The interplay between somatic and dendritic inhibition balances increased excitatory synaptic weights so that place cell firing returns to baseline.

(A) Diagram of an unstable place cell becoming stable after several laps of exploration of a novel environment (see Methods). Place cells are assumed to be unstable due to their sensitivity to noise. (B) Evolution of dendritic activity for an example place cell. Inset: first 10 laps of exploration. (C) Dendritic activity as a function of the animal’s position for three stages of the simulation: lap 1 (top, blue; blue dashed line in (B)), lap 5 (middle, purple; purple dashed line in (B)), and lap 100 (bottom, orange; orange dashed line in (B)). (D) Evolution of somatic activity for the same cell as in (B). Inset: first 10 laps of exploration. (E) Somatic activity as a function of the animal’s position for three stages of the simulation: lap 1 (top, blue; blue dashed line in (D)), lap 5 (middle, purple; purple dashed line in (D)), and lap 100 (bottom, orange; orange dashed line in (D)). (F) Evolution of mean dendritic (dashed line) and somatic (solid line) activity for the same example cell as in (B) and (D). Stars indicate laps 1 (blue), 5 (purple) and 100 (orange). Both somatic and dendritic activities increase sharply during the first laps of exploration due to synaptic plasticity. Inset: first 10 laps of exploration. (G) Diagram showing the changes in the network from the first to the last lap of exploration. Initially (left, blue), input synaptic weights are weak, dendritic inhibition is low and somatic inhibition is high. Next, synaptic weights are quickly strengthened through activity-dependent synaptic plasticity (middle, purple). During the final lap (right, orange), some input synaptic weights are strong, dendritic inhibition is high and somatic inhibition is low. Therefore, although place field amplitude and width are the same in the first and last lap (D blue and orange), the network is in a different state.