# Brain Imaging Techniques

Psychology I · Psychophysiology · https://tryals.app/learn/psychology-i/brain-imaging-techniques

## Windows into the Living Brain

For most of history the working brain was a black box. Modern **imaging techniques** opened it, dividing cleanly into two families: those that reveal **structure** (anatomy) and those that reveal **function** (activity).

| Technique | Measures | Reveals |
| --- | --- | --- |
| EEG | Electrical activity | Function (millisecond timing) |
| CT | X-ray cross-sections | Structure |
| MRI | Magnetic fields | Structure (high detail) |
| fMRI | Blood-oxygen changes | Function (localizes activity) |
| PET | Radioactive tracer | Function (metabolic use) |

The fundamental trade-off in brain imaging is between **temporal resolution** (when things happen) and **spatial resolution** (where things happen).

## Resolution and Pitfalls

**EEG** excels at timing, telling you _when_ neurons fire, but struggles to pinpoint _where_. **fMRI** provides exquisite spatial detail by tracking the **BOLD signal** (blood-oxygen-level-dependent changes), locating activity within millimeters.

> **Common Pitfall:** Treating fMRI as a direct measure of neural firing. It measures **blood-oxygen changes** that lag behind neural activity by a second or more. It is a metabolic proxy, not the electrical signal itself—which explains its poorer temporal resolution.

## Practice questions

7 of this lesson's 12 practice questions, with answers. The full set is in the app.

### 1. A study reports amygdala activation while participants view a political advert, and concludes voters felt **fear**. Why is that inference unsound?

A. Because fMRI cannot detect amygdala activity reliably
B. Because the amygdala responds to salience generally, not only fear
C. Because the amygdala is not involved in emotion at all
D. Because emotional states cannot be studied with imaging under any design

**Answer:** B. Because the amygdala responds to salience generally, not only fear

**Why:** Reverse inference: fear activates the amygdala does not license amygdala activity means fear, because the region answers to salience of many kinds. It is the commonest fallacy in popular neuroscience reporting, and the fix is to constrain the interpretation with behaviour rather than reading the state off the picture.

Page: https://tryals.app/practice/psychology-i/brain-imaging-techniques/a-study-reports-amygdala-activation-while-participants-view-a

### 2. An fMRI region 'lighting up' during a task shows that the region is necessary for the task.

**Answer:** False

**Why:** False. Activation shows the region was more active during the task, which is correlation. Necessity requires a lesion, TMS or a comparable intervention. Regions light up while merely accompanying a task, and a necessary region can fail to light up if it is equally active in the control condition.

Page: https://tryals.app/practice/psychology-i/brain-imaging-techniques/an-fmri-region-lighting-up-during-a-task-shows-that-the-region-is

### 3. The colours on an fMRI image show absolute brain activity in that region.

**Answer:** False

**Why:** False. The image shows a small statistical *difference* in blood oxygenation between two conditions, thresholded and colour-coded, never absolute activity. That is why the choice of control condition determines what appears, and why an image with no stated comparison is uninterpretable.

Page: https://tryals.app/practice/psychology-i/brain-imaging-techniques/the-colours-on-an-fmri-image-show-absolute-brain-activity-in-that

### 4. A researcher wants to know both where in the brain a decision is made and when it happens. Order the reasoning that leads to the study design.

**Answer:**

1. The question has two parts: a location and a timing.
2. fMRI can answer the location, to within a millimetre or two.
3. But its signal lags the neural event by seconds, so it cannot answer the timing.
4. EEG resolves the timing to milliseconds, and cannot say where the signal arose.
5. So the study needs both, with each method answering the half it can.

**Why:** The design follows from taking the question apart. 'Where' and 'when' are separate empirical questions, and it happens that the two dominant imaging methods are each excellent at one and poor at the other.

Working through it in this order also protects against the commonest error in imaging research, which is letting the available machine determine what gets asked. A lab with an fMRI scanner and a timing question will be tempted to answer it with the haemodynamic response, and the four-to-six second lag means the answer cannot be trusted however carefully the analysis is done.

Combining the methods is not free. Simultaneous EEG-fMRI is technically awkward - the scanner's magnetic field induces artefacts in the EEG - which is why many studies run the two separately on the same paradigm and align them afterwards.

Page: https://tryals.app/practice/psychology-i/brain-imaging-techniques/a-researcher-wants-to-know-both-where-in-the-brain-a-decision-is-made

### 5. fMRI has excellent spatial resolution and poor temporal resolution; EEG has the reverse. Why can a researcher not simply choose whichever is better?

A. Because the two measure different things: blood flow and voltage.
B. Because fMRI is more expensive, so EEG is used when funding is limited.
C. Because fMRI measures only cortical activity while EEG measures the whole brain.
D. Because EEG can only be used on patients with implanted electrodes, which restricts its availability.

**Answer:** A. Because the two measure different things: blood flow and voltage.

**Why:** Neither instrument is a compromised version of the other. The haemodynamic lag of four to six seconds is a property of blood flow, so no engineering removes it; EEG inherits the inverse problem, where infinitely many internal configurations produce the same surface pattern. Asking *where* points to fMRI, asking *when* points to EEG.

Page: https://tryals.app/practice/psychology-i/brain-imaging-techniques/fmri-has-excellent-spatial-resolution-and-poor-temporal-resolution

### 6. Sort each technique or property by the kind of resolution it excels at.

**Answer:**

- Excellent TEMPORAL resolution (when): EEG, Tells you precisely WHEN neurons fire, to the millisecond
- Excellent SPATIAL resolution (where): fMRI, Locates activity to within millimeters

**Why:** EEG has millisecond timing (temporal) but poor localization; fMRI localizes to millimeters (spatial) but lags in time. The core trade-off is knowing WHEN versus knowing WHERE.

Page: https://tryals.app/practice/psychology-i/brain-imaging-techniques/sort-each-technique-or-property-by-the-kind-of-resolution-it-excels

### 7. A famous demonstration found significant fMRI activation in the brain of a dead salmon shown photographs. What was the point being made?

A. That fish brains respond to human social images, which was the study's genuine finding.
B. That fMRI scanners malfunction when scanning non-living tissue, producing spurious signals.
C. That fMRI cannot distinguish between living and dead tissue, making it unreliable for research.
D. That with tens of thousands of voxels, some pass 0.05 by chance.

**Answer:** D. That with tens of thousands of voxels, some pass 0.05 by chance.

**Why:** Bennett and colleagues ran an ordinary uncorrected analysis on a dead salmon and found significant voxels in its brain cavity, nothing was malfunctioning. Tens of thousands of independent tests at alpha 0.05 guarantee a cluster somewhere. It changed practice quickly, largely because a dead fish is harder to ignore than a formula.

Page: https://tryals.app/practice/psychology-i/brain-imaging-techniques/a-famous-demonstration-found-significant-fmri-activation-in-the-brain