The influence of trust on the perception of social touch in lonely elderly individuals: an fMRI study

Loneliness leads to increased morbidity and mortality in elderly individuals, while social touch plays a key role in creating social bonds and is linked to positive health outcomes. Lonely individuals display hypervigilance for threat, including social threat on the one hand and an increased desire to reconnect on the other. This may open the way for introducing social cues, such as attribution of benevolence or trust, that can change the way lonely individuals perceive social interaction in an experimental and therapeutic setting. Therefore, it is important to better understand the experience of social touch in lonely individuals, as it may lead to novel touch-based therapies for loneliness. This thesis aimed to examine the neural and behavioral underpinnings of the perception of social touch in lonely elderly individuals. More specifically, the goal was to investigate whether loneliness and trust interact to influence the perception of social touch in elderly individuals. The hypothesis stated that lonelier individuals perceive and process social touch differently than less lonely individuals, and expected to find an overall positive association of loneliness and activation in social brain areas such as the insular cortex, anterior cingulate cortex and medial prefrontal cortex and, especially, areas related to reward processing such as the ventral striatum, accompanied by a positive relationship of loneliness and ratings of the experience of social touch, i.e. pleasantness, wanting, comfort and intensity. We further expected that lonelier individuals find affective social touch more pleasant, more intense, more comforting, and more wanted when touched by an individual they trust, whereas they find it less pleasant, comforting or wanted when touched by someone they distrust when compared to less lonely individuals. We expected to observe a similar interaction of loneliness and trust in the brain areas associated with social cognition. Our hypotheses were in line with the theory that lonely individuals display hypervigilance for threat, including social threat, and an increased desire to reconnect. We next focused on the anterior insula, a region contributing to the salience network that is known to regulate attention to behaviorally meaningful stimuli. We hypothesized that the anterior insula displays increased connectivity with areas from the salience network, such as the anterior cingulate cortex and the amygdala as well as with central executive network areas during slow trustworthy social touch. This is in line with the hypothesis that lonelier individuals find social stimuli preceded by cues of social acceptance to be more meaningful and salient when compared to less lonely individuals. Forty-one participants older than 64 years first underwent a trust manipulation with two confederates matching their age range and gender, resulting in one trustworthy and one untrustworthy confederate. Following the trust manipulation, we conducted a functional magnetic resonance imaging (fMRI) experiment during which the subjects were touched on the forearm by a trained experimenter while being led to believe that they were touched by one of the confederates in a slow-affective and fast-neutral touch condition. The design consisted of four conditions, comprised of two factors: trust and touch velocity. The subjects subsequently rated the experience of the touch after each trial by indicating its pleasantness, wanting, intensity and comfort. Participants found slow touch significantly more pleasant than fast touch. None of the other relationships of the behavioral variables were significant. There was a significant association of brain areas implicated in social cognition i.e. the operculum, superior temporal pole, fusiform gyrus, the cerebellum, bilateral posterior insula, left anterior insula, left caudate, middle cingulate cortex and loneliness during the experience of social touch. During the condition of slow trustworthy touch we have found a significant association of loneliness and the connectivity of the anterior insula with the amygdala and the middle frontal gyrus among other regions. Our hypothesis about the interaction of trust and loneliness on both the behavioral ratings and neural processing of touch was not confirmed. These results indicate that loneliness may be positively related to social touch reward and saliency, and highlight the need for further exploration of social touch as a possible therapy for the detrimental health effects of loneliness