does meditation change the brain? The chicken-and-egg question

Does meditation change the brain? Or do an individual brain's qualities make some people more attracted to meditation than others?

You might expect someone who meditates regularly to show up as calm and thoughtful. Yes, research shows that meditation practitioners tend to have low impulsivity. But what comes first? Does meditation make someone less impulsive? Or do naturally calm people choose to spend time meditating?

Impulsivity is a personal trait, a tendency to act on a sudden urge. Extreme impulsivity is linked to psychological disorders (ADHD, personality disorders, and even brain injuries). Studies show that impulsive behavior correlates with brain structures responsible for planning and motor control.

A 2019 study compared these brain structures in long-term meditators (people with thousands of hours of lifetime meditation practice) with people who have never meditated. Researchers found differences in the neural measures of impulsivity between the groups. However,  the brain measures were not dependent on the extent of meditation practice. Instead, differences between meditators and non-meditators may be pre-existing. People with a particular neurological make-up may be more attracted to extensive meditation practice than others. 

Another study from 2013 showed that people engaging in compassion meditation might have a neurological predisposition in the way they respond to suffering. The study participants received painful electrical stimulation, and watched others receiving same stimulation. Neuroscientists put people through this unpleasant process to measure their empathy and brain responses. Participants then took up compassion and mindfulness meditation training. The brain activity in response to pain predicted how much time they would spend practicing mindfulness and compassion.

Does meditation change the brain and personality? Or do baseline differences in impulsivity, compassion, and other characteristics make some people more attracted to meditation?

I think that, likely, both are true.  

Anything that we do over and over again shapes our brain.  At the same time, our brain determines if we stick to the practice.