COMPARATIVE-STUDY OF EVENT-RELATED POTENTIALS AND POSITRON-EMISSION-TOMOGRAPHY ACTIVATION DURING A PAIRED-ASSOCIATE MEMORY PARADIGM

Event-related potentials (ERP) and regional cerebral blood flow (rCBF) activation using O-15-labeled water associated with retrieval and ret ention of episodic memory were studied during a visual paired-associat ion task with delayed response in eight healthy subjects. In both stud ies, the subjects memorized four pairs of figures during the learning period. They were presented with each cue (S1) and asked to judge whet her the following figure (S2) formed one of the memorized pairs. In an attempt to identify brain activity related to memory function, a choi ce reaction task with delay was used as a behavioral control. The ERP study showed a posterior positive component in the difference waveform , which was obtained by subtracting responses in the choice reaction t ask from those in the paired association task, between 300 and 850 ms after S1 presentation. It was maximal at the parietal midline electrod e and distributed predominantly over the left posterior quadrant of th e scalp. The rCBF activation study showed a greater increase in rCBF i n the right dorsolateral prefrontal cortex (Brodmann's area 46), left inferior frontal cortex (Brodmann's area 44/45), left thalamus, and bi lateral cerebellar hemisphere during the paired association task as co mpared to the choice reaction task, which suggests a possible involvem ent of cerebellothalamo-cortical circuit in the memory processing. Add itionally, it is suggested that the scalp distribution of the ERP comp onent may not necessarily represent regional cortical activation below the electrodes where such a component is observed and could indirectl y represent activation in remote areas such as subcortical regions. It seems that ERP and rCBF activation may provide information about diff erent aspects of higher brain function.