title: Bi-Directional Tuning of Amygdala Sensitivity in Combat Veterans Investigated with fMRI.
abstract: OBJECTIVE
  Combat stress can be followed by persistent emotional consequences. It is thought that these emotional consequences are caused in part by increased amygdala reactivity. It is also thought that amygdala hyper-reactivity results from decreased inhibition from portions of the anterior cingulate cortex (ACC) in which activity is negatively correlated with activity in the amygdala. However, experimental support for these proposals has been inconsistent.
  
  
  METHODS
  We showed movies of combat and civilian scenes during a functional magnetic resonance imaging (fMRI) session to 50 veterans of recent combat. We collected skin conductance responses (SCRs) as measures of emotional arousal. We examined the relation of blood oxygenation-level dependent (BOLD) signal in the amygdala and ACC to symptom measures and to SCRs.
  
  
  RESULTS
  Emotional arousal, as measured with SCR, was greater during the combat movie than during the civilian movie and did not depend on symptom severity. As expected, amygdala signal during the less-arousing movie increased with increasing symptom severity. Surprisingly, during the more-arousing movie amygdala signal decreased with increasing symptom severity. These differences led to the unexpected result that amygdala signal in highly symptomatic subjects was lower during the more-arousing movie than during the less-arousing movie. Also unexpectedly, we found no significant inverse correlation between any portions of the amygdala and ACC. Rather, signal throughout more than 80% of the ACC showed a strong positive correlation with signal throughout more than 90% of the amygdala.
  
  
  CONCLUSIONS
  Amygdala reactivity can be tuned bi-directionally, either up or down, in the same person depending on the stimulus and the degree of post-traumatic symptoms. The exclusively positive correlations in BOLD activity between the amygdala and ACC contrast with findings that have been cited as evidence for inhibitory control of the amygdala by the ACC. The conceptualization of post-traumatic changes in neural function should be reconsidered.
authors.affiliation: Department of Psychiatry, University of Iowa Carver College of Medicine, Iowa City, Iowa, United States of America; Department of Psychiatry, Iowa City VA Healthcare System, Iowa City, Iowa, United States of America.
authors.forename: Tom
authors.initials: T
authors.lastname: Brashers-Krug
authors.affiliation: Mental Health Service Line, Veterans Affairs Medical Center, Houston, Texas, United States of America; Department of Psychiatry and Behavioral Sciences, Baylor College of Medicine, Houston, Texas, United States of America.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Jorge
mesh_terms: D000328:Adult; D000679:Amygdala / Q000503:physiopathology*; D001143:Arousal / Q000502:physiology; D001921:Brain / Q000503:physiopathology; D001931:Brain Mapping; D004644:Emotions / Q000502:physiology; D005260:Female; D006179:Gyrus Cinguli / Q000473:pathology; D006787:Hospitals, Veterans; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D010100:Oxygen / Q000097:blood*; D012867:Skin / Q000378:metabolism*; D013313:Stress Disorders, Post-Traumatic / Q000523:psychology; D013315:Stress, Psychological; D011795:Surveys and Questionnaires; D014481:United States; D014728:Veterans / Q000523:psychology; D055815:Young Adult
chemical_list: D010100:Oxygen