Lower limb sensorimotor network: issues of somatotopy and overlap

Area of Science:

• Neuroscience
• Motor Control
• Neuroimaging

Background:

• Understanding brain activity during lower limb movement is crucial for motor control research.
• Previous studies have detailed finger movement representations, but lower limb joint organization requires further investigation.

Purpose of the Study:

• To map whole-brain activity during isolated lower limb joint movements using fMRI.
• To investigate the somatotopic organization of knee, ankle, and toe representations in the primary sensorimotor cortex and cerebellum.
• To quantify the overlap in brain activation patterns for these lower limb joints.

Main Methods:

• Functional magnetic resonance imaging (fMRI) in a block-design study.
• Eighteen healthy volunteers performed repetitive knee, ankle, and toe flexion/extension movements, paced auditorily.
• Finger-to-thumb opposition was assessed for comparison with known motor maps.

Main Results:

• Isolated lower limb joint movements activated a widespread sensorimotor network, including primary and non-primary areas.
• A significant overlap was observed in the primary sensorimotor cortex (SM1) and cerebellum representations for the three lower limb joints.
• Despite overlap, a discernible somatotopic arrangement was identified based on the center of mass coordinates for each joint.

Conclusions:

• fMRI can detect brain regions active during lower limb joint movements.
• A somatotopic organization, albeit with considerable overlap, exists for lower limb joints in the primary sensorimotor cortex and cerebellum.
• Optimized fMRI protocols are essential for reliable detection of brain activity during lower limb movements.