Thalamocortical and Intracortical Inputs Differentiate Layer-Specific Mouse Auditory Corticocollicular Neurons

Area of Science:

• Neuroscience
• Auditory System Research
• Cortical and Thalamic Networks

Background:

• Long-range descending projections from the auditory cortex modulate the inferior colliculus.
• The auditory corticocollicular projection originates from cortical layers 5 and 6.
• Understanding the network integration of these projection neurons is limited.

Purpose of the Study:

• To investigate the differences in cortical and thalamic inputs to layer 5 and layer 6 auditory corticocollicular neurons.
• To explore the network embedding of these distinct neuronal populations.
• To validate a novel method for separating direct and indirect neural inputs.

Main Methods:

• Laser scanning photostimulation, glutamate uncaging, and channelrhodopsin-2 photoactivation were employed.
• Pre-identified layer 5 and layer 6 auditory corticocollicular neurons from mice were studied *in vitro*.
• A low-calcium/synaptic blockade approach was validated to distinguish direct inputs.

Main Results:

• Layer 5 corticocollicular neurons exhibited greater integration of supragranular excitatory and inhibitory inputs compared to layer 6.
• All layer 5 neurons received direct, substantial thalamic input, while layer 6 neurons received such input less frequently.
• Distinct cortical and thalamic input patterns were identified for layer 5 and layer 6 corticocollicular neurons.

Conclusions:

• Layer 5 and 6 corticocollicular neurons receive different cortical and thalamic inputs, supporting divergent functional roles.
• The direct thalamocortical connection to layer 5 neurons represents a novel, rapid link between ascending and descending auditory pathways.
• This study reveals distinct network integration and a new pathway for rapid online modulation of sensory perception.