Developmental, Early Relational Trauma and the roots of Borderline Pathologies
For decades, researchers have attempted to understand the root causes of the wide spectrum of mental illness (autism, adhd, borderline, narcissism etc.) and the innovation of brain scans has given much insight into what might be going wrong in child development causing the spectrum of disorders we regularly see.
For BPD (Borderline Personality Disorder) it is now widely accepted that the splitting/fragmentation and emotional instability seen in this disorder is predisposed in infancy through what Allan Schore calls Early Relational Trauma  and what Bessel van der Kolk labels as Developmental Trauma . This does not necessarily mean that environments were abusive but at the very least it is hypothesized that there is misattunement between infant and caregiver or insufficient "attachment repairs" when there were "ruptures" .
This predisposition causes the primitive splitting/fragmentation defense (which can result in idealization/devaluation patterns or emotional instability) to be stored implicitly in procedural memory and is seen as the cause of the core instability described in the BPD diagnosis. This primitive dissocation can be seen on brain scans as orbitofrontal cortex differences which is known to be involved in social, emotional information and our unconscious attachment patterns as well as our senses.
Because these primitive and secondary dissociation (secondary being depersonalization/derealization or numbing/detachment/submit) defenses remain unconscious and intact a child has a build-up of unprocessed traumatic emotional states which remain split off in implicit unconscious memory (this can be seen as co-morbid c-PTSD / Complex Trauma which ranges in severity) and because people with BPD have rigid primitive splitting defenses these states are overwhelming and experienced as being "hijacked by emotions", this fragmentation is even known to cause auditory hallucinations which in reality are often implicit unconscious early relational trauma that is now experienced as an external (often punitive / critical) voice. This symptom is also seen in PTSD veterans, childhood trauma survivors and even regular populations .
c-PTSD / Complex Trauma often refers to chronic early life adversity which results in prolonged negative emotional states and the development of unconscious triggers that cause emotional dysregulation, issues with attention, negative self-image, aggression, risk-taking and impulsivity. Although this seems to largely overlap with BPD, it is important to understand that BPD distinguishes itself through the primitive dissociation / fragmentation of emotional states that also severely affect perception and cognitions (hence the origin of the name "bordering on psychosis").
Because BPD often involves childhood neglect and misattunement in infancy causing prolonged negative states it is referred to by some as a Complex Trauma or Emotion Regulation Disorder. This is also why Bessel van der Kolk and others have tried to lobby for a Developmental Trauma Disorder (DTD) diagnosis in the DSM but so far the ICD has only acknowldged the c-PTSD diagnosis and the DSM only PTSD. Some therapists are starting to use either c-PTSD or DTD which both are outside the DSM framework.
A lot of people with BPD don't describe their childhood as traumatic, this is further evidence that BPD comes with a range of co-morbid severities like c-PTSD but can be distinguished as a developmental stage trauma disorder that can be clearly measured with brain scans as orbitofrontal brain deficits and is directly related to early life attachment misattunement. BPD is hypothesized as a lack of being seen, having no proper child-parent mirroring, causing a child to develop defenses that disconnect from Self and compartmentalize emotional states, because the orbitofrontal never fully matured, a sufferer can easily lose higher orders of consciousness and regress into more primitive immature states (we can also described this as a prefrontal brain shutdown and becoming overwhelmed / hijacked by emotions). This also explains why Mindfulness (known to involve prefrontal brain area's) seems to be core in DBT treatment (a known evidence-based BPD stabilization therapy).
Scientific References (Updated: 2022-02-26)
1. Schore, A.N. (2001), The effects of early relational trauma on right brain development, affect regulation, and infant mental health. Infant Ment. Health J., 22: 201-269. https://doi.org/10.1002/1097-0355(200101/04)22:1<201::AID-IMHJ8>3.0.CO;2-9
2. Hilary B. Hodgdon, Frank G. Anderson, Elizabeth Southwell, Wendy Hrubec & Richard Schwartz (2021) Internal Family Systems (IFS) Therapy for Posttraumatic Stress Disorder (PTSD) among Survivors of Multiple Childhood Trauma: A Pilot Effectiveness Study, Journal of Aggression, Maltreatment & Trauma, DOI: 10.1080/10926771.2021.2013375
3. Andrew M. Chanen, Dennis Velakoulis, Kate Carison, Karen Gaunson, Stephen J. Wood, Hok Pan Yuen, Murat YÃ¼cel, Henry J. Jackson, Patrick D. McGorry, Christos Pantelis,
Orbitofrontal, amygdala and hippocampal volumes in teenagers with first-presentation borderline personality disorder,
Psychiatry Research: Neuroimaging,
Volume 163, Issue 2,
4. Romuald Brunner, Romy Henze, Peter Parzer, Jasmin Kramer, Nina Feigl, Kira Lutz, Marco Essig, Franz Resch, Bram Stieltjes,
Reduced prefrontal and orbitofrontal gray matter in female adolescents with borderline personality disorder: Is it disorder specific?,
Volume 49, Issue 1,
5. Bessel A. van der Kolk, Anne Hostetler, Nan Herron, Rita E. Fisler,
Trauma and the Development of Borderline Personality Disorder,
Psychiatric Clinics of North America,
Volume 17, Issue 4,