Interpersonal Physiological Linkage Between People With Behavioral Variant Frontotemporal Dementia and Alzheimer's Disease and Their Informal Caregivers.

Physiological linkage, which refers to the degree that people's peripheral physiological responses change in coordinated ways, has been linked to a variety of psychiatric and developmental conditions. In contrast, physiological linkage in neurological conditions has been understudied. Behavioral variant frontotemporal dementia (bvFTD) is characterized by debilitating impairments in socioemotional functioning, including connections with others. We hypothesized that physiological linkage during interactions with loved ones would be reduced in bvFTD. During unrehearsed 10-min discussions of an area of disagreement in 86 dyads (n = 40 bvFTD; n = 35 Alzheimer's disease [AD]; n = 11 healthy controls), we computed dyadic physiological linkage using a composite of six peripheral physiological measures (i.e., heart rate, skin conductance, finger pulse amplitude, finger pulse transmission time, ear pulse transmission time, somatic activity). Specifically, we computed in-phase, anti-phase, and combined physiological linkage to examine each dyad's coordinated physiological changes that occur exclusively in the same direction (i.e., positively correlated), opposite direction (i.e., negatively correlated), or in either direction (i.e., correlated regardless of whether the correlation is positive or negative). Results indicate that bvFTD dyads had significantly lower combined (but not in-phase or anti-phase) physiological linkage compared to AD and healthy control dyads. To the extent that physiological linkage reflects social connection, these findings are consistent with the deficits in socio-emotional functioning that characterize bvFTD. We offer several possible explanations for this finding and consider implications for future research and clinical assessment of dyadic interpersonal processes in dementia and related disorders.