The future of electroencephalography in assessing neurocognitive functioning.

High temporal resolution is necessary to resolve the rapidly changing patterns of brain activity underlying mental function. Additionally, simple, non-intrusive equipment is needed to routinely measure such functions in doctors' offices, at home and work and in other naturalistic contexts as people perform normal everyday activities. When compared with all other modalities for measuring higher brain functions, EEG is unique in that it has both these attributes. Two factors are limiting the further development and application of EEG for measuring cognitive functioning: a technical one that is easy to overcome and a sociological one that is more problematic. The technical limitation is that traditional EEG technology and practice provides insufficient spatial detail to identify relationships between brain electrical events and structures and functions visualized by magnetic resonance imaging (MRI) or other modalities. Recent advances overcome this problem by recording EEGs from more electrodes, by registering EEG data with anatomical information from each subject's MRI, by correcting the distortion caused by volume conduction of EEG signals through the skull and scalp, and by computing hypotheses about the sources of signals recorded at the scalp. The sociological limitation is that clinical EEGs are mostly performed by neurologists with no particular special interest in cognitive brain function, while cognitive research using EEG is largely done by psychology professors and their graduate students with no clinical ambitions. The diminishing clinical role of traditional EEGs in localizing lesions in the brain, and the obvious and insistent medical need for inexpensive and accessible tests of cognitive brain functioning may serve to soon dissipate this sociological obstruction. This will lead to a golden age of EEG in which Hans Berger's vision of the EEG as a window on the mind will be realized. Rather than slowly fading into obsolescence, EEG will retain its role as the primary means of measuring higher brain function when the purpose is not 3D localization per se, and will serve as an invaluable complement to functional MRI in those instances when both high temporal and high spatial resolution are required.