Superficial Layers Suppress the Deep Layers to Fine-tune Cortical Coding

Area of Science:

• Neuroscience
• Sensory processing
• Cortical circuitry

Background:

• The descending pathway from cortical layer 2/3 (L2/3) to layer 5 (L5) is a major excitatory connection in the cortex.
• Understanding the in vivo functional role of this L2/3 to L5 pathway during active sensation is crucial but remains poorly understood.

Purpose of the Study:

• To investigate the functional impact of L2/3 neuronal activity on L5 during active sensory perception.
• To elucidate the role of specific interneurons in mediating the L2/3 to L5 pathway's influence.

Main Methods:

• Utilized optogenetic, cell-type-specific manipulation of L2/3 neurons in the barrel cortex of actively sensing mice.
• Recorded and analyzed the activity of L5 neurons in response to sensory stimuli under different L2/3 manipulation conditions.

Main Results:

• Contrary to established models, L2/3 activation predominantly suppressed spontaneous L5 activity.
• L2/3 deactivation facilitated touch responses in L5.
• Optogenetic deactivation of somatostatin interneurons significantly altered the L2/3 to L5 functional impact, suggesting their involvement in the observed suppression.

Conclusions:

• The L2/3 to L5 pathway exerts a net inhibitory effect on L5 activity during active sensation.
• This translaminar inhibition enhances stimulus selectivity and expands the receptive field range of L5 output.
• The findings suggest that feedforward inhibition, mediated by L2/3, plays a key role in sharpening sensory perception.