Waiting to retrieve: possible implications for brain function.

There is evidence that the mid-ventrolateral prefrontal cortex is involved in control processing necessary for the active retrieval of mnemonic information when retrieval cannot be triggered automatically by unique/constant associations within memory. We hypothesized that this process is initiated as soon as an instructional cue to retrieve a particular aspect of an encoded stimulus is presented prior to the appearance of the test stimulus that prompts the subjects' response. To test this hypothesis, we provided the subjects with a delay period following the presentation of the instructional cue. Across delays, the subjects took longer to respond during the active retrieval compared with the automatic retrieval trials. Importantly, for both trial types, delays of up to 300 ms improved the subjects' reaction times during the test period by an average of 101 ms. Retrieval mechanisms, therefore, are initiated early during the post-instruction delay period prior to the presentation of the test stimulus needed for the decision.