Mapping brainstem arousal systems : Developing a functional localiser for the locus coeruleus and ventral tegmental area with fMRI

Sammanfattning

The neural correlates of consciousness is a broad field of study, and several avenues of research point to the ascending reticular activating system broadly, and the neuromodulator noradrenaline in particular, as a potentially interesting modulator of subjective conscious experience. In a sample of six healthy participants, I aimed to develop a functional localiser for functional magnetic resonance imaging (fMRI), of the human locus coeruleus and ventral tegmental area that can be used in future research to better understand the role of neuromodulators in conscious experience. This was done by implementing a monetary incentive delay task and arousing white noise stimuli and comparing two fMRI protocols. To examine the validity of the task stimuli, response times and skin conductance response was also measured. No significant activation was found in the locus coeruleus, and in the ventral tegmental area only for one participant. Additionally, fMRI data from another dataset that implemented sound cues was analysed, in this dataset locus coeruleus activity was found. Taken together with the skin conductance data and lack of significant results from the current study, I hypothesise that the lack of significant activation in this current study could be explained by a low signal-to-noise ratio, and that increasing the voxel sizes is the best way to improve the protocols for future research.