The only information you get about the world comes through your senses: your eyes, your ears, your balance sense, your nose, etc. The fundamental question is: How do the senses provide you with such accurate information about the world? An early idea -- proposed before anyone knew anything about how nerves worked -- said that tiny replicas (~models) of the things we see or hear travel up the peripheral nerves to the brain. We know now that neurons in the peripheral and central nervous systems use specialized neural signals. How can these neural signals represent the objects and events we perceive in the world about us? This is the problem of coding:
Individual neurons have two kinds of codes
Anatomical or labeled line coding tells the mind/brain where a stimulus is (for example, how you can tell a singing bird is up and to your left, or where is itches on your back) It also tells (usually) which kind it is (a small, red bird, singing two notes, or that it's an itch and not a touch or pain). J. Muller proposed this idea early in the 19th century code, calling it the Law of Specific Nerve Energies. Muller proposed that we see light when visual areas of the brain become active; we hear sound when auditory areas of the brain become active; we feel touch when somatosensory (~ touch) areas of the brain become active, etc. This idea opened the modern study of how the sense work.
This idea turned into labeled line (anatomical) coding when it was extended to explain the different qualities you experience within each sense: different colors of light, pitches in sound, touch, vibration, warmth, etc. on the skin, etc. Anatomical coding states that you experience different qualities when different parts of a sensory area become active.
Another, less common kind of kind,
temporal or (time) pattern codesignals the mind/brain the kind of stimulus by the pattern of nerve impulses. For example, one model of the code for itch is bursts of impulses on certain kinds of neurons from the skin interrupted by periods of no impulses.
Labeled line (anatomical) coding is based on two ideas: