The Hippocampus is the Memory Control Center
One area of particular interest, and of which our understanding is quickly growing, is that of human memory. Our memories are astounding in their capacity — for example, a young child learns about 10 new words each day, and the average adult can easily develop a vocabulary including over 100,000 words. It is the evolution of our memories that has, in large part, preserved our species. The key to our survival has been the ability of one generation to pass along its insights, innovations, and experiences to the next, so that they can improve upon them and progress more quickly forward.
Human memory can most broadly be defined as a function of the brain that gives us our ability to store and retrieve information. Science is fairly confident of the fact that there are many different types of memory, and many different mechanisms for their storage and retrieval processes. There are, potentially, as many types of memory as there are types of information and input to remember, and so the concept of one single brain section holding responsibility for memory has become somewhat obsolete.
In fact, there is general agreement upon the existence of sensory memories (taste, visual, tactile) as well as more conceptually based memories (episodic, procedural, declarative). All of these individual memory modes can combine to form much more complex and varied remembrances. Consider any significant childhood memory, perhaps the first time you can remember riding your bicycle without training wheels. During the moments in which that memory was created, your brain was processing thousands of pieces of information, and your memory had to decide which of those pieces were important enough to be worth storing for later retrieval. You might remember the emotions of fear and excitement; the tactile sensation of wind on your arms, or of the scrape on your knee if you fell; the sound of your mother’s encouraging words; procedural information (how to move your legs to push the pedals, the fine motor control of steering), and episodic information like the time of day, your age, and your general surroundings.
You probably do not remember less-central information such as the shoes you were wearing, or the colors of the cars parked along the curb where you rode; this information might have entered into your short-term memory, from which you might have been able to retrieve it for a few hours or even a couple of days. But only that information most central to the memory as a whole makes it into your long-term memory, where it lives for years —possibly an entire lifetime.
The multitude of information stored in long-term memory, and the wide variety of types of information stored, make it difficult to believe that any one brain structure could be solely responsible for that storage. Indeed, most theories point towards a long-term memory system that stores various types of remembered information in the brain areas most closely related to it —i.e., remembered words would be stored in the brainÕs language center, whereas a remembered sound would be placed on a mental “shelf” somewhere near the brain’s temporal lobes, primarily responsible for hearing. Then, the billions of interconnected neurons link these discrete pieces of a more complex memory together, so that, when retrieved, all of the information about that first bike ride comes to mind as a whole, rather than as a jumbled assortment of parts.
While the brain’s hippocampus (meaning “sea horse” because of the similarity in outwardly appearance) seems to be more directly related than any other structure to memory, it acts as a control center rather than a storage unit in and of itself. It, along with the entire cortex, and possibly white-matter cells known as glia throughout the nervous system that protect and nourish the neurons, are generally thought to be capable of holding memories.
How should science quantify a memory? What is the smallest piece of a memory, and where and how is it stored? The physical mechanisms making this intricate process possible are still being explored, and remain little-understood. Some theories suggest that protein particles are the building blocks for individual pieces of memories, although science has yet to explain how the relatively low durability of proteins can account for the sometimes lifelong persistence of a memory. Others point to chemical changes in individual neurons as accounting for memory as well as other long-term, slowly-changing mental phenomenons like sense of identity and consciousness.
