What About the Brain Makes Us All Unique?

Most of us know that your environment can have an intense impact on your thoughts, feelings, and emotions, translating into differential personalities and tendencies amongst all people. But, what many people do not know is that there is more than just this "nurture" aspect of behavior, but a "nature" factor as well. There are several biological functions of the brain that contribute to these behavioral differences in significant ways. I have always been fascinated by what it is that specifically causes this disparity amongst people and wanted to get a better understanding on what makes us all so unique. So, I did some research on several aspects of the human brain that might have some correlations with mood and behavior to see how these may vary amongst us all.

Different Parts of the Brain and Their Functions

Differences in Brain Structure and How This May Change the Function 

What many people may not have realized about the brain, myself included, is that the structure varies for all people, contributing to the way we express different traits. In AP Bio this year, we have learned that a change in shape or structure will result in a change in function, and this can be said about the brain. Studies have found that the thickness, amount of folds, and volume of the cortex (the brain's outermost layer) may be associated with different behavioral patterns. Each of our brains folds in order to increase their surface area-to-volume ratio and maximize the amount of tissue in our confined head space. When there is more folding in the brain, the thickness of the cortex decreases and thins out. This is what allows for the greater surface area, without increasing the volume as well. All of this folding leads to greater efficiency in the brain to allow for more neurons and synapses to form, ultimately increasing our cognitive abilities and then behaviors. It seems a decrease in cortical thickness with an increase in volume and folding correlates to feelings of curiosity and sensation seeking. An increase in cortical thickness with a decrease in volume and folding seems to result in greater feelings of impulsivity and neuroticism. The temporal lobes and thalamus in more socially conscious and sensitive people have been found to have increased activity, and greater activity can also be found in the inner and lower frontal lobes, contributing to a feeling of determination. 

Different Regions of Brain Activity & What Traits are Expressed

What is temperament and how does this relate to our personality? 

Temperament refers to physical and emotional traits a person is born with that help shape and influence the decisions they make throughout the course of their life. This most often means behavioral distinctions such as how one learns (attentive/distracted) or interacts with others (introverted/extroverted) as well as several other personal attributes. These traits may be altered over time as a result of external forces and influences, but they are obtained at birth, resulting in their large role in our decision-making while growing up. I personally have had a more shy, introverted temperament since I was younger, and those tendencies have remained qualities of mine over the years. However, I have learned to be more friendly and talkative as a response to my experiences and environment thus far, even though those shy and quiet parts of me still remain prevalent.

The question of whether temperament is determined by genetics and can be inherited is still not entirely clear to neuroscientists studying this area. However, research has suggested that there are genes that act as factors in expressing certain emotional and social traits, both negative and positive and may be responsible for 20-60 percent of temperament. For example, research shows that greater interactions between the DRD2 and DRD4 genes result in greater potential for antisocial behavior or conduct disorder than those without this same level of interaction. Abnormal activity from the MAOA gene plays an active part in causing one to have more aggressive, violent, or impulsive manners. This same gene can also determine other social temperaments, like introversion, because of its role in transcribing enzymes that break down neurotransmitters, altering a person's response to their circumstances. Irregular activity of this gene causes an unstable amount of neurotransmitters in the brain, resulting in negative responses, either at higher expression levels of MAOA or decreased levels of expression. 

An Example of an Abnormal MAOA Pathway

Activity of Neurotransmitters & Its Role in Behavior 

I'm sure you've all heard of neurotransmitters like dopamine, serotonin, epinephrine, and possibly others, but most of us don't know what these neurotransmitters really are and how they work. Neurotransmitters are chemical messengers that travel between between instead of amongst your neurons (nerve cells in the brain) in order for these neurons to communicate. They are responsible for allowing our body to function both physically and psychologically, resulting in different emotions. Some of the biggest neurotransmitters that affect mood are dopamine (feeling of reward), norepinephrine (feeling of attentiveness), and serotonin (feeling of happiness).

Neurotransmitters are secreted by vesicles in the axon terminal of the neuron. They will then diffuse down ion channels out of the cell membrane until they reach the receptors on another neuron, forming what is called a synapse. This allows a ligand-gated ion channel to open or close to let/prevent ions from passing through the membrane of this new target cell. The ions that are controlled by neurotransmitters are responsible for many bodily functions, such as nerve impulses in the brain, the central nervous system, and the peripheral nervous system. Shifts in the membrane potential of the neuron are altered by the ion concentration inside and outside the cell, which will then affect the signals being sent throughout the body. Resting potential is when there is a greater concentration of positively charged ions outside the cell, creating a negative concentration gradient. Action potential is when there is a shift from this negative concentration gradient to a positive gradient because of the ligand-gated ion channel opening, causing a change in the voltage across the membrane. This change in voltage is responsible for the electrical charges in neurons that allow them to transmit information for these bodily processes/functions to occur. 

Diagram Displaying How Neurotransmitters Work 

Heightened or reduced activity of neurotransmitters plays a vital role in a person's mood, ultimately influencing what makes our individual character. An example of this is the activity levels of dopamine that have shown to differ between extroverted and introverted people. Extroverts have higher dopamine levels because they have a lower sensitivity; they don't feel its effects effects as strongly as introverts at the same dopamine levels. Because introverts have a higher sensitivity to dopamine, they can easily feel overwhelmed from it. Instead, acetylcholine has a better response for introverted people, often meaning myself, and allows us to have a more internally calm and thoughtful mood. The difference in suitable neurotransmitters for each personality type contributes further to behavior depending on the pathways caused by them. Extroverts have more talkative, quick-thinking, and social energies, whereas introverts have greater self-awareness, clearer thoughts, and a more reserved social presence. The bodies response to these neurotransmitters can result in entirely contrasting identities.

Different Neurotransmitters & Their Functions

Neuroplasticity

What exactly is neuroplasticity? Neuroplasticity is a term used to describe how the brain changes and adapts structurally throughout one's life based off of your personal experiences. This is meant to reflect the "nurture" aspect I was referring to earlier. In AP Bio, we spend a lot of time learning about how the environment shapes us, and neuroplasticity is meant to reflect how these environmental factors can play such a large role in who we are. Learning, most often correlated with neuroplasticity, is what will help strengthen and form new neurological pathways in the brain. Something like learning a new language, instrument, or skill is more likely to increase neuroplasticity than learning small facts. 

There are two types of neuroplasticity: structural and functional. Structural neuroplasticity is when the brain has a physical change in its structure due to learning new things throughout life. Functional neuroplasticity is when the brain changes the location of certain functionalities as a result of damage in that area. The function is then relocated to an undamaged area, something that happens primarily due to injury. 

So how does this affect behavior? Well, neurological connections form as a result of repetition in your life. Behavioral habits like worrying, meditation, exercise, and more become instilled in your brain and overall mindset, eventually contributing to the type of person you become. In order to change habits you feel may play a negative role in your mind, you have to re-route the pathways in your mind by adopting new behaviors and habits to replace these old ones. Learning new material takes time, and the best way to process information is through slow, consistent practice. There are no long-term benefits to trying all at once because the information will all disappear in time. The most beneficial way to grasp something new is through steady effort over time. Studies also show that social interaction also has a major influence on the brain and behavior. Experiences such as the relationship you may have with your parental figures as a child or stressors in your life shape the connections you form in your mind, and--as I said before-- these synapses are what initiates nerve impulses and the nervous system. 

I learned that there are so many factors that partake in creating this individuality amongst people. Everyone has their own response to parts of the brain, whether that be related to structure, genes, neurotransmitters, or something else. While our personal experiences do provide us with a lot of these moral and social developments throughout our lives, there is more to it than just our surroundings. So many biological processes are responsible for what makes us all special.