Dr. Rustin Berlow locates M1, the primary motor cortex for TMS stimulation.

The next area we’re going to discuss is what’s called M1 or the primary motor cortex. Its very easily located by taking half the distance of nasion to inion, and essentially, just a little bit in front of that because CZ is usually the central sulcus, and so right in front of that is the motor cortex or the primary motor cortex.

The anatomy of the motor cortex is that the feet and legs are at the top, and then the arms, and then the hands, and then the fingers, and then the thumb and down here are the face and the mouth (below the thumb). So, when stimulating the hand area, one stimulates here (below the leg area). The leg area is up here (on top). M1 is important because most of the neurological studies stimulating the brain with TMS – especially with Parkinson’s disease – have been at M1. So, when lining up the M1, you have several different options, depending on how medial or lateral you are. The more lateral, you want to take more of a 45-degree angle and usually, for stroke, the stimulation is contralateral.