Spinal circuits encode a map of the trunk to control skin twitches

Area of Science:

• Neuroscience
• Animal Behavior
• Spinal Cord Research

Background:

• Reflexive skin twitches are common mammalian behaviors triggered by touch.
• These twitches involve motor neurons in the cervical spinal cord controlling the cutaneous maximus muscle.
• Precise sensory-to-motor mapping is crucial for effective twitch responses.

Purpose of the Study:

• To elucidate the neural circuitry underlying spatially organized skin twitches.
• To identify specific neuronal populations and pathways involved in this sensory-motor behavior.
• To understand the spinal cord's role in representing external stimuli for motor actions.

Main Methods:

• Utilized mouse genetics and viral tracing techniques.
• Investigated projections from dorso-lateral dI3 neurons to motor neurons.
• Employed optogenetics to stimulate specific neural pathways and observe behavioral responses.

Main Results:

• Identified a subset of dI3 neurons projecting to motor neurons controlling skin twitches.
• Demonstrated somatotopic organization of these projections, mapping trunk space to motor pools.
• Optogenetic stimulation of dI3 projections successfully induced skin twitches.

Conclusions:

• dI3 neurons form a somatotopically organized ascending pathway in the spinal cord.
• This pathway mediates a spinal sensory-motor representation of the trunk.
• The identified circuit provides a basis for the mammalian skin-twitch reflex, aiding in irritant removal.