Over the past thirty years, few areas of psychology have developed quite so rapidly as brain research. As technology has progressed, so has our ability to monitor and map out the brain’s activity. The brain is seen as the control center of human functioning. Psychologists seek to understand how the brain matures over a lifetime and how it adapts to the environment.

Prior to the development of modern scanning technology, one of the most common ways to study the brain was through the use of case studies of brain damage. Often such studies provide researchers with a situation that they could never ethically reproduce in a laboratory. Case studies of brain-damaged patients are often carried out longitudinally - that is, over a long period of time - in order to observe both the short-term and long-term effects of damage.

In addition, case studies are often holistic in their approach, looking at a range of effects of the damage, rather than a single behaviour. In order to do this, case studies use triangulation. In the case of a patient with brain damage, this may include interviews with the family, psychometric testing – for example, IQ or personality testing, experiments and observations.

However, case studies have limitations. First, as the researchers do not manipulate an independent variable, no cause and effect relationship can be determined.  In addition, since case studies are of single individuals, from a single case study we cannot generalize the findings to all human beings. And since it is naturally occurring, the study cannot be replicated. Finally, it may be very difficult to verify information about the patient before the accident took place.  Information about the individual’s IQ, problem-solving skills, memory or interpersonal skills is often reliant on the memories of family members.  In addition to the fact that this is not an accurate measure, the memories of the family members may not be accurate.

In spite of these methodological limitations of a single case study, psychologists agree that they provide important information that can be used to study the effects of brain damage over time, as well as spark new research. Psychologists do not use a single case study to draw definitive conclusions about the role of the brain on behaviour. Instead, they often use similar cases to verify their findings and they may even perform experiments with animals to investigate the hypothesized relationship between damage to a specific area of the brain and behaviour. If there are several case studies of damage to the same area of the brain that show the same consequences on behaviour, biologists may conclude that damage to a specific part of the brain may cause a specific behaviour. This is the case with the famous case study of HM which has contributed to our understanding of the relationship between the brain and memory.

The use of technology in brain research

Many early experiments on the brain involved invasive techniques—for example, removing (ablation) or scarring (lesioning) brain tissue in animals in order to study subsequent behavioural changes. Behaviour before and after lesioning was compared. In a classic study, Hetherington and Ranson (1942) lesioned a part of the brain called the ventromedial hypothalamus (VHM) in rats, a part of the brain that is believed to control feeding. As a result of the lesioning, the rats increased their food intake dramatically and often doubled their weight. This led researchers to conclude that the hypothalamus acted as a brake on eating.

The use of invasive techniques raises serious ethical concerns and psychologists have to conform to codes of conduct for the use of non-human animals; for example, the Ethical Principles of Psychologists and Code of Conduct by the American Association of Psychologists.  This means that psychologists who engage in research with animals need to apply to an ethical committee for permission to carry out their research. If the potential harm to the animal cannot be determined, permission will only be granted if the research is considered to add to current knowledge and there are no alternatives.

Modern technology is now extensively used in psychology because it provides an opportunity to study not only brain structures but also the active brain while avoiding many of the ethical concerns of animal experimentation. This allows researchers to see localization of function – that is, the functions of specific parts of the brain and how they relate to behaviour.

One imaging technique is Magnetic Resonance Imaging [MRI]. The MRI gives a three-dimensional picture of the brain structures. The MRI was used in the case study of HM to determine the extent of his brain damage. An MRI scanner uses a magnetic field and radio waves to map the activity of hydrogen molecules, which are present in different brain tissue to different degrees. The image can either be viewed as a slice of the brain from any angle, or it can be used to create a three-dimensional image of the brain.

There are several advantages of using an MRI scan. First, the procedure is non-invasive, with minimal potential harm to the participant. Secondly, the image has high resolution; this gives researchers a good sense of the actual structure of the brain.  However, the MRI only indicates structure; it does not actually map what is happening in the brain.  In addition, MRI research is correlational in nature, not allowing researchers to establish a clear cause and effect relationship.

In order to observe the activity of the brain, other technologies are used.  Positron Emission Tomography – commonly known as PET scanning - is used to observe metabolic processes in the brain by detecting the gamma rays emitted indirectly by a tracer. PET neuroimaging is based on the assumption that areas of high radioactivity are associated with brain activity. Before a PET scan begins, a patient is given a safe dose of a radioactive tracer compound introduced into the body by a modified glucose molecule [FDG]. The injected FDG enters the bloodstream, where it can travel to the brain. If a particular area of the brain is more active, more glucose will be needed there. When more glucose is used, the radioactive tracer is detected by the PET scanner. The scan, which usually takes between 30 minutes and two hours, produces a multi-coloured image that shows which parts of the brain were the most active. The colour of each dot shows the intensity of the energy signal.

One of the key advantages of the PET scan is that it allows participants to perform psychological tasks while the researcher observes brain activity.  There are two key limitations of PET scanning.  First, it requires an injection with a small amount of radioactive material..  Although this will not cause harm to the participant, it is still an invasive practice and raises ethical concerns.  Secondly, PET scanning is quite slow and has relatively poor resolution. So, although it does indicate where brain activity is taking place, it is not as clear as more modern technology like the fMRI.

Unlike the MRI, which shows the structure of the brain, an fMRI (functional magnetic resonance imaging) shows actual brain activity and indicates which areas of the brain are active when engaged in a behaviour or cognitive process. The fMRI measures changes in blood flow in the active brain. These scans have a higher resolution than PET scans, and they are easier to carry out. This is one of the most frequently used technologies in biopsychological research today. It tracks changes in blood flow and oxygen level as a measurement of neural activity. When a specific brain area is active, it uses more oxygen, and therefore the blood flow increases. This can be detected by the fMRI scanner.

Unlike PET scanning, fMRIs are non-invasive.  There is no radioactive isotope necessary. The quality of the image is also much better and rather than a static image, the fMRI produces a film that demonstrates a change in the brain over the period of the scan.

For both the MRI and the fMRI, there are certain precautions that must be taken to protect the safety of the participant. Since the technology works with a powerful magnet, it is important that objects that contain iron be removed. In rare cases, a participant may have to be removed from a sample because of a metal implant – for example, certain types of pacemakers or cochlear implants.

 Teacher only box

You see in the news an article that says that your government is considering having all members of government who need security clearance have a PET or fMRI scan in order to determine whether they are “fit” for this position.  As a psychologist, how would you respond to this suggestion?

Students should be able to discuss the pros and cons of using brain imaging technology in predicting future behaviour.  Although there may be some trends in negative behaviors with regard to brain damage, the predictive validity of brain imaging technology is limited and highly controversial.

Very often, students will be completely against the use of brain scanning.  You may want to have them read the following articles as a way of extending the discussion.

• A dangerous brain
• Inside the brain of a killer: The ethics of neuroimaging

Checking for understanding

Localization & Plasticity