Study topic · about 4 minutes
How scientists study the brain
Scientists study the brain in two ways: by looking at its structure, what it looks like, with CT and MRI, and at its function, what it is doing, with EEG, fMRI and PET. Each method trades off how precisely it shows where something happens against how precisely it shows when.
Key points
- CT and MRI show the brain's structure; MRI gives the sharpest pictures of soft tissue.
- fMRI shows which areas are active by tracking changes in blood oxygen.
- EEG records electrical activity through the scalp: excellent timing, poor location.
- PET uses a small amount of a radioactive tracer to show activity or brain chemistry.
- Lesion studies, case studies and post-mortem examinations show what an area does by what is lost when it is damaged.
The methods compared
| Method | What it measures | Where? | When? | Good for |
|---|---|---|---|---|
| EEG (electroencephalography) | Electrical activity, through the scalp | Poorly | Within milliseconds | Sleep stages, seizures |
| ERP (event-related potential) | The EEG response to one kind of event, averaged over many repeats | Poorly | Within milliseconds | How fast the brain notices a sound, a face or a word |
| MEG (magnetoencephalography) | Tiny magnetic fields from neural activity | Fairly well | Within milliseconds | Research on timing |
| CT (computed tomography) | X-ray slices of structure | Well | No activity shown | Emergencies, bleeding |
| MRI (magnetic resonance imaging) | Structure, using magnets and radio waves | Very precisely | No activity shown | Detailed anatomy, tumors, multiple sclerosis |
| fMRI (functional MRI) | Blood oxygen changes linked to activity | Within millimeters | Within seconds | Which areas a task uses |
| PET (positron emission tomography) | Where a radioactive tracer collects | Moderately | Slowly | Metabolism, dopamine, the plaques of Alzheimer's disease |
Seeing structure: CT and MRI
A CT scan combines many X-rays into slices of the head. It is fast, so it is often the first scan in an emergency like a suspected stroke, to look for bleeding. An MRI scanner uses a strong magnet and radio waves to measure the water in tissues, giving much sharper pictures of the brain, without X-rays. The 3D brain in this app is built from MRI scans.
Seeing activity: EEG, fMRI and PET
Active neurons use more oxygen, so blood flow increases to busy areas. fMRI detects this change, called the BOLD signal, to show which areas a task uses, within a few millimeters but a few seconds late. EEG records the combined electrical activity of millions of neurons through electrodes on the scalp. It can't pinpoint where the activity comes from, but it follows changes in milliseconds, which is why it is used to define the stages of sleep.
An event-related potential (ERP) comes from the EEG. The same event, such as a beep or a word, is shown many times, and the recordings are lined up at that moment and averaged. The random background activity cancels out, leaving a series of waves that show how the brain responds to the event, millisecond by millisecond.
PET uses a tracer, such as a radioactive form of glucose, that collects where the brain is working hardest, or tracers that attach to dopamine receptors or to the plaques of Alzheimer's disease.
Learning from damage, stimulation and post-mortems
Long before scanners, scientists learned what brain areas do by studying people with brain damage. In 1861, Paul Broca studied a patient who could say little except the word 'tan', and after his death found damage in the left frontal lobe, the area now called Broca's area. Case studies like this, and of patients like Phineas Gage and H.M., showed that specific skills depend on specific areas.
A post-mortem examination studies the brain after death, so what a person could and couldn't do in life can be matched to what is found. Broca's discovery came from one. After H.M. died in 2008, his brain was cut into 2,401 thin slices, showing exactly what his surgery had removed.
Stimulation works the other way round. From the 1930s, the surgeon Wilder Penfield gently stimulated the exposed cortex of awake patients during epilepsy surgery: stimulating the motor strip made a body part twitch, and the sensory strip caused a tingle, which is how the body maps of the cortex were drawn. Today, transcranial magnetic stimulation (TMS) can briefly disrupt an area from outside the skull.
In animal research, scientists can make precise lesions, or switch groups of neurons on and off, to test what they do.
Which method answers which question?
- To see what the brain looks like: MRI, or CT when speed matters.
- Where activity happens: fMRI.
- When activity happens: EEG or MEG.
- The brain's chemistry: PET.
- Whether an area is needed for a task, not just active during it: lesion studies or TMS.
A scan that shows an area lighting up during a task is a correlation. Only damage or disruption shows that the task needs that area.
Quick quiz
5 questions. Your answers are saved and come back in your daily review.
Which method is best at showing exactly when brain activity happens?
Show the answer
EEG. EEG follows electrical changes within milliseconds.
EEG. EEG follows electrical changes within milliseconds.
What does fMRI measure?
Show the answer
Changes in blood oxygen. fMRI tracks the extra oxygen-rich blood flowing to active areas.
Changes in blood oxygen. fMRI tracks the extra oxygen-rich blood flowing to active areas.
Which scan is usually done first in an emergency, because it is fast?
Show the answer
CT. A CT scan takes minutes and shows bleeding clearly.
CT. A CT scan takes minutes and shows bleeding clearly.
Which method is used to identify the stages of sleep?
Show the answer
EEG. Each stage of sleep has its own EEG brain-wave pattern.
EEG. Each stage of sleep has its own EEG brain-wave pattern.
Paul Broca found a language area by studying one patient with brain damage. What kind of research is this?
Show the answer
A case study. A case study examines one person, or a few, in depth.
A case study. A case study examines one person, or a few, in depth.
These parts now come back in your daily review, just before you would forget them.
Slice the brain like an MRIIn these study guides
- MCATLateralization and how the brain is studied
- AP Psychology1.4 The brain
- Intro psychologyThe brain and spinal cord (section 3.4)
- A-level PsychologyWays of studying the brain
- GCSE BiologyThe brain (4.5.2.2, Biology only)
Sources
- Magnetic Resonance Imaging (MRI), National Institute of Biomedical Imaging and Bioengineering (NIH)
- Computed Tomography (CT), National Institute of Biomedical Imaging and Bioengineering (NIH)
- Nuclear Medicine, National Institute of Biomedical Imaging and Bioengineering (NIH)
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