The Somatosensory Cortex

They say a picture is worth a thousand words, but hopefully this conveys the idea brilliantly. If you tap the palm of your left hand, a sensory neuron fires - there are receptors underneath your skin for touch, cold, hot, pain, etc across your entire body. The message is sent up the spinal cord to the thalamus and then onto the somatosensory (or primary) sensory cortex. The firing of a neuron in the somatosensory cortex then is a literal representation of your body in space. Put it this way, if I directly stimulated the same neuron in the somatosensory cortex with a small amount of electricity using a probe - you would think you were touching the palm of your hand! (For the Sci Fans, this is part how "The Matrix" would work).