Differential Conditioning Research Articles

A legacy of fear: Physiological evidence for intergenerational effects of trauma exposure on fear and safety signal learning among African Americans

ObjectiveTo determine the influence of maternal trauma and posttraumatic stress disorder (PTSD) symptoms on children’s physiological response to threat and safety signals during a fear conditioning task in trauma-exposed mothers and children. MethodParticipants were African American mother-child dyads (N = 137; children aged 8–13 years). Mothers’ trauma history and PTSD symptoms were assessed; Latent Class Analysis (LCA) was conducted from these measures to identify distinct classes. Children reported violence exposure and completed a differential fear conditioning task using fear-potentiated startle (FPS) responses to conditioned danger (CS+) and safety (CS-) signals. ResultsFour classes of maternal trauma history and PTSD symptoms emerged: 1) Lower Trauma, 2) Moderate Trauma, 3) High Sexual Abuse, and 4) High Trauma and PTSD Symptoms. Children’s FPS to CS + and CS- were tested with maternal class as the between-subjects factor. FPS to the danger signal was not significantly different across maternal classes, but FPS to safety (CS-) was significantly higher for the Lower Trauma and High Trauma and PTSD Symptoms classes than either the Moderate Trauma or the High Sexual Abuse classes. ConclusionsResults indicate that maternal trauma impacts children’s ability to modulate fear responses in the presence of a safety signal, independent of the children’s own trauma exposure. To our knowledge, this is the first study to demonstrate that children’s fear inhibition is impacted by maternal trauma exposure. Prior studies have linked fear inhibition to mental health outcomes, highlighting the need to understand intergenerational modulation of fear learning and physiology.

Poor Mnemonic Discrimination Predicts Overgeneralization of Fear

Anxiety disorders are characterized by difficulty distinguishing safe contexts from previous or imagined threats. Conditioned fears spread beyond what is reasonable or adaptive, leading to broad and interfering anxieties when people overgeneralize their fears. Difficulties with mnemonic discrimination, a component process of memory supporting the integration of old and new experiences, may foster overgeneralization and increase risk for anxiety disorders. Individuals along a spectrum of anxiety severity (n = 117) completed a differential fear conditioning paradigm and the computerized Mnemonic Similarity Task. The task measures mnemonic discrimination by requiring individuals to differentiate between highly similar old and new entities. We predicted that low mnemonic discrimination would be associated with overgeneralization, i.e., flatter slopes of change in response to stimuli increasingly dissimilar to the conditioned stimulus. Conditional growth models showed that as expected, participants with the highest mnemonic discrimination scores also exhibited the steepest declines in fear ratings as stimuli increasingly differed from the conditioned stimulus. Results were unchanged after adjusting for recognition memory, self-reported anxiety, and clinical diagnoses and symptoms. Results support the hypothesis that memory interference (i.e., low mnemonic discrimination) could increase vulnerability for overgeneralization. Findings justify additional exploration of mnemonic discrimination and its role in anxious psychopathology.

Generalization of extinction with a generalization stimulus is determined by learnt threat beliefs

Expectancy violation refers to the mismatch between an expected and the actual outcome. Maximizing expectancy violation is crucial for exposure-based treatment. Since the original stimulus of fear acquisition (CS+) is rarely available, stimuli that resemble the CS+ (generalization stimuli; GSs) are presented during treatment. A given GS may evoke either strong or weak generalized fear depending on an individual's threat beliefs. Presenting this GS in extinction would then evoke different levels of expectancy violation, which determines the strength of the subsequent generalization of extinction to other stimuli, including the CS+. After differential fear conditioning, participants exhibited discrete generalization gradients depending on their inferred relational rules (Linear vs Similarity). Crucially, the Linear group showed strong generalized fear to the GS used in extinction. This strong expectancy violation led to enhanced extinction learning and subsequently to strong generalization of extinction as characterized by a flat generalization gradient, and reduced conditioned fear to the CS+. In contrast, the Similarity group showed weak generalized fear to the same GS in extinction, and limited generalization of extinction. These results corroborate the importance of expectancy violation in exposure-based treatment, and suggest that exposure sessions designed to evoke strong threat beliefs may lead to better treatment outcome.

Observational learning of fear in real time procedure

Learning to avoid threats often occurs by observing others. Most previous research on observational fear learning (OFL) in humans has used pre-recorded standardized video of an actor and thus lacked ecological validity. Here, we aimed to enhance ecological validity of the OFL by engaging participants in a real-time observational procedure (35 pairs of healthy male friends, age 18–27). One of the participants watched the other undergo a differential fear conditioning task, in which a conditioned stimulus (CS+) was paired with an aversive electric shock and another stimulus (CS−) was always safe. Subsequently, the CS+ and CS− were presented to the observer to test the OFL. While the friend’s reactions to the shock elicited strong skin conductance responses (SCR) in all observers, subsequent differential SCRs (CS+ > CS−) were found only when declarative knowledge of the CS+/US contingency (rated by the participants) was acquired. Contingency-aware observers also showed elevated fear potentiated startle responses during both CS+ and CS− compared to baseline. We conclude that our real-time procedure can be effectively used to study OFL. The procedure allowed for dissecting two components of the OFL: an automatic emotional reaction to the response of the demonstrator and learning about stimulus contingency.

Threat Conditioning and Trait-Based Vulnerability to Personality Disorder.

Some personality disorders (PDs) are accompanied by heightened threat sensitivity to benign events, whereas others are associated with minimal reactivity to danger or punishment. Such aberrant patterns of defensive responding may be due to abnormal threat learning processes, analogous to those observed in other fear- and fearlessness-based disorders. We investigated threat learning deficits with a Pavlovian differential conditioning procedure in an undergraduate sample (n = 117) overselected for negative affectivity. Contrary to predictions, maladaptive personality traits, as assessed via the Personality Inventory for DSM-5, were largely unrelated to defensive responding (i.e., subjective and electrodermal reactions to danger and safety cues) during threat conditioning. We discuss the possible boundary conditions of threat learning abnormalities in PD and suggest research designs that could more effectively reveal such deficits, if they exist.

Quantifying Human Avoidance Behavior in Immersive Virtual Reality.

Avoidance behavior is a key symptom of most anxiety disorders and a central readout in animal research. However, the quantification of real-life avoidance behavior in humans is typically restricted to clinical populations, who show actual avoidance of phobic objects. In experimental approaches for healthy participants, many avoidance tasks utilize button responses or a joystick navigation on the screen as indicators of avoidance behavior. To allow the ecologically valid assessment of avoidance behavior in healthy participants, we developed a new automated immersive Virtual Reality paradigm, where participants could freely navigate in virtual 3-dimensional, 360-degrees scenes by real naturalistic body movements. A differential fear conditioning procedure was followed by three newly developed behavioral tasks to assess participants’ avoidance behavior of the conditioned stimuli: an approach, a forced-choice, and a search task. They varied in instructions, degrees of freedom, and high or low task-related relevance of the stimuli. We initially examined the tasks in a quasi-experiment (N = 55), with four consecutive runs and various experimental adaptations. Here, although we observed avoidance behavior in all three tasks after additional reinforcement, we only detected fear-conditioned avoidance behavior in the behavioral forced-choice and search tasks. These findings were largely replicated in a confirmatory experiment (N = 72) with randomized group allocation, except that fear-conditioned avoidance behavior was only manifest in the behavioral search task. This supports the notion that the behavioral search task is sensitive to detect avoidance behavior after fear conditioning only, whereas the behavioral approach and forced-choice tasks are still able to detect “strong” avoidance behavior after fear conditioning and additional reinforcement.

Measuring fear: Association among different measures of fear learning.

Background and objectivesFear conditioning paradigms use various measures to assess learned fear, including autonomic arousal responses like skin conductance, and self-reports of both associative (US-expectancies) and evaluative (affective ratings) learning. The present study uses a dimensional approach to examine associations among fear indices directly. MethodsSeventy-three participants completed a differential fear conditioning experiment, during which a neutral stimulus (CS+) was paired with an electric shock (US), while another stimulus (CS-) was never paired with the shock (partially instructed fear acquisition). Ten minutes later, both stimuli were presented without any shocks (fear extinction). Skin conductance responses and US-expectancy ratings were recorded during each phase, while self-reported negative affect was assessed for each CS at the end of extinction. ResultsResults showed a positive association among US-expectancy ratings and skin conductance responses during acquisition and early extinction. US-expectancy ratings during overall extinction were positively associated with post-extinction negative affect. LimitationsThe lack of affective ratings post-acquisition may have obscured associations between associative and evaluative learning indices. ConclusionsResults provide evidence for the expected correspondence among different indices of associative fear learning. Findings emphasize the need for incorporating both associative and evaluative learning measures in fear conditioning paradigms.

Salient safety conditioning improves novel discrimination learning

Generalized fear is one purported mechanism of anxiety that is a target of clinical and basic research. Impaired fear discrimination has been primarily examined from the perspective of increased fear learning, rather than how learning about non-threatening stimuli affects fear discrimination. To address this question, we tested how three Safety Conditioning protocols with varied levels of salience allocated to the safety cue compared to classic Fear Conditioning in their impact on subsequent innate anxiety, and differential fear learning of new aversive and neutral cues. Using a high anxiety strain of mice (129SvEv, Taconic), we show that Fear Conditioned animals show little exploration of the anxiogenic center of an open field 24 h later, and poor discrimination during new differential conditioning 7 days later. Three groups of mice underwent Safety Conditioning, (i) the safety tone was unpaired with a shock, (ii) the safety tone was unpaired with the shock and co-terminated with a house light signaling the end of the safety period, and (iii) the safety tone was unpaired with the shock and its beginning co-occurred with a house light, signaling the start of a safety period. Mice from all Safety Conditioning groups showed higher levels of open field exploration than the Fear Conditioned mice 24 h after training. Furthermore, Safety Conditioned animals showed improved discrimination learning of a novel non-threat, with the Salient Beginning safety conditioned group performing best. These findings indicate that high anxiety animals benefit from salient safety training to improve exploration and discrimination of new non-threating stimuli.

The effect of differential disgust conditioning and subsequent extinction versus counterconditioning procedures on women's sexual responses to erotic stimuli

Recent theoretical accounts point to disgust as an important factor in the development and persistence of sexual dysfunctions. This study tested if (i) contingent disgust experiences can render initially sexually arousing stimuli disgusting, and (ii) such acquired disgust responses could be best neutralized via a CS-only extinction or a counterconditioning procedure. Participants (N = 74) were exposed to a differential conditioning procedure that was followed by either a CS-only extinction or a counterconditioning procedure. Erotic films served as the CS+/CS-. A disgusting film served as the US. During the extinction procedure, the CS+ was no longer followed by the disgusting US. During counterconditioning the CS+ was paired with positive stimuli. After conditioning, the CS + elicited lower genital arousal and was rated as significantly more disgusting, less pleasant, and less sexually arousing than the CS-. These diminished genital and subjective sexual arousal responses to the CS+ were successfully restored after both the extinction and the counterconditioning procedure, whereas conditioned feelings of disgust and behavioral avoidance persisted. There was no evidence for differential effectiveness of either procedure. Thus, sexual responses can be attenuated by learned sex-disgust associations and restored by extinction and counterconditioning procedures, but conditioned feelings of disgust seem more resistant.

State-Dependent TMS over Prefrontal Cortex Disrupts Fear-Memory Reconsolidation and Prevents the Return of Fear

Erasing maladaptive memories has been a challenge for years. A way to change fear memories is to target the process of reconsolidation, during which a retrieved memory transiently returns to a labile state, amenable to modification [1, 2]. Disruption of human fear-memory reconsolidation has been classically attempted with pharmacological [3] or behavioral (e.g., extinction) [4] treatments that, however, do not clarify the underlying brain mechanism. To address this issue, in 84 healthy humans submitted to six experiments, here, we combined a differential fear conditioning paradigm with repetitive transcranial magnetic stimulation (rTMS) administered in a state-dependent manner. In a critical condition, we stimulated the dorsolateral prefrontal cortex (dlPFC) 10min after a reminder cue that reactivated a fear memory acquired 1day before. At testing, 24h after rTMS, participants exhibited decreased physiological expression of fear, as shown by their skin conductance response. Similar reductions were observed when targeting the left and the right dlPFC. In contrast, no decrease was observed in participants tested immediately after dlPFC-rTMS or in participants receiving either control rTMS (i.e., active control site and sham stimulations) or dlPFC-rTMS without preceding fear-memory reactivation, thus showing both the site and time specificity and state dependency of our rTMS intervention. Expression of fear was indeed reduced only when dlPFC-rTMS was administered within the reconsolidation time window. Moreover, dlPFC-rTMS prevented subsequent return of fear after extinction training. These findings highlight the causal role of dlPFC in fear-memory reconsolidation and suggest that rTMS can be used in humans to prevent the return of fear.

Puberty drives fear learning during adolescence.

Risk for adverse outcomes, including the onset of mental illness, increases during adolescence. This increase may be linked to both new exposures, such as violence at home or in the community, or to physiological changes driven by puberty. There are significant sex differences in adolescent risk, for instance, anxiety disorders are significantly more prevalent in girls than boys. Fear learning is linked to mental health and may develop during adolescence, but the role of puberty in adolescent-specific change has not yet been systematically evaluated. We conducted a longitudinal study of fear learning that tested fear-potentiated startle (FPS) in 78 children (40 girls) aged 8-16years. Participants completed two to three visits that included a differential fear conditioning task and self-report of both pubertal status and violence exposure. We tested for effects of sex, pubertal status, and violence exposure on FPS over time with latent growth curve models. We also examined the association between FPS and later anxiety symptoms. We found significant changes in FPS to the threat cue, but not the safety cue, across visits. Higher pubertal status was significantly associated with increased FPS to threat cues at each visit, whereas sex and violence exposure were not. FPS to threat during the baseline visit also predicted later anxiety symptoms. These findings suggest that puberty drives increased fear response to threat cues similarly for girls and boys, and that this effect may not be significantly impacted by individual differences in violence exposure during early adolescence.

Conjunctive and Elemental Representations of a Context in Humans.

The dual-process theory assumes that contexts are encoded in an elemental and in a conjunctive representation. However, this theory was developed from animal studies, and we still have to explore if and how elemental and conjunctive representations contribute to, for example, contextual anxiety in humans. Therefore, 28 participants underwent differential context conditioning in a newly developed flip-book paradigm. Virtual rooms were presented similar to a flip-book, that is, as a stream of 49 consecutive screenshots creating the impression of walking through the rooms. This allowed registration of event-related brain potentials triggered by specific screenshots. During two acquisition phases, two rooms were shown in this way for six times each. In one room, the anxiety context (CTX+), mildly painful electric stimuli (unconditioned stimuli [USs]) were administered unpredictably after 12 distinct screenshots, which became threat elements, whereas 12 selected comparable screenshots became nonthreat elements (elemental representation); all screenshots represented the anxiety context (conjunctive representation). In the second room, the safety context (CTX-), no USs were applied; thus, all screenshots created the safety context whereby 12 preselected screenshots represented safety elements. Increased US expectancy ratings for threat versus nonthreat or safety elements reflected elemental representation. Conjunctive representation was evident in differential ratings (arousal and contingency) and increased P100 and early posterior negativity amplitudes for threat and nonthreat CTX+ versus safety CTX- screenshots. These differences disappeared during two test phases without US delivery indicating successful extinction. In summary, we revealed the first piece of evidence for the simultaneous contributions of elemental and conjunctive representation during context conditioning in humans.

Eliciting and attenuating reinstatement of fear: Effects of an unextinguished CS

Reinstatement of fear is a proposed mechanism for return of fear following exposure therapy. A standard reinstatement procedure in the laboratory involves a conditional stimulus (CS) paired with an unconditional stimulus (US) during acquisition (i.e., CS+), and a CS paired without an US (CS-) during acquisition. In extinction the CS + and CS- are presented alone, then the US is presented without the CS in reinstatement, and followed by test trials of the CS. The current study examined whether reinstatement of fear can be triggered by a CS that was previously paired with the US (i.e., unextinguished CS) and reduced by extinction to the CSextinguished and CSunextinguished but not the CS- in a sample of first year psychology students (expectancy data N = 93; heart rate data N = 73). A differential aversive conditioning procedure presented within a virtual reality environment was used to examine reinstatement of the US expectancy and conditioned heart rate responses. As predicted, presentation of an unextinguished CS reinstated fear of a second previously extinguished CS. Moreover, conducting extinction with multiple stimuli attenuated this reinstatement of fear as indexed by self-report and heart rate measures. The present results suggest that therapy should include exposure to multiple stimuli to reduce the likelihood of reinstatement of fear.

Impact of ADCYAP1R1 genotype on longitudinal fear conditioning in children: interaction with trauma and sex.

Dysregulated fear conditioned responses have been associated with PTSD in adults, with increased fear-potentiated startle (FPS) serving as a potential intermediate phenotype for PTSD risk. This phenotype has also been associated with stress-related ADCYAP1R1 gene variants in adult women. However, FPS and genotype have not yet been examined during development. The aim of this study was to examine developmental changes in fear conditioning, and to see whether these changes were impacted by genotype and trauma. Differential fear conditioning using FPS was tested in n = 63 children ages 8-13 at two visits (V1, V2) 1 year apart. Startle response was measured using electromyograph recordings of the eyeblink muscle. The rs2267735 SNP of the ADCYAP1R1 gene was extracted from genome-wide (GWAS) analyses. Trauma exposure was assessed using the Violence Exposure Scale-Revised (VEX-R). We found significant Visit by Genotype interactions, with CC genotype increasing FPS from V1 to V2. At V2 there was a Genotype by Violence interaction, with higher FPS in the CC vs G allele groups among those with higher violence exposure (F = 17.46, p = 0.0002). Females with the CC genotype had higher FPS compared to G allele females (F = 12.09, p = 0.002); there were no effects of genotype in males. This study showed Gene × Environment × Development and Gene × Sex effects of ADCYAP1R1 in a high-risk pediatric population. Those with the CC genotype and high levels of violence exposure, as well as females with the CC genotype, showed the greatest conditioned fear responses in adolescence.

Impact of acute inflammation on the extinction of aversive gut memories

Impaired extinction of pain-related fear memories can lead to persistent or resurging fear of pain, contributing to the development and maintenance of chronic pain conditions. The mechanisms underlying maladaptive pain-related learning and memory processes remain incompletely understood, particularly in the context of interoceptive, visceral pain. Inflammation is known to interfere with learning and memory, but its effects on the extinction of pain-related fear memories have never been tested. In a randomized, double-blind, placebo-controlled study, we assessed the impact of experimental acute inflammation on the extinction and reinstatement of conditioned visceral pain-related fear. Forty healthy male volunteers underwent differential fear conditioning with visceral pain as clinically relevant unconditioned stimulus (US). Participants then received an intravenous injection of either 0.8 ng/kg lipopolysaccharide (LPS) as inflammatory stimulus or physiological saline as placebo, and extinction training was conducted at the peak of the inflammatory response. Extinction recall and reinstatement test were performed after overnight consolidation. Results showed that visceral pain represents an effective US, eliciting pronounced conditioned pain-related fear responses. Repeated unreinforced presentation of the pain-predictive cue during extinction training resulted in full extinction of the conditioned behavioral response. However, unexpected re-exposure to the US during reinstatement test resulted in return of fear. Despite pronounced LPS-induced effects on inflammatory markers, cortisol, and negative affect, we did not find evidence that acute inflammation resulted in altered fear extinction. The findings support the notion that visceral pain-related fear learning establishes a robust aversive memory trace that remains preserved during inhibitory learning, leaving a latent vulnerability for the return of fear. Inflammation during inhibitory learning did neither weaken nor further amplify this aversive memory trace, suggesting that it is rather resistant to acute inflammation-induced effects, at least in healthy individuals with no additional vulnerability factors.

Social aversive generalization learning sharpens the tuning of visuocortical neurons to facial identity cues.

Defensive system activation promotes heightened perception of threat signals, and excessive attention to threat signals has been discussed as a contributory factor in the etiology of anxiety disorders. However, a mechanistic account of attentional modulation during fear-relevant processes, especially during fear generalization remains elusive. To test the hypothesis that social fear generalization prompts sharpened tuning in the visuocortical representation of social threat cues, 67 healthy participants underwent differential fear conditioning, followed by a generalization test in which participants viewed faces varying in similarity with the threat-associated face. We found that generalization of social threat sharpens visuocortical tuning of social threat cues, whereas ratings of fearfulness showed generalization, linearly decreasing with decreasing similarity to the threat-associated face. Moreover, individuals who reported greater anxiety in social situations also showed heightened sharpened tuning of visuocortical neurons to facial identity cues, indicating the behavioral relevance of visuocortical tuning during generalization learning.

Perceptual errors are related to shifts in generalization of conditioned responding.

Studies of perceptual generalization have recently demonstrated a close relationship between stimulus perception and conditioned responding, suggesting that incorrect stimulus perception might account for certain characteristics of generalization gradients. In this study, we investigated whether common phenomena, such as the area and peak shift in conditioned responding, relate to perceptual errors. After a differential conditioning procedure, in which one circle was paired with the presentation of an aversive picture whereas a different-sized circle was not, we combined a generalization test with a three-alternative forced-choice perceptual categorization task where participants had to indicate on every trial whether the presented circle was one of the two circles from the conditioning phase or a different one, after which US-expectancy ratings were collected. The typical peak and area shift were observed when conditioned responses were plotted on a physical dimension. However, when stimulus perception was incorporated generalization gradients diverged from the typical gradient. Both the area and peak shift largely disappeared when accounting for perceptual errors. These findings demonstrate the need to incorporate perceptual mechanisms in associative models.

Spaced Training Forms Complementary Long-Term Memories of Opposite Valence in Drosophila

SummaryForming long-term memory (LTM) often requires repetitive experience spread over time. Studies in Drosophila suggest aversive olfactory LTM is optimal after spaced training, multiple trials of differential odor conditioning with rest intervals. Memory after spaced training is frequently compared to that after the same number of trials without intervals. Here we show that, after spaced training, flies acquire additional information and form an aversive memory for the shock-paired odor and a slowly emerging and more persistent “safety-memory” for the explicitly unpaired odor. Safety-memory acquisition requires repetition, order, and spacing of the training trials and relies on triggering specific rewarding dopaminergic neurons. Co-existence of aversive and safety memories is evident as depression of odor-specific responses at different combinations of junctions in the mushroom body output network; combining two outputs appears to signal relative safety. Having complementary aversive and safety memories augments LTM performance after spaced training by making the odor preference more certain.

Concurrent Electrodermal and Eyeblink Conditioning With Masked and Unmasked Stimuli

Abstract. The aim of this study was to determine if contingency awareness between the conditioned (CS) and unconditioned stimulus (US) is necessary for concurrent electrodermal and eyeblink conditioning to masked stimuli. An angry woman’s face (CS+) and a fearful face (CS−) were presented for 23 milliseconds (ms) and followed by a neutral face as a mask. A 98 dB noise burst (US) was administered 477 ms after CS+ offset to elicit both electrodermal and eyeblink responses. For the unmasking conditioning a 176 ms blank screen was inserted between the CS and the mask. Contingency awareness was assessed using trial-by-trial ratings of US-expectancy in a post-conditioning phase. The results showed acquisition of differential electrodermal and eyeblink conditioning in aware, but not in unaware participants. Acquisition of differential eyeblink conditioning required more trials than electrodermal conditioning. These results provided strong evidence of the causal role of contingency awareness on differential eyeblink and electrodermal conditioning.

Fear Learning in Veterans With Combat-Related PTSD Is Linked to Anxiety Sensitivity: Evidence From Self-Report and Pupillometry

Several studies have observed heightened Pavlovian fear conditioning in PTSD. However, it is unclear how fear conditioning in PTSD is related to risk factors for the disorder, such as anxiety sensitivity. Fifty-one combat-exposed veterans (20 with PTSD, 31 without PTSD) completed a differential fear conditioning task in which one colored rectangle (CS+) predicted a loud scream (US), whereas a different colored rectangle (CS-) predicted no US. Veterans with PTSD were characterized by greater anxiety to the CS+ but not the CS- during acquisition and extinction, and greater US expectancy during the CS+ but not the CS- at extinction. Also, veterans with PTSD had greater pupil dilation to both CSs at extinction, but not at acquisition. Anxiety sensitivity was correlated with anxiety and US expectancy in response to the CS+, but not the CS-, at both acquisition and extinction, and also with pupil diameter to both the CS+ and CS- at extinction. Nearly all of these relations held when covarying for PTSD symptoms and trait anxiety. These findings suggest that increased fear conditioning in PTSD may be related to elevated anxiety sensitivity.