Fear is fast in phobic individuals: amygdala activation in response to fear-relevant stimuli.
BACKGROUND
Two core characteristics of pathologic fear are its rapid onset and resistance to cognitive regulation. We hypothesized that activation of the amygdala early in the presentation of fear-relevant visual stimuli would distinguish phobics from nonphobics.


METHODS
Chronometry of amygdala activation to phobia-relevant pictures was assessed in 13 spider phobics and 14 nonphobics using functional magnetic resonance imaging (fMRI).


RESULTS
Blood oxygen level-dependent (BOLD) responses in the amygdala early in picture processing consistently differentiated between phobic and nonphobic subjects, as well as between phobogenic and nonphobogenic stimuli among phobics. Furthermore, amygdalar BOLD responses associated with timing but not magnitude of activation predicted affective responses to phobogenic stimuli. Computational modeling procedures were used to identify patterns of neural activation in the amygdala that could yield the observed BOLD data. These data suggest that phobic responses were characterized by strong but brief amygdala responses, whereas nonphobic responses were weaker and more sustained.


CONCLUSIONS
Results are discussed in the context of the amygdala's role in rapid threat detection and the vigilance-avoidance hypothesis of anxiety. These data highlight the importance of examining the neural substrates of the immediate impact of phobogenic stimuli for understanding pathological fear.
Larson
Christine L
CL
Department of Psychology, Michigan State University, East Lansing, Michigan 48824-1116, USA. larson37@msu.edu
Schaefer
Hillary S
HS
Siegle
Greg J
GJ
Jackson
Cory A B
CA
Anderle
Michael J
MJ
Davidson
Richard J
RJ
D000293:Adolescent; D000328:Adult; D000679:Amygdala / Q000502:physiology* / Q000503:physiopathology; D001143:Arousal / Q000502:physiology; D001931:Brain Mapping; D003198:Computer Simulation; D005071:Evoked Potentials / Q000502:physiology*; D005239:Fear / Q000502:physiology*; D005260:Female; D006801:Humans; D008960:Models, Psychological; D010698:Phobic Disorders / Q000503:physiopathology*; D010775:Photic Stimulation / Q000379:methods; D012016:Reference Values