Anxiety Disorders: Amygdala Dysregulation

The amygdala is the central hub of the brain's fear circuitry, receiving dual sensory input: a rapid thalamo-amygdalar 'low road' that processes threats before conscious awareness (enabling immediate defensive responses), and a slower thalamo-cortical-amygdalar 'high road' through the sensory cortex and hippocampus that enables contextual threat appraisal. In anxiety disorders, this system is pathologically dysregulated. Amygdalar hyperreactivity produces exaggerated fear responses to non-threatening stimuli, while deficient top-down inhibition from the medial prefrontal cortex (mPFC) — specifically the ventromedial PFC and anterior cingulate cortex — fails to extinguish learned fear associations. The bed nucleus of the stria terminalis (BNST) mediates sustained anxious apprehension (as opposed to acute fear), driving the chronic worry characteristic of GAD. At the neurotransmitter level, reduced GABAergic inhibition within amygdalar microcircuits lowers the threshold for fear circuit activation, while serotonergic projections from the dorsal raphe normally dampen amygdalar output — 5-HT deficiency removes this brake. The HPA axis becomes hyperactivated with elevated CRH from the paraventricular nucleus, driving sustained cortisol release that causes hippocampal volume reduction (impairing contextual fear discrimination) and further amygdalar sensitization, creating a self-perpetuating...