Distinct organization of two cortico-cortical feedback pathways

Area of Science:

• Neuroscience
• Computational Neuroscience
• Systems Neuroscience

Background:

• Neocortical feedback is crucial for cognitive functions like attention, prediction, and learning.
• Understanding the cell-type specific wiring of these feedback circuits is key to deciphering their function.
• Previous work identified disinhibitory feedback targeting vasoactive intestinal peptide (VIP)-expressing interneurons in the motor cortex.

Purpose of the Study:

• To investigate whether the disinhibitory feedback motif observed in the motor cortex is a general principle for cortico-cortical feedback.
• To characterize the cell-type specificity and functional impact of feedback from a higher-order visual area to the primary visual cortex.
• To compare the dynamic operations implemented by different cortico-cortical feedback circuits.

Main Methods:

• In vivo electrophysiology in mice.
• Optogenetic manipulation of specific neuronal populations.
• Analysis of neuronal firing patterns under different input conditions (sustained vs. transient).

Main Results:

• Feedback from the lateromedial (LM) visual area to the primary visual cortex (V1) preferentially activates somatostatin (SST)-expressing interneurons, contrasting with the VIP-targeting rule in the motor cortex.
• Both feedback circuits temporally sharpen feed-forward excitation, causing an initial increase followed by a decrease in pyramidal cell activity under sustained input.
• Under transient feed-forward input, motor cortex feedback promotes bursting, while LM-V1 feedback enhances temporal precision.

Conclusions:

• Cortico-cortical feedback circuits exhibit diverse cell-type specific wiring principles.
• Different feedback motifs implement distinct dynamic non-linear operations, contributing uniquely to information processing.
• These findings challenge the notion of a single feedback organizing principle and highlight circuit-specific computations.