Dissociation is a mental state characterized by a disconnection between thoughts, memories, feelings, perceptions, and consciousness. It can manifest as amnesia, derealization, depersonalization, or somnambulance. Hyperarousal refers to an increased heart rate, blood pressure, perspiration, and respiration rate. Trauma-related stress responses are symptoms of post-traumatic stress disorder (PTSD), such as anxiety, irritability, flashbacks, and sleep disturbances. All three phenomena have been linked to neural and psychological mechanisms that underpin them.
Dissociative experiences involve reduced connectivity between different regions of the brain and deficits in the prefrontal cortex, hippocampus, cingulate gyrus, and limbic system. These areas regulate attention, memory, emotions, and self-awareness. The default mode network (DMN) may be involved in these processes too. Derealization involves decreased activity in the DMN and increased activity in the somatosensory cortex. Depersonalization is associated with alterations in the temporal lobe and anterior insula. Somnambulance may arise from a dysregulated thalamocortical circuit involving the amygdala, frontal cortex, and reticular activating system.
Hyperarousal is related to overactive sympathetic nervous system activation, particularly in the hypothalamic-pituitary-adrenal axis and locus coeruleus. This causes elevated levels of cortisol, norepinephrine, adrenaline, and epinephrine. It can also trigger changes in the parasympathetic nervous system, leading to increased heart rate variability, vagal tone, and respiratory sinus arrhythmia. Hyperarousal has been correlated with increased blood flow to the amygdala, insula, and prefrontal cortex.
Trauma-related stress responses are linked to abnormalities in the amygdala, hippocampus, and prefrontal cortex. They involve reduced glucose metabolism, reduced volume, disrupted connectivity, and increased reactivity. PTSD patients have lower resting-state functional connectivity between the amygdala and other brain regions, such as the cingulate gyrus and prefrontal cortex. These deficits are thought to impair emotional regulation and memory processing. Flashbacks involve excessive amygdala activity and reduced activity in the prefrontal cortex. Sleep disturbances involve hyperactivity of the amygdala and hypoactivity of the hippocampus.
Which neural and psychological mechanisms underpin dissociation, hyperarousal, and trauma-related stress responses?
Dissociation is a coping mechanism that protects individuals from overwhelmingly stressful situations. It involves temporary separation of thoughts, memories, feelings, and sense of identity from reality (Pope & Mollon, 2015). This can result in amnesia, detachment, depersonalization, derealization, or out-of-body experiences.