Download "Belief about nicotine selectively modulates value and reward prediction error signals in smokers"

Little is known about how prior beliefs impact biophysically
described processes in the presence of neuroactive drugs, which
presents a profound challenge to the understanding of the mechanisms
and treatments of addiction. We engineered smokers’ prior
beliefs about the presence of nicotine in a cigarette smoked before
a functional magnetic resonance imaging session where subjects
carried out a sequential choice task. Using a model-based approach,
we show that smokers’ beliefs about nicotine specifically
modulated learning signals (value and reward prediction error)
defined by a computational model of mesolimbic dopamine systems.
Belief of “no nicotine in cigarette” (compared with “nicotine
in cigarette”) strongly diminished neural responses in the striatum
to value and reward prediction errors and reduced the impact of
both on smokers’ choices. These effects of belief could not be
explained by global changes in visual attention and were specific
to value and reward prediction errors. Thus, by modulating the
expression of computationally explicit signals important for valuation
and choice, beliefs can override the physical presence of
a potent neuroactive compound like nicotine. These selective
effects of belief demonstrate that belief can modulate modelbased
parameters important for learning. The implications of these
findings may be far ranging because belief-dependent effects on
learning signals could impact a host of other behaviors in addiction
as well as in other mental health problems.

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