# Dual parallel stream-specific and generalized effects of corticogeniculate feedback on LGN neurons in primate and carnivore

## TL;DR

This study shows that brain feedback in visual circuits improves spatial resolution in specific pathways and timing across all pathways in primates and carnivores.

## Contribution

The study reveals dual roles of corticogeniculate feedback in stream-specific spatial resolution and general temporal precision.

## Key findings

- Optogenetic enhancement of CG feedback improved spatial resolution in magnocellular neurons but not parvocellular neurons.
- Enhanced CG feedback increased surround suppression and preferred spatial frequencies in magnocellular neurons.
- CG feedback also improved temporal response precision across all geniculate neuron types.

## Abstract

Sensory circuits are organized in parallel, e.g. parallel streams relay feedforward visual information from retina to cortex. Corticogeniculate (CG) feedback is also organized in parallel; however, stream-specific influences of CG feedback remained unresolved. We utilized optogenetics to manipulate CG feedback in monkeys while recording geniculate responses to a comprehensive set of visual stimuli designed to probe stream-specific responses. Here we show that CG feedback improved the spatial resolution of magnocellular, but not parvocellular neurons. Optogenetically enhancing CG feedback increased extraclassical surround suppression, shrunk classical receptive fields, and increased preferred spatial frequencies among magnocellular neurons. Optogenetically suppressing CG feedback reduced surround suppression. Enhancing CG feedback in female ferrets revealed similar stream-specific effects in geniculate Y, but not X neurons. Furthermore, optogenetically enhancing CG feedback improved temporal response precision across neuronal types. These results support dual functional roles for CG feedback in enhancing spatial resolution in a stream-specific manner and improving temporal precision broadly.

Whether feedback circuits exert control over how parallel visual information is relayed is not fully understood. Here authors utilized optogenetics to causally manipulate the activity of identified neuronal circuits, and showed that cortical feedback in the visual system operates in at least two modes: to regulate spatial resolution in a pathway-specific manner and to control the timing of incoming visual signals generally.