High impulsivity is an important risk factor for addiction with evidence from
endophenotype studies. In addiction, behavioral control is shifted toward the
habitual end. Habitual control can be described by retrospective updating of
reward expectations in ‘model-free’ temporal-difference algorithms. Goal-
directed control relies on the prospective consideration of actions and their
outcomes, which can be captured by forward-planning ‘model-based’ algorithms.
So far, no studies have examined behavioral and neural signatures of model-
free and model-based control in healthy high-impulsive individuals. Fifty
healthy participants were drawn from the upper and lower ends of 452
individuals, completing the Barratt Impulsiveness Scale. All participants
performed a sequential decision-making task during functional magnetic
resonance imaging (fMRI) and underwent structural MRI. Behavioral and fMRI
data were analyzed by means of computational algorithms reflecting model-free
and model-based control. Both groups did not differ regarding the balance of
model-free and model-based control, but high-impulsive individuals showed a
subtle but significant accentuation of model-free control alone. Right lateral
prefrontal model-based signatures were reduced in high-impulsive individuals.
Effects of smoking, drinking, general cognition or gray matter density did not
account for the findings. Irrespectively of impulsivity, gray matter density
in the left dorsolateral prefrontal cortex was positively associated with
model-based control. The present study supports the idea that high levels of
impulsivity are accompanied by behavioral and neural signatures in favor of
model-free behavioral control. Behavioral results in healthy high-impulsive
individuals were qualitatively different to findings in patients with the same
task. The predictive relevance of these results remains an important target
for future longitudinal studies