In honor of Father’s Day and the many wonderful memories I’ve made with my dad, I thought I’d write about a topic within both psychology and neuroscience that is quite beautiful and complex: what memories are and how memories are made. (Just a quick disclaimer: I have to admit that this post is more science-textbook-like than my usual reflections, but bear with me. After all, psychology and neuroscience act in unison and both are equally as fascinating.)
Memories are units of storage for the knowledge we acquire from the world. Without memories, the knowledge we aquire via exposure to external stimuli would not be retained nor would it be useful. Picture a colander: the function of memory is much like having your colander’s tiny holes retain pasta while allowing only the water to seep out. Instead, without memory, picture a colander that’s not really a colander but just a handle attached to an empty hole. How would you retain all the pasta (i.e. acquired knowledge)? If you can’t retain any pasta, then your pasta dish would lose its purpose.
Our memory is not only in charge of amalgamating and condensing information, but also encoding the sensory information we receive and retrieving the very information that is stored for later use.
Getting to know the vast amounts of memories that exist
While many of us know of the classic “short term” and “long term” memory, there are many ways of classifying different types of memory. Just as there exist different types of storage devices (e.g. a box, a plastic container, a jar, an envelope, etc.) that are each tailored to the type of objects they store, there are numerous ways by which we can categorize memory. The first is by durability, or the length of their life.
- Iconic memory: When stimuli is received through any of the five senses, very brief memories are made to temporarily store the sensory impression left by these stimuli. For example, say you visited your neighbor’s house for the first time and noticed a specific scent of cinnamon with a hint of vanilla. Later, when returning to your house you lit a candle and recognized it as being the same scent as the one from your neighbor’s house. Then, congratulations, you have used your iconic memory. This also often happens when you see someone or a picture for the first time and are later able to remember it.
- Short term memory: a limited amount of information is temporarily stored, for about thirty seconds. Short term memory lasts as long as one runs through the information.
- Intermediate memory: this lasts about two or three hours, but is not like long term memory. An example would be remembering where you parked your car/bike or where you last left your keys when you came home two hours ago.
- Long term memory: an unlimited amount of information can be stored for as long as days, weeks, months, or forever/permanently.
Memory can also be classified by the type of information it encodes and stores.
- Declarative memory: memory that can be described, stated or declared. An example would be your birthdate or the year the Declaration of Independence was signed (1776). Declarative memory can further be subdivided into:
- Semantic memory: general knowledge (facts, ideas, concepts, meaning, etc.). For example, basic geometry or that Florida was not one of the original thirteen colonies or that hello in French is “bonjour”.
- Episodic memory: memory of specific events/episodes in your own life, places, times, and the emotions and sensory impressions associated with the events specific to your life. For example, that an ugly clown came to your seventh birthday party or that when you graduated from college wearing a blue lace dress you cried bittersweet tears or how scared you were when you crashed your first car on the expressway at eighteen.
- Non-declarative/Procedural memory: memory that can be performed through action. For instance, playing the piano, riding a bicycle, tying your shoe, etc.
Finally, memory can be classified by the stimulus-response relationship. To better define and visualize the differences between working and reference memory (since it can be tricky) and where these two terms originated from, you can click on the link for the radial arm maze (developed in the 1980’s) provided below.
- Working/short term memory: information about things that happened just recently and are useful for a short amount of time. The relationship between the stimulus and the response is flexible and can change. E.g. where you parked your car. You won’t park your car in the same spot all the time. Thus, this memory changes often.
- Reference/long term memory: this is information that is permanent. The relationship between the stimulus and the response stays the same.
The circuitry: how memory works
Memory is a higher cognitive process that works hand in hand with learning and attention. We first place our attention on something within the world external to us. Then, we absorb the information from our surroundings (the process of learning). Finally, the information is received, consolidated, and stored (and later retrieved).
Here is a brief summary of just how information gets acquired through learning and goes through a woven circuitry to ultimately produce a response:
- Information enters our nervous system via our sensory systems
- The information then passes through some filtering (interpretation) within our neural network. Before producing a response the following must be assessed:
- Our hormonal state determined by our neuroendocrine system
- Our previous experience with the stimuli received determined by our cortex, amygdala, hippocampus, cerebellum, and so on
- Our motivational state determined by our limbic system
- Our state of readiness based on both our parasympathetic and sympathetic nervous system and our motor system
- After the above is assessed, we act accordingly on the information/stimuli received.
Our friend, the Hippocampus
Our buddy, the hippocampus is quite vital to our memory. It’s pictured above as the featured photo. What a beauty! Apart from being one of olderst cortical regions of the brain, its main function is to help us learn and navigate the environment that surrounds us. Here are two more captivating characteristics of the hippocampus:
- The hippocampus is largely responsible for place cells (neurons that fire when we find ourselves in a certain place), cognitive mapping and spatial learning.
- Because of its physical position within the brain, it receives input from the motor association cortex, sensory cortex, and the amygdala. Thus, it receives a concoction of information on our position, the environment we find ourselves in, the responses we’ve already made and our inner emotional and motivational state. It can put all the many details about an event that just occurred, including even all the things that are happening at the time that the memory is created (relational memory), together to form the complete picture of a memory (so that it is easier to retrieve, as well).
Technology has served as an essential aid for neuroimaging. There are now many different techniques for mapping areas of the brain and producing pictures of brain cells. One of the most interesting and recent developments (developed in 2007 by a group of Harvard scientists) in neuroimaging technologies has been brainbow. (That technique was actually used to produce the image of the hippocampus above, used as the featured photo for this post, by Tamily Weissman from Harvard University.) You can tell from the picture above and the link to a gallery of brainbow images below that this technique produces a very colorful image, a rainbow of neurons (hence the name “brainbow”).
Through brainbow, fluorescent proteins are used to distinguish single neurons from neighboring neurons. By giving each unique nerve cell a particular color, scientists can then identify and trace the axons and dendrites of each nerve cell over a great distance. This method is by far one of the greatest ways to visualize the thousands of connections that exist within the brain and model the intricate system of nerve cells that work to power our internal supercomputer.
While this is a small glimpse into the wondrous world of memories (which I’ll hopefully dive deeper into in the future), I consider this to be a small yet adequate introduction. With any luck, if you’ve stumbled upon this post you’ve learned a thing or two and not just that I’m an absolute nerd.
For more on:
- Brainbow and an incredible picture show with detailed captions:
- Neuropsychopharmacological approach to the various types of memory:
- Radial Arm Mazes:
- A fairly recent MIT article on how memories reside in specific clusters of brain cells:
- Cool facts about the hippocampus: