P3 response during short-term memory retrieval revisited by a spatio-temporal analysis

Abstract

The most reported event related potential (ERP) parameter during short-term memory retrieval has been P3 wave and the association has been built on the relation between P3 latency and reaction times. The aim of this study is to identify an ERP component that reflects the memory scanning process preceding the decision making stage which has been associated with the P3 peak. A spatiotemporal analysis was applied on the P3 and pre-P3 period of ERP responses obtained during the retrieval phase of the Sternberg paradigm with two memory load conditions (3 and 5 letters in the memory set). In the easy task condition with the fastest reaction times (positive probes of 3 letters condition), a single P3 was observed, whereas P3 was split into two peaks in responses to probe items of more demanding task conditions. The single P3 peak and the later components of the split P3 peaks displayed the typical P3 topography. On the other hand, the topographic mapping of the earlier peak of the split P3 wave and ascending part of the single P3 peak revealed a right parietal topography. The onset time of this earlier right lateralized topography was stable among all conditions but it persisted longer in the high memory load condition. We conclude that the right-lateralized positivity in the pre-P3 period reflects the memory scanning process followed by the P3 peak with midline parietal topography reflecting the decision making process. © 2012 Elsevier B.V..