Investigating the role of dopaminergic and noradrenergic projections in intra- and extradimensional shifts

The main objective of this study is to investigate the neurophysiological pathways (dopaminergic, noradrenergic) mediating intra- and extradimensional shifts. There are noradrenergic projections from the locus coerulus (LC) to almost all brain regions except the basal ganglia. They are assumed to be involved in intra- as well as extra-dimensional shifts (Bouret & Sara, 2005). Furthermore, release of noradrenaline is accompanied by increases in pupil diameter (Larsen & Waters, 2018). Dopaminergic projections of the receptor type D2, originating from the basal ganglia, are assumed to mediate extra-dimensional shifts. Furthermore, the activity of these projections is assumed to correlate with variations in eye-blink rate (EBR) (Kleinsorge & Scheil, 2017). The main assumption of this study is that the performance/efficiency of both intra- and extra-dimensional shifts correlates with noradrenergic activity as reflected in a covariation of noradrenergic projections from the LC (as measured by fMRI BOLD activity) and intra-trial variations of pupil diameter, whereas the performance/efficiency of only extra-dimensional shifts is correlated with the covariation of fMRI BOLD activity in the basal ganglia and interindividual differences in baseline or resting EBR as well as intraindividual between-trial variations in eye-blink rates.