Functional magnetic resonance imaging

Functional magnetic resonance imaging (fMRI) estimates changes in brain activity over time by detecting blood-oxygen-level-dependent changes in magnetic resonance signals.

Blood-oxygen-level-dependent contrast: An MRI signal contrast sensitive to changes in the magnetic properties of blood as its oxygenation changes. This contrast is the principal signal fMRI uses to estimate brain activity.
Magnetic resonance imaging: An imaging technique that uses magnetic fields and radiofrequency pulses to produce images of the body's internal structures. fMRI builds on MRI's signal formation and spatial imaging.
Task-based fMRI: An fMRI design that measures brain signals while participants perform specified tasks or experience stimuli. It estimates which regions' signals vary with controlled experimental conditions.
Electroencephalography: A method that records electrical potentials from the scalp to measure brain activity with high temporal resolution. EEG tracks electrical activity directly and quickly, unlike fMRI's indirect, delayed vascular signal.
Neurovascular coupling: The processes linking neural activity to changes in local blood flow and oxygen delivery. It explains why neural activity can produce the vascular changes measured by fMRI.
Nuclear magnetic resonance: A physical phenomenon in which atomic nuclei in a magnetic field absorb and emit radiofrequency energy. Nuclear magnetic resonance provides the physical basis for MRI signals.
Resting-state fMRI: An fMRI approach that measures spontaneous brain-signal fluctuations while participants perform no explicit task. It reveals correlated activity patterns without requiring a task contrast.
Magnetoencephalography: A method that measures magnetic fields produced by electrical activity in the brain. MEG offers millisecond timing while fMRI generally provides finer spatial localization.
Hemodynamic response function: A model of the time course of blood-flow and oxygenation changes following neural activity. Its delayed, spread-out shape determines how fMRI signals map onto neural events.
T2-star relaxation: The decay of transverse magnetization caused by both microscopic interactions and magnetic-field inhomogeneities. Blood oxygenation changes local field inhomogeneities, altering T2-star-sensitive fMRI signals.

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