Functional-anatomic correlates of sustained and transient processing components engaged during controlled retrieval.

Controlled processing is central to episodic memory retrieval. In the present study, neural correlates of sustained, as well as transient, processing components were explored during controlled retrieval using a mixed blocked event-related functional magnetic resonance imaging paradigm. Results from 29 participants suggest that certain regions in prefrontal cortex, including anterior left inferior prefrontal cortex near Brodmann's Area (BA) 45/47 and more posterior and dorsal left prefrontal cortex near BA 44, increase activity on a trial-by-trial basis when high levels of control are required during retrieval. Providing direct evidence for control processes that participate on an ongoing basis, right frontal-polar cortex was strongly associated with a sustained temporal profile during high control retrieval conditions, as were several additional posterior regions, including those within left parietal cortex. These results provide evidence for functional dissociation within prefrontal cortex. Frontal-polar regions near BA 10 associate with temporally extended control processes that may underlie an attentional set, or retrieval mode, during controlled retrieval, whereas more posterior prefrontal regions associate with individual retrieval attempts. In particular, right frontal-polar cortex involvement in sustained processes reconciles a number of disparate findings that have arisen when contrasting blocked-trial paradigms with event-related paradigms.