The brain is extremely complex, and researchers are constantly learning more about how it functions. More and more studies are done every year trying to discover more information about how the brain works, particularly about memory. A lot is known, but still, more is left to be discovered.
When faced with memory disorders or memory loss, it can be helpful to have an understanding of how the brain manipulates memory. Especially in cases of head injury, knowing which parts of the brain affect memory can help you understand what to expect in the future. Unfortunately, the brain cells responsible for memory cannot be replaced, which means that most memory loss is permanent.
Neurons, or nerve cells, are what most people call brain cells. Neurons are not like other cells. They do not divide, and if they die, they are not replaced. On average the human brain has over 100 billion neurons or brain cells.
These brain cells communicate with one another through synaptic connectors, sometimes referred to as synapses. There are over a trillion synapses in the brain that communicate information between neurons. With this complex system, it is estimated that humans have a memory capacity of anywhere between one and 1,000 terabytes worth of data.
When you are encoding or retrieving information from your memory, the neurons work together through the synapses to allow the process. It is electrical as well as electrochemical, with chemicals like dopamine and serotonin having an impact on how the neurons communicate.
The hippocampus is a small organ of its own nestled in the medial temporal lobe of the brain. The hippocampus is responsible primarily for memory, but also spatial navigation and behavioral inhibition. A healthy hippocampus is necessary for being able to create new memories and retrieve memories.
Primarily, a damaged hippocampus will mean that short-term memory fails, and new memories cannot be formed and encoded into the brain. This is one reason why Alzheimer's patients lose their short-term memory and fail to create new memories. The hippocampus is often the first part of the brain to be affected by the disease.
Overall the hippocampus memory is short-term and declarative long-term memory. In other words, the memory that allows you to state facts and figures. Some patients with damage to the hippocampus do recall memories from early childhood or early life, but they will not remember newer information and will be unable to form new memories.
However, the hippocampus does not affect procedural memory. Studies have shown that people without a fully functioning hippocampus can learn new skills such as how to play a musical instrument. This indicates that, although still long-term memory, procedural memory synapses occur in a different part of the brain.
Different parts of the brain are utilized for different types of memory, although there are some parts of the brain that share duties with more than one type of memory. There are three main types of memory: sensory memory, short-term memory, and long-term memory.
Long-term memory is further divided into subtypes of explicit and implicit memory. Explicit memory is that memory that you have to think about to recall and is divided further into episodic and semantic memory. Implicit memory is a memory that you recall without conscious thought and includes procedural memory.
Sensory memory is an ultra-short-term memory that usually lasts less than one second. As your brain takes in information through the five senses, it relays that information to sensory memory. From there, the brain makes a snap decision as to whether to store the information in short-term memory or discard it.
There are five senses, and most people would assume that there are different sensory memory types for each. However, only three types of sensory memory have been studied sufficiently to be able to know what parts of the brain affect this type of memory.
Iconic memory is a visual memory and relates to things you see. It uses the occipital lobe of the brain. Echoic memory is an audio memory, and it relates to things you hear. Echoic memory uses the temporal lobe of the brain. Finally, haptic memory is the memory of things you touch and uses the parietal lobe of the brain.
Short-term memory is where information is stored for a brief time before it is relayed to long-term memory or discarded. While short-term memory lasts much longer than sensory memory, it still has a much lower capacity than long-term memory.
The part of the brain that is most used for short-term memory is the prefrontal lobe. The prefrontal lobe is responsible for holding information in the short-term memory until it is discarded or moved to long-term memory. Information passes from short-term to long-term memory using the hippocampus.
Long-term memory is divided into multiple categories, each using different parts of the brain. However, some things are common to all types of long-term memory. For example, the hippocampus plays an important role in developing all long-term memory.
As you take in information, it is passed through the hippocampus then relegated back to other parts of the brain. The more times a piece of information passes through the hippocampus, the stronger the memory will last in long-term memory. This is why studying lists and information repeatedly makes it more likely that you will remember it in the future.
Explicit Memory is the type of long-term memory that you consciously have to recall from your mind. You are using explicit memory when you want to remember the name of your high school science teacher, or when you are trying to tell the story of how you first met your spouse.
Explicit memory is primarily formed and stored in the cerebellum. Retrieval of information has been linked through studies to the right frontal region of the prefrontal cortex. There are two types of explicit memory, episodic and semantic, and both use these areas of the brain.
Episodic memory is the memory you have of events that have happened to you throughout your life. Your wedding day, your high school graduation, the birth of your child, and special memories of holidays are all examples of episodic memory.
The hippocampus and prefrontal cortex are involved in creating episodic memories. Researchers are divided on whether episodic memories are stored in the hippocampus for a long period or are relegated to the neocortex. More studies will need to be done to determine exactly how episodic memories are stored and retrieved.
Semantic memory is your memory of certain facts and figures that you have learned over your lifetime. Examples of semantic memory are knowing the names of the past presidents, knowing that the sky is blue or the grass is green or knowing how addition works.
Semantic memory works slightly differently than episodic memory. People with a damaged hippocampus may not be able to make new episodic memories, but may be able to remember facts and figures. The part of the brain used most for semantic memory is the anterior temporal lobe.
Implicit memory is also long-term memory, but it is a memory that you do not have to access actively. With implicit memory, your brain automatically recalls the information when it is needed, without conscious thought. The main part of the brain used in implicit memory is stored in various structures of the brain, depending on what type of information is involved.
Procedural memory is the most well-known type of implicit memory. This is your memory of how to do things. When you ride a bike, drive a car, walk, talk, and use a fork, you are using procedural memory. You do not have to think about doing those things consciously, your memory simply remembers and then does them.
The main part of the brain used for procedural memory is the cerebellum. The cerebellum stores the knowledge of how to perform different tasks and then relays that information to the rest of the brain responsible for carrying out the tasks.
When Memory Fails
There can be many reasons for memory failure, not all of them having to do with damage to brain cells or parts of the brain. Sometimes just being too stressed or sleep deprived can cause you to have memory failures. However, sometimes memory loss is a sign of something deeper going on medically.
Whenever you have persistent and prolonged problems with your memory, you should contact a professional for a memory test. They can help determine the extent of your memory loss, the type of memory loss, and help you work toward diagnosis and treatment. Multiple tests and scans may need to be done to determine the part of the brain responsible for your memory loss. However, a psychologist can start the ball rolling with memory tests that can determine which types of memory you have had problems with.