The motor cortex is a strip of brain tissue running across the top of the head, organized into a map where different regions control different body parts. Neurons in the hand area fire when you move (or even intend to move) your fingers; neurons in the leg area activate during walking. This somatotopic organization makes the motor cortex the primary implantation target for BCIs aimed at restoring movement or communication to people with paralysis.
When a person with spinal cord injury thinks about moving their hand, motor cortex neurons still fire in characteristic patterns — the brain's movement commands simply cannot reach the muscles. BCIs exploit this by recording these "stranded" signals and routing them to external devices. The BrainGate trials and Neuralink's initial human implants both target the hand and arm areas of the motor cortex, decoding intended movements to control cursors, robotic limbs, or even the patient's own muscles through functional electrical stimulation.
Research is expanding BCI targeting beyond the motor cortex. Speech-related BCIs target the ventral premotor and inferior frontal areas to decode attempted speech. Cognitive BCIs may eventually target prefrontal regions. However, the motor cortex remains the best-understood and most reliably decoded brain region, making it the foundation upon which the clinical BCI field is built. Understanding motor cortex physiology is essential for designing effective electrode placements and decoding algorithms. For deeper coverage, see BCIIntel.