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Dissociative Identity Disorder and Brain Structure

Research on systems is limited and often focuses solely on DID. This is just a summary of some articles we read and not a complete literature review. We are a DID system and we have a bachelor’s degree in biochemistry. We have spent a lot of time learning how to read and interpret scientific literature but we are by no means experts.

Multiple studies have found that DID changes the size of the hippocampus. It has been found several times that DID systems have a smaller hippocampus than the general population. The hippocampus plays a major role in forming and retrieving memories.

Reinders et al. (2019) attributed the smaller hippocampus they saw in DID systems to excessive exposure to stress hormones. In another study, it was found that a smaller hippocampus is correlated to severity of dissociative symptoms (the smaller the hippocampus, the greater the dissociation; Chalavi et al., 2015). It has even been shown that as systems heal and integrate, the hippocampus grows larger (Ehling et al., 2007).

It has also been found that the amygdala is smaller in people with dissociative identity disorder (Vermetten et al., 2006). The amygdala processes fear, stress, and helps us respond to threats.

It is unclear why the amygdala would be smaller in DID systems. It is possible that this factor is related to genetics and a smaller amygdala may increase someone’s risk of developing a dissociative disorder (Vermetten et al., 2006). This would make sense since we know that genetics plays a role in the ability to dissociate. More research is needed to understand the connection between the amygdala and DID.

Other, more subtle, changes in brain structure were also found in both grey and white matter. These included structural differences in certain gyri (ridges) of the brain as well as neural pathways and nerve bundles. These biomarkers can be recognized using machine learning. This could potentially be useful in the future for diagnosing systems (Reinders et al., 2019).

Can an MRI be used to diagnose DID? Potentially, yes. More research is needed in this area but the results so far are impressive. Reinders et al. found that their model was able to recognize DID systems with a 72.84% accuracy rate compared to singlet controls. DID is underdiagnosed and frequently misdiagnosed so this could have huge implications for the future. However, since they only used healthy controls in this study, it is unclear whether singlets with CPTSD, for example, share similar brain structures to systems.

Again, it is important to keep in mind that these are just a few studies and research in this area is limited. More research is definitely needed on DID and brain structure. And what about OSDD, P-DID, and other system experiences? These studies looked almost exclusively at DID, which leaves out a huge part of the system community. Hopefully future research will fill in some of these gaps.


Chalavi, S., Vissia, E. M., Giesen, M. E., Nijenhuis, E. R., Draijer, N., Cole, J. H., ... & Reinders, A. A. (2015). Abnormal hippocampal morphology in dissociative identity disorder and post‐traumatic stress disorder correlates with childhood trauma and dissociative symptoms. Human brain mapping, 36(5), 1692-1704. Ehling, T., Nijenhuis, E. R. S., & Krikke, A. P. (2007). Volume of discrete brain structures in complex dissociative disorders: preliminary findings. Progress in brain research, 167, 307-310. Reinders, A. A., Marquand, A. F., Schlumpf, Y. R., Chalavi, S., Vissia, E. M., Nijenhuis, E. R., ... & Veltman, D. J. (2019). Aiding the diagnosis of dissociative identity disorder: pattern recognition study of brain biomarkers. The British Journal of Psychiatry, 215(3), 536-544. Vermetten, E., Schmahl, C., Lindner, S., Loewenstein, R. J., & Bremner, J. D. (2006). Hippocampal and amygdalar volumes in dissociative identity disorder. American Journal of Psychiatry, 163(4), 630-636..


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