Functional Dynamics and Selectivity of Two Parallel Corticocortical Pathways from Motor Cortex to Layer 5 Circuits in...

Area of Science:

• Neuroscience
• Systems Neuroscience
• Sensory Systems

Background:

• Active sensing and sensorimotor integration rely on dynamic interactions between the motor cortex (M1) and somatosensory cortex (S1).
• Understanding these interactions necessitates detailed knowledge of synaptic connections and neuronal responses within the rodent whisker system.

Purpose of the Study:

• To characterize the synaptic connections between M1 and distinct neuronal populations (layer 5 intratelencephalic (IT) and pyramidal tract (PT) neurons) in S1.
• To elucidate how short-term synaptic dynamics influence neuronal responses and information processing during repetitive stimulation.

Main Methods:

• Combined optogenetics, retrograde labeling, and electrophysiology in mice (both sexes).
• Investigated synaptic properties and postsynaptic responses of S1 IT and PT neurons to M1 input.

Main Results:

• M1 synapses onto S1 IT cells showed short-term depression, while synapses onto PT neurons exhibited robust short-term facilitation.
• Despite depression, IT cells showed summation due to slower kinetics, whereas PT cells had minimal summation but larger responses due to facilitation during repetitive stimulation.
• Facilitating M1 inputs increased burst probability in PT cells without altering timing.

Conclusions:

• Two parallel, dynamically distinct systems of M1 synaptic excitation exist in S1 layer 5.
• These systems are differentiated by synaptic short-term dynamics, postsynaptic neuronal class, and response patterns, contributing to distinct sensorimotor processing pathways.