# Selective plasticity of layer 2/3 inputs onto distal forelimb controlling layer 5 corticospinal neurons with skilled grasp motor training

## TL;DR

The study shows how specific brain circuits adapt during motor learning, strengthening connections that control precise movements like skilled grasping.

## Contribution

The paper reveals cell-specific plasticity in layer 2/3 projections onto distal forelimb corticospinal neurons during skilled grasp training.

## Key findings

- Layer 2/3 inputs onto distal forelimb neurons become significantly stronger with skilled grasp training.
- Excitatory response amplitude nearly doubles and latency shortens in trained animals.
- Excitatory-to-inhibitory latencies are prolonged following motor learning.

## Abstract

Layer 5 neurons of the neocortex receive their principal inputs from layer 2/3 neurons. We seek to identify the nature and extent of the plasticity of these projections with motor learning. Using optogenetic and viral intersectional tools to selectively stimulate distinct neuronal subsets in rat primary motor cortex, we simultaneously record from pairs of corticospinal neurons associated with distinct features of motor output control: distal forelimb vs. proximal forelimb. Activation of Channelrhodopsin2-expressing layer 2/3 afferents onto layer 5 in untrained animals produces greater monosynaptic excitation of neurons controlling the proximal forelimb. Following skilled grasp training, layer 2/3 inputs onto corticospinal neurons controlling the distal forelimb associated with skilled grasping become significantly stronger. Moreover, peak excitatory response amplitude nearly doubles while latency shortens, and excitatory-to-inhibitory latencies become significantly prolonged. These findings demonstrate distinct, highly segregated, and cell-specific plasticity of layer 2/3 projections during skilled grasp motor learning.

Takashima et al. uncover how neurons in the motor cortex adapt during skilled forelimb grasp training. They reveal that layer 2/3 projections strengthen connections to distal forelimb control neurons, enhancing motor control. These findings illuminate cell-specific plasticity in motor learning, shedding light on brain mechanisms behind skilled motor learning.