Does Your Prefrontal Cortex = You
The short answer is yes, but how exactly is it you. If I surgically removed your prefrontal cortex, would you no longer be anyone at all? Not exactly. This is where it gets a little bit more complicated and a whole lot more interesting.
First, where is the prefrontal cortex? Below is an image of the brain with the prefrontal cortex highlighted in yellow:
The prefrontal cortex is the anterior, the very front, part of our brain. So why does it encapsulate so much of us?
The prefrontal cortex is largely responsible for maintaining cognitive control. Cognitive control is the ability to react to your external and internal environment in an effective way. There are three aspects of cognitive control:
- Inhibition control
- Working Memory
- Cognitive Flexibility
Inhibition control is our ability to resist automatic reactions. These automatic reactions can be either physical or cognitive. For example, when you see a big piece of chocolate cake, you will want to go eat it, but many times it behooves you not to eat that piece of cake. A cognitive example is when you are sitting in class, it is easy to drift into a reverie, but it benefits you to continue to focus on the lecture.
Working memory is synonymous with short-term memory, but it also includes the manipulation of the information. For example, when someone asks you for directions to the nearest gas station, an individual will transiently hold that information in memory while also manipulating it to provide effective directions. Working memory is pretty limited; the amount of items that can be held in working memory at any one time is between 3 and 4 items. As a result, people who do well in fluid intelligence tests are usually able to focus better in order to prevent behaviorally futile information from taking up working memory rather than having the ability to hold more than 3 or 4 items in working memory at one time.
Cognitive flexibility is the brain's ability to adjust to different circumstances and goals. This can encompass anything from the basics of fluid intelligence to choosing the most efficient way to complete a task.
It's these three capabilities that allow each of us to have cognitive control, but what is the role of the prefrontal cortex in all of these. I’ve mentioned a lot of examples that would need to utilize a variety of different areas in the brain: motor actions for grabbing (or walking away from) the big piece of chocolate cake, vision for remembering the locations of streets and buildings to give directions, and more. So, let’s go through each of the three capabilities — inhibition control, working memory, and cognitive flexibility — one by one to see the role of the prefrontal cortex in these vital abilities.
Inhibition Control
Scientists have done studies on what parts of the brain are involved with inhibition control. One study that I just learned about in class is from 2003 in Nature Neuroscience. (here is the link) The study showed that the right inferior frontal cortex plays an idiosyncratic role in inhibiting actions. Additionally, studies have shown that there is a similar pattern between the right inferior frontal cortex and sensory areas — that is, right inferior frontal cortex would inhibit activity in a particular sensory area of little interest and would stimulate activity in a particular sensory area of behavioral salience. So, where exactly is the right inferior frontal cortex? Is it part of the prefrontal cortex?
Now compare it to the photo of the prefrontal cortex I showed before:
The right inferior frontal cortex is very much within the prefrontal cortex! So, we know that parts of the prefrontal cortex are idiosyncratically responsible for behavioral and cognitive response inhibition.
Now, this does not mean that other areas aren't involved. For example, the basal ganglia plays a key role in transmitting information from the right inferior frontal cortex to the thalamus where it can be directed to salient sensory or motor areas through the hyperdirect or indirect pathway. Nevertheless, based on the evidence we have, the prefrontal cortex, specifically the right inferior frontal cortex, has an idiosyncratic role in cognitive and behavioral inhibition.
Working Memory
Working memory is the ability to hold information in memory for a short period of time while manipulating it. There are two types of working memory: phonological and visuospatial. Phonological working memory is essentially any type of audio-verbal information, but the audio-verbal information can come from our external environment — such as from the loud construction ground nearby — or it can come from your internal environment when you repeat some salient information. When you say a word, a list or even a sentence over and over again, you are putting information into your working memory that is internal. On the other hand, visuospatial working memory is visual memory. Visual memory could be anything from remembering a phone number you just wrote down to remembering how to traverse through a particular part of town.
Phonological and visuospatial information comprises all the information in working memory, but working memory is severely limited. Working memory, according to scientists most recent evidence, can hold only 3 to 4 items at once. Nevertheless, working memory is critical for just about every task. So what part of the brain monitors working memory? What is the role of the prefrontal cortex, if any?
It turns out, working memory works similar to any other type of memory except the information that is remembered is also manipulated. So the images or auditory information is housed where that type of information is usually found: the posterior parietal lobe for spatial, the visual cortex and inferior temporal cortex for any other type of visual information, and language areas in the brain such as Broca’s Area, Wernicke’s Area, or the superior temporal gyrus for auditory information. In contrast to short term or long term memory, the information in working memory requires constant activity, and this activity has been observed in the prefrontal cortex.
That’s right, the prefrontal cortex is responsible for maintaining working memory! In fact, the neurons in the prefrontal cortex fire at different times in the prefrontal cortex when maintaining working memory as if the neurons were forming a reverberating pattern to make sure the information was readily available. Now, there are other parts in the brain that have been proposed to also be crucial for allowing the prefrontal cortex to connect to the necessary areas such as the mediodorsal nucleus of the thalamus. However, the prefrontal cortex still plays a major role in maintaining access to working memory.
Cognitive Flexibility
There are two types of cognitive flexibility that I am going to talk about here: fluid intelligence and task shifting. Fluid intelligence is intelligence that does not depend on any knowledge. So someone who has never attended school may do better on a fluid intelligence test that a Ph.D. student. The intelligence that includes the information you learn is called crystallized intelligence, but that is for a different time. A task set is the ability to use the right cognitive operations in order to get a job done. In congruence with task set, set shifting is the ability to change your task set based on the environment and the task you are asked to do.
Let’s look at fluid intelligence first. The frontoparietal network is associated with fluid intelligence — and also attention interestingly enough. Scientists have evidence to confirm this claim in patients who have lesions in the frontal-parietal network, but where is the frontoparietal network? Well, quite simply, it is comprised of the frontal lobe and parietal lobe:
Notice that the prefrontal cortex is a major part of the frontal lobe.
The second part of cognitive flexibility is task shifting. Different tasks activate different parts of the brain. For example, spatial tasks activate areas in the dorsolateral prefrontal cortex and the parietal lobe whereas verbal tasks activate areas in the ventrolateral prefrontal cortex and the temporal lobe. However, the area that activates regardless of the type of activity is the anterior prefrontal cortex! The anterior prefrontal cortex is associated with choosing which tasks to activate by sending signals to either of the two types of areas I just mentioned above — the dorsolateral prefrontal cortex and parietal lobe for spatial tasks and ventrolateral prefrontal cortex and temporal lobe for verbal tasks. Here is an image of the anterior prefrontal cortex:
Here is an image of the ventrolateral and dorsolateral prefrontal cortices:
Now, notice how all of these areas are very much within the prefrontal cortex.
Conclusion
As seen above, all three aspects of cognitive control — inhibitory control, working memory, and cognitive flexibility — rely on the prefrontal cortex. So, while you would not disappear if your prefrontal cortex were to be injured in some way, you would definitely not be you because you wouldn’t be able to inhibit actions as you did before, manipulate memories or the world around you as you did before, or respond as efficiently to the world around you. However, these three aspects of cognitive control are not the only functions of the prefrontal cortex. The prefrontal cortex is also involved with functions such as rules and attention which are both crucial to who you are — rules might be paramount in terms of your identity. So, yes, the prefrontal cortex is extremely important, and I am excited to see what the field of neuroscience will discover about its various roles in the coming years!
