PhD: The time course and neural correlates of nonconscious and conscious perception of emotion

Proposal details

Title: PhD: The time course and neural correlates of nonconscious and conscious perception of emotion
Research Area(s): Emotion and Self Regulation
Background: My PhD links into an ARC funded project (Imaging supra- versus sub-threshold perception: Towards a neural signature of conscious experience). Despite centuries of speculation, the underlying neural substrates of what constitutes "unconscious" processing remain elusive to the scientific community. The development of neuroimaging techniques has allowed the observation of neural activity in the intact healthy human brain, in relation to specific activities, including those emotional in nature. The human emotion system plays a vital role in regulating behaviour, in decision making and sustainability, in ensuring quality of life, as well as more fundamentally, in survival, both physically and perhaps more recently developed, in a social context. The unconscious mechanisms underlying these emotional systems are thought to be a driving force in the eventual conscious experience of emotion, and may be key in enabling a rapid and automatic neural response to threatening situations, in order to assist the individual in the preservation of life. When this delicate system is set off-balance by a traumatic life event for example, problems in appropriately interpreting and negotiating emotional situations may ensue, resulting in the manifestation of anxiety and depression disorders, including PTSD or phobias. It is therefore important to understand the neurological markers of these processes in the healthy brain, in order to provide a more thorough insight into better treatment for those individuals where these systems are rendered temporarily faulty.
Aims: The ultimate aim of my PhD is to bring together measures of the temporal (ERP) and spatial properties (fMRI) of the brain to more effectively understand how the human brain processes emotion, particularly prior to conscious awareness (ie below awareness). ERP: Previous work has revealed that the processing of nonconscious emotional stimuli (rendered so via the backwards masking technique) results in the enhancement of specific event-related potentials components in particular, the N2 and the early P3. The conscious processing of the same faces involves more elaborative, excitatory processes, later in the stream of processing and encompassing N4 and late P3 components. The aim of my project is to examine these ERPs in relation to both conscious and nonconscious emotion, expanding to a larger sample, and to look at both fear and happy in relation to neutral as exemplars of both negative/avoidance and positive/approach emotion respectively. The analysis of difference waves (neutral ERPs subtracted from emotion ERPs) and interpeak amplitudes will also allow further insights into these processes. Also of interest is concurrently recorded SCR and HR responses, which will enable an exploration of the input of different arousal systems in how the brain processes emotion (this links more closely with ARC grant ??When?, ?where? and ?how?: dimensions of emotion processing?). The startle EMG response has also been simultaneously recorded, and may provide an independent measure of the impact that the perception (or nonconscious perception) of emotion has on automatic physiological processes. It is predicted that the startle response will be potentiated in conjunction with fear stimuli and augmented for happy stimuli relative to neutral for both conscious and unconscious presentations. The exploration of the startle response to nonconsciously presented emotional faces will be a unique contribution to the literature. fMRI: The fMRI provides a parallel study to the ERP investigation, in order to examine emotional systems in the brain from a more accurate spatial perspective. Again, both fear and happy will be examined, from both a conscious and nonconscious perspective. In terms of nonconscious perception, it is predicted that the brain is able to physiologically distinguish between different emotions, despite being unable to consciously detect the presence of the stimulus. For example, the amygdala may be able to be modulated differentially by happy or fear signals, both consciously detected and undetected. Other regions of the brain that are of interest and will be explored are the frontal and temporal cortices, visual processing loops including the occipital cortex and thalamus, as well as the basal ganglia and the brainstem. Also, concurrently recorded SCR activity will also be explored in order to gain insight to the contribution of arousal systems on these emotional networks. Integrating ERP and fMRI findings: The neuroimaging world is moving towards the integration of ERP and fMRI measures, most significantly via simultaneous recording. The separate recording of ERP and fMRI in compatible paradigms provides a method to bring together spatial and temporal measures of brain function. Of particular interest is the correlation between the two measurements and the predicability of response. This also incorporates an interesting and extremely relevant issue, the role of individual differences in directing neural activity in response to particular stimuli, including emotion. The role of age, as well as personality variables and levels of anxiety, will also be preliminarily explored.
Method: As per face ERP paradigm and face fMRI paradigms included in the brain resource international database.