Topography of brain electrical activity dissociates the sequential order transformation of verbal versus spatial information in humans

Slow event related potentials (ERPs) of the electroencephalogram were recor ded while subjects performed a shortterm memory task. They had to mentally transform the order of sequentially presented words (verbal condition) or p ositions within a grid (spatial condition). The difficulty of the transform ation process was varied. The amplitudes of the slow ERPs elicited during t he transformation process varied with task difficulty. The topography of th is amplitude modulation turned out to be information specific: The maximal effect during transformation of the sequential order of verbal information was found over the left-frontal cortex and during the transformation of spa tial information over the parietal cortex. These results suggest that the m anipulation of short-term memory contents seems to take place in informatio n specific cortical areas which are thought to be also involved during on-l ine processing and long-term storage of these informations. (C) 2000 Elsevi er Science Ireland Ltd. All rights reserved.