Background. Apathy is a frequent neurobehavioural sequel in patients with acquired brain damage and it may seriously affect outcome of rehabilitation.

Methods. Patients with traumatic brain injury, cerebrovascular insults and hypoxic brain injury, categorized into four lesion localization groups: left hemisphere damage (LHD); right hemisphere damage (RHD); bilateral hemispheric damage (BHD); and subcortical damage (SCD) were assessed with the Apathy Evaluation Scale (AES) and Montgomery and Åsberg Depression Rating Scale (MADRS). Heart rate and electrodermal activity were recorded in an experimental situation that exposed the patients to mental stressors in order to measure psychophysiological reactivity.

Results. Significant differences in level of apathy were found between diagnostic groups as well as between localization subgroups. SCD and RHD patients displayed most apathy. Factor analysis of MADRS revealed a three-factor solution; depressed mood, somatic symptoms and negative symptoms. Apathy was significantly correlated with negative symptoms in all localization subgroups, except among the BHD patients. Apathy was not correlated with depressed mood or somatic symptoms. Moreover, apathy was significantly correlated with heart rate reactivity, but not with electrodermal reactivity.

Conclusion. Apathy is common, its severity depending on diagnosis and localization of lesion. Apathy and depression in brain damaged patients share common features, but may be differentiated. The significant relationship between apathy and heart rate may provide a psychophysiological correlation of the disengagement, lack of interest and absence of emotional responsivity typically seen in apathy. The results have implications for the theoretical understanding of apathy and related negative symptoms, and for rehabilitation practice.