What you need to know
- 8.15Enrichment on what MRI and fMRI can and cannot claim. Not extra diseases.
No diagnosis from a lesson. CT and PET involve radiation and are not interchanged with MRI.
By the end, you should be able to…
- Separate a structural MRI from an fMRI task result.
- Refuse a claim about intention or guilt.
- Say why a transmitter imbalance is not visible as a lobe on a standard MRI.
Build your understanding
A task result is an average of blood flow
fMRI, as NIBIB describes it, observes activation during a cognitive task. The signal is related to blood flow and oxygen use, which rise where neurones are busy. It is slow compared with an action potentialA rapid reversal of the potential difference across a neurone membrane, caused by Na⁺ ions flowing in, then K⁺ ions flowing out.. It is a region, not a single synapse. A colour blob over the cerebral hemispheres means “this area was more active during that task than during the comparison”, if the experiment was designed that way.
It does not mean the scanner saw a thought, a lie, or a memory like a video. Those are interpretations added afterwards. The specification asks you to know what the method investigates. It does not ask you to judge a person.
Dopamine loss is a different measurement
Parkinson’s is a loss of particular neurones and of dopamineA neurotransmitter in the brain involved in movement, reward and motivation. signalling. A standard structural MRI may look almost ordinary early on. A PET tracer aimed at that pathway is a different scan. Do not point at the cerebellum on an MRI and call it the substantia nigra because both words sound anatomicalDescribes an adaptation of body structure, such as thick fur..
Make your reasoning visible
Quote the task
fMRI only means something relative to what the person was asked to do.
No courtroom
Do not write that a scan proves motive.
Avoid this misconception
The claim: fMRI photographs thoughts in the same way a camera photographs a face.
The correction: It maps a blood-flow difference during a task. Thoughts are inferred, not photographed. MRI without the task is structure only.
Check your understanding
Try each question before opening the suggested answer.
Practice question
Retrieval and explanation · suggested answer
What can MRI show that fMRI is not required for?
Show suggested answer
The structure of soft tissue, such as whether a region of the brain is present and intact.
Practice question
Retrieval and explanation · suggested answer
Why is a single fMRI image not a record of one action potential?
Show suggested answer
The signal is a slower change related to blood flow in a region, not the millisecond sodium spike of one axon.
Practice question
Retrieval and explanation · suggested answer
Why might a dopamine problem be invisible on a structural MRI?
Show suggested answer
The scan shows anatomy. A loss of transmitter release can occur before the anatomy looks clearly different, and dopamine itself is not a structure the MRI draws.
Take the idea further
Apply the same specification knowledge to an unfamiliar problem. Any extra assumptions are supplied in the question.
Stretch question
A headline says “Scan proves the student intended to cheat”. The only method was a structural MRI, done while the student was lying still, with no task. What did the scan actually provide, and which method would still not prove intention even if a task had been used?
Show a hint
Structure versus a task. Then the limit of fMRI.
Explore the reasoning
A structural MRI provided a picture of anatomy, not of intention, and no task was run. fMRI during a task would show regions that were more active, and that still would not prove intention or cheating. Activation is not a motive. Neither CT nor PET would cross that line either.
Recall this lesson
Lesson recall questions
Question 1 of 5: State what PET uses to investigate brain function or metabolism.
Imaging the brain
Practice question
Retrieval and explanation · suggested answer
State what PET uses to investigate brain function or metabolism.
Lesson: 8B 3: Investigating the Human Brain
Try this from memory first.
Put your biology to work
Explore where these ideas appear in the world. Enrichment, not extra required recall.
fMRI observes activation during a task
8B · Thinking BiggerNIBIB’s description is the boundary for this enrichment: fMRI is used to observe brain activation during cognitive tasks. It is a specialised MRI. It is not a mind-reading…Specification 8.15Read & use the scienceClose article
Why this matters
NIBIB’s description is the boundary for this enrichment: fMRI is used to observe brain activation during cognitive tasks. It is a specialised MRI. It is not a mind-reading claim, and the page does not mention guilt, personality, or school discipline. 8.15: use MRI, fMRI, PET and CT for structure or function, and stop where the measurement stops. A scan or growth response is indirect evidence: it cannot alone identify every signalling step or prove the proposed cause.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.15 MRI, fMRI, PET and CT in brain investigation.
Use the science
Which word in “functional” tells you a task should be named?
Explore a possible response
Functional. MRI alone is structure. fMRI needs a comparison of activity, which means the person was doing something, or the result is not an fMRI claim.
Explore the source
- NIBIB: magnetic resonance imagingUS National Institute of Biomedical Imaging and Bioengineering
Activation during a task is not a thought transcript
8B · Investigating the Human BrainNIBIB describes MRI as magnet-and-radio pictures of soft tissue, and fMRI as a specialised MRI used to observe brain activation during cognitive tasks. That is the source for…Specification 8.15Read & use the scienceClose article
Why this matters
NIBIB describes MRI as magnet-and-radio pictures of soft tissue, and fMRI as a specialised MRI used to observe brain activation during cognitive tasks. That is the source for 8.15’s functional MRI. It does not say the scanner reads intentions. CT and PET are separate NHS descriptions: X-rays, and a radioactive tracer. 8.14 and 8.15: know the five regions, and know what each scan can show. A scan or growth response is indirect evidence: it cannot alone identify every signalling step or prove the proposed cause.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 5, pp. 35–38. The application extends beyond required recall.
- 8.15 MRI, fMRI, PET and CT in brain investigation.
Use the science
Why is “the fMRI showed the hypothalamus, so the person was thirsty” too strong?
Explore a possible response
Seeing a region, or even activation, is not a labelled thirst. Thirst would be an interpretation that needs the task and other evidence. The hypothalamus does contain water-balance centres, but a scan caption is not that conclusion by itself.
Explore the source
- NIBIB: magnetic resonance imagingUS National Institute of Biomedical Imaging and Bioengineering