A2 Only: Ways of studying the brain: scanning techniques, including functional magnetic resonance imaging (fMRI); electroencephalogram (EEGs) and event-related potentials (ERPs); post-mortem examinations.
Brain-scanning techniques (CAT, PET, and fMRI)
Intensive instruction in reading improves how a child’s brain works. In schizophrenia, key parts of the brain may not communicate well, making it hard to organise one’s thoughts. And true love wouldn’t be true without the neurotransmitter dopamine. We know all this and more thanks to neuroimaging, an increasingly sophisticated tool that sheds light — literally — on the human brain.
Doctors and scientists once had to wait until autopsy to examine the brain, and psychologists had to deduce from behaviour where the brain was injured. Now they can study detailed three-dimensional images of the brain to spot problems, to understand what happens during tasks, thoughts and emotions and to assess the effectiveness of various treatments.
Neuroimaging, or brain scanning, includes the use of various techniques to either directly or indirectly image the structure, function, or pharmacology of the brain. A wide variety of brain scanning techniques exist. These are used to provide biological data, rather than psychological. Scans have scientific purposes. They are commonly used to investigate for possible tumours, strokes or other abnormalities. However, they can be used as research methods too, such as aiding psychologists into understanding of how information is processed. Psychologists and scientists are also using brain scans as research methods, to investigate both normal differences between brains (such as differences between a male and female brain) and abnormal differences (such as differences between the brain of a murder and a non-murderer). Neuroimaging falls into two broad categories:
- Structural imaging, which deals with the structure of the brain and the diagnosis of large-scale intracranial disease (such as a tumor), as well as injury.
- Functional imaging, which is used to diagnose metabolic diseases and lesions on a finer scale (such as Alzheimer’s disease), and also for neurological and cognitive-psychology research. Functional imaging allows the brain’s information processing to be visualized directly, because activity in the involved area of the brain increases metabolism and “lights up” on the scan.
Here is a fantastic timeline of the history of neuroimaging. Click on the image below for a full-size PDF.
Psychologists employ these tools across the range of the discipline:
- Social cognitive neuroscientists, for instance, are capturing the psychological and neural processes involved in emotion, pain, self-regulation, self-perception and perception of others. Psychologists have used neuroimaging technology to demonstrate how white Americans, even those who report themselves free of prejudice, show differences in brain activity in the amygdala — a structure involved in emotional learning – when they look at pictures representing people of different racial groups. Positive emotions are also studied. Psychologists have compared functional images taken when students looked at pictures of their romantic partner versus pictures of an acquaintance. When students gazed at their beloved, two deep-brain areas that communicate as part of a circuit showed increased levels of activity. Those areas help to regulate the neurotransmitter dopamine, which floods the brain when people anticipate a reward.
- Neuroimaging is also helping us understand how the brain develops from infancy through adulthood. Developmental neuroscientists study the neurobiological underpinnings of cognitive development. Combining functional measures of brain activity with behavioural measures, they explore how subtle early insults to the nervous system affect cognitive and emotional function later in life – for example, the effects of maternal illness or early childhood neglect on learning, memory and attention later in life. Imaging tools can pay off in the classroom, too: Using such tools, literacy experts have shown that a year of intensive, methodical reading instruction makes the brains of high-risk kindergarteners look and function like those of more skilled young readers.
- To aid clinical treatments, psychologists are using functional imaging to get at the neural mechanisms involved in such difficult problems as post-traumatic stress disorder, phobias and panic disorder. For example, scans reveal that schizophrenia’s diverse symptoms may result not from faults in single neural components but rather from differences in webs of neural connections. Scans similarly help researchers follow brain activity to assess whether various treatments change the underlying brain dysfunction.
Key Types of Brain Imaging
Criticisms of Neuroimaging Studies
- They do not directly measure neural activity. For example, fMRI doesn’t measure brain activity directly, it only measures blood oxygen.
- Different groups of researchers adopt different statistical and methodological strategies.
- Another charge against neuroimaging is that brain images do not explain but only localise psychological processes. Even though it is true that studies of localisation of certain psychological functions are still published occasionally, most of modern neuroimaging research is not exclusively concerned with finding an area activated when faced with a certain task.
- Also, neuroimaging allows for determining which processes require coordinated activity of different parts of the brain: functional connectivity analysis reveals which parts are working together when faced with a given cognitive task. Since most psychological processes are caused by coordinated activity of several brain areas, this provides insight into the psychological process itself and not only into which parts of the brain are active during its course.
Brain images that we usually see are comprised of thousands of 3-D cubes called “voxels”. Each voxel contains millions of cells, hence brain activity in fMRI is represented in voxel and not in neuronal level. When we test, for example, 50.000 voxels and set significance level to exactly one twentieth (0.05), we can expect 2.500 voxels to cross the level of significance by chance alone. However, if we make the significance level too low, we will not be able to observe any difference at all. This problem is known asmultiple comparisons problem, and it is a serious shortcoming in statistical analysis of neuroimaging data.
One humorous illustration of the problem is an experiment where a dead salmon was placed in an MRI (magnetic resonance imaging) scanner and instructed to think about the emotions experienced by people in photographs that were shown. With significance level set below 0.001, certain parts of dead salmon’s brain were found to engage in perspective-taking activity. However, authors of the publication also devised a solution which did not yield the same results. This shows that the problem itself is an obstacle that is to be overcome by methodological refinement – a natural step in any scientific field.
Here is a summary of the dead salmon study.
Transcranial magnetic stimulation (TMS) is a recent innovation in brain imaging. In TMS, a coil is held near a person’s head to generate magnetic field impulses that stimulate underlying brain cells to make someone perform a specific action. Using this in combination with MRI, the researcher can generate maps of the brain performing very specific functions. Instead of asking a patient to tap his or her finger, the TMS coil can simply “tell” his or her brain to tap his or her finger. This eliminates many of the false positives received from traditional MRI and fMRI testing. The images received from this technology are slightly different from the typical MRI results, and they can be used to map any subject’s brain by monitoring up to 120 different stimulations. This technology has been used to map both motor processes and visual processes (Potts link at bottom of TMS). In addition to fMRI, the activation of TMS can be measured using electroencephalography (EEG) or near infrared spectroscopy (NIRS).
Here is a brilliant timeline of landmarks in functional brain imaging.
Here is a great example of brain scanning in action: The Love Competition