Thesis title: Affective Touch: from Attachment patterns to Borderline Personality Disorder
The construct of Affective Touch refers to pleasant, hedonic, and motivational, rather than discriminative, aspects of touch, and it has gained much interest from the international scientific community because of the implications that it appears to be linked to across different domains of our lives, such as in interpersonal relationships. Such aspects of touch are driven by a particular group of afferent fibers - CT fibers - which are optimal activated by slow stroking on the skin, similar to a human caress, and their activation typically evokes a pleasant subjective sensation. Individual differences have been shown to influence Affective Touch perception, such as low exposure to pleasant tactile interaction during the life course, insecure attachment patterns and psychiatric disorders in which interpersonal domain is compromised. For these reasons, four studies are presented in the current thesis: each study focused on a specific aspect of Affective Touch, and the rationale of each study is strongly interlocked to each other, starting from the exploration of individual differences that may affect affective touch perception in healthy subjects - i.e. attachment patterns - to features that are characteristics in psychiatric populations - i.e. Borderline Personality Disorder.
In the first study we analyzed how interpersonal attachment experiences may shape the perception and neural elaboration of Affective Touch, showing that adult healthy individuals with a disorganized attachment pattern perceive affective stimulations as less pleasant than organized people and display abnormal brain activity in regions that are known to have a role in processing affective, salient stimuli, such as the amygdala.
The second, third and fourth studies aimed at exploring psychophysical and psychophysiological aspect of Affective Touch in patients suffering from Borderline Personality Disorder (BPD), which often exhibit a Disorganized attachment patterns, abnormal nociception and self-harming as a coping mechanism, and dysregulated interpersonal relationships. Specifically, in the second study we assessed all the principal submodalities of touch in BPD patients and we showed no differences in affective touch perception when compared to healthy controls. Nevertheless, in the third study, we found significant differences in pleasantness ratings of stimulations delivered with objects typically considered as unpleasant, with BPD patients showing higher level of pleasantness than controls in response to stroking delivered with coarse and punctuate objects; furthermore, when asked to self-stimulate in the most pleasant way, healthy participants mostly selected soft objects, applied light pressure and spontaneously selected velocities of stimulation that fell into the affective touch range (i.e. between 1 and 10 cm/s), whereas BPD patients equally selected soft and coarse objects, and applied higher pressure than controls. In the fourth study, we showed that Affective Touch has a soothing effect on psychophysiological cardiac indices, namely heart rate, heart rate variability, and interoceptive awareness both on healthy participants and on BPD patients, which may have clinical implications given abnormal cardiac indices usually observed in BPD patients.
Results are discussed in terms of peripheral and central mechanisms, as well as interpersonal experiences and environmental conditions, that could affect the perception of pleasant, affective aspects of touch in such populations.