Generalization gradients for fear and disgust in human associative learning

The overgeneralization of pain-related fear in individuals with higher pain sensitivity: A behavioral and event-related potential study

Fear generalization contributes to the development and maintenance of pain. Pain sensitivity has been proposed to predict the strength of fear responses to aversive stimuli. However, whether individual variation in pain sensitivity affects pain-related fear generalization and its underlying cognitive processing remains unclear. To address this gap, we recorded behavioral and event-related potential (ERP) data among 22 high pain sensitivity (HPS) and 22 low pain sensitivity (LPS) healthy adults when exposed to a fear generalization paradigm. The behavioral results indicate that the HPS group displayed higher unconditioned stimulus expectancy and greater fear, arousal, and anxiety ratings to conditioned stimulus and generalization stimulus than the LPS group (all p values < 0.05). The ERP results showed that the HPS group exhibited a larger late positive potential evoked by GS2, GS3 and CS- (all p < 0.005) but a smaller N1 evoked by all CS and GSs (all p values < 0.05) relative to the LPS group. These findings suggest that individuals with a high level of pain sensitivity allocate more attention resources to pain-related threatening stimuli, which contributes to an overgeneralization of pain-related fear.

Common and separable behavioral and neural mechanisms underlie the generalization of fear and disgust

Generalization represents the transfer of a conditioned responses to stimuli that resemble the conditioned stimulus (CS). Previous studies on generalization of defensive avoidance responses have primarily focused on fear and have neglected disgust generalization, which represents a key pathological mechanism in some anxiety disorders. In the present study we examined common and distinct mechanisms of fear and disgust generalization by means of a fear or disgust multi-CS conditioning and generalization paradigm with concomitant event-related potential (ERPs) acquisition in n = 62 subjects. We demonstrate that compared to fear, disgust-relevant generalized stimuli (GS) elicited larger expectancy ratings and longer reaction times (RTs) reflecting stronger ratings of 'risk'. On the electrophysiological level, increased P2 amplitudes were found in response to conditioned CS+ versus CS- across both domains, possibly reflecting higher motivational and attentional salience of aversive conditioned stimuli per se. Contingent negative variation (CNV) amplitude was significantly larger for disgust-CS+ than disgust-CS-, reflecting a stronger preparation of the disgust US. Additionally, we found that the contingent negative variation (CNV) fear generalization gradient, and CNV amplitude were increased with similarity to CS+. In contrast the CNV to disgust-GS did not differ and did not reflect disgust generalization. Together this may indicate that the CNV represents a highly fear-specific index for generalization learning. This study provides the first neurobiological evidence for common and distinct generalization learning in fear versus disgust suggesting that dysregulations in separable defensive avoidance mechanisms may underly different anxiety disorder subtypes.

Enhanced Medial Prefrontal Cortex and Hippocampal Activity Improves Memory Generalization in APP/PS1 Mice: A Multimodal Animal MRI Study

Memory generalization allows individuals to extend previously learned movement patterns to similar environments, contributing to cognitive flexibility. In Alzheimer’s disease (AD), the disturbance of generalization is responsible for the deficits of episodic memory, causing patients with AD to forget or misplace things, even lose track of the way home. Cognitive training can effectively improve the cognition of patients with AD through changing thinking mode and memory flexibility. In this study, a T-shaped maze was utilized to simulate cognitive training in APP/PS1 mice to elucidate the potential mechanisms of beneficial effects after cognitive training. We found that cognitive training conducted by a T-shaped maze for 4 weeks can improve the memory generalization ability of APP/PS1 mice. The results of functional magnetic resonance imaging (fMRI) showed that the functional activity of the medial prefrontal cortex (mPFC) and hippocampus was enhanced after cognitive training, and the results of magnetic resonance spectroscopy (MRS) showed that the neurochemical metabolism of N-acetyl aspartate (NAA) and glutamic acid (Glu) in mPFC, hippocampus and reuniens (Re) thalamic nucleus were escalated. Furthermore, the functional activity of mPFC and hippocampus was negatively correlated with the escape latency in memory generalization test. Therefore, these results suggested that cognitive training might improve memory generalization through enhancing the functional activity of mPFC and hippocampus and increasing the metabolism of NAA and Glu in the brain regions of mPFC, hippocampus and Re nucleus.