Learning enhances the relative impact of top-down processing in the visual cortex.

Area of Science:

• Neuroscience
• Systems Neuroscience
• Computational Neuroscience

Background:

• Theories suggest learning modifies sensory cortices by altering top-down and bottom-up processing.
• Understanding the circuit mechanisms of these shifts is crucial for explaining learning-induced neural plasticity.

Purpose of the Study:

• To investigate the circuit mechanisms underlying learning-dependent changes in sensory processing.
• To examine the dynamic interplay between bottom-up and top-down information streams in the mouse primary visual cortex (V1) during associative learning.

Main Methods:

• Chronic two-photon calcium imaging in mouse V1 during associative learning.
• Recording activity from layer 2/3 (L2/3) excitatory neurons, layer 4 (L4) excitatory neurons, and retrosplenial cortex (RSC) projections.
• Inactivating RSC or activating somatostatin-expressing inhibitory neurons (SOM-INs) to assess their role.

Main Results:

• Learning weakened L4 (bottom-up) responses and strengthened RSC (top-down) inputs.
• L2/3 neurons developed ramp-up responses, mirroring RSC input changes.
• Learning reduced SOM-IN activity, potentially facilitating top-down modulation.
• RSC inactivation or SOM-IN activation partially reversed learning-induced L2/3 changes.

Conclusions:

• Associative learning induces a dynamic shift in the balance of bottom-up and top-down information flow in V1.
• SOM-INs play a critical role in gating and controlling these learning-dependent cortical circuit modifications.