Development and plasticity of complex movement representations.

Area of Science:

• Neuroscience
• Developmental Neuroscience
• Motor Control

Background:

• Mammalian motor cortex exhibits topographic organization into body part representations (motor maps).
• Adult rat studies show forelimb motor cortex encodes complex movements (elevate, advance, grasp, retract) via distinct areas.
• Developmental emergence and plasticity of these complex motor maps remain largely unknown.

Purpose of the Study:

• To determine the emergence and topography of complex forelimb movement representations in developing rats (postnatal days 13-60).
• To investigate how reduced cortical inhibition affects these developing maps.
• To examine the influence of skilled forelimb motor training on map topography.

Main Methods:

• Long-duration intracortical microstimulation (LD-ICMS) was used in rats across different postnatal days.
• Experiments involved conditions of reduced cortical inhibition (pharmacological manipulation) and skilled motor training.
• Analysis focused on the emergence and spatial distribution of evoked simple and complex forelimb movements.

Main Results:

• Simple forelimb movements appeared at postnatal day 25 in the caudal forelimb area (CFA); complex movements emerged at postnatal day 30 in both CFA and rostral forelimb area (RFA).
• During development, complex movement topography reorganized, with 'grasp' and 'elevate' primarily in RFA and all four in CFA.
• Reduced cortical inhibition advanced movement emergence and altered map topography; skilled training increased 'grasp' and 'retract' representations.

Conclusions:

• Complex forelimb movement representations develop progressively and undergo topographical reorganization during maturation.
• Early motor experience, including skilled learning and altered cortical inhibition, can significantly modify the developing motor cortex map topography.
• This study reveals critical insights into the developmental plasticity of complex motor control representations.