- 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

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

New M1

- 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")

Smith College

- Region of the brain involved in the initiation of movement 
- Specific regions of the motor cortex are associated with the movement of individual body parts/muscles ("maps" of M1 exhibit this concept)
- The M1 exhibits "learning" when movement is habituated

Primary Motor Cortex (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

- As show below, different regions of the body will take up dispropriate amounts of space in the M1
- Another way of visualizing this phenomena is through the "motor homunculus" which shows a figure's body parts enlarged to various degrees, based on the space it takes up in the motor cortex 
- However, this has been described as "oversimplifying"  the organization of the M1, which can be increasingly complex

Size Breakdown of M1

- As an organism continues to repeat the same movement over and over (such as grasping an object, or being able to point at an object) it will take less "effort" for the brain to initiate this movement
- This makes the organism more efficient in its ability to complete certain tasks
- This is evidence of an organism's ability to learn

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