In the 1940's, Roger Sperry did some interesting experiments on the frog visual system. I'll discuss them in a minute, but first let's look at his Chemoaffinity Hypothesis.
"It seems a necessary conclusion...that the cells and fibers of the brain and cord must carry some kind of individual identification tags, presumably cytochemical in nature, by which they are distinguished one from another almost, in many regions, to the level of the single neuron..." --Roger Sperry
In other words, each cell is specified by a distinct chemical label that signifies its address. Axons then grow, as we will see, to match this address to the address in the target, forming complementary labels.
*"In the early 1940s, Roger Sperry performed a series of insightful experiments on the visual system of lower vertebrates that led him to draw two important conclusions: When optic fibers were severed, the regenerating fibers grew back to their original loci in the midbrain tectum to re-establish a topographical set of connections; and the re-establishment of these orderly connections underlay the orderly behavior of the animal. From these conclusions, he inferred that each optic fiber and each tectal neuron possessed cytochemical labels that uniquely denoted their neuronal type and position and that optic fibers could utilize these labels to selectively navigate to their matching target cell. This inference was subsequently formulated into a general explanation of how neurons form ordered interconnections during development and became known as the chemoaffinity hypothesis. The origins of this hypothesis, the controversies that surrounded it for several decades and its eventual acceptance, are discussed in this article."
Fig. 4. Illustration of the optic nerve uncrossing surgery in frog and resulting behavior. In A, the normal optic chiasm is shown on the left wherein optic nerves cross to the contralateral side of the brain and the surgically uncrossed nerves are shown at the right wherein each optic nerve was deflected so as to regenerate to the ipsilateral side of the brain. In B, the mislocalization of flies by the frog with uncrossed optic nerves is shown by the position of the flies and the corresponding response indicated by the thick arrows. Taken from Scientific American article by Sperry.
*Taken from the abstract of Roger Sperry and his chemoaffinity hypothesis by Ronald L. Meyer
In other words, each cell is specified by a distinct chemical label that signifies its address. Axons then grow, as we will see, to match this address to the address in the target, forming complementary labels.
*"In the early 1940s, Roger Sperry performed a series of insightful experiments on the visual system of lower vertebrates that led him to draw two important conclusions: When optic fibers were severed, the regenerating fibers grew back to their original loci in the midbrain tectum to re-establish a topographical set of connections; and the re-establishment of these orderly connections underlay the orderly behavior of the animal. From these conclusions, he inferred that each optic fiber and each tectal neuron possessed cytochemical labels that uniquely denoted their neuronal type and position and that optic fibers could utilize these labels to selectively navigate to their matching target cell. This inference was subsequently formulated into a general explanation of how neurons form ordered interconnections during development and became known as the chemoaffinity hypothesis. The origins of this hypothesis, the controversies that surrounded it for several decades and its eventual acceptance, are discussed in this article."
*Taken from the abstract of Roger Sperry and his chemoaffinity hypothesis by Ronald L. Meyer
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