EVENT-RELATED POTENTIALS DURING MEMORIZATION OF SPATIAL LOCATIONS IN THE AUDITORY AND VISUAL MODALITIES

Event-related potential (ERP) studies of working memory have used dela yed S1-S2 match-to-sample tasks in which S1 is held in memory for comp arison with S2. ERP negativities in the S1-S2 interval have been inter preted either in terms of working memory operations, or in terms of ge neral preparatory motor processing. Two experiments (N = 20 each) were carried out to explore the nature of ERP negativities in a visuospati al memory task and in an auditory spatial memory task, respectively. I n the experimental condition, subjects had to memorize the location of S1 (S1-memorize) so as to respond whether S2 appeared in the same spa tial location (S2-memorize). In the control condition, subjects were r equested to ignore S1 (S1-passive), and to respond whether S2 matched or not a target location predetermined at the beginning of the trial b lock (S2-pressing). Results support the two main conclusions of Martin -Leeches et al. (Electroenceph. clin. Neurophysiol., 1994, 91: 363-373 ). Firstly, that the encoding into memory of spatial location is assoc iated with an ERP negative wave over the brain areas putatively associ ated with the processing of sensory information (i.e. right parieto-oc cipital for the visual task; fronto-central and left temporal areas fo r the auditory task). Secondly, the P300 does not seem to be an import ant ERP feature related to spatial location encoding and retaining int o memory. Despite the distinct scalp distribution of these memory-rela ted, modality-specific ERP negativities, they also showed a considerab le degree of temporal synchronicity across modalities. (C) 1997 Elsevi er Science Ireland Ltd.