A spatio-temporal analysis of recognition-related event-related brain potentials.

Words correctly recognized as previously studied (i.e. old) elicit greater amounts of positive event-related brain potential (ERP) activity over posterior scalp between 400 and 800 ms than do previously unstudied (i.e. new) words. While investigators have reported that this old/new effect consists of more than one subcomponent, the spatio-temporal parameters of these possible subcomponents, as well as any other patterns of brain activity associated with recognition, remain incompletely specified. Thus, ERPs were recorded from 32 scalp sites while 13 subjects performed four repetitions of a study-test recognition paradigm. The subjects' task was to decide whether each word was old or new and press the appropriate button as quickly as possible. The timing and topography of the ERPs elicited by old and new words was assessed with topographic profile comparisons on the areas with a variety of temporal windows, and visualized with potential and CSD maps. The results revealed that seven patterns of ERP activity, dissociable on the basis of their topography, timing and response to experimental variables, were elicited between 300 and 2000 ms. Three of these appeared as subcomponents of the old/new effect (maximal over left medial frontal, left parietal-occipital and right central-frontal scalp), another was related to decision confidence and/or memory trace strength (maximal over left central scalp) and three others appeared to be related to more general aspects of recognition (maximal over the frontal poles, midline frontal scalp and right frontal scalp). Taken together, the seven distinct patterns of neural generator activity described here support the hypothesis that retrieval of information from episodic memory depends on a collection of different processes that occur in a temporally and spatially distributed neural circuit.