The neurobiology of post-traumatic stress disorder (PTSD) involves abnormal fear processing. Which neurobiological finding is MOST consistently reported in PTSD?

• A Hypoactivation of the amygdala with increased prefrontal cortex activity
• B Increased cortisol and HPA axis hyperactivity throughout the disorder
• C Increased hippocampal volume and enhanced contextual memory consolidation
• D Hyperactivation of the amygdala and decreased activity/volume of the hippocampus ✓

Explanation

PTSD is characterised neurobiologically by: (1) amygdala hyperactivity — exaggerated fear response to trauma cues; (2) reduced hippocampal volume and activity — impairing contextual memory processing and extinction learning; (3) reduced medial prefrontal cortex (mPFC) activity — failure of top-down inhibition of the amygdala. Unlike most stress disorders, PTSD paradoxically shows HPA axis hyporeactivity (low baseline cortisol, enhanced negative feedback) — the opposite of typical stress responses. This cortisol hyporeactivity is a distinguishing feature from major depression.

Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.

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