Borderline or Bipolar: Objective Data Support a Difference

Psychiatric TimesVol 33 No 7
Volume 33
Issue 7

The Prisoner’s Dilemma reveals a clear distinction between the 2 conditions.

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When a patient presents with episodes of depression, irritability, and emotional lability (especially tears and anger, with rapid changes), might he or she have borderline personality disorder (BPD)? Or could it be rapid cycling bipolar disorder (BD)? Although there are other possibilities, such as substance use, differentiating these 2 common conditions can be extremely difficult. DSM criteria have a roughly 90% overlap. Only 2 DSM criteria features are clearly present in one and absent in the other-namely, abandonment fear and chronic emptiness.1

Indeed, Deltito and colleagues2 as well as others have argued that borderlinity is just another version of bipolarity or at least that the “broadening of the bipolar diagnosis to include a spectrum of poorly defined conditions has added to the plausibility of this idea.”3 In refutation of this notion, data that demonstrate a clear difference between the 2 conditions-involving interpersonal trust-have recently been published.3

Prisoner’s Dilemma

The social psychology research tool called Prisoner’s Dilemma is likely familiar to most readers.4 Briefly: imagine that 2 criminals are caught simultaneously. If both cooperate with one another and tell the same false story, each can get off with a light sentence. But if one finks on the other (dubbed “Defect”), he gets off scot-free while the other takes the rap. However, if both defect, both are punished. This has been modeled in a game of cooperation. If both player and partner cooperate, each earns 40 pence. If both defect, each earns only 20 pence. But if one defects while the other cooperates, the defector earns 70 pence and the cooperator, nothing: he is punished for cooperating with a defector, whose score is actually better than could be achieved through mutual cooperation.

If such a game is played between 2 partners, just once, the best strategy is to defect: it limits losses. But if the game is played repeatedly, the best strategy in most circumstances is called “tit-for-tat”: play cooperation first and then follow the move of your partner. If he cooperates, do likewise. When he defects, also do likewise and continue thus until he plays cooperate-then follow that move as well.

The result is a test of willingness to cooperate. When euthymic bipolar patients played (ostensibly with another person, though the actual partner was a computer), they made choices very like control patients, choosing to cooperate almost 75% of the time. But patients with BPD cooperated only about 50% of the time (analysis of variance difference, P = .03).

This is not a clinical tool: first of all, separation between the 2 groups was far from 100%. Second, iterative games of Prisoner’s Dilemma are not easily administered, even by computer. The point of this research is that an objectively measurable difference between BD and BPD was evident. Conclusions: (1) these 2 conditions are not variations within a species-they are different (though perhaps related) animals; and (2) the difference observed mirrors what we see clinically, namely an impairment in relationship.

Some might regard this as another instance in which social psychology goes to great lengths to prove an accepted observation (as remarked way back in 1918*: “. . . for more than 20 years I have been searching for one fact . . . discovered in a psychological laboratory which did not repeat what we already knew”5). But given the degree of controversy about the bipolar/borderline distinction, this finding seems worth passing along.

When one sits down with a patient and within 5 minutes is aware of something odd going on-excessive praise or an unwarranted devaluation or simply a sort of “latching on”-these feelings are data. Something is amiss in the social exchange. For example, you play Cooperate, he plays Defect, even after several overtures. In this context, your clinical hunch has been supported: BD may or may not be present, but the probability of borderlinity has gone up.

Acknowledgment-Thanks to our esteemed Samaritan Health Services librarian Ken Willer for access to articles like this.*


This article was originally posted on 4/12/2016 and has since been updated.


Dr Phelps is Director of the Mood Disorders Program at Samaritan Mental Health in Corvallis, OR. He is the Bipolar Disorder Section Editor for Psychiatric Times.


1. Phelps J. Bipolar Disorder and “Borderline Personality Disorder.” Updated 2013. Accessed April 3, 2016.
2. Deltito J, Martin L, Riefkohl J, et al. Do patients with borderline personality disorder belong to the bipolar spectrum?J Affect Disord. 2001;67:221-228.
3. Saunders KE, Goodwin GM, Rogers RD. Borderline personality disorder, but not euthymic bipolar disorder, is associated with a failure to sustain reciprocal cooperative behaviour: implications for spectrum models of mood disorders. Psychol Med. 2015;45:1591-1600.
4. Prisoner’s Dilemma. Accessed April 3, 2016.
5. Fite W. The human soul and the scientific prepossession. The Atlantic Monthly. 1918;122:800. Accessed April 3, 2016.

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