Our body is represented as spots on the sensory area in the brain. Each part of the body sends projections to one distinct portion of the sensory area in the brain. For example; we have portion for the legs hands abdomen trunk lips and so forth.so the lips send projections to the lips spot in the sensory area, the tongue to the tongue spot. We call this representation the homunculus or the small human, it is important to know that the body representation at the sensory area I'd disproportional to the body organ size. For example the lips are represented by large sopt compared to thier size and the truck is represented by a small spot despite it's large size so we have more sensations in the tongue compared to the trunk because we have more neurons disgenated for the tongue.

Please see this file for more clarification and images.

I am fascinated with this topic because my patients hear, see, smell, and even have tactile HALLUCINATIONS (some have what is called musical hallucinosis). Of course I ask for a neuro eval on all of them (but that rarely happens despite repeated requests especially with tactile and olfactory to r/o seizures, tumors, etc.). It is such a complex pathway where so much can go wrong. We all hear our name being called at times (or the phone/door bell ring when we get in the shower) which is normal (so what is up with that???) Seizues can cause some sensory events even gustatory!!! I'll be following this topic and will read the olson handout above. Some people respond to medications, those that don't and are bothered by evil voices, I suspect Transcaranial Magnetic Therapy might help (magnets outside of head, not internal like used for Parkinson's etc.)) in the sensory areas might work to stop them. (My clinic won't buy the machine, it is about $40,000).

The brain has to solve two problems--it has to get wired up correctly so that it can understand the outside world, and it has to have enough plasticity to learn to decode the outside world. Sensory systems are intensely studied in a variety of model animal systems because they give insight into the strategies used by the brain to accomplish these goals.

In addition to a particular sensory nerve (eg. the optic nerve (II) or auditory nerve (VIII)) projecting to a particular unique part of the brain (the 'target area"), there is a map within that area that helps the brain decode the information. For the auditory system there is a tonotopic map where different frequencies are decoded in different areas of the target. In the visual system there is a retinotopic map which allows the decoding of our visual space (right, left, up, down, etc.). Many of these maps are set up during embryonic development, but are refined by neuronal activity during the "critical period" so that inappropriate connections are eliminated. The plasticity of these connections is then greatly reduced by a variety of mechanisms so that the brain doesn't have to keep working so hard to make sure the connections remain correct.

However, not all plasticity is lost, and there is intense interest in how to reactivate these processes in a constructive manner to promote recovery of appropriate connections after damage, for instance after stroke or spinal cord damage.

In addition to the Olson handout, you might wish to find some basic undergraduate neurodevelopment textbooks. Personally, I like Development of the Nervous System by Sanes, Reh, and Harris:

https://www.amazon.com/Development-Nervous-System-Third-Sanes/dp/012374539X.

Happy reading!

Jill

I'm sorry I can't offer you the reference to this work, but it emphasizes the role of place in the brain rather than structure of the brain, indicating that cortex is pretty much cortex. If you cut a ferret's auditory nerve early enough in development, the optic nerve will project to the auditory cortex and not to the visual cortex. The ferret still learns to function visually.