Behavioural and emotional features of brain-damaged patients with abnormal social space boundaries

Introduction: The Interpersonal space (IPS) is the area surrounding the body that works as a defensive zone, and it is considered personal or private(1). The extension of this “comfort” space is flexible and modulable both by social and biological factors. These factors also include empathic abilities and personality traits such as impulsivity and behavioral regulation. It is commonly recognized that acquired brain lesions may lead to personality changes(2). Here we examine the alteration of the IPS in patients with acquired brain damage, and its association with empathy and behavior and personality changes featuring the frontal lobe syndrome. Methods: We measured IPS and empathic abilities in a group of patients (N=11) with acquired brain damage of traumatic or stroke aetiology and in a control group of age-matched healthy participants (N=40). IPS was assessed with the “stop-distance” paradigm, while cognitive and af ective emphatic abilities were assessed with the Interpersonal Reactivity Index (IRI). Moreover, in brain-damaged patients personality and behavioral changes were assessed through the Frontal Behavioral Index administered to patients’ caregivers. Noteworthy, patients’ selection was based on a clinical diagnosis of frontal lobe syndrome. Lesion size and its location were also analyzed. Results: Although the extension of the IPS in brain-damaged patients was overall comparable to that of controls, single case analyses showed that 2 out of 11 patients presented an enlargement of the IPS, which was associated with behavioral symptoms such as apathy, inattention, and emotional flatness. On the other hand, patients who showed a total loss of space boundaries exhibited impulsivity and inappropriateness. Our results also highlighted an overall reduction of empathic abilities in brain-damaged patients, as compared to healthy controls. Further single case analyses unveiled that the same patients exhibiting an IPS alteration have lower empathy. Patients exhibiting an alteration of IPS and empathy had brain lesions involving mostly frontal and temporal lobes. Discussion:The present study of ers a novel insight on the interplay between social space extension, personality traits and empathy: patients with brain damages causing clinical symptoms of frontal lobe syndrome may also present an alteration of IPS boundaries, along with behavioural dysregulation and empathic impairments. These findings support the view that the boundaries of the social, interpersonal, space are linked to empathy and behavioural regulation, likely sharing a common neural network.