The Biosocial Theory of Borderline Personality Disorder, Part I

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As a psychologist who specializes in Dialectical Behavior Therapy (DBT), I am frequently asked by clients and families about how Borderline Personality Disorder (BPD) develops. We think BPD is caused by a combination of factors, so the answer is a bit complicated! The Biosocial Theory reflects our current understanding in how BPD develops. The theory states that BPD is a disorder of emotion dysregulation, and that emotion dysregulation is the result of emotional vulnerability as well as a lack of emotion modulation skills. Moreover, the Biosocial Theory postulates that these difficulties are rooted in biological predispositions that are exacerbated by the environment. 

Emotional Vulnerability

 When we discuss emotional vulnerability, we are specifically referring to three things: sensitivity, reactivity, & slow return to baseline. When an individual is “sensitive,” it means that person has a low threshold for an emotional reaction. What may not be bothersome to most is bothersome to the emotionally sensitive person. If a child is sensitive, they may react to even the slightest frustration or annoyance. Emotional sensitivity is often what causes friends and family members of those with BPD to “walk on eggshells.” Furthermore, the emotionally sensitive individual may also be able to detect subtle emotional information in their environment that others don’t notice (hint: many therapists are sensitive). They experience emotions much more frequently than others, and sometimes for seemingly no reason and out of the blue. 

Emotional reactivity refers to the intensity of emotions and reactions. I’ve had clients tell me that their emotions hit them like a ton of bricks and last forever. What may be disappointing or annoying to many, may cause an emotionally reactive person to feel overwhelming sadness or rage. On the other hand, emotionally reactive individuals are like to experience joy more easily and fall in love faster, so it isn’t limited to emotions that we don’t like to experience!

Slow return to emotional baseline means that reactions to emotional stimuli are long lasting; therefore, once upset or dysregulated, the body takes a long time to return to baseline. This doesn’t mean that the person is holding a grudge, but it is their body’s physiological response to stress. Also, as they return to baseline, they are even more vulnerable and susceptible to other emotionally laden events and hardly ever do they get a “break.” Those who have experienced invalidation or trauma, or identify as emotionally reactive, tend to have higher baselines. A higher baseline can be difficult to sustain long term and can lead to self-harm and suicidal behaviors.

 Emotional vulnerability is not a lack of self-control. We now know from a scientific perspective that emotionally vulnerable isn’t a matter of choice. Studies have shown that newborn babies have varying degrees of emotional responses before they even learn what emotions are. In one study, newborns were tickled on their nose with a feather. Some babies did absolutely nothing while being tickled, others had a mild response in that they moved around a bit, and others began crying and were difficult to console. The babies who were difficult to console were viewed as being more sensitive to emotional stimuli.


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There has been modest research support for the neurobiology of BPD, particularly within the limbic system and prefrontal cortex. The limbic system is the primary processing center for emotions and memory within the brain, whereas the prefrontal cortex is implicated in planning, personality, decision making, and behavioral control. A meta-analysis in 2009 reported structural changes within the limbic system in those with BPD, which may contribute to emotional dysregulation.

When researchers had participants diagnosed with BPD undergo brain imaging while completing an assessment, it was found that negative emotional words caused the participants to have more difficulty with the task and act more impulsively. Moreover, the brain imaging showed that there was less activity in the part of the brain that is responsible for behavioral control, reflecting the mood dependent behavioral dysregulation that occurs in BPD.

There has also been consistent research support demonstrating that those with BPD tend to misclassify and misinterpret neutral faces as negative, which may contribute to interpersonal sensitivity. Another study revealed that those with BPD demonstrated a lower resting parasympathetic tone, the part of our nervous system responsible for slowing heart rate and relaxing muscles, suggesting that individuals diagnosed with BPD have to work even harder to regulate their emotions from a biological perspective. However, there is good news! Small scale studies have reported findings that Dialectical Behavior Therapy (DBT) targets amygdala hyperactivity, which is a part of the emotional processing center in the brain.


 Impulsivity also has a biological basis in that regulating action is harder for some than others and it can feel nearly impossible to control impulsive behaviors. My clients often, without thinking, can do things that get them into trouble and sometimes the behavior appears to come out of nowhere. People with BPD can find it really hard to be effective and their moods can get in the way of organizing behavior to achieve their goals. They also have difficulty controlling behaviors that are linked to their moods, like lashing out at others when angry, or drinking when sad. 

Invalidating Environments

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The social part of the theory refers to an invalidating social environment, particularly caregivers. If you are a parent whose child has BPD, take a deep breath, I will explain! An invalidating environment is one that doesn’t seem to understand your emotions, which is problematic if you are an emotionally vulnerable person. The environment may communicate that your emotions are wrong, weird, or bad. It can ignore emotional reactions and does nothing to help with appropriate emotional expression. Children who grow up in invalidating environments learn that they cannot trust themselves- that their interpretations of their behaviors, emotions, thoughts, and perspectives cannot be trusted. 

Here are some examples of invalidation:

Comments such as:

  • “Don’t be such a baby” 

  • “Quit your crying” 

  • “Pull yourself up by the bootstraps” 

  • “Stop crying, this isn’t that big of a deal, it’s okay”

  • “Talking about problems just makes them worse”

Parents who punish emotional expression:

  • “We don’t talk about emotions in this house”

  • “Leave your bad mood at the front door”

  • “If you’re going to cry, go to your room”

Oversimplification of problem solving, which does not teach the child to tolerate distress or form realistic goals or expectations about life:

  • “You just need to try harder to stop drinking”

  • “If you really cared, you’d be able to change”

  • “Maybe if you got out of the house more often, you wouldn’t be so depressed”

  • “You just have to CHOOSE to be happy”

  • “Everything happens for a reason”

Confusing one’s own emotions with the emotions of others:

  • “I’m exhausted, let’s all go to bed”

 When kids don’t get their needs met, they may increase the intensity of emotional expression, but that doesn’t actually help. What they need is for a parent to validate them. Instead, the child unconsciously escalates their level of emotional intensity and behaviors. They eventually get to a level that forces the environment to respond (screaming children in Target, anyone?). When the caregiver sees that the child truly needs help and does something, that interaction reinforces (strengthening the behavior through reward) high level emotions and behaviors. The child then unconsciously learns that people respond to them and meet their needs when they react in an intense manner.

 DBT therapists use the “Tulip in the Rose Garden” metaphor to demonstrate the Goodness of Fit principle, which talks about how an award-winning rose gardener decides to plant tulips in his rose garden. He doesn’t realize that tulips and roses have very different requirements in order to grow. If he treats the tulip like his roses, the tulips won’t be able to flourish! Emotionally vulnerable people in invalidating environments are the tulips in this metaphor. If the conditions aren’t right, they are going to struggle. Goodness of fit results when the child’s environment, expectations, and demands match the child’s emotional sensitivity, capacities, and characteristics.

Trauma and Abuse

Sexual or physical abuse is an extreme form of invalidation and is often a precursor for BPD. Abuse communicates to the individual that they do not deserve basic respect or safety, and can make the victim feel worthless, rejected, and devoid of human value. The rates for co-occurring PTSD in individuals with BPD vary, ranging from 30% to 68% depending on the study; although, other studies have reported rates of childhood physical abuse in BPD of 71% and rates of childhood sexual abuse up to 86%. Regardless, sexual abuse predicts a more severe and chronic presentation. However, not everyone with BPD has experienced a significant traumatic event in their life.

Info for Parents

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 If you are a parent or caregiver to someone with BPD, know that it is our assumption as DBT therapists that people who invalidate are often doing the best they can! Normal parenting includes periods of ineffectiveness, and life can certainly interfere with one’s ability to parent. There are many reasons why this occurs:

  • Some kids are so emotionally vulnerable that even our best efforts to validate are ineffective 

  • You think you’re validating, but notice it just makes your kids more upset

  • You may not know how to validate or maybe your parents never taught you

  • You aren’t aware of how important validation is or even what it is

  • Fear that if you validate the emotion, your child may become more emotional and not less

  • You believe that by validating your child’s emotions, you will make them weak

  • High stress and pressure at home or work

  • Having too few resources

  • The ways in which you learned to regulate your emotions are not as helpful to your child

  • Validation may seem like agreeing or approval 

  • Your child is super great at pushing your buttons and pushing you into emotional dysregulation

  • You’re emotionally vulnerable, or experience mental health symptoms that impact your ability to understand your child’s emotions

 The development of BPD is clearly complicated and likely looks very different for each individual. If you, or someone you love has BPD, contact us to make an appointment today!

Ashley Allen