The involvement of the dopaminergic midbrain and cortico-striatal-thalamic circuits in the integration of reward prospect and attentional task demands.

Reward has been shown to promote human performance in multiple task domains. However, an important debate has developed about the uniqueness of reward-related neural signatures associated with such facilitation, as similar neural patterns can be triggered by increased attentional focus independent of reward. Here, we used functional magnetic resonance imaging to directly investigate the neural commonalities and interactions between the anticipation of both reward and task difficulty, by independently manipulating these factors in a cued-attention paradigm. In preparation for the target stimulus, both factors increased activity within the midbrain, dorsal striatum, and fronto-parietal areas, while inducing deactivations in default-mode regions. Additionally, reward engaged the ventral striatum, posterior cingulate, and occipital cortex, while difficulty engaged medial and dorsolateral frontal regions. Importantly, a network comprising the midbrain, caudate nucleus, thalamus, and anterior midcingulate cortex exhibited an interaction between reward and difficulty, presumably reflecting additional resource recruitment for demanding tasks with profitable outcome. This notion was consistent with a negative correlation between cue-related midbrain activity and difficulty-induced performance detriments in reward-predictive trials. Together, the data demonstrate that expected value and attentional demands are integrated in cortico-striatal-thalamic circuits in coordination with the dopaminergic midbrain to flexibly modulate resource allocation for an effective pursuit of behavioral goals.