Infrabarrels Are Layer 6 Circuit Modules in the Barrel Cortex that Link Long-Range Inputs and Outputs

Area of Science:

• Neuroscience
• Cortical Circuitry
• Somatosensory System

Background:

• Rodent barrel columns are defined by layer 4 neuronal clusters.
• The organization of deeper cortical layers, particularly layer 6, remains less understood.
• Understanding distinct neuronal populations and their connectivity is crucial for deciphering cortical function.

Purpose of the Study:

• To investigate the organization of layer 6 neurons in the rodent somatosensory cortex.
• To characterize the connectivity and intrinsic properties of different neuronal populations within layer 6.
• To elucidate the functional role of infrabarrels in cortical processing.

Main Methods:

• Utilized the Ntsr1-Cre mouse line for cell-type-specific analysis.
• Employed optogenetic techniques to study neuronal activity and connectivity.
• Investigated intrinsic neuronal excitability through electrophysiological recordings.

Main Results:

• Identified infrabarrels in layer 6 that align with layer 4 barrels.
• Demonstrated that corticothalamic (CT) neurons and their axons cluster within infrabarrels.
• Showed that corticocortical (CC) neurons are densest between infrabarrels.
• Found CC cells receive strong thalamic input, while CT cells receive weaker input.
• Revealed CT neurons possess lower intrinsic excitability.

Conclusions:

• Infrabarrels represent discrete cortical circuit modules.
• These modules contain two partially segregated excitatory networks.
• The findings highlight both synaptic and intrinsic mechanisms underlying CT neuron activity.
• Infrabarrels integrate thalamic inputs with specific long-range cortical outputs.