State-Dependent Modulation of Activity in Distinct Layer 6 Corticothalamic Neurons in Barrel Cortex of Awake Mice

Area of Science:

• Neuroscience
• Sensory processing
• Cortical circuits

Background:

• Layer 6 corticothalamic (L6 CT) neurons are crucial for sensory input to the neocortex.
• Their function during behavior remains poorly understood due to challenges in accessing their activity.

Purpose of the Study:

• To investigate the in-vivo activity of L6 CT neurons during natural behaviors in awake mice.
• To characterize the diversity of L6 CT neuron responses and their relationship to whisking, locomotion, and arousal states.

Main Methods:

• Juxtacellular recordings from optogenetically identified L6 CT neurons in the whisker somatosensory cortex (wS1) of awake mice.
• Monitoring of spontaneous whisking, locomotion, and pupil diameter during quiet wakefulness.

Main Results:

• L6 CT neurons displayed diverse spiking patterns: ~28% were modulated by whisking, showing activation or suppression aligned with whisking onset.
• ~72% of L6 CT neurons were unresponsive to whisking, with some exhibiting sparse firing during transitions to quiet wakefulness.
• Whisking behavior better explained firing rate changes than overall arousal levels.

Conclusions:

• L6 CT neurons in wS1 exhibit significant response diversity, suggesting distinct functional roles.
• These neurons may contribute to precisely timed sensory processing during complex behaviors and state transitions.
• Different L6 CT populations could differentially modulate thalamocortical excitability in awake, behaving animals.