Storing Memories

Memory Consolidation

Consolidation, which is facilitated by sleep, helps people hold on to their memories.
Memory consolidation is the process of transferring information from short-term and working memory to long-term memory. Initial consolidation occurs within seconds or minutes of forming a new memory. However, newly encoded memories are fragile because it takes time for changes in neural circuits to occur. New memories can be disrupted in many ways, including by competition with other new learning, by pharmacological agents, and by electrical activity in the brain. Consolidation continues over days, weeks, or even years. Retrieving memories can make them unstable, requiring them to be reconsolidated.

Sleep facilitates consolidation, particularly for information important to the learner. For example, in a 2012 study, participants studied pictures of buildings and furniture. Participants had their memory for those items tested immediately. Researchers then told half of the participants that they would have their memory of furniture items tested in 14 hours. They told the other half of participants that they would have their memory of buildings tested in 14 hours. Within each group of participants, half did their initial learning early in the day and were retested at the end of the day. The other half did their initial learning toward the end of the day and were retested after getting a typical night of sleep. During the restesting period, all participants were tested for their memory of both furniture and buildings. People who slept before retesting remembered more items from the category on which they expected to be tested. In other words, those who expected to be tested on their memory of furniture remembered more furniture items than buildings. People who did not sleep before retesting remembered fewer items overall and were equally likely to remember expected and unexpected items. In other words, regardless of whether they expected to be tested on furniture or buildings, people had equal difficulty remembering all pictures.

Schemas

Memories are consolidated within highly organized frameworks called schemas, which facilitate rapid retrieval but also make stored memories prone to errors.
Schemas are mental representations or frameworks for organizing knowledge and experiences. They are composed of memory units and relationships between those units. Schemas allow people to interpret experiences quickly, make inferences about missing information, and decide what to do. They are formed through exposure to multiple instances of an object or idea. For example, over the course of a lifetime, people see many instances of houses. Some houses have features that other houses don't have, such as a front porch or shutters. But houses also have many features in common, such as roofs, doors, and windows. People learn they can gain entrance to a house by knocking on a door or by opening a door or window themselves. As a result of these encounters, people form a "house" schema that includes features houses have in common. The resulting schema represents what people know and understand about houses. It allows them to make inferences when they have incomplete information. For example, if the view of a new house is obscured by a tree, people can still infer the house has at least one door.

People typically are better at remembering information consistent with their schemas. But schemas can also lead people to remember features that were not actually present. For example, in 1981, American cognitive psychologists William Brewer and James Treyens had people wait in a professor's office for 35 seconds. After exiting the room, the people were asked to list everything they could recall seeing. People were better at recalling objects that fit their schema of "professor's office" (such as a chair and desk) than unusual objects (such as a skull). Some people also recalled seeing objects that had not been present but were consistent with their schema for "professor's office," such as books.