Free Inventing Iron Man by E. Paul Zehr Page B

huge advance in the ability to record a large numbers of neurons simultaneously.
Creating Commands from the Cortex
    An important insight into the role of the cortex in movement control came from the work of John Hughlings Jackson (1835–1911). He was a British neurologist who studied patients with epilepsy. His clinical observations suggested to him that certain parts of the brain must be closely related to specific motor commands. He saw that during a seizure there was a consistent and organized spread of muscle contraction across the body. This made him think that certain parts of the brain should have specific actions in causing movement and that the whole system must be organized in a way reminiscent of the layout of the body. However, he had to wait until the work of Gustav Fritsch (1838–1927) and Eduard Hitzig (1838–1907) for confirmation. Fritsch, while working as a military surgeon had noticed that hisefforts to treat a head wound would sometimes (accidentally) cause small contractions on the side of the body opposite to the injury. In 1870 Fritsch and Hitzig used electrical stimulation of the brain to generate detailed maps of the brain of the dog and showed clearly that movements could be created by stimulating certain brain areas. So, at this point it was known that electrical stimulation of certain parts of the brain (but not others) could evoke twitches in muscles of the body and that there was a kind of map of the body muscles represented somehow by the neurons in the brain. These studies also revealed that the control of activity in muscles is generally found on the opposite side of the brain. If you are using your right hand to turn the pages of this book, it is the cells in the motor cortex of the left side of your brain that are sending the commands. Also, if you choose to turn the page with your left hand, it’s the command cells in the motor cortex on the right side.
    Canadian neurologist Wilder Penfield and his friend Edwin Boldrey followed up on this work of locating the centers for different functions in the human brain. They did a detailed stimulation exercise and found that they could generate a kind of “map” of the muscles of the body from stimulation of the brain. The basic concept is this: if you give electrical pulses of stimulation to the motor areas of the brain, you can trigger the output cells of the brain to relay commands to the cells in the spinal cord that activate muscle. By moving electrodes over the surface of the brain, movements in different muscles can be observed. Through painstaking effort, it is possible to create a kind of input-output map of the surface of the brain, which is weighted differently depending upon how much area (and therefore numbers of cells) on the brain are devoted to a particular part of the body. Think of how a huge city with 15 highway interchanges compares with a small village with no exits off a highway are represented on a road map.
    Penfield and Boldrey’s work was the basis for the “homunculus” (little man) concept that describes the map of the muscles of the body on the surface of the brain ( figure 3.5 ). The surface area of the body on the map is an indication of the number of brain cells controlling those muscles. These cells are found in the “motor execution” part of the brain shown in figure 3.4 . We also have similar maps related to the sensory areas of the brain. In that case, the maps are created by recording activity of brain cells when different skin areas are activated. Understanding this is important in grasping whether it mightbe possible to tap into this system to control computers and robotic devices. To set the stage for that, I think it is probably useful to ensure that we understand how movement commands arise and are relayed.

    Figure 3.5. “Map” of the neurons (upper motor neurons) in the brain used for activating muscle. The distorted shapes of the body part represent the