Locus Coeruleus-Noradrenergic Activity During a Reward Oddball Task: an fMRI Study

Introduction: The Locus Coeruleus (LC) is a small structure residing in the midbrain and is the primary source of Noradrenaline (NA) in the brain. The LC-NA system’s roles include focusing attention towards salient stimuli. Animal studies suggest that the LC-NA system plays a role in reward related functions, an aspect primarily attributed to the Ventral Tegmental Area (VTA) Dopamine (DA) system. Animal studies suggest that habituation of the LC to salient stimuli occurs rapidly. The Dorsal and Ventral attentional networks (DAN and VAN respectively) are other regions relevant in attentional focus. Thus, we hypothesise that the reward and salient stimuli will elicit higher responses in the LC compared to the control, the LC will habituate across trials, the DAN network will respond highest to reward, and the VAN highest to salience. Methods: Forty-five healthy participants were recruited to complete a reward-oddball task during fMRI scanning. Repeated Measures (RM)-ANOVAs assessed...Show moreIntroduction: The Locus Coeruleus (LC) is a small structure residing in the midbrain and is the primary source of Noradrenaline (NA) in the brain. The LC-NA system’s roles include focusing attention towards salient stimuli. Animal studies suggest that the LC-NA system plays a role in reward related functions, an aspect primarily attributed to the Ventral Tegmental Area (VTA) Dopamine (DA) system. Animal studies suggest that habituation of the LC to salient stimuli occurs rapidly. The Dorsal and Ventral attentional networks (DAN and VAN respectively) are other regions relevant in attentional focus. Thus, we hypothesise that the reward and salient stimuli will elicit higher responses in the LC compared to the control, the LC will habituate across trials, the DAN network will respond highest to reward, and the VAN highest to salience. Methods: Forty-five healthy participants were recruited to complete a reward-oddball task during fMRI scanning. Repeated Measures (RM)-ANOVAs assessed changes in BOLD levels in our regions of interest (LC, VTA, DAN, VAN) as participants responded to the different stimuli oddballs (reward, salient, no reward). Results: A main effect for stimulus type on LC activity was not found (p=.079). Activity in the LC did not significantly habituate (p=.469). The DAN had overall higher activation than the VAN and had higher activation to the reward oddball compared to the salient (p<.001). The VAN region also had higher activation to the reward compared to the salient condition (p<.001). Conclusion: Results suggest that the LC had a similar degree of activation to each stimulus. This may suggest that the LC responds to contextual saliency and may not account for how goal relevant a stimulus is. We did not find a statistically significant habituation across trials. This may suggest that habituation in humans happens at a slower/less extensive rate than rats. The DAN region had globally higher activation than the VAN, reflecting this region’s role in sustained and goal related attention. The lack of activation within the VAN may suggest an orientation response was not required during this task. Strengths, limitations, and directions for future research are discussed.Show less

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Locus Coeruleus-Noradrenergic Activity During a Reward Oddball Task: an fMRI Study