Neuronal Correlates of Small Animal Phobia in Human Subjects through fMRI: The Role of the Number and Proximity of Stimuli

Toward a reliable detection of arachnophobia: subjective, behavioral, and neurophysiological measures of fear response

Introduction

The administration of questionnaires presents an easy way of obtaining important knowledge about phobic patients. However, it is not well known how these subjective measurements correspond to the patient's objective condition. Our study aimed to compare scores on questionnaires and image evaluation to the objective measurements of the behavioral approach test (BAT) and the neurophysiological effect of spiders extracted from fMRI measurements. The objective was to explore how reliably subjective statements about spiders and physiological and behavioral parameters discriminate between phobics and non-phobics, and what are the best predictors of overall brain activation.

Methods

Based on a clinical interview, 165 subjects were assigned to either a "phobic" or low-fear "control" group. Finally, 30 arachnophobic and 32 healthy control subjects (with low fear of spiders) participated in this study. They completed several questionnaires (SPQ, SNAQ, DS-R) and underwent a behavioral approach test (BAT) with a live tarantula. Then, they were measured in fMRI while watching blocks of pictures including spiders and snakes. Finally, the respondents rated all the visual stimuli according to perceived fear. We proposed the Spider Fear Index (SFI) as a value characterizing the level of spider fear, computed based on the fMRI measurements. We then treated this variable as the "neurophysiological effect of spiders" and examined its contribution to the respondents' fear ratings of the stimuli seen during the fMRI using the redundancy analysis (RDA).

Results

The results for fear ranks revealed that the SFI, SNAQ, DS-R, and SPQ scores had a significant effect, while BAT and SPQ scores loaded in the same direction of the first multivariate axis. The SFI was strongly correlated with both SPQ and BAT scores in the pooled sample of arachnophobic and healthy control subjects.

Discussion

Both SPQ and BAT scores have a high informative value about the subject's fear of spiders and together with subjective emotional evaluation of picture stimuli can be reliable predictors of spider phobia. These parameters provide easy and non-expensive but reliable measurement wherever more expensive devices such as magnetic resonance are not available. However, SFI still reflects individual variability within the phobic group, identifying individuals with higher brain activation, which may relate to more severe phobic reactions or other sources of fMRI signal variability.

A Voxel-Based Morphometric Study of Gray Matter in Specific Phobia

The objective of this study was to analyze the neurostructural abnormalities of brain areas responsible for the acquisition and maintenance of fear in small animal phobia by comparing gray matter volume (GMV) in individuals with phobia and non-fearful controls. Structural magnetic resonance imaging was obtained from 62 adults (79% female) assigned to one of two groups: 31 were diagnosed with small animal phobia and 31 were non-fearful controls. To investigate structural alterations, a whole-brain voxel-based morphometry analysis was conducted to compare the GMV of the brain areas involved in fear between both groups. The results indicated that individuals with a small animal specific phobia showed smaller GMV in cortical regions, such as the orbitofrontal (OFC) and medial frontal cortex, and greater GMV in the putamen than non-fearful controls. These brain areas are responsible for avoidant behavior (putamen) and emotional regulation processes or inhibitory control (prefrontal cortex (PFC)), which might suggest a greater vulnerability of phobic individuals to acquiring non-adaptive conditioned responses and emotional dysregulation. The findings provide preliminary support for the involvement of structural deficits in OFC and medial frontal cortex in phobia, contributing to clarify the neurobiological substrates for phobias.

Neuronal Activity during Exposure to Specific Phobia through fMRI: Comparing Therapeutic Components of Cognitive Behavioral Therapy

Cognitive behavioral therapy (CBT) packages for anxiety disorders, such as phobias, usually include gradual exposure to anxious contexts, positive self-verbalizations, and relaxation breathing. The objective of this research was to analyze the specific neural activation produced by the self-verbalizations (S) and breathing (B) included in CBT. Thirty participants with clinical levels of a specific phobia to small animals were randomly assigned to three fMRI conditions in which individuals were exposed to phobic stimuli in real images: a group underwent S as a technique to reduce anxiety; a second group underwent B; and a control group underwent exposure only (E). Simple effects showed higher brain activation comparing E > S, E > B, and S > B. In particular, in the E group, compared to the experimental conditions, an activation was observed in sensory-perceptive and prefrontal and in other regions involved in the triggering of emotion (i.e., amygdala, supplementary motor area, and cingulate gyrus) as well as an activation associated with interoceptive sensitivity (i.e., insula and cingulate cortex). According to the specific tool used, discrepancies in the neural changes of CBT efficacy were observed. We discuss the theoretical implications according to the dual model of CBT as a set of therapeutic tools that activate different processes.

Implicit emotion regulation improves arithmetic performance: An ERP study

Available evidence suggests that emotions influence arithmetic, and explicit emotion regulation modulates the effect of anxiety on arithmetic performance. However, neural mechanisms by which implicit emotion regulation affects these phenomena remain unclear, particularly under distinct affective priming contexts. Twenty-two college students were required to perform multiple tasks in sequence, including an idioms matching task, a multiplication computational estimation task (MCE task), an emotion judgement task (EJ task), and an emotion assessment task (EA task). Behavioral performance was measured via accuracy and response time during the MCE task, and ratings of the EA task, while eletrophysiological response was measured via the contingent negative variation (CNV) elicited by completing the MCE task. Decreased response time and emotional intensity ratings were observed for priming emotion regulation idioms compared to priming neutral idioms. Priming emotion regulation idioms attenuated early CNV amplitudes under happiness priming, and attenuated both early and late CNV amplitudes under fear priming. These results suggested that implicit reappraisal and suppression are promising strategies to enhance arithmetic performance and alleviate the adverse effects of affective priming, especially under fear priming.

Changes in Brain Activation through Cognitive-Behavioral Therapy with Exposure to Virtual Reality: A Neuroimaging Study of Specific Phobia

Background: Cognitive-behavioral therapy (CBT) with exposure is the treatment of choice for specific phobia. Virtual reality exposure therapy (VRET) has shown benefits for the treatment and prevention of the return of fear in specific phobias by addressing the therapeutic limitations of exposure to real images. Method: Thirty-one participants with specific phobias to small animals were included: 14 were treated with CBT + VRET (intervention group), and 17 were treated with CBT + exposure to real images (active control group). Participants’ scores in anxiety and phobia levels were measured at baseline, post-treatment, and 3-month follow-up, and brain activation was measured through functional magnetic resonance imaging (fMRI) baseline and post-treatment. Results: Both groups showed a significant decrease in anxiety and phobia scores after the therapy and were maintained until follow-up. There were no significant differences between both groups. Overall, fMRI tests showed a significant decrease in brain activity after treatment in some structures (e.g., prefrontal and frontal cortex) and other structures (e.g., precuneus) showed an increasing activity after therapy. However, structures such as the amygdala remained active in both groups. Conclusions: The efficacy of CBT + VRET was observed in the significant decrease in anxiety responses. However, the results of brain activity observed suggest that there was still a fear response in the brain, despite the significant decrease in subjective anxiety levels.