TOPOGRAPHY OF BRAIN ELECTRICAL-ACTIVITY DISSOCIATES THE RETRIEVAL OF SPATIAL VERSUS VERBAL INFORMATION FROM EPISODIC LONG-TERM-MEMORY IN HUMANS

Topography and amplitude of slow event-related potentials (ERPs) of th e electroencephalogram (EEG) were studied during acquisition and recal l of spatial and verbal associations. Subjects learned associations be tween line drawings and two types of mediators. The latter were either positions in a grid or concrete nouns. In a cued recall test subjects had to decide whether two drawings were linked to each other or not v ia an associated position or noun. The topography of slow ERPs 1-4 s a fter stimulus presentation obtained from 18 scalp electrodes dissociat ed the memory processes: The maximum potential was found over the pari etal cortex with spatial and over the left frontal cortex with verbal information. The same topographic pattern emerged during both anticipa tion learning and cued recall. Moreover, the amplitude at the topograp hic maximum increased when more associations had to be retrieved. Thes e results are compatible with the idea that memory representations are reactivated in localized cortical cell assemblies specialized for par ticular codes. (C) 1997 Elsevier Science Ireland Ltd.