Given that people with borderline personality disorder are impulsive, we would expect them to do poorly on tests that measure functioning of the____.

Question

Psychology question here.

Personality disorders (PD) are a group of psychiatric conditions characterized by experience and behavior patterns that cause serious problems with respect to any two of the following: thinking, mood, personal relations, and the control of impulses.
The functioning of the left side of the brain is associated with analysis and thinking, the right side with emotion, feeling, and impulse.

http://www.1000ventures.com/business_guide/crosscuttings/mind_how-it-works.html

Without a specific context, from the sentence you give, it is hard to tell what you are searching for. If you are speaking in psychoanalytic terms, it might be "superego." If you are talking about brain physiology, it could be something like "frontal lobe."

I searched Google under the key words "borderline personality disorder" to get these possible sources:

http://www.nimh.nih.gov/publicat/bpd.cfm
http://www.palace.net/~llama/psych/bpd.html
http://en.wikipedia.org/wiki/Borderline_personality_disorder
http://www.stanford.edu/~corelli/borderline.html
http://www.psycom.net/depression.central.borderline.html

I hope this helps a little more. Thanks for asking.