The method of event-related brain potentials
Event-related brain potentials (ERPs) are a non-invasive method of measuring brain activity during cognitive processing. The transient electric potential shifts (so-called ERP components) are time-locked to the stimulus onset (e.g., the presentation of a word, a sound, or an image). Each component reflects brain activation associated with one or more mental operations. In contrast to behavioral measures such as error rates and response times, ERPs are characterized by simultaneous multi-dimensional online measures of polarity (negative or positive potentials), amplitude, latency, and scalp distribution. Therefore, ERPs can be used to distinguish and identify psychological and neural sub-processes involved in complex cognitive, motor, or perceptual tasks. Moreover, unlike fMRI (even Event-Related fMRI, which precludes the need for blocking stimulus items), they provide extremely high time resolution, in the range of one millisecond.
The methodological advantages of ERPs have resulted in an ever increasing number of ERP studies in cognitive neuroscience, cognitive psychology, psycholinguistics, neurolinguistics, neuropsychology and neurology. Language-related ERP components such as the N400, LAN (Left Anterior Negativity) and P600 have proven useful in understanding the processing of language in children and adults, in native and non-native language, in normal processing and in language disorders. The establishment of specific and reliable ERP components in language and other domains has led to a growing number of clinical applications, including diagnostic procedures. EEG/ERPs are especially crucial in the localization of epileptic foci. Moreover, the ability to run complex tasks while collecting ERP data is of particular relevance for the examination of the many patients who are able to provide only minimal cooperation, with little or no response ability. Thus ERPs have been used to identify patients who seem to be "brain-dead" but in fact are not.
The Georgetown EEG/ERP Laboratory
The Georgetown EEG/ERP Laboratory provides a state-of-the-art facility for the acquisition of human electroencephalography (EEG) and event-related potentials (ERPs). The lab's Neuroscan SynAmps2 EEG/ERP system can be used for up to 64-channel EEG/ERP acquisition. Additionally, we have a 64 channel BrainAmp MR Plus system from Brain Products that allows one to carry out simultaneous EEG/ERP and fMRI acquisition in Georgetown's Center for Functional and Molecular Imaging (CFMI) 3T Siemens Magnetom Trio scanner.
ERP Lab Director: Michael Ullman