Introduction

Borderline Personality Disorder (BPD) is a common and serious mental illness that affects about 1-2% of the general population, up to 25% of psychiatric inpatients, and 10% of outpatients [1,2]. The exact causes of BPD are not known, but both genetic and environmental risk factors are believed to contribute to the aetiology of the disorder [1,2], with childhood trauma showing a particularly strong association with the later development of BPD [2,3]. Individuals with a diagnosis of BPD often have difficulties in forming and maintaining interpersonal relationships, and such social impairments are a diagnostic feature of the disorder [4]. Difficulties in social interaction, as seen in BPD, can make maintaining a job or achieving sustained success in the workplace or in education challenging. Furthermore social difficulties experienced by individuals with BPD often show little or no improvement with time [5]. In the current study we sought to characterise social cognition in BPD using well-validated tests of social judgement from faces.The term ‘social cognition’ refers to the way in which we gather information about the people around us, allowing us to make judgements and inferences about their characteristics, including personality and intentions [6]. Key to social cognition is the ability to judge how people may feel or think in a given situation [7–10]. Effective social functioning requires the involvement of a network of brain areas in order to gather, retrieve and process relevant information in the correct way, and is fundamental not just in cultivating relationships with others, but for everyday functioning and social interaction of all kinds. A very important source of social information is the face, and consequently, one major means through which social brain function has been investigated in healthy volunteers and patient groups has been through the study of face perception [11]. Investigations of social perception from faces have implicated several brain areas as important in social cognition, including the medial frontal cortex, the amygdala, the insula, the cingulate cortex and precuneus, regions of superior temporal cortex and the fusiform gyrus [7,12–16].

Previous studies have investigated social cognition in BPD using a range of measures. Studies of facial expression recognition in BDP to date have recorded inconsistent findings – two studies reported impairments in recognising facial emotions [17,18], while another study found no significant deficit of facial emotion identification, but noted a tendency of individuals with BPD to rate ambiguous faces as negative or aversive [19]. Three studies further identified a more intense response of those with BPD to images of negative facial emotion compared to positive, a finding which was not evident in control participants [17,18,20]. Using interview-based methods Hill and colleagues demonstrated impairments in social function in BPD [21]. Preißler and colleagues also found evidence of social cognition deficits in BPD when asked to attribute mental states to characters in short films [22]. Two studies have investigated social cognition in BPD using the ‘Reading the Mind in the Eyes’ test (RMET), which involves participants inferring the mental state of individuals by viewing pictures of the eye region. Of the studies, one reported no difference between BPD and control participants [22], although this group did question the ecological validity of the test, and the other reported enhanced sensitivity to social characteristics in BPD [23]. The apparent inconsistencies in the literature may be explained by inherent task differences, with conditions in the RMET less representative of a “real life” or familiar situation than in the other tasks described. Fertuck and colleagues also acknowledge that the RMET represents a very low stress task and does not allow for the detection of negativity bias [23]. Findings of altered social cognition in BPD are consistent with structural imaging studies of the disorder, which have found that brain areas involved in social cognition, including frontal and medial temporal lobe regions, differed from that of healthy participants [24].Because previous studies of social cognition in BPD have failed to identify consistent findings, we sought to introduce a more systematic approach involving a variety of social inferences commonly made to faces using a well established task [29–31]. Hence, in order to arrive at a more precise characterisation of areas of relative strength and weakness in social decision making in individuals with BPD, we chose characteristics that included those with a clear and relatively well-established physical basis (age, distinctiveness, attractiveness) and those with a more purely social function involving an inference about a psychological trait or disposition (intelligence, approachability, trustworthiness). Considering previous literature, we hypothesised that differences between groups would be evident in those judgements that required inferences about social characteristics and, in particular, that the BPD group would perform significantly poorer that controls in judgements related to the perception of threat (approachability and trustworthiness). We further investigated the association of social performance with clinical measures and measures of childhood trauma in the BPD group. Measuring childhood trauma was of particular interest due to the strong association between childhood adversity and BPD [2,3]. Furthermore, studies of both bipolar disorder and schizophrenia have reported correlations between childhood experience and common symptoms of these disorders [32–34].

Methods

Ethical approval

The study was approved by The Lothian Research Ethics Committee. All participants gave written informed consent, and were able to withdraw from the study at any time. Participants who withdrew from the study remained eligible for all treatments (where required) and were not disadvantaged in any way. Anonymised study data can be made available upon application to the authors.

Results

Demographic Characteristics

Discussion

Participants with a diagnosis of BPD performed less well than controls in a test of social judgement from faces. Those in the BPD group scored lower overall than healthy participants and, in particular, this group had difficulty judging trustworthiness and approachability. Notably, the BPD group judged more faces as unapproachable and untrustworthy than the control group. Furthermore, bias towards judging approachable faces as unapproachable in those with BPD correlated with childhood trauma scores as measured by the CTQ.Both approachability and trustworthiness judgements are related to threat detection, as incorrectly judging a person as approachable or trustworthy could have potentially hazardous consequences. Although efficient social functioning requires a network of brain areas for information processing, it is the amygdala that is principally involved in fear and threat detection, and this area has been shown consistently to be necessary for normal social cognition in animal and human studies [35]. There is evidence from neuropsychological studies [12] that the amygdala plays a role in social judgements and functional brain imaging studies have also reported amygdala involvement in the judgement of trustworthiness [13,] and approachability [31]. Martens and colleagues [37] also noted a relationship between amygdala volume and approachability in patients with Williams syndrome, with increased amygdala volume correlating with higher approachability ratings of faces. Patients with BPD have been shown to have decreased amygdala volume in structural MRI studies, and heightened amygdala responses to facial stimuli in functional MRI studies [26,28,,39,]. Furthermore, previous studies of facial emotion recognition in BPD have suggested that individuals with BPD may show an increased tendency to rate neutral faces as negative or threatening [17,19]. The present findings are therefore consistent with suggestions of heightened amygdala-mediated threat responses to facial and social stimuli in BPD.

Todorov and colleagues [41,], have developed an important perspective on how social characteristics are evaluated in faces that suggests they are based on orthogonal dimensions involving the appraisal of valence (positive or negative intentions) and dominance (ability to enact intentions). In this approach, the appraisal of trustworthiness and approachability are closely linked to the valence factor, raising the interesting possibility for future research that it may be this factor that is particularly affected in BPD.Our findings also indicate that skewed perception of approachability in those with a diagnosis of BPD is specifically related to childhood adversity, suggesting that trauma in childhood has a sustained and lasting impact on social cognition in BPD. Although the neurobiological substrates of this effect are not known, childhood adversity has recently been related to enhanced amygdala reactivity in a healthy population sample [39] and in major depressive disorder [42], suggesting that childhood trauma may alter social judgement in BPD by modulating amygdala activation [43].

The current results are also consistent with a broader dysfunction in brain networks sub-serving social cognition and mentalising in BPD. Previous studies in healthy individuals have demonstrated the importance of a number of brain regions in social judgement including the medial prefrontal cortex, inferior prefrontal cortex, cingulate cortex and superior temporal cortex [13,16,,]. Structural imaging studies of patients with BPD have also shown altered structure of distributed brain regions implicated in social cognition including reductions in volumes of regions of the frontal and medial temporal lobes [24]. Furthermore, dysfunctional connectivity between the amygdala and PFC has been reported in studies of BPD [45,]. Taken together with these previous findings, our present results suggest negative bias in approachability and trustworthiness judgements may derive from a wider disruption of fronto-limbic circuits in BPD, with a failure of frontal regions to regulate affective responses in individuals with the disorder.The current findings suggest that individuals with BPD display differences in social cognition which are distinct from those seen in other neuropsychiatric disorders. The pattern of results we observed in the tests of social judgement in individuals with BPD differed from those seen on the same tests in patients with schizophrenia [29], patients with autism [46], and patients with depression (Hall et al, unpublished data). These results suggest a degree of specificity to the breakdown of social inferences in individuals with BPD, which may be particularly related to increased sensitivity to threat.

In a previous study of social cognition in BPD Fertuck and colleagues found an increased ability of their BPD group to correctly identify the mental state of others using the ‘Reading the Mind in the Eyes’ test [23]. Whilst these results may appear contradictory to the present findings, this is not necessarily the case. Heightened responsiveness of those with BPD to certain types of social cues, such as perceived threat in social situations, could contribute to both findings. Thus in our task (with dichotomous choices on a single characteristic) a heightened sensitivity to certain types of cues would be evident as biased performance (and hence a lower score on a given characteristic). However in the ‘Reading the Mind in the Eyes’ test, where the participant is given the choice of four potential social labels which are not related, heightened sensitivity to one particular dimension could appear as improved overall performance. However in the future, a study administering both tests to the same group would be helpful to further reconcile these results and to understand the possible causes of any apparent discrepancy in their findings.The heightened responsiveness of patients to potentially threatening situations, illustrated by increased judgements of trustworthy faces as untrustworthy and approachable faces as unapproachable, highlights the social difficulties experienced by those with a diagnosis of BPD, and has clinical implications for the management of patients. Individuals with BPD appear more likely to view neutral situations as threatening, and may require additional reassurance and assistance in understanding social cues. In addition, it appears that childhood trauma is an important risk factor in the development of BPD, and earlier intervention or symptom treatment may be prudent to prevent the disorder, or to minimise the difficulties experienced. It has been suggested that disruption in mentalisation may underpin many of the core features of BPD, including social difficulties [9], and our results are consistent with this idea, supporting the potential value of mentalisation based therapies as a treatment for individuals with a diagnosis of BPD [47].