NUCLEUS ACCUMBENS DOPAMINE SIGNALLING THAT LINKS PREDICTIVE CODING AND MOTIVATIONAL SALIENCE THROUGH THE ENCODING OF STATISTICAL DEVIANCE

This study investigated whether nucleus accumbens (NAc) dopamine encodes sensory prediction errors (SPE) for non-rewarding stimuli, challenging the traditional view that dopamine signaling is primarily limited to reward-related information. Using fiber photometry with the GRAB-DA2m sensor in freely moving rats, we implemented an oddball paradigm to validate NAc dopamine as a general SPE encoder. First, we demonstrated that unpredicted deviant stimuli evoke significantly larger biphasic responses compared to both predicted standards and physically identical controls. By decomposing these responses, we identified that while the initial positive peak aligns with stimulus salience, the subsequent negative phase specifically carries the prediction error signal. To define the temporal scope of this system, we extended the inter-stimulus interval to 1.65 seconds; the persistence of deviance detection at this interval reveals a broader temporal integration window than that of cortical mismatch negativity (MMN). Furthermore, we employed an omission paradigm to strictly dissociate prediction error signals from stimulus-driven activity. Dopamine responded to expected but missing stimuli in a manner significantly modulated by predictability, thereby isolating pure prediction errors from simple sensory offsets. Finally, by showing dopamine’s deviance detection within two-tone oddball sequences, we confirmed the capacity of this system to monitor complex auditory structures. Collectively, these findings suggest that NAc dopamine processes SPE, evaluating environmental changes even in the absence of reward.