Alexa Kightlinger
Introduction to DID
We’ve all been there. From forgetting where we’ve haphazardly thrown our car keys to missing an important meeting that simply slipped from our minds, we are all prone to forgetfulness or memory lapses. However, for individuals with dissociative identity disorder or DID, these memory lapses, which are characterized as dissociation, can severely impact the individual's daily life. Many who suffer from DID are forced to put together the missing pieces of their life which are now lost due to alter switches. This dissociation is characterized by the presence of two or more separate identities that each have their own pattern of perceiving the environment and self. It often occurs as a response to highly traumatic events an individual underwent at a young age which lead to the development of DID. However, controversy still surrounds the existence of dissociative identity disorder (DID) despite its first introduction to the DSM-III in 1980, where it was first coined as multiple personality disorder. Many skeptics believe this disorder is created through iatrogenesis, where the diagnosis through the power of suggestive questioning can create or worsen it. Other versions of this belief follow the idea that clinicians would “implant” false memories of childhood trauma (Loewenstein, 2018). This false-memory viewpoint continues to play a large role in other dissociative disorders as well as a significant presence in psychology textbooks and media representation (Loewenstein, 2018).
Current Literature
Much like a coin, there are two sides to every debate with many researchers accepting the existence of DID. While many studies have shown an association between a DID diagnosis and a previous history of childhood trauma, little research has been conducted on the neurobiology of the disorder (Vermetten et. al, 2006). This has allowed researchers to perform more in-depth neuroimaging studies on individuals diagnosed with the disorder. A 2006 study done by Vermetten et. al used magnetic resonance imaging to measure the volumes of the hippocampus and amygdala in 15 patients with DID and 23 patients who had neither DID nor any other psychiatric disorder to serve as the control. Since early stress has been associated with changes to the hippocampal structure in both animal and human studies, researchers hypothesized that patients with DID would have smaller hippocampal and amygdala volumes in comparison to their healthy counterparts (Vermetten et. al, 2006). This idea held true as researchers found that the hippocampus and amygdala volumes were 19.2% and 31.6% smaller respectively in comparison to the control group (Vermetten et. al, 2006). These findings make sense when you consider some primary functions of the hippocampus and amygdala - memory, emotion regulation, and stress response. Smaller volumes in these areas could be indicative of how individuals with DID process their memories and may help explain one of the main symptoms of DID: dissociative amnesia.
Another study done by Dimitrova et. al (2021) was conducted on 32 individuals with DID and 43 healthy controls. This study focused primarily on how the substructures of the hippocampus volumes differed between the two groups. Using MRI neuroimaging, they were able to measure the bilateral global hippocampus and more specific areas which include the CA1-4, GC-ML-DG, fimbria, HATA, parasubiculum, and subiculum. A brief description of these areas is detailed below.
Cornu Ammonis (1-4)
CA1: Plays a role in memory consolidation and spatial navigation.
CA2 + CA3: Involved in memory processes such as associative memory and pattern separation.
CA4: Contextual information and pattern completion.
Granule Cells, Molecular Layer, Dentate Gyrus (GC-ML-DG)
Granule Cells: Pattern separation, neurogenesis, network excitation, and spatial memory.
Molecular Layer: Synaptic integration, facilitating neuron communication, learning, memory, and integration of information.
Dentate Gyrus: Input region of the hippocampus from the entorhinal cortex. Involved in pattern separation.
Fimbria
Fibrous bundles that connect the hippocampus to other regions of the brain.
Hypothalamus, Amaydgala, Thalamus, and Anterior nuclei of the dorsal thalamus (HATA)
A term that emphasizes how the hippocampus is connected to other brain regions involved in memory, emotion, and sensory processing.
Parasubiculum
Helps to process spatial information.
Subiculum
Serves as a main output structure of the hippocampus and plays a role in spatial memory and decision making
Image Source: https://radiopaedia.org/articles/hippocampus
Using Freesurfer, a software package for analyzing neuroimaging data, they found differences in hippocampus volumes between patients with DID and the healthy group. Specifically, they found these differences in the bilateral global hippocampus, bilateral CA1, right CA4, right GC-ML-DG, and the left presubiculum (Dimitrova et. al 2021). In addition to the volumetric analysis conducted, they also chose to run several correlational analyses for possible relationships between the factors of dissociative experience: dissociative amnesia, absorption, depersonalization/derealisation as well as traumatization. For this, dissociative amnesia was the only dissociative symptom that was correlated with the significant reduction for the bilateral hippocampal CA1 (Dimitrova et. al 2021). This finding indicates dissociative amnesia may be linked to the decreased volume of the CA1. For traumatization, emotional neglect was negatively correlated with several regions, including the bilateral global hippocampus, bilateral CA1, CA4, GC-ML-DG, and right CA3 (Dimitrova et. al 2021). The negative correlation suggests that more severe symptoms may be connected to the smaller hippocampal volumes, specifically in the CA1.
Moving Forward
While both studies made great strides in supporting the existence of DID by providing solid evidence showing differences in brain structure, much more research is called for. For one, both the Vermetten and Dimitrova studies were conducted entirely on a female database, making it impossible to generalize these findings to men. Additionally, DID is a complex condition that is not yet fully understood. This includes the complexity of dissociation itself, symptom variability, and diagnostic challenges as the disorder is often misdiagnosed. Its stigmatization in the media with films such as Split (2016) works to portray those who suffer from DID as villainous and may lead to many not seeking out the proper help they need due to the fear of societal backlash.
Citations
Dimitrova, L. I., Dean, S. L., Schulmpf, Y. R., Vissia, E. M., Nijenhuis, E. R., Chatzi, V., Jäncke, L., Veltman, D. J., Chalavi, S., & Reinders, A. A. (2021). A neurostructural biomarker of dissociative amnesia: a hippocampal study in dissociative identity disorder. Psychological Medicine 53(3), 805-813. https://doi.org/10.1017/S0033291721002154
Loewenstein, R. J. (2018). Dissociation debates: everything you know is wrong. Dialogues in Clinical Neuroscience 20(3), 229-242. https://doi.org/10.31887/DCNS.2018.20.3/rloewenstein
Vermetten, E., Schmahl, C., Lindner, S., Loewenstein, R. J., & Bremner, J. D. (2006). Hippocampal and Amygdalar Volumes in Dissociative Identity Disorder. The American Journal of Psychiatry 163(4), 630-636. https://doi.org/10.1176/appi.ajp.163.4.630
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