Anxiety and the search for safety: An fMRI study

Abstract

While limbic responses to anxiety have been extensively studied, sensory region involvement is less understood. We utilized fMRI combined with a modified instructed fear/anticipatory anxiety paradigm to test our hypothesis that secondary visual areas demonstrate differential responsivity to fear / anxiety stimuli in select neuropsychiatric patients vs. normal controls. Methods: 24 unmedicated subjects (7 PTSD, 7 Panic disorder & 10 normal) were scanned while observing one of two visual stimuli (blue or yellow squares) serially-presented within a block design paradigm. Subjects were instructed that while one color could be associated with an electrodermal stimulation (never delivered during the experiment phase), the other would not. Stimulus colors were counterbalanced across subjects and groups to control for time and order effects. EPI BOLD scans were acquired on a GE 3T MRI Scanner. Data were analyzed using SPM99+. Results: Although stronger activations in regions known to be selective for color were observed in normal subjects when contrasting the “potential threat” with “safe” condition, the opposite was observed in color selective regions for each of the patient populations. These results were reflected in patient vs. normal group comparisons, revealing greater activations in color selective regions for “safe” stimuli in patients. Conclusion: Research on color and visual recognition has mostly focused on bottom-up regulation. Our findings indicate early top-down modulation of visual processing to emotionally charged color stimuli. Results may also suggest that while normal subjects may be concerned to a greater extent with the possibility of encountering an aversive stimulus, anxiety patients appear to attend more to conditions allowing them to feel safe. These results provide additional early evidence that fear and anxiety effects are not limited to the limbic system but also involve cortical sensory areas. 1.Phelps et al.(2001) 2.Bartels et al.(2000)