Activity-dependent plasticity improves M1 motor representation and corticospinal tract connectivity.

Area of Science:

• Neuroscience
• Developmental Neuroscience
• Motor Control

Background:

• Motor cortex (M1) activity from postnatal weeks 5-7 is crucial for corticospinal tract (CST) development and visually guided movements.
• Unilateral M1 inactivation during this period leads to permanent deficits in CST termination patterns and motor skills.

Purpose of the Study:

• To investigate the impact of alternate M1 inactivation on the motor representation of the initially inactivated M1.
• To understand the plasticity of M1 motor maps in relation to CST development.

Main Methods:

• Utilized intracortical muscimol infusion for reversible M1 inactivation in rodents.
• Employed intracortical microstimulation to map M1 motor representations post-inactivation.
• Compared motor maps between unilateral and alternate inactivation groups.

Main Results:

• Alternate inactivation transformed a sparse M1 motor representation into a complete proximal-distal map.
• The M1 motor map was restored by week 11, coinciding with CST spinal connectivity recovery.
• Motor skill recovery lagged behind motor map restoration, requiring an additional 3 weeks.

Conclusions:

• M1 motor map plasticity parallels CST spinal termination plasticity during development.
• Restoration of the M1 motor map is necessary but not sufficient for immediate motor skill recovery.
• Additional time and experience are required to utilize restored neural pathways for motor function.