NAc-DBS selectively enhances memory updating without effect on retrieval.

Deep brain stimulation (DBS) has emerged as a widely used therapeutic option when pharmacological treatments prove ineffective or refractory for psychiatric patients. The nucleus accumbens (NAc) represents a frequently targeted site in DBS interventions due to its demonstrated safety profile and therapeutic efficacy in obsessive-compulsive disorder, major depression, and anorexia nervosa. However, limited mechanistic understanding hampers its broader clinical applicability. This study sought to delineate the distinct behavioural dimensions modulated by NAc-DBS, its impact on distinct facets of memory, and to elucidate the underlying brain-network mechanism of action. We developed a novel spatial navigation task for rats and employed a high-dimensional behavioural analysis complemented by fMRI to dissect the cognitive, behavioural and neurobiological effects of NAc-DBS. Active NAc-DBS in male rats produced a selective enhancement of long-term memory encoding without affecting memory recall or working memory. We found a small but statistically significant rewarding effect of NAc-DBS, with no detectable impact on motor or stress-related behaviours. Sustained neuronal activation in the NAc, septum, entorhinal and insular cortex demonstrated no desensitisation to chronic NAc-DBS, which triggered a functional reorganisation among dopaminergic-related structures. These findings suggest that NAc-DBS induces a functional reorganisation in the mesocorticolimbic system, potentially mimicking a dopaminergic novelty signal to enhance memory updating. This provides a mechanistic basis for the therapeutic use of NAc-DBS, particularly in improving cognitive flexibility in psychiatric disorders.