Neurophysiological evidence for dynamic competition between encoding and retrieval operations in long-term memory

Many theories of long-term memory propose that encoding and retrieval processes have an overlapping functional neuroanatomy. We tested this notion using novel dual-task procedures that force encoding and retrieval into 'competition' with one another. We observed a striking and highly robust asymmetrical pattern of ‘interference’: the ability to remember previously studied verbal material is unimpaired by interference from concurrent encoding of new material, whereas the act of remembering has a significant detrimental impact on the ability to selectively encode elements of one's current experience. These findings replicate much prior work showing that retrieval is impervious to interference or ‘divided attention’ effects. However, our neurophysiological (ERP) measures of the brain’s functional mnemonic state during retrieval suggest that interference qualitatively alters the basis on which participants respond. Interference appears to reduce participants’ ability to recollect the past and to increase their reliance upon ‘familiarity’. These neurophysiological findings reveal the dynamic interplay between encoding and retrieval operations at work within neocortical representation systems as trace re-activation and trace formation are taking place.