- The "old" region of the M1 lacks CM cells, and is typically found in mammals. This region communicates with the spinal cord/ related pathways to perform motor output

Smith College

- Recent studies have looked at the cell types that constitute the M1, and have utilized a cell population known as cortico-motoneuronal cells (CM) to differentiate between different regions of the M1 (described as "old" vs "new")

Subdivisions of M1

Rathelot JA, Strick PL (2009). Subdivisions of primary motor cortex based on cortico-motoneuronal cells. Proc Natl Acad Sci U S A, 106:918–923. https://doi.org/10.1073/pnas.0808362106 

Subdivisions of primary motor cortex based on cortico-motoneuronal cells

Old M1

- The "new" region of the M1 contains CM cells, and has been found in higher primates and in humans. This region utilizes CM cells to forgo communication pathways associated with the spinal cord in order to create motor outputs from the shoulder, finger, and elbow

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