It’s not even noon and you’ve already misplaced your car keys, snuck a peak at the molarity conversion figures you wrote on a sticky note on your lab bench, and reminded yourself to button your lab coat before working under the hood. All of these activities are the work of memory, and each of them involved a different part of the brain.
What makes memories?
No single memory is just an isolated file in the brain. No matter whether it’s a memory of something you saw or smelled, an emotion or something you’ve read, any given memory is an amalgam of many other memories, and involves many areas of the brain.
The three stages of memory formation—encoding, storage, and retrieval—all require many parts and pathways of the brain in order to work:
- Frontal lobes—handle “working memory” and memories of something you need to do (button your lab coat, for example). The frontal cortex handles explicit memories (those based on learning, space and navigation).
- The hippocampus—also handles explicit memories, including processing spatial, learning and navigation cues. The hippocampus is a key transit point for directing explicit memories from the senses to receiving areas of the cerebral cortex.
- Temporal lobes—handle memories that deal with a sense of “self.”
- Basal ganglia—handle “implicit” memories (those that are unconscious, related to perception, or trained responses – such as driving a car, once you’ve located your keys!).
- The amygdala—the central processor for emotional memories.
- Senses (eyes, ears, nose, touch, taste)—process memories, either implicit or explicit, emotional or cognitive.
All of these areas are extensively connected via neuronal pathways to each other and to other parts of the brain (the visual or parietal cortices, for example). And every time you experience something new, these networks reorganize a little.
How does memory work?
- First, encoding. If you’re paying attention, your senses will generate an image or concept (i.e. “perception”), which goes directly to the hippocampus. The hippocampus and the frontal cortex “rank” the perception, determining whether the memory is worth storing (and if not, then “forgotten.” These brain areas differentiate between memories that are more necessary (like, when to avoid being hit by a car) and thus avoid “memory overload” (imagine being bombarded by every perception you’ve ever had, all at once). This consolidation process involves new expression of genes and protein synthesis, resulting in neuronal structure changes that enable long-term storage.
- Then, if it’s saved in sensory memory (located in a lot of places), it’s stored. Repetition of a task or fact can make an explicit memory implicit, and aid in storage. Memories that have been “packaged” in the hippocampus are slowly transferred to the cortex. There’s no one place in the cortex that stores all memories. For example, the prefrontal cortex contains a “central executive” system that controls perceptions of specific events. However, visual memories are stored in either the occipital or parietal lobes of the cortex.
- Retrieval is usually unconscious (or implicit), and the result of an emotional impact or some repetitive activity. Memories generated by fear, for example, are transmitted through another brain structure, the amygdala (bypassing the hippocampus). Working memory and repetitive memories are retrieved through other pathways, depending on the type of memory.
What can go wrong?
Most common memory loss is caused by distractions. Your brain simply can’t process and prioritize every input it receives. Chemical interference (such as drugs, alcohol, or certain diseases) can also impair memory processing. So, to keep your memory pathways flowing freely, don’t do too many lab tasks at once, always leave your car keys (and pipettes) in the same place, and watch what you eat (and drink)!
Can you tell differences in memory effectiveness in your life or work? Can you remember all the steps to an exciting experiment? Do you forget to calculate the right amount of buffer if somebody’s asking you to do something else at the same time?
Online Colleges (2012). How Memory Works. http://www.onlinecolleges.net/2012/01/09/memory-works/
Kandel, E.R., Schwartz, J.H., and Jessell, T.H. (2000). Learning and Memory, in Principles of Neural Science, New York: McGraw Hill, 1227-1246.