Environmental factors are known to have far reaching effects on nervous system function, and in the adult brain, it is clear that a wide range of environmental stimuli modulate cell proliferation and survival (e.g., neurogenesis). This project investigated whether social stimulation and concomitant changes in gonadal hormones can influence the proliferation of new cells in the adult brain. The adult green treefrog (Hyla cinerea)was used as the model system; studying the courtship behavior of the highly social treefrog affords a direct, quantifiable way to measure the effects of acoustic social cues and hormonal intervention on adult brain cell proliferation. Using immunohistochemistry techiques, endocrinological manipulations, and socially-relevant acoustic stimulus presentations, I report that social cues modulate cell proliferation in the brains of adult male and female H. cinerea. I first mapped the distribution of proliferative areas in the adult treefrog brain using 5-bromo-2′- deoxyuridine (BrdU) labeling. I then exposed naturally-cycling male and female treefrogs to random tones or a recording of a natural H. cinerea chorus for ten days during the breeding season. I found that male and female treefrogs that heard their conspecific chorus exhibited increased brain cell proliferation compared to animals that heard random tones. Moreover, this modulation was region-specific and occurred in those regions which reflected their presumed involvement in reproductive physiology and behavior: the preoptic area (POA) and the infundibular hypothalamus (IF). To determine the involvement of gonadal hormones in cell proliferation with and without social stimulation, I gonadectomized and implanted male and female H. cinerea with blank or steroid-filled implants. After exposing the treefrogs to the same acoustic conditions as above, I discovered that social modulation of adult cell proliferation can occur without the influence of gonadal hormones (i.e., androgens in the male and estrogen in the female). Furthermore, the results revealed that neither hormone was neurotrophic and in fact, chronically-elevated estrogen levels decreased cell proliferation in the female POA and IF. Together, these results indicate that the reception of acoustic social cues increases cell proliferation in brain regions mediating sexual behavior and endocrine regulation; furthermore, this modulation occurs in a sexually-differentiated fashion without gonadal hormone influence. / text

In the last decade, neuroscience and psychology alike have paid increasing attention to the study of affective touch, which refers to the emotional and motivational facets of tactile sensation. Some aspects of affective touch have been linked to a neurophysiologically specialised system, namely the C tactile (CT) system. While the role of this system for affiliation, social bonding and communication of emotions have been investigated, less is known about the potential role of affective touch in the awareness of the body as our own, i.e. as belonging to our psychological 'self'. This thesis attempted to contribute to the knowledge on affective touch and its relation to body awareness, by exploring the potential role of this modality to the way we perceive and make sense of our body as our own. Specifically, this work aimed to advance the current state of knowledge by investigating: 1) the effect of affective touch on the sense of body ownership, which is a fundamental aspect of body awareness; 2) the relation between interoceptive modalities, originating both internally (i.e. cardiac awareness) and peripherally (i.e. affective touch), and exteroception in body awareness; 3) the effect of intranasal oxytocin on the perception of affective touch and bodily awareness; 4) the perception and social modulation of affective touch in psychiatric patients who show difficulties in body awareness, namely patients with Anorexia Nervosa, and 5) the modulating role of self-other distinction and of self-other relation in the perception of affective touch and body awareness. In a first experiment (N = 52) the rubber hand illusion paradigm was used to investigate the role played by CT-optimal, affective touch in the sense of body ownership. The results showed that slow, pleasant touch enhanced the experience of embodiment in comparison to faster, neutral touch, suggesting that affective touch might uniquely contribute to the sense of body ownership. The following study (N = 75), used a similar methodology to test whether interoceptive sensitivity as measured by a heartbeat counting task would modulate the extent to which affective touch influences the multisensory process taking place during the rubber hand illusion. The results could not confirm a systematic relation between interoceptive sensitivity and the perception of affective touch, nor its influence on body ownership. The next study (N = 41) included a double-blind, placebo-controlled, randomised, cross-over design testing the effect of intranasal oxytocin on the perception of affective touch and body ownership, as measured by means of the rubber hand illusion. There was no evidence supporting the hypothesis that intranasal oxytocin could influence the CT system as tested in this study. The next study (N = 55) applied some of the above methodologies to investigate the perception of CT-optimal touch in patients with anorexia nervosa and its emotional modulation by top-down factors. The results confirmed the hypothesis that people with anorexia nervosa show a reduced perception of affective touch compared to healthy controls, but its perception was not influenced by top-down affective modulation, in the sense that both patients and healthy controls perceived touch as more pleasant when presented concurrently with positive facial expressions compared to neutral and negative faces. Finally, the last two studies (N = 76 and 35 healthy volunteers, respectively) focused on the relationship between affective touch and body awareness in the context of social cognition. These studies used both online and offline social modulation paradigms to investigate the role of self-other distinction and of self-other relation in the perception of affective touch. The results showed that positive top-down social information can enhance the perceived pleasure of tactile stimulation. Taken together, these studies point to the central role of affective touch in body awareness and social cognition. Finally, they also pave the way for future studies examining the role of disruptions of the CT system in the development of neuropsychiatric impairments of body awareness and social cognition.

In der vorliegenden Dissertation werden vier Studien vorgestellt, in denen untersucht wurde, wie altrozentrische (Mimikry) und egozentrische (Selbstprojektion) Prozesse der sozialen Kognition in Abhängigkeit vom sozialen Kontext und persönlichen Dispositionen reguliert werden. Studie 1 zeigte, dass die Tendenz, fröhliche Gesichtsausdrücke anderer nachzuahmen abhängig von dem mit der beobachteten Person assoziierten Belohnungswert ist. Die Auswirkung der Belohnung ging jedoch weder in die vorhergesagte Richtung, noch konnten wir einen Einfluss von Oxytocin, einem Hormon, das der Neurobiologie der sozialen Anpassung zugrunde liegt, finden. Studie 2 zeigte, im Vergleich zu vorherigen Studien, keine allgemeine Verbesserung der automatischen Nachahmung nach direktem Blickkontakt im Vergleich zum abgewandten Blick. Wir konnten jedoch potenzielle dispositionelle Faktoren (z.B. autistische Eigenschaften) identifizieren, denen unterschiedlichen Mimikry-Reaktionen auf den Blickkontakt zugrunde liegen könnten. Studie 3 kombinierte kurze Phasen der Emotionsinduktion mit psychophysischen Messungen der Emotionswahrnehmung. Es zeigte sich, dass emotionale Gesichtsausdrücke tendenziell als fröhlicher beurteilt werden, wenn Personen angeben, dass sie sich fröhlich im Vergleich zu traurig fühlen. Emotionale egozentrische Verzerrungen wurden in Studie 4 erneut untersucht. Im Gegensatz zu unseren Vorhersagen fanden wir jedoch keine stärkeren egozentrischen Verzerrungen, wenn die Teilnehmenden emotionale Gesichtsausdrücke von ähnlichen im Vergleich zu unähnlichen Personen beurteilten. In allen Studien fanden wir Hinweise für den kontextabhängigen Charakter der sozialen Kognition. Allerdings konnten wir einige der in der Literatur berichteten Phänomene nicht replizieren. Diese Ergebnisse unterstreichen die Notwendigkeit, die Robustheit und Generalisierbarkeit früherer Befunde systematisch neu zu bewerten. / This dissertation presents four studies that investigated how altercentric (mimicry) and egocentric (self-projection) processes of social cognition are regulated according to the social context and personal dispositions. Study 1 showed that the tendency to mimic others’ happy facial expressions depends on the reward value associated with the observed agent. However, the effects of reward were not in the hypothesised direction, nor could we detect an influence of oxytocin treatment, a hormone involved in the neurobiology of social adaptation. Study 2 could not detect a general enhancement of the tendency to automatically imitate others’ hand actions following direct gaze compared to averted gaze, in contrast to previous studies. However, we could identify dispositional factors (e.g., autistic traits) that might underlie different mimicry responses to gaze cues. Combining brief emotion induction blocks with psychophysical measures of emotion perception, Study 3 showed that facial emotional expressions tend to be judged as happier when individuals feel happy than when they feel sad. Emotional egocentric biases were replicated in Study 4. But contrary to our predictions, we did not find stronger egocentric biases when participants judged emotional facial expressions of similar compared to dissimilar others. Across all studies, we found evidence supporting the contextual nature of social cognition. However, we could not replicate some of the phenomena reported in the literature. These results highlight the need to systematically re-evaluate the robustness and generalizability of prior findings.