We have recently done a similar experiment but in a spatial setting (VR) and see very different properties emerging across learning, stay tuned! Special kudos to our PhD student Ingeborg Nymoen who performed most of the experiments.

5/6: The responses are anatomically separated in MEC (but not in POR).

4/6: While POR neurons respond to cues and cue-outcome associations - only a few MEC neurons develop visual cue selectivity, but large populations develop a bias towards the reward or the cue-reward association

3/6: A large fraction of POR neurons are visual cue-responsive from the beginning as mice begin to learn the task, while MEC neurons develop responses especially to the plus cue during learning.

2/6: We compare the neural dynamics in postrhinal (POR) and medical entorhinal cortex (MEC) as mice learn a visual Go/NoGo task. Same cells recorded from completely naïve to expert and through rule reversal.

Check out the full paper here: www.nature.com/articles/s41...

In contrast, AAV-mediated ACAN knockout in adult mice increased ocular dominance plasticity. Moreover, in vivo Chondroitinase ABC treatment of KO mice resulted in reduced firing rate of PV+ cells. Suggesting that compensatory mechanisms may be activated in response to the germline loss of aggrecan.

We established both a germline knockout (KO) mouse model (ACANflx/PVcre) and an adeno-associated virus to eliminate aggrecan production from PV+ neurons. Surprisingly, electrophysiological properties of PV+ interneurons and ocular dominance plasticity of adult KO mice were similar to controls.

Strikingly different responses to visual stimuli in postrhinal (POR) cortex compared to MEC. Following the same neurons through the learning process. Single cell example from each region below.

www.biorxiv.org/content/10.1...

We find that reduction of PV+ neuron activity in offline periods after learning selectively attenuates reactivations and learning, with no apparent effects on normal function during training.