Hippocampal pyramidal cells encode memory engrams, which guide adaptive behavior.
Selection of engram-forming cells is regulated by somatostatin-positive dendrite-targeting
interneurons, which inhibit pyramidal cells that are not required for memory formation.
Here, we found that gamma-aminobutyric acid ( GABA)-releasing neurons of the mouse
nucleus incertus (NI) selectively inhibit somatostatin-positive interneurons in the
hippocampus, both monosynaptically and indirectly through the inhibition of their
subcortical excitatory inputs. We demonstrated that NI GABAergic neurons receive monosynaptic
inputs from brain areas processing important environmental information, and their
hippocampal projections are strongly activated by salient environmental inputs in
vivo. Optogenetic manipulations of NI GABAergic neurons can shift hippocampal network
state and bidirectionally modify the strength of contextual fear memory formation.
Our results indicate that brainstem NI GABAergic cells are essential for controlling
contextual memories.