Neurosurgeon Wilder Penfield first mapped the cortex in humans while operating on the brains of patients with epilepsy and other disorders. Together, they form a full, representative map of your body called a "homunculus," which means "little man" in Latin. Instead, they're grouped by body part - all of the hand neurons together, then all of the face neurons, then the tongue neurons and so on, as you can see in the diagram of the motor cortex. The neurons in the motor cortex and somatosensory cortex aren't just thrown together in a big jumble of cells. The motor nerves that helped you move your finger connect to the "motor cortex," while the sensory nerves that tell your brain about a feeling (like texture) connect to the "somatosensory cortex." In the brain, those lines converge in a region called the cortex. The signals in both directions - brain to finger and finger to brain - run along particular pathways, says Michael Paradiso, a Brown University neuroscientist. They send a series of impulses that your brain interprets as texture - rough or smooth. You read the directions, and your brain gives your fingers a set of instructions that say, "Rub." But how did your mind deliver the message to your fingers?Īt the same time, your fingers are giving your brain a set of instructions about the floor as well. Reach down and rub the rug or floor below you. In the motor homunculus (right), the fingers are even larger because of the complex range of motion involved in activities like typing or grasping an object. In the somatosensory homunculus (left), that's because your fingers receive so much sensory data as they touch the world around you. In both of the "little men," the fingers appear enormous. Put together all the disproportionate body parts from your cortical maps, and you get homunculus men- little guys that look more cartoon than human.
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