Abstract
Previous studies have revealed top-down control during memory retrieval from the prefrontal cortex to the temporal cortex. In the present functional MRI study, we investigated whether the fronto-temporal functional interaction occurs even during fixation periods after memory retrieval trials. During recency judgments, subjects judged the temporal order of two items in a study list. The task used in the present study consisted of memory trials of recency judgments and non-memory trials of counting dots, and post-trial fixation periods. By comparing the brain activity during the fixation periods after the memory trials with that during the fixation periods after the non-memory trials, we detected heightened brain activity in the lateral prefrontal cortex, the lateral temporal cortex and the hippocampus. Functional interactions during the fixation periods after the memory vs. non-memory trials as examined using a psychophysiological interaction revealed a decreased interaction from the lateral prefrontal cortex to the lateral temporal cortex, but not to the hippocampus. The functional interaction between the same frontal and temporal regions was also present during the memory trials. A trial-based functional connectivity analysis further revealed that the fronto-temporal interaction was positive and decreased during the fixation periods after the memory trials, relative to the fixation periods after the non-memory trials. These results suggest that the fronto-temporal interaction existed during the post-trial fixation periods, which had been present during the memory trials and temporally extended into the fixation periods.
Highlights
The lateral prefrontal cortex has been implicated in various types of cognitive control that guides our behavior, including memory control
It is possible that memory retrieval processes and fronto-temporal interaction continue even after memory retrieval trials are completed, which may raise the possibility that the post-trial fixation periods may not be regarded as an ideal low-level control
In the present functional MRI study, we investigated whether functional interaction between the lateral prefrontal cortex and the temporal cortex exists even after memory retrieval trials
Summary
The lateral prefrontal cortex has been implicated in various types of cognitive control that guides our behavior, including memory control. It is possible that memory retrieval processes and fronto-temporal interaction continue even after memory retrieval trials are completed, which may raise the possibility that the post-trial fixation periods may not be regarded as an ideal low-level control. In the present functional MRI study, we investigated whether functional interaction between the lateral prefrontal cortex and the temporal cortex exists even after memory retrieval trials. The task consisted of recency judgment trials, non-memory trials of counting dots, and post-trial fixation periods of the same durations (3 sec each). The recency judgment task can be expected to require retrieval of greater amount of episodes for judgment of temporal order of studied items, which might resulted in greater degree of recruitment of processing related to memory retrieval even after the memory trials are completed. We used resting-state data to contrast with the post-trial fixation periods where control processing was enhanced
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