Translaminar synchronous neuronal activity is required for columnar synaptic strengthening in the mouse neocortex

Area of Science:

• Neuroscience
• Developmental Neuroscience
• Cortical Development

Background:

• Synchronous neuronal activity is crucial in the developing brain.
• Layer 2/3 activity in the mouse somatosensory cortex is well-documented, but its source remains unclear.

Purpose of the Study:

• To identify the source of synchronous neuronal activity in developing cortical layer 2/3.
• To investigate the role of layer 5 inputs in synchronizing barrel column activity.

Main Methods:

• In vivo 2-photon imaging in neonatal mice using a novel microprism preparation.
• Monosynaptic rabies tracing and slice electrophysiology.
• Silencing experiments targeting layer 5 synaptic outputs.

Main Results:

• Synchronous neuronal activity is organized across layers within barrel columns.
• Layer 2/3 pyramidal neurons receive substantial input from layer 5 neurons early in development.
• Layer 5 silencing significantly reduced spontaneous activity, altered sensory-evoked responses, and disrupted layer 4-layer 2/3 connections.

Conclusions:

• Translaminar layer 5 to layer 2/3 connectivity is vital for synchronizing the developing barrel column.
• This connectivity ensures the strengthening of layer 4-layer 2/3 connections, supporting canonical cortical organization.