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

Abstract

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.

Keywords: Alzheimer's disease; behavioral variant frontotemporal dementia; caregivers; dementia; dyadic social interactions; physiological linkage.

FIGURE 1

Illustration of methods for computing physiological linkage for individual physiological measures and a physiological composite measure using example data from one study dyad. (A) Physiological reactivity (patient in black, caregiver in gray; artefacts removed/corrected and data smoothed) by individual physiological measures. (B) Physiological total linkage by individual physiological measures. Note that physiological total linkage was computed using a 15‐s rolling window, i.e., for any given second of the conversation (e.g., the two blue dots), a Pearson's correlation coefficient was computed based on the 15 s of physiological data surrounding that specific second (the two blue boxes). (C) Physiological linkage (total, in‐phase, anti‐phase, and combined linkage) of the physiological composite measure. ACT, somatic activity; EPT, ear pulse transmission time; FPA, finger pulse amplitude; FPT, finger pulse transmission time; IBI, cardiac interbeat intervals; SCL, skin conductance level.

FIGURE 2

Three types of physiological linkage by diagnostic groups. *p < 0.05. ***p < 0.001. bvFTD, behavioral variant frontotemporal dementia. AD, Alzheimer's disease; HC, healthy controls. Mean ± 1SEM.