortex (mPFC) and amygdala and that theta oscillations support interregional communication within the fear network. However, it remains unclear whether these results can be generalized to fear learning in humans. We addressed this question using intracranial electroencephalography recordings in 13 patients with epilepsy during a fear conditioning paradigm. We observed increased power and inter-regional synchronization of amygdala and mPFC in theta (4 to 8 hertz) oscillations for conditioned stimulus (CS+) versus CS-. Analysis of information flow revealed that the dorsal mPFC (dmPFC) led amygdala activity in theta oscillations. Last, a computational model showed that trial-by-trial changes in amygdala theta oscillations predicted the model-based associability (i.e., learning rate). This study provides compelling evidence that theta oscillations within and between amygdala, ventral mPFC, and dmPFC constitute a general mechanism of fear learning across species.

Aerobic exercise and consolidation of fear extinction learning among women with posttraumatic stress disorder

This study tested whether aerobic exercise delivered during the consolidation window following fear extinction learning reduces the return of fear among women with posttraumatic stress disorder (PTSD). Participants (n=35) completed an initial clinical assessment followed by a 3-day fear acquisition, extinction, and recall protocol. On day 1, participants completed a fear acquisition training task in which one geometric shape (conditioning stimulus; CS+) was paired (with 50% probability) with a mild electric shock (unconditioned stimulus; US), while a different shape (CS-) was never paired with the US. On day 2 (24 h later), participants completed a fear extinction training task in which the CS+ no longer predicted administration of the US. Shortly following extinction, participants were randomly assigned to complete either moderate-intensity aerobic exercise (EX) or a light-intensity exercise control (CON) condition. On day 3 (24 h later), participants completed fear recall tests assessing the return of fear (spontaneous recovery, renewal, and reinstatement). Fear responding was assessed via threat expectancy ratings and skin conductance responses (SCR). In the threat expectancy ratings, there were no significant differences between groups in spontaneous recovery; however, EX significantly (p=.02) reduced threat expectancy ratings following reinstatement relative to CON. In SCR measures, there were no significant differences between groups in spontaneous recovery, renewal, or reinstatement. These results support a role for moderate-intensity aerobic exercise during the consolidation window in reducing threat expectations following reinstatement in women with PTSD. Research should continue to examine exercise as a potential method for improving the efficacy of exposure-based therapies. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT04113798.

Evidence for a minimal role of stimulus awareness in reversal of threat learning

In an ever-changing environment, survival depends on learning which stimuli represent threat, and also on updating such associations when circumstances shift. It has been claimed that humans can acquire physiological responses to threat-associated stimuli even when they are unaware of them, but the role of awareness in updating threat contingencies remains unknown. This complex process-generating novel responses while suppressing learned ones-relies on distinct neural mechanisms from initial learning, and has only been shown with awareness. Can it occur unconsciously? Here, we present evidence that threat reversal may not require awareness. Participants underwent classical threat conditioning to visual stimuli that were suppressed from awareness. One of two images was paired with an electric shock; halfway through the experiment, contingencies were reversed and the shock was paired with the other image. Despite variations in suppression across participants, we found that physiological responses reflected changes in stimulus-threat pairings independently of stimulus awareness. These findings suggest that unconscious affective processing may be sufficiently flexible to adapt to changing circumstances.

Filtering and model-based analysis independently improve skin-conductance response measures in the fMRI environment: Validation in a sample of women with PTSD

Numerous methods exist for the pre-processing and analysis of skin-conductance response (SCR) data, but there is incomplete consensus on suitability and implementation, particularly with regard to signal filtering in conventional peak score (PS) analysis. This is particularly relevant when SCRs are measured during fMRI, which introduces additional noise and signal variability. Using SCR-fMRI data (n = 65 women) from a fear conditioning experiment, we compare the impact of three nested data processing methods on analysis using conventional PS as well as psychophysiological modeling. To evaluate the different methods, we quantify effect size to recover a benchmark contrast of interest, namely, discriminating SCR magnitude to a conditioned stimulus (CS+) relative to a CS not followed by reinforcement (CS-). Findings suggest that low-pass filtering reduces PS sensitivity (Δd = -20%), while band-pass filtering improves PS sensitivity (Δd = +27%). We also replicate previous findings that a psychophysiological modeling approach yields superior sensitivity to detect contrasts of interest than even the most sensitive PS method (Δd = +110%). Furthermore, we present preliminary evidence that filtering differences may account for a portion of exclusions made on commonly applied metrics, such as below zero discrimination. Despite some limitations of our sample and experimental design, it appears that SCR processing pipelines that include band-pass filtering, ideally with model-based SCR quantification, may increase the validity of SCR response measures, maximize research productivity, and decrease sampling bias by reducing data exclusion.

Social exclusion influences conditioned fear acquisition and generalization: A mediating effect from the medial prefrontal cortex

Fear acquisition and generalization play key roles in promoting the survival of mammals and contribute to anxiety disorders. While previous research has provided much evidence for the repercussions of social exclusion on mental health, how social exclusion affects fear acquisition and generalization has received scant attention. In our study, participants were divided into two groups according to two Cyberball paradigm conditions (exclusion/inclusion). Both groups underwent a Pavlovian conditioning paradigm, functional near-infrared spectroscopy (fNIRS), and skin conductance response (SCR) assessments. We aimed to determine the effects of social exclusion on fear acquisition and generalization and whether modulation of the medial prefrontal cortex (mPFC) mediates this relationship. Our results showed that socially excluded participants featured significantly higher and lower shock risk scores to safety stimuli (conditioned stimulus, CS-) and threatening stimuli (CS+), respectively, than did socially included subjects during fear acquisition. The exclusion group had increased skin conductance responses (SCRs) to CS and exhibited heightened shock risk and increased SCRs to generalized stimuli compared with the inclusion group. The fNIRS results demonstrated that the CS ​+ ​evoked larger oxy-Hb changes in the mPFC in the inclusion group than in the exclusion group during fear acquisition. Furthermore, the oxy-Hb of left mPFC of CS ​+ ​mediated the effect on the association between social exclusion and perceived risk of CS+ in the fear acquisition. Our results indicate that social exclusion impairs fear acquisition and generalization via the mediation of the mPFC and that social exclusion increases susceptibility to anxiety disorders through bias processing of fear discrimination in fear acquisition and generalization. By studying the role of social relationship in fear acquisition and generalization, our research provides new insights into the pathological mechanisms of anxiety disorder.

Psychophysiological modelling and the measurement of fear conditioning

Quantification of fear conditioning is paramount to many clinical and translational studies on aversive learning. Various measures of fear conditioning co-exist, including different observables and different methods of pre-processing. Here, we first argue that low measurement error is a rational desideratum for any measurement technique. We then show that measurement error can be approximated in benchmark experiments by how closely intended fear memory relates to measured fear memory, a quantity that we term retrodictive validity. From this perspective, we discuss different approaches commonly used to quantify fear conditioning. One of these is psychophysiological modelling (PsPM). This builds on a measurement model that describes how a psychological variable, such as fear memory, influences a physiological measure. This model is statistically inverted to estimate the most likely value of the psychological variable, given the measured data. We review existing PsPMs for skin conductance, pupil size, heart period, respiration, and startle eye-blink. We illustrate the benefit of PsPMs in terms of retrodictive validity and translate this into sample size required to achieve a desired level of statistical power. This sample size can differ up to a factor of three between different observables, and between the best, and the current standard, data pre-processing methods.

Impact of a reminder/extinction procedure on threat-conditioned pupil size and skin conductance responses

A reminder can render consolidated memory labile and susceptible to amnesic agents during a reconsolidation window. For the case of threat memory (also termed fear memory), it has been suggested that extinction training during this reconsolidation window has the same disruptive impact. This procedure could provide a powerful therapeutic principle for treatment of unwanted aversive memories. However, human research yielded contradictory results. Notably, all published positive replications quantified threat memory by conditioned skin conductance responses (SCR). Yet, other studies measuring SCR and/or fear-potentiated startle failed to observe an effect of a reminder/extinction procedure on the return of fear. Here we sought to shed light on this discrepancy by using a different autonomic response, namely, conditioned pupil dilation, in addition to SCR, in a replication of the original human study. N = 71 humans underwent a 3-d threat conditioning, reminder/extinction, and reinstatement, procedure with 2 CS+, of which one was reminded. Participants successfully learned the threat association on day 1, extinguished conditioned responding on day 2, and showed reinstatement on day 3. However, there was no difference in conditioned responding between the reminded and the nonreminded CS, neither in pupil size nor SCR. Thus, we found no evidence that a reminder trial before extinction prevents the return of threat-conditioned responding.

Primary auditory cortex representation of fear-conditioned musical sounds

Auditory cortex is required for discriminative fear conditioning beyond the classical amygdala microcircuit, but its precise role is unknown. It has previously been suggested that Heschl's gyrus, which includes primary auditory cortex (A1), but also other auditory areas, encodes threat predictions during presentation of conditioned stimuli (CS) consisting of monophones, or frequency sweeps. The latter resemble natural prosody and contain discriminative spectro‐temporal information. Here, we use functional magnetic resonance imaging (fMRI) in humans to address CS encoding in A1 for stimuli that contain only spectral but no temporal discriminative information. Two musical chords (complex) or two monophone tones (simple) were presented in a signaled reinforcement context (reinforced CS+ and nonreinforced CS−), or in a different context without reinforcement (neutral sounds, NS1 and NS2), with an incidental sound detection task. CS/US association encoding was quantified by the increased discriminability of BOLD patterns evoked by CS+/CS−, compared to NS pairs with similar physical stimulus differences and task demands. A1 was defined on a single‐participant level and based on individual anatomy. We find that in A1, discriminability of CS+/CS− was higher than for NS1/NS2. This representation of unconditioned stimulus (US) prediction was of comparable magnitude for both types of sounds. We did not observe such encoding outside A1. Different from frequency sweeps investigated previously, musical chords did not share representations of US prediction with monophone sounds. To summarize, our findings suggest decodable representation of US predictions in A1, for various types of CS, including musical chords that contain no temporal discriminative information.

Sharing the filmic experience - The physiology of socio-emotional processes in the cinema

As we identify with characters on screen, we simulate their emotions and thoughts. This is accompanied by physiological changes such as galvanic skin response (GSR), an indicator for emotional arousal, and respiratory sinus arrhythmia (RSA), referring to vagal activity. We investigated whether the presence of a cinema audience affects these psychophysiological processes. The study was conducted in a real cinema in Berlin. Participants came twice to watch previously rated emotional film scenes eliciting amusement, anger, tenderness or fear. Once they watched the scenes alone, once in a group. We tested whether the vagal modulation in response to the mere presence of others influences explicit (reported) and implicit markers (RSA, heart rate (HR) and GSR) of emotional processes in function of solitary or collective enjoyment of movie scenes. On the physiological level, we found a mediating effect of vagal flexibility to the mere presence of others. Individuals showing a high baseline difference (alone vs. social) prior to the presentation of film, maintained higher RSA in the alone compared to the social condition. The opposite pattern emerged for low baseline difference individuals. Emotional arousal as reflected in GSR was significantly more pronounced during scenes eliciting anger independent of the social condition. On the behavioural level, we found evidence for emotion-specific effects on reported empathy, emotional intensity and Theory of Mind. Furthermore, people who decrease their RSA in response to others' company are those who felt themselves more empathically engaged with the characters. Our data speaks in favour of a specific role of vagal regulation in response to the mere presence of others in terms of explicit empathic engagement with characters during shared filmic experience.

Threat Memory Reminder Under Matrix Metalloproteinase 9 Inhibitor Doxycycline Globally Reduces Subsequent Memory Plasticity

Associative memory can be rendered malleable by a reminder. Blocking the ensuing reconsolidation process is suggested as a therapeutic target for unwanted aversive memories. Matrix metalloproteinase-9 (MMP-9) is required for structural synapse remodeling involved in memory consolidation. Inhibiting MMP-9 with doxycycline is suggested to attenuate human threat conditioning. Here, we investigated whether MMP-9 inhibition also interferes with threat memory reconsolidation. Male and female human participants (N = 78) learned the association between two visual conditioned stimuli (CS⁺) and a 50% chance of an unconditioned nociceptive stimulus (US), and between CS^- and the absence of US. On day 7, one CS⁺ was reminded without reinforcement 3.5 h after ingesting either 200 mg of doxycycline or placebo. On day 14, retention of CS memory was assessed under extinction by fear-potentiated startle. Contrary to our expectations, we observed a greater CS⁺/CS^- difference in participants who were reminded under doxycycline compared with placebo. Participants who were reminded under placebo showed extinction learning during the retention test, which was not observed in the doxycycline group. There was no difference between the reminded and the nonreminded CS⁺ in either group. In contrast, during relearning after the retention test, the CS⁺/CS^- difference was more pronounced in the placebo group than in the doxycycline group. To summarize, a single dose of doxycycline before threat memory reminder appeared to have no specific impact on reconsolidation, but to globally impair extinction learning, and threat relearning, beyond drug clearance.SIGNIFICANCE STATEMENT Matrix metalloproteinase-9 inhibition appears to attenuate memory consolidation. It could also be a target for blocking reconsolidation. Here, we test this hypothesis in human threat conditioning. We find that doxycycline has no specific impact on a reminded cue, but confers a global reduction in extinction learning and threat learning beyond the clearance of the drug. This may point toward a more long-lasting impact of doxycycline treatment on memory plasticity.

A Bayesian Filtering Approach for Tracking Arousal From Binary and Continuous Skin Conductance Features

OBJECTIVE

Neuroanatomical structures within the cortical and sub-cortical brain regions process emotion and cause subsequent variations in signals such as skin conductance and electrocardiography. The signals often encode information in their continuous-valued amplitudes or waves as well as in their underlying impulsive events. We propose to track psychological arousal from this hybrid source of skin conductance information.

METHODS

We present a point process state-space method in tandem with Bayesian filtering for determining a continuous-valued arousal state from skin conductance measurements. To perform state estimation, we relate arousal to binary- and continuous-valued observations derived from the phasic and tonic parts of a skin conductance signal, and recover model parameters using expectation-maximization. We evaluate our model on both synthetic and two different experimental data sets. Stress was artificially induced in the first experimental data set and the second comprised of a fear conditioning experiment.

RESULTS

Results on the first data set indicate high levels of arousal during exposure to cognitive stress and low arousal during relaxation. Plausible results are also obtained in the fear conditioning data set consistent with previous skin conductance studies in similar experimental contexts.

CONCLUSION

The state-space approach-which does not rely on external classification labels-is able to continuously track an arousal level from skin conductance features.

SIGNIFICANCE

The method is a promising arousal estimation scheme utilizing only skin conductance. The approach could find applications in wearable monitoring and the study of neuropsychiatric conditions such as post-traumatic stress disorder.

Pavlovian-to-instrumental transfer after human threat conditioning

Threat conditioning is a common associative learning model with translational relevance. How threat-conditioned cues impact on formally unrelated instrumental behavior in humans is not well known. Such an effect is known as Pavlovian-to-instrumental transfer (PIT). While PIT with aversive primary Pavlovian reinforcers is established in nonhuman animals, this is less clear in humans, where secondary reinforcers or instructed instrumental responses are most often investigated. We modified an existing human PIT procedure to include primary reinforcers. Participants first learned to obtain (or avoid losing) appetitive instrumental reinforcement (chocolate) by appropriate approach or avoidance actions. They either had to act (Go) or to withhold an action (NoGo), and in the Go condition either to approach a reward target to collect it or to withdraw from the reward target to avoid losing it. Then they learned to associate screen color (CS) with aversive Pavlovian reinforcement (electric shock US). In the transfer phase, we conducted the instrumental task during the presence of Pavlovian CS. In a first experiment, we show that the aversive Pavlovian CS+, compared to CS−, increased response rate in Go-Withdraw trials, i.e., induce conditioned facilitation of avoidance responses. This finding was confirmed in a second and independent experiment with an increased number of Go-Withdraw trials. Notably, we observed no appreciable conditioned suppression of approach responses. Effect size to distinguish CS+/CS− in Go-Withdraw trials was d = 0.42 in the confirmation sample. This would require n = 37 participants to demonstrate threat learning with 80% power. Thus, the effect size is on a practically useful scale although smaller than for model-based analysis of autonomic measures. In summary, our results indicate conditioned facilitation of formally unrelated instrumental avoidance behavior in humans and provide a novel behavioral threat learning measure that requires only key presses.

Common Functional Brain States Encode both Perceived Emotion and the Psychophysiological Response to Affective Stimuli

Multivariate pattern analysis (MVPA) of functional magnetic resonance imaging (fMRI) data has critically advanced the neuroanatomical understanding of affect processing in the human brain. Central to these advancements is the brain state, a temporally-succinct fMRI-derived pattern of neural activation, which serves as a processing unit. Establishing the brain state's central role in affect processing, however, requires that it predicts multiple independent measures of affect. We employed MVPA-based regression to predict the valence and arousal properties of visual stimuli sampled from the International Affective Picture System (IAPS) along with the corollary skin conductance response (SCR) for demographically diverse healthy human participants (n = 19). We found that brain states significantly predicted the normative valence and arousal scores of the stimuli as well as the attendant individual SCRs. In contrast, SCRs significantly predicted arousal only. The prediction effect size of the brain state was more than three times greater than that of SCR. Moreover, neuroanatomical analysis of the regression parameters found remarkable agreement with regions long-established by fMRI univariate analyses in the emotion processing literature. Finally, geometric analysis of these parameters also found that the neuroanatomical encodings of valence and arousal are orthogonal as originally posited by the circumplex model of dimensional emotion.

Human Pavlovian fear conditioning conforms to probabilistic learning

Learning to predict threat from environmental cues is a fundamental skill in changing environments. This aversive learning process is exemplified by Pavlovian threat conditioning. Despite a plethora of studies on the neural mechanisms supporting the formation of associations between neutral and aversive events, our computational understanding of this process is fragmented. Importantly, different computational models give rise to different and partly opposing predictions for the trial-by-trial dynamics of learning, for example expressed in the activity of the autonomic nervous system (ANS). Here, we investigate human ANS responses to conditioned stimuli during Pavlovian fear conditioning. To obtain precise, trial-by-trial, single-subject estimates of ANS responses, we build on a statistical framework for psychophysiological modelling. We then consider previously proposed non-probabilistic models, a simple probabilistic model, and non-learning models, as well as different observation functions to link learning models with ANS activity. Across three experiments, and both for skin conductance (SCR) and pupil size responses (PSR), a probabilistic learning model best explains ANS responses. Notably, SCR and PSR reflect different quantities of the same model: SCR track a mixture of expected outcome and uncertainty, while PSR track expected outcome alone. In summary, by combining psychophysiological modelling with computational learning theory, we provide systematic evidence that the formation and maintenance of Pavlovian threat predictions in humans may rely on probabilistic inference and includes estimation of uncertainty. This could inform theories of neural implementation of aversive learning.

Brain States That Encode Perceived Emotion Are Reproducible but Their Classification Accuracy Is Stimulus-Dependent

The brain state hypothesis of image-induced affect processing, which posits that a one-to-one mapping exists between each image stimulus and its induced functional magnetic resonance imaging (fMRI)-derived neural activation pattern (i.e., brain state), has recently received support from several multivariate pattern analysis (MVPA) studies. Critically, however, classification accuracy differences across these studies, which largely share experimental designs and analyses, suggest that there exist one or more unaccounted sources of variance within MVPA studies of affect processing. To explore this possibility, we directly demonstrated strong inter-study correlations between image-induced affective brain states acquired 4 years apart on the same MRI scanner using near-identical methodology with studies differing only by the specific image stimuli and subjects. We subsequently developed a plausible explanation for inter-study differences in affective valence and arousal classification accuracies based on the spatial distribution of the perceived affective properties of the stimuli. Controlling for this distribution improved valence classification accuracy from 56% to 85% and arousal classification accuracy from 61% to 78%, which mirrored the full range of classification accuracy across studies within the existing literature. Finally, we validated the predictive fidelity of our image-related brain states according to an independent measurement, autonomic arousal, captured via skin conductance response (SCR). Brain states significantly but weakly (r = 0.08) predicted the SCRs that accompanied individual image stimulations. More importantly, the effect size of brain state predictions of SCR increased more than threefold (r = 0.25) when the stimulus set was restricted to those images having group-level significantly classifiable arousal properties.

Augmentation of Fear Extinction by Transcranial Direct Current Stimulation (tDCS)

Although posttraumatic stress disorder (PTSD; DSM-V 309.82) and anxiety disorders (DSM-V 300.xx) are widely spread mental disorders, the effectiveness of their therapy is still unsatisfying. Non-invasive brain-stimulation techniques like transcranial direct current stimulation (tDCS) might be an option to improve extinction learning, which is a main functional factor of exposure-based therapy for anxiety disorders. To examine this hypothesis, we used a fear conditioning paradigm with female faces as conditioned stimuli (CS) and a 95-dB female scream as unconditioned stimulus (UCS). We aimed to perform a tDCS of the ventromedial prefrontal cortex (vmPFC), which is mainly involved in the control of extinction-processes. Therefore, we applied two 4 × 4 cm electrodes approximately at the EEG-positions F7 and F8 and used a direct current of 1.5 mA. The 20-min stimulation was started during a 10-min break between acquisition and extinction and went on overall extinction-trials. The healthy participants were randomly assigned in two double-blinded process into two sham stimulation and two verum stimulation groups with opposite current flow directions. To measure the fear reactions, we used skin conductance responses (SCR) and subjective ratings. We performed a generalized estimating equations model for the SCR to assess the impact of tDCS and current flow direction on extinction processes for all subjects that showed a successful conditioning (N = 84). The results indicate that tDCS accelerates early extinction processes with a significantly faster loss of CS+/CS– discrimination. The discrimination loss was driven by a significant decrease in reaction toward the CS+ as well as an increase in reaction toward the CS– in the tDCS verum groups, whereas the sham groups showed no significant reaction changes during this period. Therefore, we assume that tDCS of the vmPFC can be used to enhance early extinction processes successfully. But before it should be tested in a clinical context further investigation is needed to assess the reason for the reaction increase on CS–. If this negative side effect can be avoided, tDCS may be a tool to improve exposure-based anxiety therapies.

Testing a linear time invariant model for skin conductance responses by intraneural recording and stimulation

Skin conductance responses (SCR) are increasingly analyzed with model-based approaches that assume a linear and time-invariant (LTI) mapping from sudomotor nerve (SN) activity to observed SCR. These LTI assumptions have previously been validated indirectly, by quantifying how much variance in SCR elicited by sensory stimulation is explained under an LTI model. This approach, however, collapses sources of variability in the nervous and effector organ systems. Here, we directly focus on the SN/SCR mapping by harnessing two invasive methods. In an intraneural recording experiment, we simultaneously track SN activity and SCR. This allows assessing the SN/SCR relationship but possibly suffers from interfering activity of non-SN sympathetic fibers. In an intraneural stimulation experiment under regional anesthesia, such influences are removed. In this stimulation experiment, about 95% of SCR variance is explained under LTI assumptions when stimulation frequency is below 0.6 Hz. At higher frequencies, nonlinearities occur. In the intraneural recording experiment, explained SCR variance is lower, possibly indicating interference from non-SN fibers, but higher than in our previous indirect tests. We conclude that LTI systems may not only be a useful approximation but in fact a rather accurate description of biophysical reality in the SN/SCR system, under conditions of low baseline activity and sporadic external stimuli. Intraneural stimulation under regional anesthesia is the most sensitive method to address this question.

The Role of Ethnicity and Environment in the Regulation of Response to Sensory Stimulus in Children: Protocol and Pilot Findings of a Neurophysiological Study

BACKGROUND

The ability to regulate the response to sensory stimuli has been associated with successful behavioral patterns necessary for daily activities. However, it is not known whether a child's ethnicity and environment can influence autonomic regulatory mechanisms.

OBJECTIVE

This study aims to explore the role of ethnicity and environment in the regulation of responses to sensory stimuli in children.

METHODS

In this study, we intend to recruit 128 children from different ethnic groups or environment contexts as follows: (1) 32 typically developing Chinese children living in Hong Kong; (2) 32 typically developing Filipino children living in Hong Kong; (3) 32 typically developing Filipino children who are living in urban areas; and (4) 32 typically developing Filipino children who are living in rural areas in Philippines. Autonomic activity (heart rate variability [HRV] and electrodermal activity [EDA]) will be measured and recorded using Polar H2 heart rate monitor and eSense GSR skin response sensor. Autonomic activity (HRV-low frequency, HRV-high frequency, and EDA) at different conditions between pairwise groupings will be tested using multivariate analysis of variance (MANOVA). All significant levels will be set at P ≤.05.

RESULTS

We present the research protocol of this study, as well as a short discussion of the preliminary findings from our pilot data, with consequent power and sample size analysis that informs the appropriate sample needed to test our hypothesis.

CONCLUSIONS

This study will increase the understanding on the role of individual differences related to a child's ethnicity and environment in the regulation of response to sensory stimuli. The findings of this research may further shed light on the evaluation and treatment planning for children across and within cultures.

Blocking human fear memory with the matrix metalloproteinase inhibitor doxycycline

Learning to predict threat is a fundamental ability of many biological organisms, and a laboratory model for anxiety disorders. Interfering with such memories in humans would be of high clinical relevance. On the basis of studies in cell cultures and slice preparations, it is hypothesised that synaptic remodelling required for threat learning involves the extracellular enzyme matrix metalloproteinase (MMP) 9. However, in vivo evidence for this proposal is lacking. Here we investigate human Pavlovian fear conditioning under the blood-brain barrier crossing MMP inhibitor doxycyline in a pre-registered, randomised, double-blind, placebo-controlled trial. We find that recall of threat memory, measured with fear-potentiated startle 7 days after acquisition, is attenuated by ~60% in individuals who were under doxycycline during acquisition. This threat memory impairment is also reflected in increased behavioural surprise signals to the conditioned stimulus during subsequent re-learning, and already late during initial acquisition. Our findings support an emerging view that extracellular signalling pathways are crucially required for threat memory formation. Furthermore, they suggest novel pharmacological methods for primary prevention and treatment of posttraumatic stress disorder.

Stimulus-invariant auditory cortex threat encoding during fear conditioning with simple and complex sounds

Learning to predict threat depends on amygdala plasticity and does not require auditory cortex (ACX) when threat predictors (conditioned stimuli, CS) are simple sine tones. However, ACX is required in rodents to learn from some naturally occurring CS. Yet, the precise function of ACX, and whether it differs for different CS types, is unknown. Here, we address how ACX encodes threat predictions during human fear conditioning using functional magnetic resonance imaging (fMRI) with multivariate pattern analysis. As in previous rodent work, CS+ and CS- were defined either by direction of frequency modulation (complex) or by frequency of pure tones (simple). In an instructed non-reinforcement context, different sets of simple and complex sounds were always presented without reinforcement (neutral sounds, NS). Threat encoding was measured by separation of fMRI response patterns induced by CS+/CS-, or similar NS1/NS2 pairs. We found that fMRI patterns in Heschl's gyrus encoded threat prediction over and above encoding the physical stimulus features also present in NS, i.e. CS+/CS- could be separated better than NS1/NS2. This was the case both for simple and complex CS. Furthermore, cross-prediction demonstrated that threat representations were similar for simple and complex CS, and thus unlikely to emerge from stimulus-specific top-down, or learning-induced, receptive field plasticity. Searchlight analysis across the entire ACX demonstrated further threat representations in a region including BA22 and BA42. However, in this region, patterns were distinct for simple and complex sounds, and could thus potentially arise from receptive field plasticity. Strikingly, across participants, individual size of Heschl's gyrus predicted strength of fear learning for complex sounds. Overall, our findings suggest that ACX represents threat predictions, and that Heschl's gyrus contains a threat representation that is invariant across physical stimulus categories.

Prazosin during threat discrimination boosts memory of the safe stimulus

The α-1 adrenoreceptor antagonist prazosin has shown promise in the treatment of post-traumatic stress disorder (PTSD) symptoms, but its mechanisms are not well understood. Here we administered prazosin or placebo prior to threat conditioning (day 1) and tested subsequent extinction (day 2) and reextinction (day 3) in healthy human participants. Prazosin did not affect threat conditioning but augmented stimulus discrimination during extinction and reextinction, via lower responding to the safe stimulus. These results suggest that prazosin during threat acquisition may have influenced encoding or consolidation of safety processing in particular, subsequently leading to enhanced discrimination between the safe and threatening stimuli.

A pupil size response model to assess fear learning

During fear conditioning, pupil size responses dissociate between conditioned stimuli that are contingently paired (CS+) with an aversive unconditioned stimulus, and those that are unpaired (CS-). Current approaches to assess fear learning from pupil responses rely on ad hoc specifications. Here, we sought to develop a psychophysiological model (PsPM) in which pupil responses are characterized by response functions within the framework of a linear time-invariant system. This PsPM can be written as a general linear model, which is inverted to yield amplitude estimates of the eliciting process in the central nervous system. We first characterized fear-conditioned pupil size responses based on an experiment with auditory CS. PsPM-based parameter estimates distinguished CS+/CS- better than, or on par with, two commonly used methods (peak scoring, area under the curve). We validated this PsPM in four independent experiments with auditory, visual, and somatosensory CS, as well as short (3.5 s) and medium (6 s) CS/US intervals. Overall, the new PsPM provided equal or decisively better differentiation of CS+/CS- than the two alternative methods and was never decisively worse. We further compared pupil responses with concurrently measured skin conductance and heart period responses. Finally, we used our previously developed luminance-related pupil responses to infer the timing of the likely neural input into the pupillary system. Overall, we establish a new PsPM to assess fear conditioning based on pupil responses. The model has a potential to provide higher statistical sensitivity, can be applied to other conditioning paradigms in humans, and may be easily extended to nonhuman mammals.

Assessing fear learning via conditioned respiratory amplitude responses

Respiratory physiology is influenced by cognitive processes. It has been suggested that some cognitive states may be inferred from respiration amplitude responses (RAR) after external events. Here, we investigate whether RAR allow assessment of fear memory in cued fear conditioning, an experimental model of aversive learning. To this end, we built on a previously developed psychophysiological model (PsPM) of RAR, which regards interpolated RAR time series as the output of a linear time invariant system. We first establish that average RAR after CS+ and CS− are different. We then develop the response function of fear‐conditioned RAR, to be used in our PsPM. This PsPM is inverted to yield estimates of cognitive input into the respiratory system. We analyze five validation experiments involving fear acquisition and retention, delay and trace conditioning, short and medium CS‐US intervals, and data acquired with bellows and MRI‐compatible pressure chest belts. In all experiments, CS+ and CS− are distinguished by their estimated cognitive inputs, and the sensitivity of this distinction is higher for model‐based estimates than for peak scoring of RAR. Comparing these data with skin conductance responses (SCR) and heart period responses (HPR), we find that, on average, RAR performs similar to SCR in distinguishing CS+ and CS−, but is less sensitive than HPR. Overall, our work provides a novel and robust tool to investigate fear memory in humans that may allow wide and straightforward application to diverse experimental contexts.

An efficient automatic workload estimation method based on electrodermal activity using pattern classifier combinations

Automatic workload estimation has received much attention because of its application in error prevention, diagnosis, and treatment of neural system impairment. The development of a simple but reliable method using minimum number of psychophysiological signals is a challenge in automatic workload estimation. To address this challenge, this paper presented three different decomposition techniques (Fourier, cepstrum, and wavelet transforms) to analyze electrodermal activity (EDA). The efficiency of various statistical and entropic features was investigated and compared. To recognize different levels of an arithmetic task, the features were processed by principal component analysis and machine-learning techniques. These methods have been incorporated into a workload estimation system based on two types: feature-level and decision-level combinations. The results indicated the reliability of the method for automatic and real-time inference of psychological states. This method provided a quantitative estimation of the workload levels and a bias-free evaluation approach. The high-average accuracy of 90% and cost effective requirement were the two important attributes of the proposed workload estimation system. New entropic features were proved to be more sensitive measures for quantifying time and frequency changes in EDA. The effectiveness of these measures was also compared with conventional tonic EDA measures, demonstrating the superiority of the proposed method in achieving accurate estimation of workload levels.

Modeling startle eyeblink electromyogram to assess fear learning

Pavlovian fear conditioning is widely used as a laboratory model of associative learning in human and nonhuman species. In this model, an organism is trained to predict an aversive unconditioned stimulus from initially neutral events (conditioned stimuli, CS). In humans, fear memory is typically measured via conditioned autonomic responses or fear‐potentiated startle. For the latter, various analysis approaches have been developed, but a systematic comparison of competing methodologies is lacking. Here, we investigate the suitability of a model‐based approach to startle eyeblink analysis for assessment of fear memory, and compare this to extant analysis strategies. First, we build a psychophysiological model (PsPM) on a generic startle response. Then, we optimize and validate this PsPM on three independent fear‐conditioning data sets. We demonstrate that our model can robustly distinguish aversive (CS+) from nonaversive stimuli (CS‐, i.e., has high predictive validity). Importantly, our model‐based approach captures fear‐potentiated startle during fear retention as well as fear acquisition. Our results establish a PsPM‐based approach to assessment of fear‐potentiated startle, and qualify previous peak‐scoring methods. Our proposed model represents a generic startle response and can potentially be used beyond fear conditioning, for example, to quantify affective startle modulation or prepulse inhibition of the acoustic startle response.

A linear model for event-related respiration responses

BACKGROUND

Cognitive processes influence respiratory physiology. This may allow inferring cognitive states from measured respiration. Here, we take a first step towards this goal and investigate whether event-related respiratory responses can be identified, and whether they are accessible to a model-based approach.

NEW METHOD

We regard respiratory responses as the output of a linear time invariant system that receives brief inputs after psychological events. We derive average responses to visual targets, aversive stimulation, and viewing of arousing pictures, in interpolated respiration period (RP), respiration amplitude (RA), and respiratory flow rate (RFR). We then base a Psychophysiological Model (PsPM) on these averaged event-related responses. The PsPM is inverted to yield estimates of cognitive input into the respiratory system. This method is validated in an independent data set.

RESULTS

All three measures show event-related responses, which are captured as non-zero response amplitudes in the PsPM. Amplitude estimates for RA and RFR distinguish between picture viewing and the other tasks. This pattern is replicated in the validation experiment.

COMPARISON WITH EXISTING METHODS

Existing respiratory measures are based on relatively short time-intervals after an event while the new method is based on the entire duration of respiratory responses.

CONCLUSION

Our findings suggest that interpolated respiratory measures show replicable event-related response patterns. PsPM inversion is a suitable approach to analysing these patterns, with a potential to infer cognitive processes from respiration.

Modeling fear-conditioned bradycardia in humans

Across species, cued fear conditioning is a common experimental paradigm to investigate aversive Pavlovian learning. While fear‐conditioned stimuli (CS+) elicit overt behavior in many mammals, this is not the case in humans. Typically, autonomic nervous system activity is used to quantify fear memory in humans, measured by skin conductance responses (SCR). Here, we investigate whether heart period responses (HPR) evoked by the CS, often observed in humans and small mammals, are suitable to complement SCR as an index of fear memory in humans. We analyze four datasets involving delay and trace conditioning, in which heart beats are identified via electrocardiogram or pulse oximetry, to show that fear‐conditioned heart rate deceleration (bradycardia) is elicited and robustly distinguishes CS+ from CS−. We then develop a psychophysiological model (PsPM) of fear‐conditioned HPR. This PsPM is inverted to yield estimates of autonomic input into the heart. We show that the sensitivity to distinguish CS+ and CS− (predictive validity) is higher for model‐based estimates than peak‐scoring analysis, and compare this with SCR. Our work provides a novel tool to investigate fear memory in humans that allows direct comparison between species.

Modeling event-related heart period responses

Cardiac rhythm is generated locally in the sinoatrial node, but modulated by central neural input. This may provide a possibility to infer central processes from observed phasic heart period responses (HPR). Currently, operational methods are used for HPR analysis. These methods embody implicit assumptions on how central states influence heart period. Here, we build an explicit psychophysiological model (PsPM) for event‐related HPR. This phenomenological PsPM is based on three experiments involving white noise sounds, an auditory oddball task, and emotional picture viewing. The model is optimized with respect to predictive validity—the ability to separate experimental conditions from each other. To validate the PsPM, an independent sample of participants is presented with auditory stimuli of varying intensity and emotional pictures of negative and positive valence, at short intertrial intervals. Our model discriminates these experimental conditions from each other better than operational approaches. We conclude that our PsPM is more sensitive to distinguish experimental manipulations based on heart period data than operational methods, and furnishes a principled approach to analysis of HPR.