Generalization Stimuli Research Articles

VENTROMEDIAL PREFRONTAL CORTEX REACTIVITY IS ALTERED IN GENERALIZED ANXIETY DISORDER DURING FEAR GENERALIZATION

Fear generalization is thought to contribute to the development and maintenance of anxiety symptoms and accordingly has been the focus of recent research. Previously, we reported that in healthy individuals (N = 25) neural reactivity in the insula, anterior cingulate cortex (ACC), supplementary motor area (SMA), and caudate follow a generalization gradient with a peak response to a conditioned stimulus (CS) that declines with greater perceptual dissimilarity of generalization stimuli (GS) to the CS. In contrast, reactivity in the ventromedial prefrontal cortex (vmPFC), a region linked to fear inhibition, showed an opposite response pattern. The aim of the current study was to examine whether neural responses to fear generalization differ in generalized anxiety disorder (GAD). A second aim was to examine connectivity of primary regions engaged by the generalization task in the GAD group versus healthy group, using psychophysiological interaction analysis. Thirty-two women diagnosed with GAD were scanned using the same generalization task as our healthy group. Individuals with GAD exhibited a less discriminant vmPFC response pattern suggestive of deficient recruitment of vmPFC during fear inhibition. Across participants, there was enhanced anterior insula (aINS) coupling with the posterior insula, ACC, SMA, and amygdala during presentation of the CS, consistent with a modulatory role for the aINS in the execution of fear responses. These findings suggest that deficits in fear regulation, rather than in the excitatory response itself, are more critical to the pathophysiology of GAD in the context of fear generalization.

Neural reactivity tracks fear generalization gradients

Recent studies on fear generalization have demonstrated that fear-potentiated startle and skin conductance responses to a conditioned stimulus (CS) generalize to similar stimuli, with the strength of the fear response linked to perceptual similarity to the CS. The aim of the present study was to extend this work by examining neural correlates of fear generalization. An initial experiment (N=8) revealed that insula reactivity tracks the conditioned fear gradient. We then replicated this effect in a larger independent sample (N=25). Activation in the insula, anterior cingulate, right supplementary motor cortex and caudate increased reactivity as generalization stimuli (GS) were more similar to the CS, consistent with participants’ overall ratings of perceived shock likelihood and pupillary response to each stimulus.

The development of fear learning and generalization in 8–13 year‐olds

The current study examined developmental changes in fear learning and generalization in 40 healthy 8-13 year-olds using an aversive conditioning paradigm adapted from Lau et al. [Lau et al. [2008] Journal of the American Academy of Child and Adolescent Psychiatry 47:94-102]. In this task, the conditioned stimuli (CS+/CS-) are two neutral female faces, and the unconditioned stimulus is a fearful, screaming face. The second phase of the study also included a generalization stimulus (GS): a 50% blend of the CS± faces. The eye-blink startle reflex was utilized to measure defensive responding. Patterns of fear learning and generalization were qualified by child age. Older children demonstrated greater fear learning (i.e., larger startle during CS+ than CS-) than younger children. In addition, older children exhibited the typical pattern of generalization observed in adults, whereas younger children did not. Finally, fear learning also related to contingency awareness; only children who correctly identified the CS+ demonstrated fear-potentiated startle to the CS+. Clinical implications and future directions are discussed.

Generalization of conditioned responding: Effects of autobiographical memory specificity

Generalization of acquired responses appears to be a crucial, yet under investigated process in emotional disorders. Generalization occurs when a conditioned response is elicited by a stimulus different from the original conditioned stimulus. The expansion of complaints, often seen in emotional disorders, is at least in part due to processes of generalization. In the present study, generalization is approached from a memory perspective. It is hypothesized that generalization of conditioned responding is associated with autobiographical memory specificity. Higher levels of generalization are predicted for people who are characterized by limited memory specificity. In a human contingency-learning procedure, participants learned the association between two pictures of female faces and a schematic drawing of a lightning bolt. Subsequently, six morphed pictures functioning as generalization stimuli (GSs) were introduced and conditioned responses to these GSs were measured. The results showed that memory specificity was significantly associated with the extent of generalization. Participants low in autobiographical memory specificity exhibited significantly stronger conditioned responses to GSs as compared to participants high in autobiographical memory specificity.

Generalization of conditioned fear-potentiated startle in humans: Experimental validation and clinical relevance

Though generalization of conditioned fear has been implicated as a central feature of pathological anxiety, surprisingly little is known about the psychobiology of this learning phenomenon in humans. Whereas animal work has frequently applied methods to examine generalization gradients to study the gradual weakening of the conditioned-fear response as the test stimulus increasingly differs from the conditioned stimulus (CS), to our knowledge no psychobiological studies of such gradients have been conducted in humans over the last 40 years. The current effort validates an updated generalization paradigm incorporating more recent methods for the objective measurement of anxiety (fear-potentiated startle). The paradigm employs 10, quasi-randomly presented, rings of gradually increasing size with extremes serving as CS+ and CS−. The eight rings of intermediary size serve as generalization stimuli (GSs) and create a continuum-of-similarity from CS+ to CS−. Both startle data and online self-report ratings demonstrate continuous decreases in generalization as the presented stimulus becomes less similar to the CS+. The current paradigm represents an updated and efficacious tool with which to study fear generalization—a central, yet understudied conditioning-correlate of pathologic anxiety.