Emotion is a multifaceted construct comprised of cognitive, physiological and behavioural elements. In the neuroscience of emotion, central (neural) and peripheral (physiological) responses are often studied. The objective characterisation of both these processes separately and concomitantly, is thus a crucial step towards elucidating the neuro-biological underpinnings of emotions.Studying these processes requires induction of an emotional state through appropriate stimuli, classically achieved by presentation of emotionally expressive faces. However, the push for ecological validity in the past few decades has led to development of naturalistic paradigms to induce complex emotional states. These novel stimuli have been employed to capture neuronal and psycho-physiological processes with fMRI, EEG/MEG, PET and heart rate, skin conductance respectively, and which have accordingly yielded fundamental insights into our understanding of the “emotional brain”. However, alternative techniques may add valuable new knowledge whilst also providing further validation and convergence of existing evidence.Employing novel experimental paradigms which emphasize the use of naturalistic stimuli, and using unique data acquisition tools of thermal imaging and intracranial EEG, this thesis addresses the dynamics underlying the neural and peripheral responses underlying emotional states. The thesis comprises seven chapters reporting four experimental studies and a narrative review. In Chapter 1 I first introduce the core research question I address in the context of emotion. In doing so, I introduce the stimuli to evoke emotions in the laboratory setting, the physiological measures to study these and the neuroimaging techniques to probe corresponding brain responses. I then present a brief conceptual description of the analytical methods used in neuroscience and which I have employed subsequently in this thesis.In Chapter 2 I critically review use of naturalistic stimuli in neuroscience. Naturalistic paradigms are an alternative to strict laboratory-controlled stimuli sets of picture and sounds which are strong in simplicity but arguably fall short on ecological validity. Naturalistic paradigms offer greater contextualization of emotions than standard, briefly presented static stimuli. I also describe the methodological developments that the use of naturalistic stimuli has required to build on initial reports. I conclude this chapter with the promise of naturalistic stimuli to provide translational benefits.I follow this with 2 chapters with experimental studies focussed on the physiological responses induced by emotional stimuli. These studies highlight the use of thermal imaging to quantify temperature fluctuations of the faces of participants as a contact-free alternative to the traditional measures of skin conductance and heart rate. Specifically, Chapter 3 provides a validation of a new region of interest (ROI) based facial thermal imaging extraction method based on deep learning algorithms. I validate this method by using an acoustic startle probe showing a decrease in temperature in nose and cheeks replicating previously reported findings. Such ROI based method is hoped to make thermal imaging easier to use for wide application in psychophysiological research.In Chapter 4 I used a naturalistic stimulus to induce dynamic affective states. Here, I quantify physiological correlates (thermal, GSR and heart rate metrics) of the emotional responses. I demonstrate a synchrony in physiological responses of participants and thus by extension their emotional state. I also demonstrate the ability of thermal responses to vary according to emotional states encouraging its uses in emotional state identification. On top of these results, facial thermal responses are quantified by an innovative method of spatial independent component analysis. This method consistently captures a few regions of the face (nose, cheeks, and philtrum) and supersedes ROI based approach as an unbiased data driven method.Moving on from the physiological responses, in Chapter 5 and Chapter 6, I investigate the brain responses underlying emotional processing using a unique and rare neuroimaging technique of stereo-electroencephalography. Performed in clinical contexts, it overcomes the major short comings of EEG and fMRI of poor spatial and temporal resolution respectively when investigating a few brain regions. I use this technique to elucidate the dynamics of the temporal pole (TP) and the amygdala activity underlying emotional processing. Specifically in Chapter 5 I use an affective picture paradigm and in Chapter 6 I use naturalistic stimuli of emotional music and movies. Employing comprehensive hierarchical analyses; probing localised responses, functional connectivity and effective connectivity, I demonstrate that the TP exerts a modulatory influence on the amygdala activity according to valence of emotionally salient stimuli irrespective of the modality of stimuli. The TP function has often been inconsistently reported in literature and these results provide crucial evidence for TP’s vital role in emotional processing.Finally in Chapter 7 I summarise the overall contributions of this thesis, namely; the development of two new novel complementary facial thermal analysis methods; thermal imaging as a contactless tool to capture physiological changes potentially useful in emotional state identification; and the TP’s modulatory influence on amygdala activity according to valence of emotional stimuli emphasizing a vital role of TP in emotion processing via its role as conceptual store.
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