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Abstract
To make optimal predictions in a dynamic environment, the impact of new observations
on existing beliefs-that is, the learning rate-should be guided by ongoing estimates
of change and uncertainty. Theoretical work has proposed specific computational roles
for various neuromodulatory systems in the control of learning rate, but empirical
evidence is still sparse. The aim of the current research was to examine the role
of the noradrenergic and cholinergic systems in learning rate regulation. First, we
replicated our recent findings that the centroparietal P3 component of the EEG-an
index of phasic catecholamine release in the cortex-predicts trial-to-trial variability
in learning rate and mediates the effects of surprise and belief uncertainty on learning
rate (Study 1, n = 17). Second, we found that pharmacological suppression of either
norepinephrine or acetylcholine activity produced baseline-dependent effects on learning
rate following nonobvious changes in an outcome-generating process (Study 1). Third,
we identified two genes, coding for α2A receptor sensitivity (ADRA2A) and norepinephrine
reuptake (NET), as promising targets for future research on the genetic basis of individual
differences in learning rate (Study 2, n = 137). Our findings suggest a role for the
noradrenergic and cholinergic systems in belief updating and underline the importance
of studying interactions between different neuromodulatory systems.