When comparing MEG to functional MRI, which of the following statements is INCORRECT?

Question

BlackTom AI · Accepted Answer

MEG does not have higher spatial resolution than functional MRI because fMRI (BOLD) routinely achieves millimeter-scale localization while MEG localization is fundamentally limited by the ill-posed inverse problem and sensor geometry.

Relevant knowledge points and concepts:
- Spatial resolution: the ability to localize neural activity in space (mm scale for fMRI).
- Temporal resolution: the ability to resolve fast changes in neural activity (ms for MEG, seconds for fMRI).
- Direct vs indirect measurement: MEG records magnetic fields generated by postsynaptic currents (a direct electromagnetic correlate); fMRI measures the hemodynamic BOLD response (an indirect metabolic/vascular correlate).
- Inverse problem: MEG sensors measure extracranial fields; determining the exact intracranial current sources from those fields is non-unique and requires modeling, which limits spatial accuracy.

Step-by-step reasoning:
1. Compare spatial resolution: High-field fMRI commonly uses voxels ~1–3 mm and can localize activity to cortical columns or small cortical areas; MEG localizes sources using source modeling (minimum-norm, beamformers), but accuracy depends on SNR, head model, and sensor coverage. Typical practical localization precision for MEG is on the order of several millimeters to centimeters—generally worse than fMRI’s typical spatial resolution. Therefore the statement “MEG has higher spatial resolution than functional MRI” is incorrect.
2. Temporal comparison: MEG measures neural currents with millisecond resolution; fMRI BOLD is hemodyamic and evolves over seconds—so “MEG has a higher temporal resolution than functional MRI” is correct.
3. Sustained signal: BOLD responses are slow and sustained relative to transient MEG signals, so “functional MRI signal changes are more sustained than MEG” is correct.
4. Directness: MEG measures electromagnetic fields arising from neuronal currents directly, while fMRI measures secondary vascular changes—so “functional MRI is a less direct measure of neural activity than MEG” is correct.

Why the correct answer is correct:
The first option contradicts well-established instrumentation and physiological limits: fMRI provides superior spatial localization compared with MEG. Other options accurately describe temporal dynamics and directness.

Conclusion: The incorrect statement is “MEG has higher spatial resolution than functional MRI,” which matches the provided answer.

When comparing MEG to functional MRI, which of the following statements is INCORRECT?Single choice

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