With the so-called electroencephalography (EEG) we can directly measure electrical brain activity in a non-invasive way. Special electrodes are placed on the scalp which can then detect the small voltage fluctuations generated by changes of neural activity in the underlying brain regions involved in a given (cognitive) process.
One advantage of EEG is the superior temporal resolution being in the range of milliseconds. On the downside, the spatial resolution is rather limited, especially in comparison with other imaging techniques such as functional magnetic resonance imaging (fMRI). The simultaneous application (EEG-fMRI) may enable researchers to use the strength of both methods, achieving an optimized spatial and temporal precision.