What would you do if you were a doctor and had patients who were missing pieces of their skulls? If you were Eduard Hitzig, a German doctor working at a military hospital in the 1860s, you'd conduct some experiments. Hitzig, working on patients who had pieces of their skulls blown away in battle, stimulated exposed brains with wires connected to a battery. By doing so, he discovered that weak electric shocks, when applied to areas at the back of the brain, caused the patients' eyes to move.
Wilder Penfield, a pioneering brain surgeon, mapped the motor cortex using mild electric current.
Later, around 1870, Hitzig teamed up with another doctor, Gustav Fritsch. Setting up a makeshift lab in Fritsch's house, the two stimulated the brains of live dogs. They found that not only could they cause crude movements of the dogs' bodies, but that specific areas of the brain controlled specific movements.
John Hughlings Jackson, an English scientist, soon after took the work of Fritsch and Hitzig even further. Based on his observations of his wife's epileptic seizures, Jackson came up with a more detailed theory of how the brain controls muscles. He knew that every one of her seizures followed the same pattern: It would start at one of her hands, move to her wrist, then her shoulder, then her face. It would finally affect the leg on the same side of her body, then stop.
Jackson believed that the seizures were electrical discharges within the brain. The discharges started at one point and radiated out from that point. This suggested that the brain was divided into different sections, and that each section controlled the motor function (or movement) of a different part of the body. And since the pattern never varied, the way the brain is organized must also be set.
A brain exposed during surgery.
Wilder Penfield took the next exploratory voyage into the brain starting in the 1940s. While operating on epileptic patients, Penfield applied electric currents to the surface of patients' brains in order to find problem areas. Since the patients were awake during the operations, they could tell Penfield what they were experiencing. Probing some areas triggered whole memory sequences. For one patient, Penfield triggered a familiar song that sounded so clear, the patient thought it was being played in the operating room.
During these operations, Penfield watched for any movement of the patients' bodies. From this information, he was able to map the motor cortex, the very part of the brain you can map in this feature's activity.