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Learn more about how different memories form
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by Beth Howard
Updated September 28, 2022
When most people think of memory, they're concerned primarily about declarative memory (also called explicit memory), which refers to conscious memories that can be described to others. Declarative memories include facts, people, places and experiences in life.
A subcategory of declarative memories is semantic memories — those involving factual information that doesn't relate to a person's individual experience, such as components of language and general knowledge. Examples include vocabulary words or your city's main streets. Your brain also stores episodic memories — memories of a specific personal event, such as first leaving home for college or the moment your child was born.
Laying down these memories involves the hippocampus, the amygdala and other nearby brain regions, which are connected by an intricate neural network to the cerebral cortex, where memories are stored. When we first experience an event or encounter new information, the hippocampus forms links that allow us to recall the information in the future.
To become a long-term memory, the information or event is first encoded and then stored. The more memories your brain associates with the new memory, the greater the chance of it being remembered.
How well memory functions also depends on how attentive you are at the time you're exposed to new information, your need or motivation to remember it, and your emotional state at the time. "You remember the things that are important to you and the things you pay attention to," says André A. Fenton, professor of neural science at New York University's Center for Neural Science.
The final step of the process is consolidation. If, for example, you are actively learning new information, such as a second language, solid review of the material helps strengthen the neural pathways and makes the information more likely to be stored and later recalled. Sleep also plays a role.
Short-term memories are held and retrieved briefly and don't become consolidated. Long-term memories do and result in actual changes in the neurons, or nerve cells, including the strengthening and growth of new synapses — the connections between neurons. "Long-term memory changes the brain in a long-term and quite often permanent fashion," Fenton says.
To improve your ability to remember new information, experts recommend these steps:
Some forgetting is normal. After all, your brain works more efficiently if it discards memories that are no longer useful, such as algebraic formulas or how to diagram sentences, assuming you're not an engineer or an English teacher.
• “Learning and memory,” Handbook of Clinical Neurology, October 2013. In this chapter, the researchers review and define the neuropsychological aspects of human learning and memory. They summarize the current state of research in this field and discuss the promise and limitations of noninvasive brain stimulation, which can be used to interfere with and study cognitive processes. Read a summary of the chapter. (A fee is required to access the full chapter.)
• “Human emotion and memory: interactions of the amygdala and hippocampal complex.” Current Opinion in Neurobiology, April 2004. In this review, researchers discuss the roles of the amygdala and the hippocampus in memory formation and the links between the two that indicate how emotion influences memory. Read a summary of the study. (A fee is required to access the full study.)
• “Memory Consolidation,” Cold Spring Harbor Perspectives in Biology, August 2015. In this review, the researchers examine studies that investigated the process of memory consolidation, including studies with memory-impaired patients, neuroimaging of healthy brains and animal research. Together, these studies provide evidence for some of the mechanisms underlying the process of consolidation and how it works for different types of memories. Read the full study.
• “Rehearsal initiates systems memory consolidation, sleep makes it last,” Science Advances, April 2019. In this study, 32 participants (average age 23.81) completed word learning and recall tests inside an MRI scanner. Half the participants took the tests in the morning and were instructed not to sleep before repeating the tests with some familiar and some unfamiliar aspects that night. Half the participants took the tests in the evening and were instructed to sleep normally before repeating the tests the next morning. People who slept had less hippocampal activity with words they had already learned, while those who stayed awake had the same hippocampal response to new and old words, indicating that the hippocampus had “forgotten” the old words without sleep. Read the full study.