Which technique measures brain activity at millisecond resolution?

Magnetoencephalography (MEG) is the technique that measures brain activity with millisecond resolution. This is possible because MEG detects the magnetic fields generated by neuronal activity, which occur on very fast timescales. Neurons communicate through electrical impulses, and MEG is sensitive enough to record these changes almost instantaneously, providing real-time insights into brain function.

In contrast, other techniques such as functional Magnetic Resonance Imaging (fMRI) and Positron Emission Tomography (PET) operate on much longer timescales, often measuring blood flow or metabolic processes rather than direct neuronal activity. fMRI typically has a temporal resolution of several seconds, while PET can take minutes to reflect changes in brain activity. Electroencephalography (EEG), although it also tracks electrical activity and has good time resolution, does not provide the same spatial resolution as MEG and can be less precise in localizing specific brain functions. Thus, MEG's combination of high temporal resolution and good spatial resolution makes it unique among these options for measuring brain activity quickly.