19.03.2 Neurochemistry of Anxiety

Fear and anxiety activate many brain circuits, including those involved in sensory input (thalamus and sensory cortex), contextual memory (hippocampus), conditioned emotional responses and fear responses (central nucleus of the amygdala), activation of hypothalamic-pituitary-adrenal (HPA) axis (hypothalamus) and cortisol release, salience and conditioned avoidance (striatum), arousal and vigilance (locus coeruleus and raphe nuclei) and cognition and executive functions (neocortex, especially prefrontal cortex). Research has shown that the central nucleus of the amygdala, mediates certain responses to immediate aversive stimuli while other limbic structures such as the bed nucleus of the stria terminalis and septohippocampal regions are also implicated in the more contextual, chronic and general stimuli involved in the genesis of anxiety. Anxiety disorder sufferers appear to demonstrate hyperresponsive amygdala circuitry (involved in fear responses) and decreased prefrontal cortex activity that usually functions to suppress fear and anxiety.

The neurotransmitters and hormones implicated in fear and anxiety include γ-aminobutyric acid (GABA), serotonin, noradrenaline, adrenaline and corticotropin releasing factor (CRF). The involvement of these transmitter substances will be further outlined in subsequent sections.