7.4 The Brain’s Role in Implicit & Explicit Memory
The Brain: The Master Computer
Memory is one of the most fascinating and complex functions of the brain. The ability to remember allows us to learn, to change our future behavior based on our past experiences.
Our brains processes, stores and retrieves information in several ways. Short-term or working memory allows us to hold small pieces of information long enough to use them, but long-term memory is stored for a lengthier period.
Long-term memory is in turn divided into two types: implicit or procedural and explicit or declarative. Each is centered in particular areas of the brain, and is stored and recalled in its own particular way. Let’s take a look at them through the everyday life of one woman, Tara.
Explicit Memory: Episodic and Semantic
Explicit memory is specific recall. It is deliberate, conscious and intentional. For example, Tara mentions an adorable small town she passed through on a road trip with her cousin last year. Her friend Kristen asks what the name of the town was, and Tara says, ”Oh gosh, let me think. I can’t remember!”
Tara’s recollection of the experience of visiting the small town is episodic memory, an aspect of explicit memory. Like all memories, it is not a snapshot, but a representation encoded electrically in the brain. As this example shows, it isn’t perfect, either. Tara remembers being charmed by the small town’s shops and square, but can’t recall its name!
Semantic memory is another aspect of explicit memory. It is our memory for concrete information, not tied to a particular event. Tara is a museum docent, so she has a deep reservoir of information stored in her brain about the artworks at the museum. But she does not necessarily recall when or where she learned, for example, that the sculpture of an angel in Gallery 1 was inspired by Led Zeppelin, or that the painter of the mural on the museum mezzanine was shot by a lover’s jealous husband in 1935.
Many factors affect how explicit memories are stored and recalled. One of the most influential is the emotion associated with a given event. Tara was a young grade school teacher on September 11, 2001, and her recall of that day and how she managed her students’ distress is crystal clear. Strong emotion, positive or negative, causes strong storage of memory.
Explicit memory is mediated largely by structures in the frontal and temporal areas of the brain. The hippocampus, located in the temporal lobe, is especially important in episodic memory. Semantic memory also uses the hippocampus, but its storage is spread into numerous other areas as well.
Tara’s mother Jean has Alzheimer’s disease. When Tara visits her, they converse about places they traveled when Tara was young. Jean recalls a great deal about the Colorado Rockies or Jamaica, but can’t remember having visited them with her husband and little girl. The hippocampus is one of the first structures damaged by dementias, and this may explain in part why her semantic memory is better than her episodic: it is redundant, or stored in multiple backup areas.
Implicit Memory: It’s Like Riding a Bike
Implicit memory, sometimes called nondeclarative, is our memory for actions, things we do often enough they require no conscious thought. Tara hasn’t ridden a bicycle in years, but when she and her husband buy their daughter one, she decides she needs some fresh air and exercise. She’s a little anxious when she first gets on the secondhand bike she buys for herself, but is pleasantly surprised when the skill comes right back.
This type of implicit memory is called procedural memory. It flows automatically. It’s hard to put into words; in fact, if you think too hard about it, your flow may break down completely. Tara swings a mean golf club, but when her husband tries to give her tips, she finds herself unable to swing at all!
While explicit memory is housed primarily in the cerebral cortex, the main body of the brain that manages higher functions, implicit memory is mainly controlled from the cerebellum. This section of the brain has traditionally been associated with motor function more than with thought, but by that reasoning, it makes sense that memory for overlearned motor actions would be centered there, too.
Memory Management: How the Brain Does It
You might guess that outside influences that negatively affect the cerebral cortex might also impair explicit memory. Sure enough, studies have shown that factors from brain injury to intoxication limit ability to complete explicit memory tasks. Tellingly, however, those same impaired people do relatively well on implicit memory tasks, because their cerebellums are intact.
Memory is stored as electrical impulses in the brain, transmitted by synapses, the points at which brain cells meet. The chemicals transferred by the synapses are altered by various incoming stimulation, and end up being stored and then reactivated as a reconstruction of the original event. Explicit memories in particular are part of a network of associations; when Tara sees a jet fly over, it often triggers a cascade of memories of happy times traveling with her parents. Associations and redundancy of storage help keep memories safe.
Implicit or procedural and explicit or declarative are two types of long-term memory. Memory is stored as electrical impulses in the brain transmitted by synapses, where brain cells meet. Explicit memory, including episodic memory for events and semantic memory for information, is stored mainly in the cerebral cortex, which manages higher functions, and specifically in the hippocampus. Implicit memory is spread out in the brain, with motor recall centered in the cerebellum. Memories are often part of a network of associations, and are stored in several places, which helps protect them.