Oxytocin as the Neurobiological Basis of Synchronization: A Research Proposal in Psychotherapy Settings.

Synchronization of physiological signals between individuals seems to originate from intra-uterine life between mother and fetus (Feldman, 2006) and continues to characterize relational events in the entire human lifespan. Although referable to a wide pattern of phenomena underpinned both by central and peripheral nervous system, the term physiological synchronization (PS) is mostly used in literature to denote the autonomic nervous system mutual modulations (Palumbo et al., 2017), of two or more people interacting [even without eye contact, e.g., only by hearing each other; Vanutelli et al. (2017)]. Even though PS seems to occur also during behavioral coordination, the great majority of studies are recently addressed to define the intriguing phenomenon of the co-occurrence of PS and emotional/affective attunement, happening even when interacting people are involved in minimal and not necessarily coordinated behaviors [e.g., eye gaze; Palumbo et al. (2017)]. The neurotransmittitorial system underpinning PS has never been investigated. Our idea is that oxytocin may be the eligible candidate to be investigated as a mediator of PS, on the basis of the following arguments: (a) Both PS and oxytocin release occur in the same affiliative processes; (b) Aggressivity and conflictual exchange are characterized by both PS and oxytocin release, an aspect that is only in ostensible contradiction with the previous one; (c) PS and oxytocin system functioning have compatible neural underpinnings; (d) PS and oxytocin have all shown an association with psychotherapy process and outcome. Oxytocin, Physiological Synchronization, and Affiliative Processes Oxytocin and PS have both been previously and extensively associated to social and affiliative processes such those attachment system–related, and to affective empathy and social engagement. Namely, the link between oxytocin and attachment has already been established in the 1990's (e.g., Insel, 1997), with studies correlating oxytocin receptor polymorphism with attachment behaviors (Chen et al., 2011). Ham and Tronick (2009) associated the attachment system with synchronization patterns of child-caregiver dyads by demonstrating how attachment task of the still-face paradigm was characterized with high PS during reunion episode, in which mother and infant generate a new attunement. In clinical settings, the manipulation of the sense of attachment security in therapists produced an effect on the lag of the patients' and therapists' PS during clinical interactions (Palmieri et al., 2018). Similarly, speech markers identified as related to secure attachment were positively associated with patterns of high PS (Kleinbub et al., 2020a). Experimental studies have also demonstrated that long-term oxytocin administration enhances the experience of attachment between interacting adults (Bernaerts et al., 2017). Both oxytocin and PS are significantly associated to empathy. A series of studies in psychotherapy research field, for instance, demonstrated a positive correlation between the amount of therapist-patient PS and the level of affective empathy (Messina et al., 2013; Kleinbub et al., 2019). As a whole, Palumbo et al. (2017) review highlighted that manifestations of PS in human interactions occur during shared experience marked by empathy and its validity as an objective index of empathic, affiliative phenomena, has been demonstrated (Kleinbub et al., 2019). Oxytocin release has also been found to be associated with affective empathy: studies indicate that dispositional empathy traits are sensitive to genetic variations of oxytocin receptor (Smith et al., 2014), and that oxytocin administration enhances the ability to correctly infer the emotional content of social stimuli (Hurlemann et al., 2010). Social engagement was recently linked to PS as well as to oxytocin in mice (Kingsbury et al., 2019) as well as in humans, by demonstrating that a physiological biofeedback-based training can ameliorate people's ability to empathize with others (Gennaro et al., 2019; Kleinbub et al., 2020b). Oxytocin has also been suggested to mediate social engagement dynamics by facilitating trust and cooperation needed to adjust to new social groups (Anacker and Beery, 2013).