Comparing neural correlates of conditioned inhibition between children with and without anxiety disorders – A preliminary study

Highlights

• Cross-species research suggests that conditioned inhibition reduces fear responding.

• This is the first study of conditioned inhibition in pediatric anxiety.

• Children with anxiety disorders showed differential activity in vmPFC.

• Future research should further examine conditioned inhibition in pediatric anxiety.

Abstract

Cognitive-behavioral therapy (CBT), a first-line treatment for pediatric anxiety disorders, is based on principles of threat learning and extinction. However, CBT does not work sufficiently for up to 40% of clinically anxious youth. The neural and behavioral correlates of conditioned inhibition might provide promising targets for attempts to improve CBT response. During conditioned inhibition, threat and safety cues appear together, forming a safety compound. Here, we test whether this safety compound elicits a reduced fear response compared to pairing the threat cue with a novel cue (novel compound). The current pilot study compares behavioral, physiological, and neural correlates of conditioned inhibition between children with (n = 17, M_age = 13.09, SD_age = 3.05) and without (n = 18, M_age = 14.49, SD_age = 2.38) anxiety disorders. Behavioral and physiological measures did not differ between children with and without anxiety disorders during fear acquisition. During testing, children with anxiety disorders showed overall higher skin conductance response and expected to hear the aversive sound following the novel compound more often than children without anxiety disorders. Children with anxiety disorders showed more activity in the right ventromedial prefrontal cortex (vmPFC) to the safety versus novel compound. Children without anxiety disorders showed the opposite pattern – more right vmPFC activity to the novel versus safety compound (F(1,31) = 5.40, p = 0.03). No group differences manifested within the amygdala, dorsal anterior cingulate cortex, or hippocampus. These pilot findings suggest a feasible approach for examining conditioned inhibition in pediatric anxiety disorders. If replicated in larger samples, findings may implicate perturbed conditioned inhibition in pediatric anxiety disorders and provide targets for CBT.

Introduction

CBT, a first-line treatment, fails to produce remission in at least 40 % of anxious children [1,2]. Since CBT applies threat-learning principles, translational neuroscience research on threat learning and extinction informs attempts to target CBT-resistant anxiety [3,4]. Findings from animal studies suggest that CBT might be improved by extending research on conditioned inhibition, which occurs when threat and safety cues are processed simultaneously [5,6]. However, minimal research examines conditioned inhibition in pediatric anxiety disorders. To launch this line of research, we compare behavioral, physiological, and neural correlates of conditioned inhibition in children with and without anxiety disorders to gain more insight into conditioned inhibition as a potential mechanism for improving CBT.

Pediatric anxiety disorders are common and impactful [[7], [8], [9], [10], [11]], and often emerge during late childhood or early adolescence [12]. It is important to study mechanisms underlying anxiety, such as threat learning, in youth in an attempt to interrupt cycles leading to chronic anxiety. In threat learning paradigms, a previously-neutral threat cue (conditioned stimulus, CS+) is repeatedly paired with an aversive stimulus (typically electric shock or loud noise, the UCS), whereas a safety cue (CS-) is never paired with the aversive stimulus [13]. During fear acquisition, differentiating between threat and safety cues engages the amygdala, dACC, hippocampus, and vmPFC [14,15]. During such paradigms, adults with anxiety disorders show an increased fear response (measured via subjective ratings of anxiety, SCR, or startle response) to safety cues [16], and children with anxiety disorders show an increased fear response (i.e., subjective anxiety, SCR, or startle response) to both threat and safety cues [17] during fear acquisition relative to age-matched participants without anxiety disorders.

Another important process in threat learning is extinction. During extinction, the threat cue is no longer paired with the aversive stimulus, thereby forming a new association between the threat cue and the absence of the aversive stimulus. As a result, the subsequent fear response to the threat cue is diminished. Extinction is related to activity in brain regions such as the amygdala, dACC, and vmPFC [18,19]. Adults with anxiety disorders display increased fear responses to the threat cue [16], and children with anxiety disorders show increased fear responses to both threat and safety cues [17] compared to age-matched participants without anxiety disorders. CBT-based exposure is based on these processes of threat learning and extinction [20]. Therefore, research on such processes informs attempts to treat CBT-resistant anxiety in children [1,2].

Conditioned inhibition supports fear reduction in ways that differ from extinction. During conditioned inhibition, threat and safety cues are presented simultaneously as a safety compound to test whether the safety cue reduces the fear response to the threat cue. Unlike extinction memories, which compete with an earlier threat memory evoked by a single cue, safety cues in conditioned inhibition are never paired with the aversive stimulus [5,21]. Animal studies have shown a reduction in the fear response to a safety compound relative to a threat cue presented by itself [5,6]. Behavioral evidence in rodents further suggests that fear reduction via conditioned inhibition may be less susceptible to the effects of prior stress than extinction [22], particularly during adolescence [23]. In studies with humans, a novel compound (i.e., threat cue paired with a novel cue) is often included as a control condition to test whether the safety stimulus (presented during the acquisition phase) reduces the fear response over and above a novel stimulus (not yet presented during the task). Indeed, healthy adults show reduced fear responses to a safety compound compared to a novel compound [24]. In contrast, adults with PTSD show less fear reduction in response to the safety compound, suggesting deficient conditioned inhibition [25]. To date, only one study has investigated the neural correlates of conditioned inhibition in humans. Specifically, findings demonstrated that the ventral hippocampus interacts with the dACC in both mice and healthy adults during conditioned inhibition to support fear reduction [26].

Conditioned inhibition is particularly relevant for pediatric anxiety disorders. Threat and safety learning undergo marked changes during development [[27], [28], [29]], as does the neural circuitry that supports these processes [30,31]. Cross-species research finds reduced fear extinction in adolescents compared to juveniles and adults, and this effect is related to reduced vmPFC synaptic plasticity in mice [32]. Moreover, as compared to adults, adolescents also show higher amygdala reactivity and delayed vmPFC engagement during extinction learning [33] and altered vmPFC activation and amygdala-vmPFC connectivity during extinction recall [34,35]. Conditioned inhibition may be more dependent on a broader network of regions [21], including the hippocampus and dACC [26], that develop later in life [36]. Delineating the neural mechanisms supporting conditioned inhibition during development and examining how they may differ in youth with anxiety disorders is a critical next step in translating research on conditioned inhibition.

The current pilot study compares behavioral, physiological, and neural correlates of conditioned inhibition between children with and without anxiety disorders. Participants performed a conditioned inhibition task [26] in the MRI scanner while we continuously measured SCR. We hypothesized that children with anxiety disorders would show differential behavioral, physiological, and neural responses during fear acquisition and conditioned inhibition compared to children without anxiety disorders. Given the preliminary nature of the current study, we did not specify a direction for the hypothesized group differences. We focused on the threat versus safety cue contrast for fear acquisition and on the safety compound versus novel compound contrast for conditioned inhibition. In light of prior research on aberrant threat and safety learning in anxiety disorders, our analyses focused on group differences in neural response in the amygdala, dACC, hippocampus, and vmPFC [14,18,26,34,35,[37], [38], [39], [40], [41], [42]]. As this was the first study of conditioned inhibition in youth, we also performed a whole-brain analysis to characterize broader differences between children with and without anxiety disorders in brain activity during fear acquisition and conditioned inhibition.