The dissociative type of PTSD is one where, instead of having ‘flashbulb’ memories of a traumatic event – along with a racing heart, shortness of breath, and all the other hallmarks of a brain and body on high alert – the person reports feeling nothing. He or she is seemingly unaffected by reminders of the disturbing episode; yet there is some influence since these individuals are bothered by a nagging sense of unreality at times. They feel not fully present, or strangely numb, or have the sense of not fully inhabiting their own bodies. These symptoms add up, in the parlance of psychology, to conditions known as depersonalization and derealization.
Let’s examine what’s happening in the brain in each of these cases. In the more typical form of PTSD, the medial prefrontal structures that regulate the emotional, or limbic, part of the brain under-modulate, so that the limbic structures go hyper and the person becomes highly aroused. But in the dissociative form, the pattern is just the opposite. The medial prefrontal part of the brain over-modulates, causing the limbic structures to become inhibited and the person to profess that he or she feels nothing.
In either case, it’s a matter of what neuroscientists and psychologists call dysregulation: an exaggeration or underplay of normal emotional activity. The type of dysregulation has actually been found to correlate with a particular part of the brain known as the insula. A prune-size structure, one in each hemisphere, the insula is where sensory information converges from throughout the body: from the skin, muscles, and internal organs signaling sensations such as hot, cold, itch, tickle, ache, burn, pain, sensual touch, hunger, and thirst. The insula integrates such information to produce an impression about the body’s overall felt state – how one feels at any given moment. Scientists call this information gathering process interoception – how the brain “minds the body,” one might say.
The forward end of the insula in our right hemisphere (known as the anterior right insula) seems, in particular, to be where our felt sense is produced. The right anterior insula is also the part that corresponds most closely to the severity of a person’s PTSD symptoms. When someone is having a fearful flashback, that part of the insula is highly activated; when someone is feeling distant or nothing at all, that part of the insula shows very low activation. A person’s felt state, therefore – one’s very sense of self – is tangibly diminished when he or she is in the throes of dissociation. The flip side is that people who are ‘tuned in’ to their bodies (and who, consequently, are more emotionally attuned) actually have more developed right anterior insulas, as measured by the amount of gray matter residing there.
It seems, then, that people who relive a traumatic episode in the here and now have more sensory information being collected via their insulas than people who dissociate when reminded of a trauma. The felt state of the former is literally more coherent and a whole lot more assertive. We could term these individuals “high reactors” versus the “low reactors” who effectively tune out. (All of these reactions are unconscious and instantaneous, of course; no one suffering from PTSD chooses their biology. The under- or over-modulation of limbic structures is done entirely out of awareness.)
Interestingly, it’s been proposed that people become high reactors or low reactors based on the frequency and timing of the trauma they suffered. An individual who faced a single intensely threatening experience is, according to this theory, more likely to exhibit the high-reactive form of PTSD, whereas someone who suffered prolonged threats or injury is more likely to exhibit the low-reactive form. Likewise, someone who encounters a traumatic episode in adulthood, when he or she has better developed appraisal and coping skills, is more likely to manifest the high-reactive form of PTSD, whereas a child – who is typically unable to evade a threat (especially the recurrent kind) – is more likely to manifest the low-reactive form. Dissociation, then, can be seen as a psychological evasion of recurrent physical and emotional harm; the child copes by closing in on him or herself, much as a turtle withdraws from threat by retreating into its shell.