Why you remember your birthday but not where you left your keys

According to a recent research According to the Salk Institute in California, the brain’s storage capacity may be ten times greater than previously thought. Instead of holding information in specific parts of the brain, our memories are represented by the connections between neurons, called synapses. How our brains learn and store information depends on synaptic plasticity, or the tendency of these connections to strengthen or weaken. By applying highly precise algorithms, the team of computational neuroscientists was able to measure the strength of these syntactic connections, and indirectly the maximum storage capacity of our brains.

To understand how memories are stored, it must first be recognized that there are different types of memory. Short-term memory contains information that our brains actively process, while working memory allows us to manipulate those ideas in real time. Let’s say you’re tasked with remembering a random list of numbers. After a short delay, the average person can only remember about 5-9 songs. Short-term memory has a limited storage capacity and only holds information for a few seconds to a minute. The flexibility of short-term memory allows us to focus attention on immediate tasks, such as remembering a phone number long enough to call it.

Long-term memory, on the other hand, is virtually unlimited. This is where our brains store information, skills and experiences that make us who we are. However, not every thought or experience is stored for the long term. Have you ever entered a room looking for something only to forget what you were looking for? Or maybe forgot someone’s name right after being introduced? Transferring information from short-term to long-term memory requires active encoding, which involves linking this information to existing memories, giving it meaning and organizing it into long-term storage for easy retrieval.

When a memory is encoded, activated neurons send chemical signals through their synapses or connections to other neurons. This forms an interconnected network of neurons that contain information about that memory. As you continue to recall or rehearse the memory, the network becomes stronger. The more you are exposed to that information, the more likely you are to remember it. In their study, Samavat et. already found that activating parallel neural networks with the same number of connections, or synapses, produces a consistent increase in strength. Given that the brain contains trillions of synapses, they were able to estimate the brain’s storage capacity, which appears to be much larger than previously thought.

If long-term memory is so great, why are our brains prone to forgetting? Forgetting is a normal part of being human and increases with age. Psychologists and neuroscientists have proposed several theories about why and how forgetting occurs. For example, famed psychologist Sigmund Freud argued that forgetting allows individuals to avoid unwanted memories. Freud proposed that these memories are not just erased, but rather pushed into our subconscious.

However, modern theories in neuroscience suggest that information is forgotten as the connections between neurons become weaker. The less a memory is activated or rehearsed, the weaker the connection becomes. Ultimately, the connection is so weak that retrieving that memory is no longer possible.

Structural changes in the brain as we age also reduce these connections, increasing forgetfulness. In fact, significant loss of synapses is a key feature of Alzheimer’s disease and other forms of dementia. Reduced synapses between neurons prevent the formation and maintenance of memories, because information cannot be passed from one neuron to another. Alzheimer’s disease also impairs synaptic plasticity, making the brain less responsive to learning.

The technique that researchers at the Salk Institute used to study synaptic strength could help us unravel the mysteries of Alzheimer’s disease. Deciphering how the brain makes and stores memories could one day pave the way for treatments that protect against this and other forms of dementia. As Alzheimer’s disease becomes more common, it becomes increasingly important to develop tools that can identify and treat individuals early.