Oscillatory Activity in Prefrontal Cortex during Implicit Letter-Location Binding

Abstract

In this study we demonstrated implicit verbal-spatial binding effects that were dependent on the task-relevant feature. We used MEG to measure brain activity underpinning the maintenance of verbal and spatial features in two recognition tasks, based on a letter-location paradigm previously used in binding studies. Both tasks were identical in terms of their perceptual characteristics and only differed with respect to the instructions given. Thus, in the verbal task participants attended consonants, while in the spatial task they attended locations. We observed that maintaining the identity of verbal information (consonants) arranged in a spatially distributed manner resulted in the concurrent processing of task-irrelevant location information. Critically, the reverse relationship does not hold true, supporting the notion of associative asymmetry. This implicit verbal-spatial binding was linked to a specific effect described as a greater oscillatory activity over prefrontal regions in “classical” frequency bands during the first half of the retention period and accompanied by greater activity in PPC and temporal regions.