Memory, it turns out, is both far more complex and more primitive than we knew. Ancient parts of the brain can record memory before it even reaches our senses--our sight and hearing, for instance. At the same time, "there are between 200 and 400 billion neurons in the brain and each neuron has about 10,000 connections," notes psychiatrist Daniel Siegel, M.D. "The parallel processing involved in memory is so complex we can't even begin to think how it works."
The one thing that we can say for certain is this: If memory is the bedrock of the self, then even though that self may seem coherent and unchanging, it is built on shifting sands.
13 WAYS OF LOOKING AT THE BRAIN
Moments after being removed from the skull, the brain begins to collapse into a jellylike mass. And yet this wet aspic of tissue contains a fantastic archeology of glands, organs, and lobes, all of which have their own specialized jobs. Much of this archeology is devoted to the complex tasks of memory.
But just what is memory? According to Nobel Prize-winning neuroscientist Gerald Edelman, Ph.D., author of Bright Air, Brilliant Fire (Basic Books), memory is the ability to repeat a performance--with mistakes. Without memory, life itself would never have evolved. The genetic code must be able to repeat itself in DNA and RNA; an immune cell must be able to remember an antigen and repeat a highly specific defense next time they meet; a neuron in the brain must be able to send the same signal each time you encounter (for example) a lion escaped from the local zoo. Every living system must be able to remember; but what is most dangerous and wonderful about memory is that it must occasionally make errors. It must be wrong. Mere repetition might explain the way a crystal grows but not the way a brain works. Memory classifies and adapts to our environment. That adaptation requires flexibility. The very ability to make mistakes is precious.
Now you can bravely step into the hall of mirrors that is memory. And though our words to describe this evanescent process are still crude and oversimplistic, here are a few tools to travel with:
Memory can be implicit or explicit. Implicit memory is involved in learning habits--such as riding a bicycle or driving a car. It does not require "conscious" awareness, which is why you can sometimes be lost in thought as you drive and find you've driven home without realizing it. Explicit memory is conscious, and is sometimes called declarative. One form of declarative memory is autobiographical memory--our ability to tell the story of our life in the context of time.
We often talk of memory storage and retrieval, as if memory were filed in a honeycomb of compartments, but these words are really only metaphors. If memory is the reactivation of a weblike network of neurons that were first activated when an event occurred, each time that network is stimulated the memory is strengthened, or consolidated. Storage, retrieval, consolidation--how comforting and solid they sound; but in fact they consist of electrical charges leaping among a vast tangle of neurons,
In truth, even the simplest memory stimulates complex neural networks at several different sites in the brain. The content (what happened) and meaning (how it felt) of an event are laid down in separate parts of the brain. In fact, research at Yale University by Patricia Goldman-Rakic, Ph.D., has shown that neurons themselves are specialized for different types of memories--features, patterns, location, direction. "The coding is so specific that it can be mapped to different areas...in the prefrontal region."
What is activating these myriad connections? We still don't know. Gerald Edelman calls this mystery "the homunculus crisis." Who is thinking? Is memory remembering us? "The intricacy and numerosity of brain connections are extraordinary," writes Edelman. "The layers and loops between them are dynamic, they continually change."
Yet the center holds. The master regulator of memory, the hub at the center of the wheel, is a little seahorse-shaped organ called the hippocampus. Like the rest of the brain, it is lateralized; it exists in both the right and left hemispheres. Without it, we learn and remember nothing--in fact, we are lost to ourselves.
THE SEAHORSE AND THE SELF
"He's 33 years old, and he never remembers that his father is dead. Every time he rediscovers this fact he goes through the whole grieving process again," Mark Gluck, Ph.D., a professor at the Center for Molecular and Behavioral Neuroscience at Rutgers University, says of M.P., a young man who lost his memory after a stroke six years ago. Gluck has been studying M.P. for several years. After his stroke, M.P. forgot that on that very morning he had proposed marriage to his girlfriend. "He can store no new information in his long-term memory. If you tell him a phone number and ask him to repeat it, he will; but if you change the subject and then ask him the number, he can't remember. M.P. is going to be living in the present for the rest of his life. He has lost the essential ability of the self to evolve."
M.P. is uncannily similar to one of the most remarkable and intensively studied patients of all time, a man called H.M., who lost his memory after undergoing brain surgery to treat epilepsy. This type of memory loss, called anterograde amnesia, stops time. It usually results from damage to the hippocampus, which normally processes, discards, or dispatches information by sending signals to other parts of the brain.
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