Investigating visuo-tactile mirror properties in borderline personality disorder: A TMS-EEG study

Objectives: Patients with borderline personality disorder (pw-BPD) have decreased levels of cognitive empathy, which may be subtended by mirror-like mechanisms in the somatosensory cortices, i.e., the Tactile Mirror System (TaMS). Here, we aimed to shed light on the TaMS and empathic deficits in pw-BPD focusing on connectivity, using transcranial magnetic stimulation and electroencephalography (TMS-EEG). Methods: After study preregistration, we collected self-report measures of empathic abilities, behavioral performance in a visuo-tactile spatial congruency task investigating TaMS activity, and TMS-evoked potentials (TEPs) from 20 pw-BPD and 20 healthy controls. TMS was delivered over the right primary somatosensory cortex (S1) during touch observation and real touch delivery. Results: Pw-BPD reported significantly lower levels of cognitive empathy than controls and made significantly more errors in reporting the side of real touches during touch observation. Moreover, pw-BPD presented an altered connectivity pattern from S1-TEPs during touch perception and touch observation, in the last case without differences between human- and object-directed touches. Conclusions: The results do not support a specific impairment of TaMS in pw-BPD, but reveal significant behavioral and connectivity alterations within the somatosensory network during touch processing. Significance: The present findings temper the proposed role of the TaMS in BPD, while still highlighting the involvement of somatosensory network alterations.