Memory

Encyclopedia of Childhood and Adolescence

Memory refers to the abilities to store and retrieve information for later use. How memories are stored and then recalled is not fully understood by scientists, although new evidence is helping them to develop theories. Researchers believe that regions in the temporal and frontal cortex, and the hippocampus are critical for various forms of memory.

It is now believed that (1) conscious recall of facts, called declarative memory, (2) memory of the time and place of an event, called episodic memory, and (3) memory of a previously learned motor habit, called procedural memory, involve different mechanisms. In addition, implicit memory, which is not conscious, involves recognition of prior experience. Further, the duration of a memory trace is important. Working memory, popularly referred to as short-term memory, lasts for about 20-30 seconds. Working memory is the moment-to-moment memory function--the brain's ability to keep track of two activities at once, such as opening the mail while talking on the phone. Researchers have found that working memory deteriorates noticeably for most people in their 40s, but cannot explain why. Amnesia, or damage to the memory, is caused by any number of factors, including viral infection, head injury, near drowning or suffocation, or any other event that deprives the brain of oxygen for a period of time.

Studies indicate that by six months, infants have developed memory skills to recall some experiences. In fact, as early as six weeks of age, some infants stare more intensely at unfamiliar objects, a behavior researchers interpret as evidence that infants can distinguish the unfamiliar from the familiar.

Researchers studying older infants between 12 and 24 months have found that they are beginning to develop the memory necessary to recall specific events. This recall ability is stronger when the event has been experienced more than once. Hints, cues, or reminders also improve the young child's ability to retrieve a memory.

Researchers believe that working memory involves complex interactions of different areas of the brain--one for visual memories and another for verbal memories. In the early 1970s, researchers at UCLA gathered evidence that the prefrontal cortex, the region of the brain just beneath the forehead, was stimulated when monkeys looked for a hidden item. In the late 1980s, researchers at Yale University expanded upon this experiment to confirm the prefrontal cell activity during experiments with monkeys.

In 1993, activity in the prefrontal regions of the brain refined the identification of object identity memories and spatial relationship memories. This led to the development of a model for working memory that features parallel areas processing different types of sensory memory information. Researchers at the National Institute of Mental Health, using positron emission tomography (PET) to map neuronal activity, found that working memory for facial features and for locations are centered in different areas of the prefrontal cortex. University of Michigan research teams corroborated this evidence that working memory for spatial relations is centered in a different location from working memory for verbal information.

As of the late 1990s, the evidence seems to indicate that the prefrontal cortex is the site of working memory. To perform this function, however, it must interact with the areas of the brain that receive sensory input. As available imaging and other research techniques become more refined, researchers will also refine their understanding of how the memory works. Memories that can be retrieved when needed (one's phone number, for example) appear to be coordinated through the hippocampus deep in the core of the brain, while other types of memories are handled by other areas.

As of the late 1990s, research into recovered memories was characterized by tremendous controversy. A leading researcher in this subject, Elizabeth Loftus, conducted studies on over 20,000 subjects, and pointed to evidence she felt was convincing that memory is both fragile and unreliable. Her work supported ,the notion that eyewitness accounts of events are often inaccurate, and that false memories can be created through suggestion in approximately 25% of the population. Loftus's work calls into question the validity of memories that are recovered under coaching or questioning; such memories have provided the basis for countless lawsuits brought against adults who are accused of molesting children. Her research has shown that emotional state-either low points, such as boredom or sleepiness or high points, such as stress or trauma-decrease the reliability of memory. She has also shown that experiencing violent and traumatic events decrease the accuracy of memory. Loftus theorizes that memory is suggestible and deteriorates over time. In her classic study, known as "Lost in the Shopping Mall," she demonstrated that subjects-children and teenagers-could be induced to remember being lost in a mall at an early age, even though it never actually happened, by simply questioning them about it as if it had happened.