“Where did you park the car?” Upon hearing this question, my mind races to recreate the picture of the aisle number in front of my car. We all face a similar situation in every interaction in our lives. Memory plays such a vital role in daily lives in every single one of our thought processes and actions. Without it, we would lose ourselves in an infinite matrix of time and space, losing all perception of our existence. When we think about where we parked, or what we had for breakfast, or even when we’re just having a conversation, we initiate an intricate chain of events in our brain. Memory is so complex and profound that to this day, we still do not know everything about it. What we do know is that our ability to make decisions, interact with our surroundings, and consciously recall specific events is all founded on memory.
There are two main types of memory: short term memory and long term memory. The section of the brain responsible for creating memories is called the “hippocampus.” Every sensory input - whatever we taste, see, feel, hear, or smell - involves a very specific interaction between certain neurons. Although the message travels electrically along the length of each neuron, there is a synapse - a gap - the message needs to cross to depolarize the next neuron. Electricity cannot just jump gaps, so the presynaptic neuron translates the electrical information into chemical messengers called neurotransmitters which will diffuse through the synapse and bind to receptors on the postsynaptic neuron, further transmitting the message. When a particular event happens for the first time, this electrical and chemical information is stored as a short-term memory for any time between just seconds to a couple of minutes. After this period of time, if that exact same interaction between neurons is not repeated, the information is lost, an event more commonly regarded as “forgetting.”
However, if that interaction is repeated, eventually the efficiency of the communication between these neurons increases - a phenomenon known as long term potentiation (LTP). This is one of the first steps involved in creating a long term memory. According to Eric Kandel, a neuroscientist at Columbia University, the process for creating memories that last for prolonged periods of time involves an anatomical change in the structure of these neurons - a process called synaptic plasticity (5). The more the action repeats, the more the neuron produces certain proteins that increase the efficiency of transmission in the synapse by releasing a higher amount of neurotransmitter, increasing the density of receptors on the postsynaptic neuron, or increasing the speed of the neurotransmitters through the synapse. Another event that initiates the formation of long term memories is consolidation, which is when a certain process is repeated, but it utilizes a different variation of the information. This is exemplified by thinking about your daily schedule, but instead of running through the events in the original order, you start at the end and work backward. When the hippocampus is converting short term memories into long term memories, it combines all variations of input associated with that short term memory. In other words, long term memory is a combination of all the sensory information delivered to the brain relating to that specific event.
Although the hippocampus is known to create memories and put sensory input together, it is not where the memory is stored (3). In fact, memory is not any typical object that can be touched or seen. It’s not stored in any one place like a hard drive; in retrospect, it is scattered throughout our brain. When neuroscientists at the University College London analyzed MRIs of people recalling specific events of their life, they compared the imaging they got with a jigsaw puzzle: so many different parts of the brain lit up together - the visual cortex, the auditory cortex, the olfactory cortex, among many others - indicating that the person was trying to recreate every detail (4). Looking at it holistically, memory is an amalgamation of patterns created by different types of sensory input, all of which are interconnected and associated with each other than organized into different parts of the brain.
One of the biggest breakthroughs made in the world of neuroscience was the discovery of neuroplasticity. This is a vital asset that allows us to anatomically adapt to our environment, giving us the ability to interact more effectively with our surroundings (3). The process involves changing synaptic connections, strengthening some, and weakening others. These connections are influenced by two processes: long term potentiation (LTP) and long term depression (LTD) (2). As I explained previously, long term potentiation increases the efficiency of communication between two neurons by modifying the anatomy of the synapse - thus, strengthening the connections. Long term depression, on the other hand, is the controlled decrease in the efficiency of communication between neurons (2). This is accomplished by releasing a smaller amount of neurotransmitters, making the postsynaptic neuron less receptive to the neurotransmitter, or even entirely eliminating the connection between these two neurons. LTP and LTD allow the more environmentally relevant neural pathways to become more active and strengthen with time, allowing the person to learn and connect with their surroundings with greater magnitude.
While our knowledge of memory is still limited, the opportunities we can still create are limitless. Ted Berger and Sam Deadwyler - neuroscientists at the University of Southern California and Wake Forest University - are attempting to take the implications of memory to the next level: they are trying to create and download memories into rats (1). They intend to do this by utilizing electrical signals to disable the hippocampus, then stimulating different parts of the brain to create new, directed memories - such as being able to differentiate between a Red Bull can and a can of Coke. The discovery of channelrhodopsin, a protein in algae that converts light into electricity, initiated Berger and Deadwyler’s odyssey to download memories into living creatures. When channelrhodopsin is administered to certain neurons, exposure to light triggers the production of electrical impulses which could be traced in the rat’s brain, creating a computerized, binary format of memory. As scientists slowly uncover more about our brain, the way it works, and why it works, this information can be employed to transform the trajectory of neuroscience.
Our existence is founded upon our ability to remember. We need to make decisions - decisions that were made through the intake of sensory information, stored, then analyzed to create action. Memory allows us to process our life, giving it meaning. Without it, life as we know it would just be a blur.
To know more, please refer to the following links:
https://www.seeker.com/download-your-memories-retrieve-them-later-1767577488.html
https://www.nature.com/subjects/long-term-depression
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4392917/
https://www.psychologytoday.com/us/blog/the-athletes-way/201507/the-neuroscience-recalling-old-memories
https://zuckermaninstitute.columbia.edu/pinpointing-how-cells-regulate-long-lasting-memories
Image Credit: https://media.wired.com/photos/596e98b857beec1e84cbd878/master/w_2400,c_limit/BrainMemory-TopArt.jpg
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