What does it mean when someone (specifically with BPD) says that they can’t process emotions? For example, when something occurs, the person in question has “to think about how they feel.”

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It means they have one or both of two things.

First, they can have limbic system deactivation. The limbic system is the area of the brain responsible for regulating what we call emotion. “Underneath” the limbic system is the basal ganglia, colloquially called the “lizard brain,” The thinking, rational part of the brain is called the neocortex.

Physically, these are stacked on top of each other to form a sandwich of sorts, with the limbic system mediating between lizard brain survival instinct and the thinking mind. What we think of as emotions are cognitive experiences of what the limbic system is doing.

If the limbic system is deactivated, then the person involved does not feel emotion at all. The limbic system is responsible for altruism, empathy, and what’s called “theory of mind.” Theory of mind is what allows mammals to read and understand each others’ emotions through various things like tone of voice and facial expressions. If the limbic system has diminished capacity, then parts of it will work while others don’t.

The other thing that can be happening, is poor self-awareness. This can exist independently of limbic deactivation. Nothing about having a well-functioning limbic system means that you can actually access the knowledge and understanding of how it’s functioning.

Remember I said earlier that emotions are cognitive experiences of limbic functioning? What you’re describing is when people feel emotions happening, but can’t really process what they are or what they mean. People can be angry without feeling like they’re angry. Jealous while believing they’re not jealous. This results from poor self-awareness, and can also involve diminished limbic capacity.

In order to provide for the survival of the organism, the primary function of both the limbic system and the basal ganglia is to override both the conscious mind and the nervous system of the body and inject an instinctual behavioral response to stimulus. Basal ganglia overrides are called the “fight or flight” response.

Limbic overrides are generally referred to as ‘irrationality’. Have you ever seen a person react irrationally strongly to something that a normal person wouldn’t? Hysteria? This is limbic override at work.

Healthy cognitive functioning rests on a teetering precipice of conditions that the scientific community has given the name “emotional health.” The thing we’re coming to understand about limbic overrides is that they’re a normal, healthy part of mental functioning and trying to avoid them all the time creates a ‘brittle’ mind.

Another thing we’re also coming to a realization of is what happens in the brain when traumatic events happen. Essentially all mental disorders are responses to some kind of brain trauma. Trauma shuts down parts of the brain that are damaged so they don’t continuously impede conscious functioning. The downside of this protective mechanism is that it renders those traumatized incapable of being fully emotionally healthy.

While limbic overrides are relatively common and healthy, fight or flight overrides are uncommon and so can induce traumatic brain response. Limbic deactivation is just one of the many many responses to trauma. It can cause the poor self-awareness that is described by your question.