Brain Localization

Human beings are special.  If you compare our species to all other animals, we are fairly unremarkable in most respects.  We can't run very fast, our bodies are quite weak and puny, and we don't have particularly sharp teeth or claws.  How do we even manage to survive?

But what humans lack in brawn, we certainly make up in terms of brain.  In just an evolutionary blink of an eye, humans have developed ingenious tools, invented languages, built cities, even travelled to outer space.  All of this can be traced to our exceptional brains.  

All of our ideas, thoughts, feelings, impulses, and emotions seem to be produced by a mysterious lump of squishy grey matter encased between our ears.  How does this all work?  While the mysteries of the human mind are far from being solved, we know far more about the brain than ever before.  In the Biological level of analysis, psychologists study how the brain works, and how our biology shapes our behavior.  Are you ready to dive in?
Video Activity

In the video below, you'll see what an actual human brain looks like (be warned: it might make you squeamish!)  Don't worry too much about the information in the video.  Just imagine that you are a curious scientist, who is trying to understand how the brain works.

How would you go about studying the brain?  How is this even possible?
How to study the brain?

As you may have realized, studying the brain is a very challenging task.  The only time you would ever see someone's brain was once they were already dead, and then what?  You can see the physical shape and size of the brain, but not much else.  How this strange lump of matter produces conciousness, personality, memory, emotion and thought seems like an unsolvable riddle.

In fact, for much of the 19th century, brain scientists mainly wasted their time on a scientific dead-end known as phrenology.  In this field, scientists studied the brain in the only way they knew how - by taking records on the personality and intelligence of people, and then comparing these notes to the size and shape of their brain, once they had died.  For example, if a cruel murderer was found to have bumps on a certain part of his brain, it was assumed that those bumps had caused his criminal activity.

Unfortunately for phrenology, the brain is not that nearly that simple.  Phrenology turned out to be completely useless to understanding the brain.  However, one of the underlying ideas of phrenology has stood the test of time.  Brain localization refers to the idea that brain is made up of specialized modules (to put it simply, different parts), and that each module has a certain function.  For instance, one part of the brain might be involved in storing memories, another in recognizing faces, another in producing language.  Phrenologists drew up complex diagrams of the brain, illustrating the supposed function of each part, like the one below.  These have turned out to be false, but the underlying principle of brain localization (as you will see) is now widely accepted in brain science. 

TOK Link

By the end of the 19th century, many Scientific fields had seen great leaps of progress.  For instance, the Periodic table had been invented in 1869, Darwin's theory of Natural Selection had been published in 1859, and Newton's laws of motion had already been around for 200 years!  In contrast, the field of brain science had yet to see any progress at all.  Phrenologists put forward theories that were nothing more than wild (and, it turns out, false) guesses about the workings of the brain.

Why has knowledge of the brain taken so long to develop?  How have methodological difficulties halted progress?  What role (if any) did faith, religion and superstition play in holding back the Science of the human brain?

Case Studies of Brain Damaged People: Tan and Phineas Gage

After many false starts and dead ends, brain scientists finally got their lucky break with a number of cases of brain-damaged people.  In those rare cases, a person (through illness or accident) suffers damage to a specific part of their brain.  Consequently, scientists could see what (if anything) changed in that person's behavior.  For instance, in one famous case, a man suffered brain damage and completely lost the ability to speak.  He could only repeat a single word over and over again: "Tan, tan, tan".  After the man died, a doctor by the name of Broca conducted an autopsy, and found a lesion (damage) in a specific part of his brain, which later became known as "Broca's area".  This case study suggested that Broca's area plays a key role in language production.  Finally, scientists seemed to be making progress in understanding how the brain worked.

Although case studies helped make progress in brain science, we need to be cautious in interpreting the results.  We need to keep the following points in mind:

  • These case studies usually involve just one person.  We can't be completely sure that other people with the same kind of brain damage will be affected in the same way.  Therefore, generalizability of results is low

  • It is not possible to replicate these case studies.  It would obviously be highly unethical to intentionally damage someone's brain on purpose, just to see what would happen

  • There is usually limited information on what the person was like before the brain injury, so comparisons of the person "before and after" the injury are usually incomplete

  • However, if a number of similar case studies emerge, in which people with the same kind of brain damage experience similar effects, then the findings from one case study can be triangulated with the other case studies, increasing the generalizability of the results

Try it Out

You are about to learn about one of the most famous case studies in the history of Psychology.  Read the article "Phineas Gage and the effect of an iron bar through the head on personality" and watch the video below.  Make notes on the following:

1.  Which parts of Phineas Gage's brain were damaged?

2.  How did Phineas Gage's personality change after the accident?

3.  What does this case study tell us about the brain?
When the iron rod passed through Phineas Gage's brain, it destroyed most of his left frontal lobe.  Somehow, Phineas managed to survive - but he was not quite the same person after.  Read the box below for a summary of the case study on Phineas Gage.
Research: Phineas Gage 

Aim: Investigate how serious damage to the left frontal lobe affects behavior

Procedure: Harlow conducted a case study on Phineas Gage, a railroad worker who suffered a sever accident.  A metal rod passed through Gage's skull, nearly destroying his left frontal lobe.  Harlow observed Gage's behavior after the accident, and interviewed people who knew Gage both before and after the brain damage.

Findings: Phineas Gage's personality changed dramatically as a consequence of brain damage.  Beforehand, he was known as a responsible and capable worker.  Afterwards, he became highly unemotional, unable to control his impulses.  He would make plans, but was incapable of following through with them.  He would also behave inappropriately, using vulgar language, acting violently, even possibly molesting children.

Conclusion: This case study suggests that the frontal lobe plays an important role in personality, particularly in goal setting, self-regulating behavior, and following social conventions.


  • This case study is historically important because it provided the first evidence of the role of the frontal lobe in behavior​​

  • This study supports the principle of brain localization - that a specific part of the brain (in this case, the frontal lobe) has a particular function (in this case, self-regulation)

  • It is not possible to replicate this case study, so the findings may not generalize to other people.  Not everyone may respond to a left frontal lobe injury in a similar way

  • Many of the reports on Phineas Gage's behavior are inconsistent.  It is not clear if the personality changes were permanent, or just lasted a short time
  • We don't have much knowledge of Phineas Gage's personality before the accident, so it is difficult to know with certainty how much Gage's personality really changed
Role of the Frontal Lobe

The brain is divided into four lobes.  The frontal lobe is situated in the front part of the brain, under your hand when touching your forehead.  The very outermost layer of the frontal lobe is called the prefrontal cortex, and it is hard to overestimate how importance of this part of the brain in human behavior.

At the time that a metal rod passed through Phineas Gage's skull, destroying much of his left frontal lobe, scientists and doctors didn't know much about the frontal lobe.  But the Phineas Gage case provided important clues.  Phineas Gage had lost the ability to regulate his social behavior, control his impulses, and resist urges.  It was as if he had become a slave to his passions, with no ability to regulate himself.  This provided important clues to the role of the frontal lobe in decision making, self-regulation, and social behavior.

After decades of research, we now know far more about the frontal lobe.  The frontal lobe is now believed to be the source of executive functions in the brain, almost like your brain's CEO.  Just like the CEO of a company, executive functions include making big decisions, and controlling the urges and whims of the rest of your more primitive brain.  Briefly, the executive functions of the frontal lobe include the following:

  • Recognizing future consequences from current actions.  Suppose you go to buy a few things from a store, and see a display of delicious, imported (and very expensive) Belgian chocolates.  You are very hungry, and have a sudden urge to just grab the chocolates and run away.  But then you stop and think.  You might get caught.  The security guards would call your parents, you might have to pay a large fine, or even go to court.  You decide the future consequences just aren't worth it, and walk away.  Imagining the future consequences of your actions, and adjusting your behavior accordingly, is a function of your frontal lobe.

  • Resist urges. You are driving to your part-time job, and another car cuts you off.  You have a strong urge to honk loudly, maybe even raise your middle finger to the driver.  But then you check your impulse, realize that nothing good is going to come of it, and continue on your way.  Resisting urges is a function of your frontal lobe

  • Make deliberate decisions, and following through on them.  After carefully considering the merits of various universities, you decide on your top choices based on their reputation, campus culture, location, and your chances of getting in.  Next comes the hard part - preparing your applications.  You need to fill in forms, book an SAT test, get reference letters from your teachers, write your personal statement, and apply for financial aid.  It is a very complicated process, but you are able to make a plan a follow through on it.  Making careful, deliberate decisions, and following through on them through careful planning, is a function of your frontal lobe.​​

As you will later learn, the development of brain imaging technology has meant that case studies of brain damaged people are no longer so important.  We can now scan the brains of thousands of people, and correlate areas of brain activity with different sorts of behaviors.  But the case study of Phineas Gage provided the first clues to the function of the frontal lobe, clues which have since been verified by far more advanced research methods. 

Think Critically

Teens are often accused of being reckless, hot-tempered, and risk-seeking.  They drive too fast.  They do stupid things to show off to their friends.  They do what feels good in the moment, ignoring future consequences.

Interestingly enough, the prefrontal cortex is the area of the brain that takes the longest to develop, not reaching fully maturity until around the age of 25.  ​You can see this in the brain scans below.  In teens, most of the brain is more mature (blue / purple) except the prefrontal cortex, which is still mostly green (less fully mature).

Explain why teens sometimes tend to behave in a reckless or irresponsible manner, making reference to the development of the frontal lobe, and other possible factors which might influence teen behavior.

  • I can explain the concept of brain localization

  • I can explain how case studies of brain-damaged people can be used to investigate the functions of different parts of the brain

  • I can discuss some of the limitations of case studies

  • I can describe the Aim, Procedure, Findings, and Conclusion of Harlow's case study on Phineas Gage, as well as Evaluate the findings of the study

  • I can explain the significance of Harlow's study on Phineas Gage in understanding the function of the frontal lobe in behavior
Quiz Yourself!

1.  Research has suggested that a part of the brain called the hippocampus plays an important role in converting short-term memories to long-term memories.  This is an example of

(a) Phrenology

(b) Brain localization

(c) Executive function

(d) Replicability of results

2.  Case studies of brain-damaged people have a number of limitations.  Which of the following is not one of them?

(a) Low ecological validity

(b) Impossible to replicate

(c) Low generalizability

(d) Limited information on the person before the brain damage

3.  Which of the following statements does not describe the consequences of Phineas' Gage's brain injury?

(a) He had trouble behaving in a socially acceptable manner

(b) He could not regulate his behavior succesfully

(c) He could not control his emotions

(d) He could only repeat a single word, "Tan"

4.  Which part of the brain has been linked to "executive functions"?

(a) Broca's area

(b) The occipital lobe

(c) The temporal lobe

(d) The prefrontal cortex

5.  Which of the following behaviors is most closely associated with the frontal lobe?

(a) Recognizing your friend from across a busy street

(b) Remembering your first day of primary school

(c) Eating a healthy snack instead of chocolate cake

(d) Catching a ball thrown in mid-air


1 - B, 2 - A, 3 - D, 4 - D, 5 - C