The Prefrontal Cortex - An Introduction to What Makes Us Human

Besides being relatively hairless apes, there are some things about humans that make us special among animals.  In the past we have noted things like, “We have big brains and we use tools,” or “We contemplate the future and our own mortality,” or “We use a truly complex language both verbal and written to communicate complex ideas.”  These are things we have and do, but what is it about our brains that makes that possible.  More and more we are identifying crucial hubs or nodes within our brain that specialize in various tasks, but none of these work alone. I am going to start by discussing that big blob of gooey mush on the front of our brains called the prefrontal cortex, and in subsequent episodes, I will discuss how these regions function in tandem with deeper structures within the brain to create what we think of when we say “human.”

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Transcript

Welcome to PsyDactic - Residency edition.  I am Dr. O’Leary and today is… This is a podcast about psychiatry, psychology, and neuroscience.  If you haven’t been here before, then I welcome you.  I put these episodes together primarily for my own benefit.  By having to make something like this, I am forced to really dig deep into things, re-read and try to interpret what I don’t get the first time.  This means that what you get when you listen to this is my own formulation.  I have no editorial staff, and I do try to verify and fact check everything I report here, but I know that I will be wrong about some things, so please, use this to inspire your own curiosity and don’t forget to do your own search to see if what I say or what you understood me saying is in fact the truth.

Besides being relatively hairless apes, there are some things about humans that make us special among animals.  In the past we have noted things like, “We have big brains and we use tools,” or “We contemplate the future and our own mortality,” or “We use a truly complex language both verbal and written to communicate complex ideas.”  These are things we have and do, but what is it about our brains that makes that possible.  More and more we are identifying crucial hubs or nodes within our brain that specialize in various tasks, but none of these work alone.  Each has a set of complex inputs (things that neuroscientists call afferents) and outputs (that neuroscientists call efferents) and the networks that these form are what make truly complex thinking possible.

When a basketball is unexpectedly flying at my face, I am doing more than merely swatting it away to protect myself.  In milliseconds, I have already determined its position and estimated its path through space, made a guess as to what kind of object it is, determined which limb would be the best to block it with, placed myself in a social context, and with that information guessed whether or not that ball was an intentional threat or an accident. My brain has also done a lot of other things that I am not consciously aware of.  We do all of this because we have trained our brain over years or decades to pick up on multiple cues from our environment and construct a reality that we can place ourselves in.  That is truly amazing.

Neuroscience is painstakingly picking apart the various details of our brains organization and function that help us to do these things.  In this episode, I am going to start a series that looks deeper into various brain regions and the networks that they are a part of in order to help myself understand a little bit more about how this happens, and hopefully, make me a better psychiatrist.

I am going to start by discussing that big blob of gooey mush on the front of our brains called the prefrontal cortex, and in subsequent episodes, I will discuss how these regions function in tandem with deeper structures within the brain to create what we think of when we say “human.”

When I realize something that I feel like I should have known or see something truly amazing, I often facepalm.  My hand lands on my forehead, and ironically it is anatomically correlating itself with the part of the brain that can help me to actually understand what has happened.  That is the prefrontal cortex.  There are three anatomical divisions of this part of the brain that do a lot to make us human.  If I had X-ray vision and could stare up and slightly backward into my brain, the first section I would encounter is called the orbitofrontal cortex.  It's above the orbits in the front part.  It sits just above and extends a little behind our orbits or eye sockets as they are more commonly known.  If I then could slip my hand through my skull and rest it on the orbitofrontal cortex and slide it over that bumpy surface into the center plane of my brain where there is a small space between my lobes, I would be touching my medial prefrontal cortex.  It is in the middle front part.  If I follow my medial prefrontal cortex up and over the sharp angle above it onto the surface of the brain that extends from that angle all the way down to the next angle, I would have tickled my dorsolateral prefrontal cortex.  It is the top and outside part of the front.  If I kept going over the next curve, I would end up back where I started, in the orbitofrontal cortex.  Now I am going to go wash all the cerebral spinal fluid off of my hands before I continue.

** Sound of washing hands **

Each of the regions that I just violated has specialized functions built into it.  They get information from various other parts of the brain and body and they think about that information.  They make sense of it.  Then they send a signal to other parts of the brain to communicate that sense.  In this episode, I am going to review what each of these regions is known to do and in future episodes, I am going to deal with each of them separately and talk more about how they get information and how they send that processed information to other places to figure out what to do about it.

Let’s start with the orbitofrontal cortex.  If I were to damage one or both of your orbitofrontal cortices, people may no longer be able to recognize you.  I don’t mean you would appear different in your anatomy.  Even if there was no damage to your face, you would no longer act the way you did before.  You may be more outspoken and less concerned with what others think about you.  You may be described as tactless or rude.  You could be inexplicably irritable and mean, or have an inappropriately good mood when you really ought to at least pretend to be sad.  Your interests might change.  You may be less conscientious, meaning that you no longer care as much about the consequences of your actions or the quality of your work.  You might even develop a kind of euphoria that looks a lot like mania. Overall, you could be concerned less about your environment, or even your own well-being.  You might not even feel hungry at the sight of your favority food.  In general, you have lost a lot of the ability to place yourself in your environment the way most people would and socially, you might be a jack-ass.  If you turn your eyes up and back at your brain, you would be staring at a relatively small region of the brain that in many respects determines your personality.  That is your orbitofrontal cortex.  The orbitofrontal region processes a lot of information from your internal and external environment and relays the importance or salience of that information to other regions.  Without the same kind of awareness, you may be awkward, inappropriate, and poorly kempt.

However, you would maintain your ability to do logical operations like sort cards, and make plans.  That is because your Dorsolateral Prefrontal Cortex is still functioning.  The prefrontal cortex has been referred to as the executive center of the brain.  It does not receive somatosensory information directly from the spinocortical or cranial nerve tracks.  Instead, it gets this information after it has already been processed in other parts of the brain, and then processes that information further in order to plan and give orders to the rest of the brain.  One side of the DLPFC, usually the left, contains an area called Broca’s area that is specialized to process language and helps produce speech.  The DLPFC also contains a large portion of our brain's working memory, which is the part of our memory system that stores currently relevant information (both new and already learned) about whatever it is we are thinking or doing at that moment in order to keep us on track and give us options.  This has been compared to the RAM memory on your computer or cell phone.  Here is where we make more considerate and conscious decisions, where we follow a train of thought and consider multiple scenarios, where we calculate risk, where we make decisions despite having conflicting information.  Damage to this area can make it difficult to actually decide on a course of action or to initiate action.  Hypofunction or dysfunction of this area is thought to be part of the pathogenesis of ADHD, with poor concentration and difficulty suppressing speech or movements, and also in schizophrenia, where hypofunction or relative disconnection of this area may contribute to the formation of delusions, or the inability to consider alternatives, or to move on from one topic to another, making the patient disorganized in their thinking, but it is almost certainly involved in many, many other disorders.  The dorsolateral prefrontal cortex is responsible for cognitive organization and flexibility.  It might even be crucial when we need to lie.  Part of us deciding on what to say or not to say includes how much of the truth that content will contain.  The dorsolateral prefrontal cortex can help us to lie.

The dorsolateral prefrontal cortex is not the only part of our brain that helps us make decisions.  Parts of the medial prefrontal cortex are crucial for this as well, especially if there is some very personal or immediate social content to consider.  While the dorso-lateral prefrontal cortex is more like Mr. Spock, arriving at decisions more exclusively on the basis of logic, the medial prefrontal cortex is more like Captain Kirk, using his intuition and feelings to inform his final decision.   If you were able to take your brain out and set it  on the table in front of you with the frontal lobes facing you, then you could put your hands in the praying position and slide them between the left and right frontal lobes.  They would be resting against the left and right medial prefrontal cortex.  To get to the entire medial prefrontal cortex you would need to open some space between your fingers and let the genu of the corpus callosum slide between them, because this region wraps itself around the genu and rostrum of the corpus callosum.  This anatomical definition captures many different regions, including the anterior cingulate gyrus, which can be separated based on their functional specializations.

The ventral section of the medial prefrontal cortex appears to take socially relevant information and help us make decisions based on that.  It could be said to be our conscience, helping enforce moral principles, helping us to understand that other people have their own mind and motivations that should be valued.  It is also heavily involved in emotional and autonomic regulation and it may also help with extinction learning (which is basically unlearning something, especially conditioned responses).  Damage to the ventral medial prefrontal cortex can result in antisocial behavior and less emotional response to things like the suffering of others.  If you have seen the Red Dragon/Silence of the Lambs movies, you may have noted a complete lack of empathy in Hannibal Lecter, so much so that he can pass a lie detector test effortlessly.  That is because his ventromedial prefrontal cortex is not activating his autonomic nervous system the way it would in a normal person.

Another part of the medial prefrontal cortex is the dorsomedial prefrontal cortex and from what I can tell, the dorsomedial prefrontal functions are not known to be that differentiated from the ventromedial prefrontal cortex.  It aids in social salience, emotional regulation, theory of mind (which is understanding that others have their own thoughts and feelings), and also is crucial to maintaining our sense that we have a separate and distinct identity from the rest of the world.  In patients who experience depersonalization, this area of the brain has been shown to be hypofunctioning compared with non-affected controls.

Finally we have the anterior cingulate cortex, which is a major hub of the brain, helping to assign salience or meaning to both externally and internally generated information.  It is highly connected to other parts of the cortex as well as the anterior insula, nucleus accumbens, hypothalamus, hippocampus, and amygdala.  I am going to save this one for later.

In the next few episodes I am going to treat each of these regions separately and explore in more depth how they are organized from a cellular to network level, how they communicate with other parts of the nervous system, and how dysfunction in any of these regions can result in problems for an individual or for society in general.  In some cases, we may be able to harness what we know about these regions in order to treat a wide range of neuropsychiatric disorders.

Thank you for listening. I am Dr. O’Leary, and this has been an episode of Psydactic - Residency Edition.