Fig. 6: The inhibition of deep layer cells by SOM⁺ GABAergic interneurons regulates short-term memory formation without influencing spatial navigation.

a Schematic indicating the design of the Y-maze experiment combined with optogenetic stimulation of SOM⁺ cells in the MEC. Light was illuminated into the MEC during exploration, when animal was in the center area (gray). Alternation was considered correct, when after two entries (e.g., arms #1, #2) the animal entered the unvisited (#3) arm. b Correct spontaneous alternations of ChR2-expressing SOM-Cre (left), EGFP-expressing SOM-Cre (middle), and ChR2-expressing PV-Cre animals (right) during control (CTRL) and during ChR2 exciting light (ON) (*p < 0.05, paired Student’s T test). c Schematic representing the Morris water-maze experiments. Light pulses exciting ChR2⁺ SOM cells were applied while the animal was finding the hidden platform on the last day (day 6) of the trainings. d Escape latencies of ChR2-expressing SOM-Cre (left), EGFP-expressing SOM-Cre (middle), and ChR2-expressing PV-Cre animals (right) during control (CTRL) and during light pulses (ON). e Schematic summarizing the network motif revealed in the present study. Layer_II pyramidal (black, left), layer_II stellate (black, right), layer_III–V pyramidal (black, bottom), PV⁺ interneuron (PV, blue), and SOM⁺ interneuron (SOM, red). Thicker axons represent stronger inhibition on the targeted cells.