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Two different areas within the primary motor cortex of man
S Geyer1, A Ledberg, A Schleicher
1Department of Neuroanatomy, Heinrich Heine University Düsseldorf, Germany.
Nature
|August 29, 1996
Summary
The primary motor area (M1) is not homogeneous. New research shows area 4 in humans can be divided into 4 anterior (4a) and 4 posterior (4p), with distinct functions for finger representation.
Area of Science:
- Neuroscience
- Human Brain Anatomy
- Motor Cortex Function
Background:
- The primary motor area (M1), Brodmann's area 4, was traditionally viewed as structurally and functionally uniform.
- Previous studies suggesting dual representation of the arm and hand in M1 and distinct somatosensory connections were largely overlooked.
Purpose of the Study:
- To investigate the structural and functional subdivisions within the human primary motor area (M1).
- To determine if cytoarchitecture and neurochemistry support functional segregation within M1.
Main Methods:
- Quantitative cytoarchitectural analysis of human area 4.
- Quantitative analysis of transmitter-binding sites in area 4.
- Positron emission tomography (PET) to map finger representations during motor tasks.
Main Results:
- Human area 4 can be subdivided into '4 anterior' (4a) and '4 posterior' (4p) based on cytoarchitecture and neurochemistry.
- Two distinct representations of the fingers were identified using PET, one in 4a and one in 4p.
- Area 4p showed significantly greater activation during roughness discrimination compared to self-generated movements.
Conclusions:
- The primary motor area (M1) is not homogeneous and can be subdivided into functionally distinct regions (4a and 4p).
- These subdivisions are supported by differences in anatomy, neurochemistry, and functional activation patterns.
- This challenges the traditional view of M1 as a uniform structure.