from behaviour to functional brain imaging

PhD thesis - University of Veterinary Medicine Vienna - 2021 The full text is only available to university members. Please log in!

The main objective of this thesis was to investigate the underlying mechanisms and neural correlates of the dog-human relationship and a putative attachment system between dogs and humans. Since most of the previous dog attachment studies were mainly based on behavioural investigations, we intended to use additional methods such as functional magnetic resonance imaging (fMRI) and eye-tracking in pet dogs to get further insights. Thereby, this thesis was performed in the framework of a multidisciplinary collaboration combining existing dog expertise with proficiency in MRI. To accomplish the goals of the PhD proposal, I trained various pet dogs to stay motionless in an eye-tracking apparatus and in an MRI scanner while attentively looking at visual stimuli. This was achieved through rewards- (food, praise, play) and choice-based, positive reinforcement training and operant conditioning without any force. I developed and established a training protocol in accordance with the subjects’ wellbeing consisting of incremental consecutive training steps and defined training criteria (Study 1). At the beginning, I trained the dogs in a mock scanner and with a mock coil in the Clever Dog Lab as preparation for the fMRI tests. Subsequently, I completed the training and testing in the real MRI scanner (Siemens Skyra, 3T) environment at the University of Vienna MRI Centre. To produce accurate structural brain scans of each dog and measure the dogs’ brain activity during the visual stimulus presentation, we used a human knee coil (Siemens, 15-channel). To gain a manifold view into the dog-human relationship, we conducted a multi-method investigation combining fMRI, eye-tracking, and behavioural preference tests (Study 2). Thus, we were able to provide novel and converging insights into the engagement of the putative dog-human attachment system. More precisely, in the fMRI test we found that the visual presentation of the human caregiver’s face led to increased activation in areas associated with emotion and attachment processing, and brain regions sensitive to reward processing, regardless of the emotional facial expression. In contrast, the presentation of the stranger’s face mainly resulted in increased activation in motor and higher-order visual processing areas. Interestingly, the well-known, familiar person elicited the weakest brain response compared to the other two faces and, generally, we observed no significant activation changes in brain regions associated with attachment processing for the stranger and the familiar person. These converging results indicated a superior role of the caregiver’s face. Based on these findings, we wanted to investigate how dogs would perceive human behaviours and specific, presumable meaningful activities of their caregivers compared to a stranger performing the same ones. Therefore, we extended our previous stimuli from dynamic pictures of human faces and different emotional facial expressions to short videos of various dog-human interactions. Specifically, we aimed at exploring how pet dogs would react to positive, social interactions between their caregiver and another dog contrasted to a stranger (Study 3). These actions were compared to neutral, rather non-social (i.e., non-affective) dog-human interactions similarly performed by the caregiver and the stranger. We found that the dogs’ hypothalamus responded strongest when the dogs saw their caregiver interacting in a socially engaging manner with the actor dog, which suggests that this specific situation and the putative social rival were perceived as particularly salient. Furthermore, an increased activation in the amygdala and the insular cortex indicated that especially the social dog-human interaction could have been perceived as a potential threat to the perceiver dogs’ caregiver bond and therefore called for homeostatic regulation. Taken together, these studies provided insights into the dog-human relationship, in particular, the neural correlates of social and emotional processing in pet dogs and shed light into the perception and role of the human primary caregiver (attachment figure) from the dogs’ perspective.

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