Brain Imaging Technology

Case studies of brain damaged people provided some important clues about the inner workings of the mind.  However, in the last 30 years or so, advances in technology have led to a revolution in the science of the brain.  To understand how this technology can be used, let's begin by looking at a man with one of the baddest brains imaginable. 
​Video Activity

Tommy Lynn Sells was an American serial killer, suspected of murdering over 20 people.  Watch the documentary about him below, and think about why he did it.

What is it about Sells that is abnormal - different from you and me?  Think about his emotional response to his victims, and how it would differ from a normal person's.

How the technology works:   PET and MRI scans

Sells felt no pity, remorse or fear when killing his victims.  Unlike any normal person - who would be completely disgusted and horrified by the thought of slitting an innocent girl's throat - Sells felt nothing.   A scientist by the name of Raine - who you briefly saw in the video - began to wonder if brain defects might be responsible for such callousness.  To investigate, Raine used a technology called PET scans.  Along with MRI, these brain scans have become powerful tools for studying the brain.  Let's briefly look at how they work.

PET scans work on a simple idea - the brain needs energy to work.  The more "active" a certain part of the brain is, the more energy it requires.  PET scans involve injecting the subject with radioactive glucose (sugar).  The glucose is a source of energy, and being radioactive, it can then be detected by the PET machine.  The most active parts of the brain use the most glucose, and this is shown in a PET scan.  After the scan is complete, a colored map of brain activity is produced.  More active parts of the brain - indicated by a higher concentration of glucose - are colored in red.  Take a look at the video below to see a PET scan in action.

MRI scans work on a similar idea, except that magnetic fields are used to track the flow of oxygenated blood within the brain.  More active parts of the brain require more oxygen, and so blood flow (which carries oxygen to the brain) will be more concentrated in more active regions.  The MRI machine is a powerful magnet, which can track the flow of the oxygenated blood to different parts of the brain. A variation on MRI scans, called fMRI (f stands for function), allows for many images to be taken in a short period of time.  This allows for a "movie" of brain activity, showing which parts of the brain become active on a moment-by-moment basis.  Take a look at the video below, which explains how an fMRI works.  (The video goes in more detail then you really need to know, but it is interesting anyways!)

Brain technology: Uses

Although this technology is fascinating in its own right, we need to think carefully about how to use this technology to investigate human behavior.  Here are two ways to do this:

  • Compare brain activity between two "groups" of people.  Suppose, like Raine, you wonder if serial killers have something wrong with their brain.  You could carry out a study in which you scan the brains of serial killers, and compare that with brain scans of "normal" people.  In fact, you could use technology to compare patterns of brain activity between any two groups of people.  You could compare the brain activity of mentally healthy people with those suffering from depression, compare the brain activity of children with adults, even the brain activity of men with women.  Someday, scientists may be able to diagnose a mental health problem - like depression or anxiety - simply by scanning your brain, and seeing which regions are more or less active.  Either PET or MRI scans can be used to compare brain activity between two groups of people.

  • Investigate which parts of the brain are involved in specific thoughts & behaviors. Using an fMRI scanner, scientists can investigate which parts of the brain "light up" (i.e. becomes more active) when doing something - solving a Math problem, looking at a picture of your romantic partner, or even telling a lie.  This is a powerful tool for investigating brain localization, which was introduced in the previous lesson.  By looking at which parts of the brain become active in different tasks, scientists can get a much better idea of the function of each brain region.  For instance, if a certain part of the brain seems to "light up" every time you look at a picture of a human face, then that part of the brain is probably involved in reading people's faces.
PET vs MRI: A comparison

Considering the similarity of the two technologies, you might wonder why scientists might choose to use one rather than the other.  Here are some points which might factor into their decision:

Advantages of PET scans

  • Many people find PET scans to be less castraphobic than the MRI, since the machine consists of an open ring, rather than a closed chamber

  • Unlike the MRI, in which participants must keep completely still, minor movements do not affect the results of a PET scan

Disadvantages of PET scans

  • The images produced by PET scans are of lower resolution compared with the MRI

  • PET scans involve injection of a radioactive substance, which not all participants are comfortable with

Advantages of MRI scans

  • Images produced by MRI scans are of high resolution

  • Many hospitals already have an MRI scanner for medical purposes, so no additional equipment is required

Disadvantages of MRI scans

  • Small movements can ruin MRI scans, so participants must keep completely still.  (However, as technology continues improving, this may no longer be the case in the future)

  • Many people find MRI machines to be claustrophobic

Video Activity

Now that you know a little more about how brain imaging technology works, let's return to the question that we started with - whether brain abnormalities could explain why some people turn out to be serial killers.  Watch the video below on brain imaging research carried out on psychopaths and serial killers. Which two regions of the brain are important in understanding them?
Research: Raine

Aim: To investigate the brains of violent murderers

Procedure: This study involved a comparison of two groups of people: murderers who had pleaded not guilty for reasons of insanity (NGRI) and normal, non-violent people.  A total of 41 murderers had their brains scanned, and this was compared with 41 control participants.

Findings: Murderers tended to have less activity in their prefrontal cortex.  (Remember where we first learned about the prefrontal cortex?  As we saw with the case of Phineas Gage, the prefrontal cortex is associated with controlling impulsive behaviour - including violent and sexual impulses).  Murderers also tended to have a shrunken amygdala, a part of the brain associated with emotion and fear.  

Conclusion: Brain abnormalities may explain why some people turn out to be killers.  Lack of activity in prefrontal cortex may make it difficult for killers to control their violent impulses.  And a deformed amygdala could explain the lack of empathy, remorse and guilt of psychopathic killers.


  • Findings are consistent with other brain research and observations of serial killers, many of whom show no empathy for their victims or remorse for their actions

  • The study was done on a very specific group of people - murderers who had admitted to their crimes, but who were claiming they were insane.  We can't be sure these results generalize to other murderers or violent criminals

  • This is correlational study, so we can't be certain that brain abnormalities cause someone to become a killer.  It could be the other way around - perhaps living a life of violence and murder causes changes to the brain.  Or, perhaps, another factor (like being abused as a child) could be responsible for both brain abnormalities and an increased likelihood of becoming a killer

Think Critically

Brain imaging technology has resulted in tremendous growth in brain research.  A slew of studies have been published in recent years which claim to understand everything from romantic love to religious experience on the basis of which parts of the brain "lig0 up".  But how much do these brain images really tell us?  Read this article from Scientific American titled "The Brain is not Modular: What fMRI Really Tells Us" , and make notes on some of the limitations of brain imaging studies.
Limitations of PET & fMRI

  • Multiple areas of the brain "light up" in any situation, making interpretation difficult. No matter what you are doing, many parts of your brain are at work.  This makes it difficult to really say for certain what each part of the brain "does".  For example, in one study on political preferences, the word "Republican" caused the amygdala and insula to light up (which are associated with disgust), but also activated a part of the brain normally associated with reward.  This makes it difficult to pinpoint the role of any one part of the brain.

  • Brain areas activate for multiple reasons. For instance, we know that the amygdala "lights up" when people are in frightening situations.  But can you conclude that someone is afraid every time their amygdala lights up?  Not so fast.  The amygdala also lights up for positive emotions as well.  There isn't a simple "one to one" relationship between parts of the brain and behaviors.  Many different behaviors activate the same part of the brain, and many parts of the brain are involved in any behavior.

  • Results are correlational.  For instance, Raine found that murderers had deformities in their amygdala compared to normal people.  But that doesn't tell us that deformities in the amygdala cause someone to become a killer.  There are simply too many other factors that may also play a role.  For instance, perhaps murderers were also more likely to have been abused in their childhoods, and that's why they have deformed amygdalas.  Correlation does not equal causation.

  • fMRI measures changes in oxygenated blood flow, not neural activity. The brain is actually made up of billions of neurons, and the activity of each neuron plays a role in behavior.  But no brain scan is detailed enough to reveal activity at the level of neurons.  Instead, fMRI measures the flow of oxygenrated blood, which is taken as a measure of how active a region of the brain is.  While this is useful, it is a simplification of what is really happening in the brain.

  • Brain scans are not a natural environment, so ecological validity may be low.  Brain scans take place in a laboratory, in a highly controlled environment, in which you are laying down with your head inside a huge machine, following the instructions of a scientist.  It is questionable whether your brain will behave the same way in real life situations.  For instance, some researchers have tried to use fMRI as a sort of lie detector test, measuring which parts of the brain are active when people are telling lies.  But telling "lies" as a part of a research study (when you are actually instructed to lie) is very different from lying in a real-life situation (with real-life consequences).

Think Critically

Imagine you were a participant in Raine's study on the minds of murderers.  You look at an image of a brain, with a deformed amygdala and lower activity in the prefrontal cortex.  You wonder what sort of heinous crimes a man with such a brain may have committed.  And then you get the news - that's actually an image of your brain.

Watch the video below, which describes exactly that situation.  What does this video tell us about the complexity of human behavior?

Brain imaging technology can sometimes lead to overly simplistic explanations.  It is deceptively easy to conclude (based on Raine's study), that some people are just born with defective brains, and that's why they become serial killers.  This is called a reductionist explanation, because it tries to explain a complex behavior (becoming a killer) as a result of a single cause (a defect in brain function).  But human behavior is rarely so straightforward.  

As the video on Jim Fallon demonstrates, measures of brain activity alone can't determine who will become a killer.  Jim has patterns of brain activity and genetics that are similar to those of psychopathic murderers.  But instead of ending up as a serial killer on death row, he has become a sucessful professor, husband, and father.  Clearly, there are other factors besides genetics and brain function that determine who becomes a serial killer and who doesn't.  Experiences in childhood, family and peer influence, and social learning all likely play a role.

So always be wary of reductionist explanations.  Humans are very complex creatures, and there is rarely a single cause for any behavior.

IB Psych Matters

Research on the brains of serial killers have all sorts of fascinating real-life implications.  Using your knowledge of brain imaging technology (and its limitations), how would you respond to the following ideas?

  • A lawyer argues that his defendant, a convicted serial killer, should be sent to a mental health hospital, rather than a prison.  Brain scans of the defendent show structural abnormalities.  If a brain defect is responsible for the defendant's murderous behavior, was it really his fault?

  • As part of a campaign to fight crime, a new law requires that every adult is required to have their brain scanned when they turn 18.  People identified as "high-risk" for criminal activity must regularly meet with a counsellor, and wear an ankle bracelet equipped with a GPS tracker.  

  • I can explain the basics of how a PET scan and fMRI work

  • I can discuss how brain imaging technology can be used to compare two groups of people, or to investigate which parts of the brain are involved in specific behaviors

  • I can compare strengths and limitations of PET and fMRI scans

  • I can summarize the Aim, Procedure, Findings, and Conclusion of Raine's research on the brains of serial killers, and Evaluate the study

  •  I can discuss some of the limitations of brain imaging studies, and explain why reductionist explanations should be avoided
Quiz Yourself(

1.  Which of the following statements are true regarding PET scans?

(a) Uses magnets to track the flow of oxygenated blood in the brain

(b) Participants must keep very still while being scanned

(c) It is a cost-effective technology, since most hospitals already have PET scanners

(d) It involves an injection of radioactive glucose

2.  All of the following statements about MRI scans are true, except for _____

(a) MRI scans involve measuring the flow of oxygenated blood

(b) The MRI scanner is an open machine, decreasing the risk of claustrophobia

(c) Several scans can be made in a short time, showing moment-by-moment changes

(d) No radioactive substances are involved

3.  A study seeks to examine the brain structure of people with generalized anxiety disorder compared with healthy controls.  Which technology would be useful?

(a) PET 

(b) (f)MRI

(c) Either PET or (f)MRI

(d) Neither technology can be used

4.  A study seeks to examine which brain regions become activated when looking at images of objects compared to looking at images of people.  Which technology would be useful?

(a) PET

(b) (f)MRI

(c) Either PET or (f)MRI

(d) Neither technology can be used

5.  Which two groups of participants did Raine study?

(a) Serial killers, and normal controls

(b) Murderers who had pled not guilty for reasons of insanity, and serial killers

(c) Murderers who had pled not guilty for reasons of insanity, and normal controls

(d) Violent criminals, and non-violent criminals

6.  Which of the following statements is true regarding Raine's results?

(a) Murderers had increased activity in frontal regions, and deformed hippocampus

(b) Murderers had decreased activity in frontal regions, and deformed hippocampus

(c) Murderers had increased activity in frontal regions, and deformed amygdala

(d) Murderers had decreased activity in frontal regions, and deformed amygdala

7.  Which statement is true regarding Raine's results?

(a) Demonstrate a cause-and-effect relationship between brain defects & behavior

(b) Carried out on a representative sample of murderers

(c) Findings contradicted previous research on the role of the prefrontal cortex

(d) Are correlational in nature

8.  What is the main problem with reductionist explanations in Psychology?

(a) Fail to control for extraneous variables

(b) Are based on a non-representative sample

(c) Behavior is rarely the result of a single causal factor

(d) Do not take gender and cultural diversity into account


1 - D, 2 - B, 3 - C, 4 - B, 5 - C, 6 - C, 7 - D, 8 - C