Functional dynamics and selectivity of two parallel corticocortical pathways from motor cortex to layer 5 circuits in...

Area of Science:

• Neuroscience
• Sensory processing
• Cortical circuits

Background:

• Active sensing and sensorimotor integration rely on dynamic interactions between the motor cortex (M1) and somatosensory cortex (S1).
• Understanding these interactions requires detailed knowledge of synaptic connections and neuronal responses within S1.
• Layer 5 (L5) of S1 contains distinct neuronal populations, including intratelencephalic (IT) and pyramidal tract (PT) neurons, which receive input from M1.

Approach:

• Combined optogenetics, retrograde labeling, and electrophysiology in mice (both sexes).
• Characterized synaptic connections between M1 and S1 L5 IT and PT neurons.
• Investigated short-term synaptic dynamics and postsynaptic responses to M1 input.

Key Points:

• M1 synapses onto S1 IT cells show short-term depression, while synapses onto S1 PT neurons exhibit robust short-term facilitation.
• Despite depression, M1 inputs to IT cells summate due to slower kinetics, enhancing responses during short trains.
• Facilitating M1 inputs to PT neurons lead to larger response amplitudes and increased burst probability during repetitive stimulation.

Conclusions:

• Two parallel, dynamically distinct systems of M1 synaptic excitation exist in S1 L5.
• These systems are defined by unique short-term synaptic dynamics, postsynaptic neuron classes, and response patterns.
• These findings elucidate how M1 differentially modulates S1 activity during sensory processing.