Have you ever wondered what is going on inside your brain? Theories about how the brain works and how it affects who we are, have been around since ancient times. However, the explosion in neuroscientific research and understanding of brain function has only occurred within the last century, which can be attributed to the invention of neuroimaging techniques. In this explanation, we will learn about the different brain scanning techniques and their contribution to psychology.
- We will start by outlining what neuroimaging techniques psychology is.
- Next, we will look at the neuroimaging techniques definition.
Then, we will examine the types of neuroimaging techniques, including invasive and new neuroimaging techniques.
Finally, we will evaluate the use of neuroimaging techniques.
Neuroimaging techniques allow a deeper look into the function of the brain, freepik
Neuroimaging Techniques in Psychology
Aristotle considered the heart to be responsible for human psychological functioning. Later, the focus of many great thinkers shifted to the brain when Galen, an ancient Roman physician and philosopher, linked brain ventricles to human thought and personality.
Brain functioning remained a mystery for long after. In the nineteenth century, post-mortem brain autopsies were conducted on brain-damaged patients to link their cognitive impairments to the damaged regions. During this time, researchers identified brain regions associated with personality by investigating the case of Phineas Gage and areas responsible for speech production and comprehension, investigated by Paul Broca and Carl Wernicke.
However, the breakthrough in our understanding of brain activity occurred in the twentieth century, with the invention of neuroimaging techniques, which led to an explosion of neuroscience research.
Neuroimaging Techniques Definition
As the name suggests, neuroimaging techniques allow us to create images of brain structure. Moreover, they can measure the activity in different sites of the brain.
Before, researchers were limited to post-mortem autopsies to learn about the patients' neurological damage. Nowadays, thanks to neuroimaging techniques, clinicians and researchers can investigate the brains of people while they are still alive.
Neuroimaging techniques include structural and functional imaging. Structural imaging produces a detailed image of brain structures, while functional imaging measures changes in the activity of different brain regions by recording the changes in brain physiology.
Neuroimaging techniques can be split into structural and functional imaging techniques, which are of great importance for research and clinical practice. Structural imaging, conducted with MRI (Magnetic Resonance Imaging) or CT (Computed Tomography) scans, allows clinicians to diagnose brain injuries and neurodegenerative diseases like dementia, identify bleeding, swelling, and tumours, and see the extent of the damage following a stroke.
Structural imaging techniques can be used to see if someone suffered brain damage after an accident.
On the other hand, PET (Positron Emission Tomography) scans, fMRI (Functional Magnetic Resonance Imaging) scans and EEG (Electroencephalography) is used to investigate the activity of the brain which occurs while we perform particular actions. This allows researchers to link the activity of specific brain areas to behaviour and cognitive functioning. They also give researchers a unique insight into the differences in brain functioning between a healthy person and a person with a neurological disease.
To investigate which brain areas are involved when we are listening to music, researchers can use fMRI scans and see what brain areas light up in people when they listen to music compared to when they listen to different noises.
Types of Neuroimaging Techniques
Let's now take a closer look at how the different neuroimaging techniques work and how they are used in clinical practice and research.
Computed Tomography (CT)
A computed tomography scan or CT scan is an example of structural imaging. During a CT scan, a person is exposed to X-ray radiation. Since different tissues in the brain (bone, brain matter or cerebral spinal fluid) differ in their absorption of the radiation, they will appear differently on the scan.
Structures that absorb the most radiation look the brightest on the scan, while structures absorbing the least radiation are much darker. CT visualises the X-ray absorption over the different slices of a brain, which allows precise localisation of abnormalities.
Clinicians use CT scans to visualise abnormalities in bone structure and identify tumours or bleeding sites in the brain.
Although the CT scan is a less precise structural imaging technique than magnetic resonance imaging (MRI), it is much cheaper and can be more available in clinical settings.
CT brain scans can reveal a lot about the brain, freepik.com
Positron Emission Tomography (PET)
PET brain scan is a functional imaging technique that measures brain activity by recording the changes in blood flow to different brain areas. More blood flow indicates greater activity.
When areas of the brain and body are active, they consume more oxygen, leading to greater blood flow to that region to replenish oxygen availability.
Before a PET scan is conducted, the person undergoing the scan is injected with a radioactive tracer. As the tracer decays, it emits positrons that are picked up by the scanner. Areas where the blood flow is greater, appear redder on the image produced by the scanner, indicating greater activity of this brain region.
- Some limitations of PET scans are that they are less precise than an fMRI scan.
- Moreover, since the tracer decays quickly, measuring the brain's activity during longer tasks is difficult. PET is also an invasive procedure; the need to administer the radioactive tracer raises the risks associated with PET scans.
PET scans can identify tumours or the brain regions where seizures start in epileptic patients before they undergo surgery.
PET scans were also used in Tulving's (1989) Gold memory study. Tulving asked participants to recall episodic and semantic memories and injected them with a radioactive isotope of gold to see how their brain activity changed.
Results were consistent in only 3 of the 6 participants. When the 3 participants recalled episodic memories, their frontal and temporal lobes showed greater activity. In contrast, their parietal and occipital lobes showed greater activity when they thought about semantic memories.
PET brain imaging, Health and Human Services Department, National Institutes of Health, National Institute on Aging : p.24[1], Public domain, via Wikimedia Commons
Functional Magnetic Resonance Imaging (fMRI)
Similarly to PET imaging, fMRI visualises the activity of different brain regions by measuring changes in blood flow to other brain areas. However, fMRI does it a bit differently – by using a strong magnetic field. This field can be distorted by a molecule called deoxyhemoglobin, indicating greater brain activity.
The BOLD signal is how fMRI's identify functional areas.
Haemoglobin is a protein in blood cells that deliver oxygen to brain regions. When neurons consume oxygen, haemoglobin turns to deoxyhemoglobin.
One advantage of this technique is that it's non-invasive and doesn't expose the individual to harmful substances or radiation. Moreover, it is much more precise than PET scans, as it measures changes in activity in the image's small pixel cubes.
These 3-D units, called voxels, cover all the 3 × 3 × 3 mm3 unit structures.
The fMRI is very precise as it has a high spatial resolution. It allows researchers to observe what brain areas become active when a person performs a task in the scanner. However, it is very noisy, which can interfere with the experiment, and requires patients to remain very still.
fMRI is used in clinical practice to identify brain abnormalities and evaluate the brain functioning of patients with neurological diseases.
It is also a valuable technique for neuroscience research. For example, using fMRI, de Vignemont and Singer (2006) studied brain activation associated with empathy for pain. They could identify the precise brain areas that were active in participants both when they experienced pain and when they saw their partner in pain.
Electroencephalography (EEG)
EEG was invented 50 years before PET scans and instead of producing maps of brain activity, it records electrical signals from the brain's cortical layer. To measure the brain's electrical activity, researchers place 25 to 34 electrodes on the person's scalp, which are then used to record the electrical activity of the brain.
Next, researchers average the signal from the multiple trials and clean it up to create an event-related potential (ERP).
ERPs show the brain's electrical activity changes that occurred in response to the stimuli multiple times.
Measuring people's brain activity during sleep with an EEG led to the discovery of REM sleep. Researchers found that the brain is not only active during sleep. Its activity becomes greater during a phase of sleep that we call REM sleep.
Electroencephalography can show areas of activity, flaticon
New Neuroimaging Techniques
One of the newest brain imaging techniques introduced recently is the 3D amplified MRI. It visualises how the brain moves in great detail. This is an important new technique for clinical practice, as abnormal brain motions have been linked to neurological disorders, and abnormalities in motion can't be observed using structural or functional imaging.
Invasive Neuroimaging Techniques
Invasive techniques involve inserting something into the body. Out of all the scanning techniques we discussed, only PET scans can be considered invasive because they involve the injection of a radioactive tracer. However, it is essential to remember that invasive doesn't always mean dangerous. The amount of radiation you are exposed to during a PET scan is considered safe, as the radioactive substance decays quickly.
While CT scans involve exposure to X-ray radiation, this procedure is considered safe and non-invasive. The amount of radiation you are exposed to in a CT scan equals about 8 months of background radiation that we are exposed to in our everyday life.
Evaluation of neuroimaging techniques
Brain scanning techniques have given researchers a great understanding of how our brain functions when performing different activities.
For example, they showed that other brain regions are active when we recall different types of memories. They also led researchers to discover the paradoxical brain activity that occurs during REM sleep.
Since neuroimaging techniques give us insight into the brain of people still alive, they are an essential tool for diagnosing people with neurological conditions. This also allows clinicians to choose appropriate treatments for people or exclude improper diagnoses.
Neuroimaging techniques allow clinicians and researchers to identify what brain areas are affected in people with different cognitive deficits. This shows us how different functions and behaviours rely on particular brain regions.
Clive Wearing was a patient who lost most of his memories and the ability to form new memories. His brain scans revealed extensive damage to the temporal lobes. This case study supports the importance of temporal lobes in the processes of making and keeping memories.
Limitations of neuroimaging techniques
It is important to remember that the results produced by scanning techniques are correlational, and these correlations might as well be accidental if the data is not analysed properly.
The problem of false positive results associated with fMRI research was addressed by the study of Bennett and colleagues (2010), which won a Nobel Prize for its findings.
The researchers put a dead salmon into the fMRI machine, showed it photos of people in different social situations, and asked how a person might have felt in that situation.
Interestingly, when researchers didn't properly analyse the data, it appeared that there was activity in the salmon's brain and spinal cord. These results were false positives, but if the researchers didn't ensure a proper analysis of the data, we would have evidence that dead salmon can be quite empathic.
Use of scanning techniques - Key takeaways
- Neuroimaging techniques include structural and functional imaging. Structural imaging produces a detailed image of brain structures, while functional imaging measures changes in the activity of different brain regions by recording the changes in brain physiology.
- CT is a structural imaging technique that creates a map of brain structures by exposing them to X-ray radiation. These structures can be differentiated on the scan because different tissues absorb different amounts of radiation.
- PET brain scan is a functional imaging technique that measures brain activity by recording the changes in blood flow to different brain areas. PET is considered to be an invasive neuroimaging technique.
- fMRI uses a strong magnetic field to visualise the activity of different brain regions by measuring changes in blood flow to different brain areas.
- While brain scanning techniques have contributed significantly to neuroscience research and clinical practice, it is essential to remember that the results of some scanning techniques are correlational and can be inaccurate if analysed improperly, see Bennett and Colleagues (2010).
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