Resting parasympathetic dysfunction predicts prosocial helping deficits in behavioral variant frontotemporal dementia

In the behavioral variant of frontotemporal dementia (bvFTD), left-lateralized salience network dysfunction reduces basal activity in the parasympathetic nervous system, a branch of the autonomic nervous system that reduces arousal and fosters empathy and prosociality. Here we examined whether resting parasympathetic deficits in bvFTD related to diminished prosocial behavior. Eighty participants [30 with bvFTD, 25 with Alzheimer's disease (AD), and 25 healthy controls] completed a "helping task" in which we quantified participants' spontaneous reactions to an experimenter who struggled to find a lost key. Participants also underwent an assessment of baseline autonomic nervous system activity and structural magnetic resonance imaging. An exploratory factor analysis of participants' behaviors during the helping task revealed four factors: empathic concern, consolation, disengagement, and impatience. Patients with bvFTD had lower empathic concern and greater disengagement and impatience than the AD and healthy control groups. Patients with bvFTD had lower resting respiratory sinus arrhythmia and faster respiration and heart rates than patients with AD and healthy controls, a pattern consistent with parasympathetic dysfunction. Skin conductance level was also lower in bvFTD than in the other groups. Lower baseline respiratory sinus arrhythmia and faster baseline respiration rates, but not skin conductance level, predicted lower prosocial helping behaviors. Voxel-based morphometry analyses revealed that atrophy in the bilateral medial pulvinar nucleus of the thalamus, midcingulate cortex, and caudate was associated with lower empathic concern and consolation, and atrophy in the bilateral medial pulvinar nucleus of the thalamus, left frontoinsula, and left ventral striatum was associated with greater disengagement and impatience. Left-lateralized frontoinsula atrophy was associated with not only lower respiratory sinus arrhythmia but also with lower consolation and greater disengagement. This study offers evidence for prosocial behavior deficits in bvFTD and suggests that left-lateralized salience network atrophy reduces patients' resting parasympathetic activity and motivation to help others in need.