Generalization of Conscious Fear Is Positively Correlated with Anxiety, but Not with Depression

Abstract

Generalization of learned fear has been considered to be critical for our survival. Patients with anxiety problems show overgeneralization of learned fear, as reflected by defensive physiological responses to harmless stimuli. Together with these physiological responses, conscious feeling of fear is a seminal part of emotional process that is directly related to the suffering of anxiety patients. However, the effect of anxiety on the generalization of conscious feeling remains unclear. We thus focused on the question whether the generalization of conscious feeling of fear depends on individual anxiety level in nonpatient participants. To address this question, we developed a fear generalization paradigm using natural scene images. We found that subjective feeling of fear was generalized to similar stimuli with the conditioned stimuli (CS), and that this generalization of conscious fear was positively correlated with the level of individual anxiety. Anxiety and depression frequently co-occur, but the individual depression level was not correlated with the fear generalization. These suggest that individual anxiety level mainly affects the generalization of conscious fear.

Keywords: anxiety; conditioning; conscious feeling; depression; fear; generalization.

Fig. 1. Experimental design. (A) Sample scene images used in the experiment. Natural scene images from continuously changing seven categories served as conditioned stimuli (CS+), unpaired conditioned stimuli (CS−), and generalization stimuli (GSs). The seven categories were sandy desert, gravel desert, vegetated desert, grassland, mountain, forest, and swamp. Participants were counterbalanced into two groups. For half of the participants (Group 1), scenes of the sandy desert category were paired with US, while scenes of the swamp category were paired with US for the other half (Group 2). (B) The experiment was conducted for two consecutive days. On the first day (Day 1), participants were introduced to the familiarization, pre-learning test, and learning sessions, and they performed post-learning test on the next day (Day 2). During the familiarization, scene images of all seven categories and US were presented in random order. During the learning, only scenes from the CS+ and CS− categories were presented, and half of the CS+ presentations were co-terminated with US. During the pre-learning or post-learning test, participants rated the subjective feeling or US-expectancy for each scene on a 1~5 scale while each scene image was presented. ITI=intertrial interval.

Fig. 2. Generalization of conditioned fear. (A) The change of subjective feeling induced by fear conditioning. (B) The change of US-expectancy. (C) Average subjective feeling scores during the pre-learning test. (D) Average US-expectancy scores during the pre-learning test. (E) Average subjective feeling scores during the post-learning test. (F) Average US-expectancy scores during the post-learning test. Numbers in x-axis indicate scene categories. ^**p<0.01, Friedman test for the scene category effect. Error bars indicated between-subjects s.e.m.

Fig. 3. Relationship between the generalization of conscious feeling induced by fear conditioning and individual anxiety (or depression) level. To determine the degree of fear generalization, we derived the maximum category number of scenes for which the participants rated as score 2 (category threshold) or the change of subjective feeling scores (or average feeling scores during the post-learning test) to scene category 6, which is the last category of GS. (A~C) Correlation between fear generalization and BAI scores. (D~F) Correlation between fear generalization and BDI scores.

Fig. 4. Relationship between the generalization of US-expectancy and individual anxiety (or depression) level. To determine the degree of fear generalization, we derived the maximum category number of scenes for which the participants rated as score 2 (category threshold) or the change of US-expectancy scores (or average US-expectancy scores during the post-learning test) to category 6 scenes. (A~C) Correlation between fear generalization and BAI scores. (D~F) Correlation between fear generalization and BDI scores.

Fig. 5. Relationship between the strength of conscious feeling induced by fear conditioning and anxiety (or depression) level. To determine the strength of fear memory, the change of the feeling scores (or the average feeling scores during the post-learning test) to category 1 scenes (CS+ scenes) were used. (A, B) Correlation between the strength of fear memory and BAI scores. (C, D) Correlation between the strength of fear memory and BDI scores.

Fig. 6. Relationship between the strength of US-expectancy and anxiety (or depression) level. To determine the strength of fear memory, the change of the US-expectancy scores (or the average US-expectancy scores during the post-learning test) to category 1 scenes (CS+ scenes) were used. (A, B) Correlation between the strength of fear memory and BAI scores. (C, D) Correlation between the strength of fear memory and BDI scores.