Item-related versus task-related activity during encoding and retrieval in verbal and non-verbal episodic memory: an event-related potential study

Abstract

In the past 10 years, functional neuroimaging studies have elucidated the role of the prefrontal cortex in memory encoding and retrieval. However, it is still unclear whether these activations reflect item- or task-related activities. In the present study, Event-Related Potentials (ERPs) were used to distinguish item-related activity from task-related activity in both encoding and retrieval processes. This activity was assessed with both verbal and non-verbal material. A recognition paradigm with words or random shapes was administered to 12 young participants. Memory elicited ERPs were compared to those evoked by control tasks that used similar material. The distribution of the N400 was found to be larger on left frontal than right frontal areas for verbal material, however, this was the case in the control and memory conditions as well. This finding likely reflects the sensitivity of this component to processing verbal material. The LPC amplitude was greater in the non-verbal encoding than the non-verbal control condition, whereas in retrieval it was larger than the control condition for both verbal and non-verbal material. Thus, item-related activity is determined by an interaction between properties of the material and the task instructions. Task-related activity was found for non-verbal material: compared to the control condition, the memory condition of non-verbal material elicited bilateral and right frontal activity in encoding and retrieval processes. No task-related effect was reported with the verbal material. Material differences in eliciting task-related effects are discussed in terms of their relation to elaborative and effortful processes.