Hippocampal input-driven plasticity of prefrontal interneurons reveals a circuit basis for impaired spatial working memory.

Dynamic functional connectivity between the ventral hippocampus (vHPC) and medial prefrontal cortex (mPFC) is essential for spatial working memory (SWM). Interactions between vHPC projections and mPFC interneurons, and their plasticity, are uniquely positioned to influence SWM, yet the nature of these interactions remains unclear. Here, we combined optical stimulation of vHPC inputs to mPFC with calcium recordings of discrete mPFC interneuron populations in mice, revealing class-specific response profiles and plasticity. Repeated vHPC input stimulation persistently depressed activity in vasoactive intestinal peptide (VIP)-expressing interneurons and potentiated activity in somatostatin-expressing interneurons. whole-cell electrophysiology and computational modeling revealed that these divergent effects likely arise from a primary weakening of monosynaptic vHPC input onto VIP interneurons. Leveraging this plasticity to inform the circuit interactions that support SWM, we found that mice with prior vHPC input stimulation displayed elevated VIP interneuron activity during the delay epoch in early SWM task training, and this enhanced activity correlated with poorer training performance. Accordingly, mice modeling the schizophrenia-predisposing 22q11.2 deletion syndrome with known SWM learning deficits recapitulated this aberrant VIP interneuron activity profile and showed reduced vHPC targeting of mPFC VIP interneurons. Together, these findings reveal novel cell-type-specific plasticity in cognition-supporting circuits and illustrate how reweighting of inputs to VIP interneurons may contribute to working memory dysfunction.