Memory is an inherent part of our life without which we would not have a sense of self or our surroundings. Without memories, our minds would become a clean slate and we couldn’t possibly function in the present or have a framework to move forward to live a meaningful life.
We depend on memories all the time, to do even the simplest of activities like making a grocery list, going to a particular destination, remembering birth dates of friends and family, and holding on to a conversation and understanding what is being said to you. It is only because of our memories that we are able to do most of the tasks of our everyday life.
But, how do we make memories?
Neuroscientists believe that when we experience any of the sensory inputs, the neurons in our brain pass signals to each other about what we have perceived and communicate with each other, making either temporary or permanent connections. The neural activity between them and the strength of those connections is what makes a memory.
“These connections can be made stronger or weaker depending on when and how often they have been activated in the past. Active connections tend to get stronger, whereas those that aren’t used get weaker and can eventually disappear entirely,” according to the Australian Brain Institute.
Memory is one of the most intricate functions of our brain, allowing us to store information and retrieve it again when we need it. Unlike the physical parts of our body located in specific areas, memory is elusive and is placed in different regions within the brain to process and remember different types of recollections.
Many experts have categorized memory into three types: sensory memory, short-term (working memory), and long-term memory.
Sensory memory allows us to remember the small amount of sensory information that we have just been exposed to. When we try to recall what we have just seen, heard, or touched, sensory memory is in use. It lingers for a fraction of seconds (0.5-3 seconds) before it disappears. Sensory memory needs to be stimulated to move to short-term memory, or it may be lost from consciousness forever.
Short-term memory, on the other hand, has limited capacity of retaining about 7±2 items at a given moment for about 30 seconds. It contains information that we need in the moment, but won’t necessarily need in the future. Failing to create short-term memories will make it impossible to understand long sentences and even follow along in a conversation. It is also a doorway to long-term memory, where the information is temporarily stored in the hippocampus before it vanishes. For example, when we are purchasing a list of things online, the name of items are stored in our memory for a few seconds, but once we’ve placed the order, they will vanish from our memory, unless we make a conscious effort to remember it.
Long-term memory can be retained for a long period of time. It may last from a few hours to as long as we live. We may not be aware of the information stored in long-term memory, but they are easily recalled and decay very little with time. There are two types of long-term memory: implicit (non-declarative) and explicit (declarative). Implicit memory includes procedural memory and things that we learn through conditioning, and they can be accessed effortlessly.
Procedural memory combines both cognitive and motor skills and is responsible for knowing how to do a particular task without consciously thinking about it like typing on the keyboard, getting dressed, and brushing teeth. According to the Australian Academy of Science, when we learn a certain skill, a key part of the brain called the basal ganglia is responsible for processing and coordinating the muscle movements and habitual actions required to achieve the goal, thus enabling us to do things automatically.
Non-declarative memory also refers to perceptional and emotional unconscious memories, and it has the power to invoke involuntary responses from our body like salivating at the sight of certain food or tensing up when you see or think of something you fear. Likewise, we know we are being conditioned when we associate one thing with another without realizing it. For example, when somebody blows a whistle in the neighborhood, we know the trash collectors will knock at our door any minute now.
Explicit or declarative memories are those that must be consciously brought into awareness. They include the facts, previously learned information, and memories of past events that we can remember consciously and intentionally articulate. It is further divided into two sub-types: semantic and episodic.
Semantic memory involves factual and conceptual knowledge about the world and meaning of words. It allows us to remember facts and figures and general knowledge, such as George Orwell wrote the novel 1984, and Kathmandu is the capital of Nepal.
Episodic memory enables us to recall events of our personal experiences from our own perspective. It makes mental travel possible, allowing us to relive our childhood experiences that are most dear to us. Other examples are, remembering your first solo trip, or your friend’s wedding. Episodic memory also provides the context of who was there, how we felt, what, when, and where the personal events in our lives had occurred. The prefrontal cortex and the hippocampus are said to be involved in forming and storing declarative memories.
While memory is a wonderful and magical thing that not only allows us to travel back in time to relive the most beautiful experiences of our life, there are also times when we get a little concerned and frustrated when we keep misplacing and forgetting things.
Age, according to studies, is one factor for our forgetfulness. As we get older, our mental and physical health tends to interfere with our ability to pay attention, and communication between the neurons begin to falter and weaken, affecting how easily we can retrieve memories. Likewise, scientists link the shrinkage of brain size for this deterioration, as the hippocampus loses five percent of neurons every decade, with 20 percent of neurons lost by the time you’re 80 years old (Yale Scientific, 2009). The drop in the percentage of acetylcholine, which is vital to learning and memory, they believe, affect how people retrieve stored information.
While occasionally forgetting why you came to the room, and misplacing keys, is quiet normal as we age, when these memory lapses occur in older people, they could raise a red flag of Alzheimer’s or other type of dementia. Some of the signs indicating serious memory problems include getting lost in a familiar place, having trouble following directions, becoming more confused about time, people, and places, and neglecting to care for self.
While it may be hard to pinpoint our first memory, studies suggest that we are capable of making memories since we are babies. Our memories, however, fade after a certain age, which is why it is difficult to remember anything before our third birthday. This phenomenon, where we naturally and gradually lose our memories from the first few years of our life, is known as childhood amnesia. This happens because our brain is still young, and only around the age of seven, when the hippocampus and the frontoparietal regions undergo important developmental changes, we are able to recall events more clearly.
On a similar note, “What is memory without forgetting?” asks Oliver Hardt, a cognitive psychologist studying the neurobiology of memory at McGill University in Montreal, Canada. “It’s impossible,” he says.
“In the course of a single day, the brain registers hundreds of thousands of bits of information, some of it relevant, and much of it utterly inconsequential….And each time you want to think about something—something key to your survival, such as the location of food or the signs of an approaching predator—all these memories would pop up that are completely meaningless, and that make it hard for you to actually do the job of predicting what is next.”
To have proper memory function, you need to forget things. Without forgetting, the evolutionary benefits of a strong memory would become redundant, he says.