Neuroplasticity refers to the ability of the brain to undergo changes throughout the life of a person. It does this by modifying synapses and forming new connections between neurons, this happens all the time.
It happens when you learn something new, when you go through something in your life, when you perceive something in the environment, and it’s actually happening right now while you’re reading this.
Memory plays a role that is crucial to our existence. It’s really hard to put its importance into words, we’re the only species that can associate ethics with being able to remember things. However, for humans to be able to capture what’s going on around them and transform those events into memories, there needs to be some kind of plasticity in our brains, an ability to change formation to carve the new data.
Memory only exists because the human brain has the ability to be soft-wired, to form new interconnections between neurons, to be plastic.
Let’s briefly discuss the structure of neurons to figure out what’s going on at the cellular level.
The structure of a neuron:
Inside the brain, there are approximately 100 billion neurons. Each neuron has a cell body, dendrites, and an axon.
The cell body is the core of the cell, with organelles inside producing energy to transmit the electrical current reaching it.
Dendrites are tree-like projections that come out of the cell body and form connections with other neurons, their length is relatively short.
Axons are the main way that neurons communicate with one another, unlike dendrites they are very long and can reach up to 90 cm (3 feet), they are also covered with what’s called myelin sheaths which serve to increase the velocity of electrical signal transmission (up to 100 meters/second).
This is helpful when you put your hand on a hot stove, you can’t afford to wait for a slow signal to go to your central nervous system and come back stimulating your muscles to move the hand away from the stove.
Hardwiring Vs. Softwiring
A lot of the interconnections axons forms are predetermined genetically, our brains do have some kind of hard-wiring sort to speak. It is seen predominately in long axons pathways that make different structures be connected to one another as they should be. An example would be the pathway of the optic nerve.
The nerve starts at the level of the retina then projects to a specific nucleus in the thalamus called the lateral geniculate nucleus (LGN), and then those neurons project to the visual center in the most posterior aspect of the brain. The neurons of the eye don’t project all over the place, this is genetically preprogrammed.
Just as some systems are hardwired with little to no room for change, it’s equally clear that in humans much of what happens to us that is important to our behavior and our response to the world is learned. If we had to guess how does that happen? What part of the brain is responsible for this?
We would guess that some changes occur in the limbic system, which is a region located in the middle of the brain, responsible for engaging us with the outside world. It’s the most easily modifiable system by the experience that we have in the world. So, the question is:
What is the thing being modified by experience?
Neuroscience tells us that we don’t generate a lot of new neurons, so we know that can’t be the answer. Thus, the modification must be happening in the already existing neurons, in the connections between different areas of the brain to be more accurate.
In order to get a firm understanding of the neurobiology involved in memory, we first have to tackle some basic concepts about memory.
The diferent types of memory:
From a functional perspective, memory is divided into two major categories:
- Explicit (declarative) memory: which includes semantics (words) and episodic (events) memory.
- Implicit (non-declarative) memory: which primarily includes nonverbal and motor (brushing your teeth, driving) memory.
On the other hand, memory can be divided into 3 categories from a temporal perspective:
- The working or immediate memory (less than 30 seconds). e.g. remembering a phone number to make a call.
- Short-term memory: necessary as a first stage in learning.
- Long-term memory: may last a lifetime, but can be modified.
Brain areas implicated in memory:
- Higher-order areas of the prefrontal cortex
- Hippocampus: has the shape of a sea horse. Thus the nomenclature hippocampus which means sea horse in Greek.
| Region/ Memory | Working memory | Short term memory | Long term memory |
| Prefrontal cortex | Yes | No | No |
| Hippocamps | Yes | Yes | Yes |
- The extrapyramidal motor system and cerebellum: this involves the non-declarative and motor memory.
- Amygdala: a small gland in the brain responsible for emotional processing. Positive emotions help us learn while negative emotions if excessive prevent us from learning. So, it shouldn’t be a surprise that a structure dedicated to emotions plays a role in memory.
- Association areas of the neocortex: changes in protein synthesis in these areas seem to be implicated in the long term-memory. This is why when a person goes through severe brain damage, he/she won’t lose their long-term memory.
A word about the hippocampus
In humans, there appears to be a specialization of function between the right and the left hippocampi. It turns out that the left hippocampus plays a role in memories that involve language and as we all know the left hemisphere of the brain seems to be the one in control of language.
The right hippocampus however, is better at spacial memory that gives us the ability to find our way through the maze of life. This is absolutely fascinating.
It is important to note that the left hippocampus is also involved in the formation of what is referred to as an autobiography. So, what the brain does is construct a story from bits and pieces of events that happened to you in your life, and create a story that we see internally as the story of our lives.
Now, that we have the semantics and the definitions straight up. Let’s take a look at what neuroscientists say about what happens when we learn something.
The neurobiology of learning
We already established that the connections of neurons are the ones responsible for this process. And if that’s the case, then it means that changes have to happen at the level of synapses.
We call these changes ‘synaptic plasticity’ which implies that the synapse is not a static structure, rather a dynamic one. It’s a property that allows synapses to be modified and underlie learning and memory.
Another thing neuroscientists discovered is that many of the processes that are involved in learning and memory in humans are conserved throughout the animal kingdom.
The different ways synapses are modified
- The postsynaptic receptor could be influenced by a non-specific release of a neurotransmitter that occurs anywhere along the synaptic cleft and as a consequence there will be changes in the responsiveness of the receptor and that might change the membrane potential, which means that when the normal action potential comes back again, it will be altered.
- The postsynaptic action potential can be either increased or decreased. It all depends on the amount of the neurotransmitters released which can be modified all the time.
- The spines found on dendrites are these little projections coming out of the dendrites with a main role of increasing surface area. But, those little spines also isolate synapses. As it turns out, they are dynamic structures and can change their shape very rapidly. Three main shapes were identified. Going from the most efficacious synapse to the least effective one, we have: thin, stubby, and mushroom shaped spines respectively. These shapes are changing all the time even while you’re reading this article; experience transforms these structures into very dynamic entities.
- In addition to all the possible modifications that can take place at the level of synapses, we are also equipped with the ability of forming new synapses, which as it turns out happens throughout our lives and is mainly triggered by experience. However, this is especially obvious in patients who suffered from minor brain injury, and after a while became as good as new. All thanks to the formation of new synapses.
Real life examples
These modifications and new formations of synapses have been studied over and over again. Scientists did this experience on rats. Where they left a group of rats in small individual cages without any social interactions.
And put another group in what they called an enriched environment that had little toys and a play area with a lot of social interaction. It turned out that the brains’ autopsies of the animals who were kept in the enriched environment had significantly more synapses than the animals in the individual cages. And this has been proved multiples times.
Another example would be of people who were born blind, and were rumored to have better senses of hearing and smelling than those of others.
At first, neuroscientists didn’t know what to make of it. But nowadays, we know that this is true. Remember the example of the visual pathway and optic nerve, we said that at the end of the pathway there is what’s called the visual area (area 17) in the cerebral cortex.
Well, it turns out that auditory areas develop in area 17 that is usually responsible for vision contributing to a better sense of hearing. This wouldn’t have happened if these individuals weren’t deprived of visual input.
Learning is for everyone
So, neuroplasticity is the core of our ability to learn, your brain’s plasticity is the only reason you’re able to read and comprehend this article. It’s the only reason I was even able to write this article. Our brains have been plastic since the day we were born and they will remain that way until the day we die. So, no matter how old we are, we can always learn.