fMRI Investigation of Explicit Cue and Contextual Fear
Overview
- Phase
- Not Applicable
- Intervention
- Not specified
- Conditions
- Anxiety Disorders
- Sponsor
- National Institute of Mental Health (NIMH)
- Enrollment
- 1080
- Locations
- 1
- Primary Endpoint
- Percent of Correct No Button Presses During Functional MRI
- Status
- Completed
- Last Updated
- 2 years ago
Overview
Brief Summary
The purpose of this study is to use brain imaging technology to investigate brain changes in people exposed to predictable versus unpredictable unpleasant stimuli. Unpleasant events that can be predicted evoke a response of fear, whereas unpredictable, unpleasant stimuli cause chronic anxiety not associated with a specific event. Information gained from this study may help in the development of more effective treatments for anxiety disorders.
When confronted with fearful events, people eventually develop fear of specific cues that were associated with these events as well as to the environmental context in which the fearful event occurred. Evidence suggests that cued fear and contextual fear model different aspects of anxiety. However, studies that examine the way the brain affects expression of contextual fear have not been conducted. This study will use magnetic resonance imaging (MRI) or Magneto-encephalography (MEG) to compare the brain activity underlying fear brought on by predictable and unpredictable aversive stimuli.
Detailed Description
This protocol examines the neurobiology of fear and anxiety using various approaches. During fear conditioning in which a phasic explicit cue (e.g., a light) is repeatedly associated with an aversive unconditioned stimulus (e.g., a shock), the organism develops fear to the explicit cue as well as to the environmental context in which the experiment took place. Experimental evidence suggests that cued fear and contextual fear model different aspects of anxiety. Studies in patients indicated that contextual fear may model an aspect that is especially relevant to anxiety disorders. However, the neural basis for the expression of contextual fear has not previously been elucidated in human imaging studies. One important determinant of contextual fear is predictability: contextual fear increases when a threat (e.g., electric shock) is unpredictable, as opposed to when the threat is predictable. The aim of this study is to compare the neural substrates underlying fear evoked by predictable versus unpredictable shocks. Animal studies have indicated that conditioned responses to predictably cued threat and to less explicit threat are separate processes mediated by distinct brain structures. Psychophysiological data suggest that the proposed procedure can differentiate between these two responses. Hence, we anticipate that this procedure will allow us to compare brain correlates of these responses in humans. Another objective is to study effects of threat of shock on processing and learning of threat cues in the amygdala, the visual and auditory systems, and motivation/reward systems. This will be investigated by means of event-related magneto-encephalography (MEG) and fMRI measurements using various paradigms. Finally, a last project will examine how pharmacologic manipulation of gamma-aminobutyric acid (GABA) levels with the benzodiazepine alprazolam affects the relationship between GABA concentration (quantified with magnetic resonance spectroscopy, MRS), visual- and auditory-induced gamma oscillations (measured with MEG), and fMRI BOLD response.
Investigators
Eligibility Criteria
Inclusion Criteria
- Not provided
Exclusion Criteria
- Not provided
Outcomes
Primary Outcomes
Percent of Correct No Button Presses During Functional MRI
Time Frame: 2000 milliseconds during trial
Subjects participated in go/nogo (91% GO trials with the " = " symbol indicating button push and 9% NOGO trials with the "O" symbol indicating no push)) task condition during 3 Tesla (3T) or 7 Tesla (7T) functional MRI with periods of threat of shocks and periods of safety when no shock could be administered. During the GNG stimuli were presented on a monitor and randomly distributed. A correct go hit was a response recorded during these 2000 ms to a go trial. Similarly, a correct nogo omission was a no response during the same period to a nogo trial. Performance was first averaged across condition (threat, safe) and trial type (go, nogo) by dividing the number of correct responses by the total number of each trial type. The NOGO and GO behavioral effects were then separately compared between 3T and 7T strength. Accuracy was measured as a percent of correct button presses during fMRI (3T or 7T).
Difference in Volume - Left & Right Habenula
Time Frame: 10 minutes
Images were acquired on a 7 T Siemens Magnetom MRI with a 32-channel head coil over 10 minutes. Participants were instructed to keep their eyes open and look at a white fixation cross on a black background during image acquisition. Following manual tracing of the habenula, the volumes of the left and right habenulae for each subject were computed separately. The left and right habenula volumes were then compared using a paired t-test.
Average Correlations Between Average Time Series - Left & Right Hemisphere of the Brain
Time Frame: 10 minutes
The average bed nucleus of the stria terminalis (BNST) correlations between all averaged time series were extracted from the raters' individual masks. Blood Oxygenation Level Dependent (BOLD) signals were used to extract a mean time series from the BNST masks. This time series was correlated across the rest of the brain using 3dTcorr1D, which computes the correlation coefficient between each voxel time series. Raters were blinded to subject identity for subjective sensory effects at high field and inter-rater and volume measurements for the drawn BNST masks. Correlations were calculated between average time series extracted between all raters' masks for each subject. Two separate analyses for the left and right BNSTs were performed.