Current flow in vibrissa motor cortex can phase-lock with exploratory rhythmic whisking in rat

Area of Science:

• Neuroscience
• Motor Control

Background:

• Rats use rhythmic vibrissae sweeps for environmental exploration.
• The role of the primary motor cortex (M1) in initiating whisking is unclear.

Purpose of the Study:

• To investigate if vibrissa M1 cortex activity synchronizes with whisking behavior.
• To determine if this synchronization is sensory-dependent.

Main Methods:

• Rats were trained to whisk for rewards.
• Electromyography (EMG) of the mystacial pad measured whisking.
• Field potentials were recorded from vibrissa M1 and S1 cortices using multi-channel probes.
• Current source density analysis estimated radial current flow.

Main Results:

• M1 cortex current flow showed coherence with mystacial EMG, indicating synchronized activity.
• This M1-EMG coherence persisted even after transecting the infraorbital nerve (IoN), the primary sensory input for vibrissae.
• Coherent current flow was also observed in S1 cortex, persisting after IoN transection.

Conclusions:

• M1 cortex electrical activity is phase-locked to whisking movements.
• This motor-sensory coupling in M1 and S1 is independent of direct vibrissal sensory input.
• The findings support the hypothesis that M1 cortex can initiate vibrissae motion rhythmically.