X-Message-Number: 13070 Date: Fri, 07 Jan 2000 21:57:48 -0500 From: Jan Coetzee <> Subject: A Look at Memory A Look at Memory Friday, January 07, 2000 [By Sally Squires in the Washington Post.] Without memory, people would be unable to read this sentence or find their way home tonight or grasp the jokes on their favorite television sitcom. Memory provides the foundation for learning throughout life, whether it's to explore emotions through psychotherapy, become fluent in a second language or master snowboarding. All animals, from the lowly sea snail to humans, have some form of memory. But people possess the remarkable ability to make a nearly infinite number of memory associations. It's why the loss of memory - due to normal aging, illnesses such as Alzheimer's disease or accidents - is so profound. And it's why, as the Decade of the Brain draws to a close, neuroscientists are pressing to better understand this still mysterious process. "Every thought we have, every word we speak, every action we engage in - indeed, our very sense of self and our sense of connectedness to others - we owe to our memory, to the ability of our brains to record and store our experiences," explain neuroscientists Larry R. Squire and Eric Kandel in their book, "Memory: From Mind to Molecules." "Memory is the glue that binds our mental life, the scaffolding that holds our personal history and that makes it possible to grow and change throughout life." Researchers, using a variety of sophisticated new imaging devices, are beginning to understand some of neuroscience's most central questions: How are memories organized in the brain? Is there a particular location in the brain for the seemingly mindless daily habits, from climbing out of bed to brushing your teeth or making coffee? How does the brain recall vivid details from a movie, a book or a painting? Where does the memory for recognizing a face exist? "It's a very difficult thing to find the anatomic parts of memory in the brain," said Daniel Alkon, director of the Laboratory of Adaptive Systems at the National Institute of Neurological Disorders and Stroke (NINDS). " ... We see a picture of our father's face and hear his name and recall our relationship with him. But to find where that is stored [in the brain] is an incredibly difficult task." Until recently, memory research was largely confined to animals and to those individuals in whom memory had begun to unravel. People suffering from amnesia, the aftermath of a stroke and various forms of dementia gave scientists rare glimpses into the mysteries of memory. One of the most fascinating cases was of a 9-year-old boy who cracked his head on the sidewalk after being knocked down by a bicycle. His misfortune turned into a lengthy, classic study that provided the first riveting proof that memory is not one single process in the brain. The child suffered debilitating seizures and frequent blackouts. By age 27, he was so incapacitated that neurosurgeons removed part of his brain - the hippocampus and two areas known as the medial temporal lobes. The operation in the mid-1950s cured the man's seizures, but it left him unable to retain new information. Meals eaten, people met, even photos of himself as he aged held no meaning because he could not transfer them to his long-term memory. The man retained enough knowledge of language and life to hold a normal conversation. What he couldn't recall - even a few minutes afterward - was having the conversation. Yet the man could vividly remember events that occurred before the accident and he could even learn some new skills. In a standard laboratory test, he was asked to trace the figure of a star. His tracings improved each day, just as they would in normal subjects. The difference was that the man had no memory of his previous drawings. McGill University psychologist Brenda Milner, who has studied this man for 40 years, concluded that he couldn't retain new memories because he no longer had the medial temporal lobes and the hippocampus in his brain to store them. Yet since the man could recall events before his injury, Milner and her team determined that neither the temporal lobes nor the hippocampus could be the final storage sites in the brain for longer term memories. The fact that the man could learn to trace a star and progressively improve at doing so - even if he didn't remember it - helped scientists to understand that memory is divided into two major forms, declarative and nondeclarative. The surgery destroyed the man's declarative memory, or the "conscious recognition of facts and events," according to Squire, research career scientist at the Veterans Affairs Medical Center in San Diego. Left intact was his nondeclarative memory, which includes the subconscious recall of motor skills and the ability to identify familiar objects more quickly with experience. In healthy individuals, the hippocampus and the medial temporal lobes are at the heart of declarative memory. But the process of capturing and recalling information spreads throughout the brain, often in milliseconds. Each memory seems to be a compilation of tiny bits of information stored in a vast network of different cells. Just the simple ability to recall a phone number is believed to involve the activation of several thousand nerve cells, called neurons, distributed throughout the brain. "Humans are in a class by themselves," said NINDS's Alkon. "The wiring inside the brain is designed to allow us at the flip of a coin or the snap of fingers to connect or associate any bits of information with any other bit. We can do it lightning fast. In terms of learning new associations, most of what we do can be formed in fractions of a second." And the potential for storing long-term memories is thought to be nearly endless, given the multiple associations between cells. Each human brain contains an estimated 100 billion neurons, each capable of making up to 10,000 connections with other brain cells. The number of possible memories starts to approach the number of molecules in the universe, Alkon said. There are, of course, highly skilled individuals who aptly demonstrate the vast capacity for declarative, long-term memory. The Olympic gymnast or gold medal ice skater who moves nonstop in intricate ways through a long routine relies on long-term memory. So does the concert pianist who plays an entire concerto by heart. At Carnegie Mellon University in Pittsburgh, psychologists Herbert Simon and William Chase studied chess players and found that practice - more than exceptional memories - could account for differences between individuals. In the study, each player was asked to spend five seconds examining a chessboard with 26 pieces arranged in game positions. The players were then told to reproduce what they had seen on an empty board. On average, skilled chess players - including some grandmasters - correctly replaced 16 of the 26 pieces, while beginners only positioned four pieces correctly. But the differences between skilled chess players and beginners disappeared when Simon and Chase randomly positioned chess pieces on the board. Simon and Chase concluded that the grandmaster chess players had trained so much that they had stored thousands of game position variations in their brains but were no better than the beginner players in recalling random positions on the board. Modern imaging techniques are enabling scientists to study the brain in ways once unimaginable and providing an understanding of the chemical processes that make memories. With positron emission tomography (PET) and functional magnetic resonance imaging (fMRI), for example, neuroscientists can pinpoint brain activity during different memory tasks. At NIMH, Alex Martin, chief of the section on cognitive neuropsychology, and colleagues James Haxby, chief of the section on functional brain imaging, and Leslie Ungerleider, chief of the Laboratory of Brain and Cognition, use these techniques to explore how the brain stores information. They begin with such simple objects as animals, houses, chairs, pencils and tools. "We can now see this whole network, this whole cascade that is going on in milliseconds within the brain," Martin said. The findings reveal a brain organized around the processes of learning, not the objects themselves, and by the way in which these objects are used. "A hammer, for instance, is stored in an area that involves motion, while the image of a cat is placed in a part of the brain that contains other visual shapes," Martin said. To identify an object, he said, "we instantly retrieve information by the features that define it. What does it look like? What color is it? How does it move or how do we manipulate it, if it's a tool?" For example, the studies found that verbs are stored in areas of the brain just in front of regions involved in the perception of motion. Colors of objects - the memory of a bright yellow hue of a pencil, for example - are stored next to the perception of color. Thus a hammer is stored three ways in the brain: once for its form, once for its use or motion and once for the memory of the motor skill needed to use it. "We store these bits of information about objects near their features," Martin said. " ... It's all very logical." These findings also support clinical observations made by British researchers Elizabeth Warrington and Rosaleen McCarthy, who noticed a highly selective loss in the ability to name or retrieve objects in some brain-damaged patients. Depending on where the injury occurred in the brain, some patients lost the ability to name small inanimate objects, such as mops, forks and chairs, but retained the ability to recall living things and large objects, such as kittens, autos and clouds. "It looks like how we store information is not randomly scattered, but follows a plan and the plan is organized the same way our sensory and motor systems are organized," Martin said. "Color goes with color, form goes with form, motor information with motor information." But scientists are searching even deeper, seeking to unravel how individual brain cells store and share information. Last month, researchers at the University of Geneva in Switzerland announced that they had captured what appears to be the first electron micrograph image of the cellular changes involved in long-term memory. Reporting in the journal Nature, the team showed how the connections between two nerve cells in a rat's brain change significantly when long-term memory is established. In an alteration that is believed to occur across nearly all species from rat to human, the team found significant changes in the spiny dendrites that form at gaps between nerve cells called synapses. Scientists believe that this change allows for a host of associations to be made linking a particular memory with experiences, thoughts, emotions, sights, sounds and smells. Copyright 1999 The Washington Post Company Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=13070