Chapter 9. Dissociation and Neuroscience (2) the Mechanism of Switching (3)

This understanding based on the structural dissociation theory is in accordance with recent findings of neuroimaging studies. They basically class brain imaging of traumatized people into PTSD type and dissociative type, roughly corresponding to two neurophyisiological states that van der Hart et al. state: EP and ANP. Only difference is that structural dissociation theorists are more inclusive in their use of the notion of dissociation: they basically understand that PTSD is also a sort of dissociative pathology.
So far we discussed dissociative switching in its relation to direct stimulus to the brain and the use of dissociative drugs. What do these neuroscientific data indicate? Relative to the amount of data available, its contribution to the understanding of dissociation is still very limited, and neurological basis of dissociation is far from being understood. The finding that electrical stimulus to the temporo-parietal area can elicit dissociative experiences is not particularly surprising. If we take into consideration that various perceptive and somatosensory inputs come into temporal and parietal lobes, and they merger in the associative cortex (angular gyrus, i.e., temporoparietal area) direct stimulus to the area may well elicit very complex, realistic, but virtual experiences such as out of body experiences or perceptual distortion. However, this does not mean at all that this area is directly involved in switching mechanism so crucial to the dissociative experiences. This only indicates that this area is somehow involved in the complex mechanism of dissociation.
Another thing that these studies show us clearly is that seemingly unsubstantiated and apparently simulated symptoms of dissociation certainly have neurological basis.
Next I will show a couple of models of the switching mechanism of dissociation that I think are plausible.
Understanding dissociation as a switching in the brain
I would like to start from the textbook definition of dissociation. In chapter 8, when I introduced the idea of neural network model, I mentioned that dissociation understood from this perspective goes well with the current definition of dissociation ICD-10 and DSM-IV-TR, where dissociation is explained as follows. "… Partial or complete loss of the normal integration between memories of the past, awareness of identity and immediate sensations, and control of bodily movements". For the sake of explanation, I drew a diagram that I indicate here (Figure ##) in order to show how dissociation occurs based on this model.

Figure## simple model of dissociation

The central oval shape indicates the location of the current conscious awareness which works as a hub, connecting with solid lines to modules in charge of “memories of the past, awareness of identity and immediate sensations, and control of bodily movements” as well as emotion. In this diagram we are assuming that there is a dissociative amnesia: a temporary loss of a memory.
A dotted line across the solid bar connecting hub and memory indicates the location of the switching.