4.3 Aetiology of anxiety disorders and the basic neural circuitry involved in anxiety
The causes of anxiety disorders are complex and multifactorial and can include (among others) psychological trauma, psychosocial stressors and conflict, as well as physical illness. Current models for GAD point to an underlying dysregulation in the physiological and behavioural responses to stress (which involves the hypothalamic-pituitary-adrenal axis), and activation of brain networks responsible for threat detection, introspective thinking as well as learning and memory (e.g. conditioned and social learning and social referencing). Twin studies suggest that environmental (e.g. psychosocial) and genetic factors are likely involved.
A key brain structure involved in the neural circuitry of anxiety is the amygdala, located within the temporal lobes and forming part of the limbic system regulating mood and emotional responses. Parts of the amygdala are involved in triggering the responses we associate with fear (e.g. submission, fleeing, or ‘freezing’ on the spot). Other regions within the amygdala elicit feelings of bliss or peacefulness, or evoke aggression and attack. Life-or-death situations are processed within fractions of a second. To do this, sensory information from the external environment must first reach the amygdala. This is achieved in two ways – a direct route to the amygdala via the thalamus (taking about 1/50 of a second), and an indirect route to the amygdala via the cerebral cortex, which takes slightly longer (about a fifth of a second) but allows information about the stimulus (its nature, location, threat level, etc.) to be consciously processed and an assessment to take place. Interaction between the amygdala, prefrontal cortex and hippocampus modulates the response (e.g. through assignment of emotional salience, monitoring and detection, and an awareness of the context in which a stimulus is received and any memory or recall of its previous experience or encounter). The main outputs of the amygdala are the hypothalamus, basal forebrain and brainstem, pathways that elicit the physiological, cognitive and emotional responses associated with fear and anxiety.
In the remainder of this section we explore two key issues − gender and work-related stress − as risk factors for anxiety disorders. We specifically ask whether women are more likely to suffer from anxiety than men, and consider whether work is good or bad for your mental health.