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Introduction Traumatic brain injury is the most significant contributor to worldwide neurological disability. Patients with moderate to severe head injuries (msTBI) can have floridly abnormal socioemotional behaviour with variable insight, yet our understanding of these changes is limited.Aim To investigate whether socio-emotional dysfunction after msTBI is linked to defective interoception.Methods 34 msTBI patients were recruited from specialist clinics if the carer/relative endorsed items on the Barsuglia social dysfunction questionnaire. 40 age matched healthy controls were also recruited. Self-report questionnaires were completed to quantify alexithymia, empathy and aggression. Non-emotional interoceptive task Interoceptive accuracy (a and b) with judgements of performance/interoceptive sensibility after each trial on a Visual analogue scale (VAS).Heartbeat TrackingHeartbeat discriminationSensibility-accuracy correspondence is generated from b) discrimination task and confidence measures. Area under the receiver operated curve represents interoceptive awareness. Emotional interoceptive task (dynamic signals) ViewingEmpathy invoking images with continuous recording of heart rate (objective arousal) with subjective report on a VAS scale of how painful the image is and the intensity of their internal responseContinuous ECG recording was performed before and during the task. Heart rate variability was calculated using rmssd during the rest period and spectral characteristics were calculated during image presentation.Results msTBI patients were significantly more alexithymic (p<0.0001), less empathic (p=0.0002) and more aggressive (p=0.0173) than the control group.There were no significant differences between the groups performance on measures of non-emotional interoception at rest.There were no significant differences in the subjective ratings of responses between groups using either scale. The interaction effect between group and rating of pain was p=0.0542.At rest the heart rate variability was not significantly different between the groups (p=0.0587). During the task the normalised low frequency power was significantly different between groups (p=0.0183) and on the subset analysed for normalised high frequency power (p=0.0234).Discussion The msTBI patients did not demonstrate a generalised failure of interoception. On testing of emotional interoception there was no difference between the groups subjective reporting. There were significant differences in sympathetic-vagal balance (msTBI showing sympathetic predominance) during the presentation of empathy-inducing images.Implications There was evidence for autonomic dysfunction during an emotional task in the msTBI cohort. This may be a relevant mechanism for their socio-emotional abnormalities. This presents an opportunity for early detection and to inform targeted interventions.