There have been some studies focusing
on the neurological background of the formation of personalities in DID.
Already in 1980s, Bessel van der Kolk discussed biological basis for the
formation of traumatic memories which underlies clinical manifestation of flashbacks
and trauma-related memories. He stressed that intense emotional experiences
affect amygdala and hippocampus, and trauma-related memories are ingrained on
the body/visceral level on a traumatized individuals, in a way quite different
from the ordinary formation of episodic memories.
Bessel van der Kolk (2015) The Body Keeps the Score: Mind, Brain and Body in the Transformation of Trauma. Penguin.
Although this view helps
clinicians understand quite well the way traumatized individuals suffer from
flashbacks and sudden recollection of past atrocious memories, this does not
help us explain how this mechanism is translated to the way different memory
systems are formed for the each personality in DID.
In this context, studies by
Reinders et al. are of our great help and interest.In their studies in 2003, Reinders et al. used functional neuroimaging (PET scan) and demonstrated particular changes in localized brain activity and other biological markers of eleven individuals with DID who are able to switch between normal personality state (NPS) and traumatized personality state (TPS). In the state of TPS, they showed the deactivation of a brain network including the mPFC, which is involved in conscious processing of experience. In contrast, in the NPS, they demonstrated disturbances in the parietal and occipital blood flow, indicating an inability to integrate visual and somatosensory information. This way, the NPS in DID exerts some defense mechanism against traumatic stimuli that prevents further emotional processing (2003).
Reinders et al. in their 2006 study, had their DID individual listen to trauma script as well as neutral script in their NPS and TPS states. They found that in response to the trauma script, the TPS showed increased heart rates and blood pressure, as well as strong emotions and sensory reminders of the traumatic event. In their NPS, however, they did not show that response, possibly due to its own defense mechanism discussed above. When the neutral script was shown, neither TPS nor NPS displayed any cardiovascular activation.
Reinders, AA.T.S., Nijenhuis, E.R.S., Paans, A.M.J., Korf, J., Willemsen, A.T.M.,& den Boer, J.A. (2003). One brain. two selves. Neurolmage. 20, 21 19-2125.
Reinders, A.A.T.S., Nijenhuis,E.R.S., Quak,J., Korf,J.,Paans, A.M.J., Haaksma,J., Willemsen, A.T.M., & den Boer, J.A. (2006). Psychobiological characteristics of dissociative identity disorder: A symptom provocation study. Biolog1cal Psychiatry, 60,730-740.
In my
view this study suggests that these two personality states might engage in two
different neural networks, or “dynamic cores.” This would explain why NPS state
shows no difference in response to either trauma script or neutral script. Reportedly,
NPS shows practically no response to trauma script, indicating that it does not
particularly inhibit (or “repress”) that stimuli. Thus NPS acts practically as
a bystander, an individual unrelated to past traumatic events.
When
we hypothesize a presence of only one mind or a single dynamic core shared by
different personalities in DID, there should be some type of communication on a
sub-conscious or unconscious level, in this case between TPS and NPS,
responding to each other’s experiences at least on a unconscious, physical, or
emotional level. The “nonchalant” response of NPS to trauma-related stimuli
strongly speaks to the fact that two different personality states have biological
correlate of two independent dynamic cores.
