The Cerebral Cortex And Hippocampus

Most pictures of the brain usually show the deeply grooved and folded cerebral cortex: a thin sheet of cells (no thicker than twenty pages of this book) wrapped around the other "core" parts of the brain like a rind on a grapefruit. Although thin, the cortex is very large (spread out it would cover the front page of a newspaper) and contains an astounding number of nerve cells—about one hundred million in every square inch. And while the cortex may look like a uniform sheet, it actually consists of dozens, perhaps hundreds, of smaller, specialized regions (some as small as a fingernail, others as large as a credit card). Each of the senses has its own dedicated portions of cortical real estate—forexample, there are at least thirty specialized areas just for vision.

Processing information as it comes in from the senses involves a network of many smaller regions. In addition, other regions of the cortex specialize in integrating information from two or more different senses (so, for example, when you hear a sound you know where to look).

These hundreds of regions are linked together by the brains equivalent ofwires: thin threads called axons (each only one hundredth the thickness of a human hair) that extend

There are 30 specialized areas in the visual cortex alone; each area links up (communicates) with its neighbors (shown here in simplified form). A realistic diagram would show over 200 \ linkages.

from nerve cells and conduct electrical impulses from one part of the brain to another. Every cortical region sends and receives millions of impulses via these axons to and from dozens of other cortical regions. The brain contains literally hundreds of miles of such wires. Thus, the cortex resembles an intricate web, VISUAL AREAS OF THE (

with each region linked directly or indirectly to many other regions. Some of these connections are between areas that process similar information, such as the thirty involving vision, while other connections are between dissimilar areas, such as touch and smell. The network of pathways between cortical regions that do many different things is what allows the cortex to be so adept at forming associations.

Like the cortex, the hippocampus plays an important role in forming associations. The senses continually flood the brain

with information, some of it vital but much ofit unimportant.

You don't need to remember the face of everyone you pass on the street, but you do want to recognize someone youjust met at your boss's party! To prevent the information overload that would accompany having to remember too much, the hippocampus sifts through the barrage of incoming information from the cortex and picks out what to store or discard. In other words, the hippocampus acts like a central clearinghouse, deciding what will be placed into long-term memory, and then, when called upon, retrieving it. The hippocampus'sdecision to store a memory is believed to hinge on two factors: whether the information has emotional significance, or whether it relates to something we already know.

The hippocampus is also vital for making mental maps, allowing us to remember things like where our car is parked or how to get from home to work. Animals in which the hippocampus has been removed cannot learn or remember simple mazes.

Most problems that cause mental deficiencies involve the cerebral cortex or the hippocampus. So keeping mentally fit really means exercising these parts of our brain so they function at their best. And what they do best is to form associations between different kinds of information they receive.

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