Dissociating the role of the medial and lateral anterior prefrontal cortex in human planning

Koechlin, Étienne; Corrado, Gregory; Pietrini, Pietro; Grafman, Jordan · 2000 · OpenAlex-citations

DOI: 10.1073/pnas.130177397

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Summary

This study investigates the functional specialization of the anterior prefrontal cortex (APFC) in humans, specifically addressing how this region supports higher cognitive functions such as task management and planning. While the posterior prefrontal cortex is well-characterized for roles in working memory and task switching, the APFC’s specific contributions remain less understood. The authors hypothesized that distinct APFC networks mediate endogenous plans (fixed, predictable sequences) and exogenous plans (sequences contingent on unpredictable events), extending a known medial-lateral dissociation in motor control to executive functions. To test this hypothesis, the researchers employed functional MRI (fMRI) in six healthy subjects performing a branching paradigm. Subjects executed a primary matching task on capital letters but were occasionally cued to suspend this task to perform intermediate tasks on lowercase letters. Two experimental conditions manipulated the predictability of these cues: a "predictive" condition where cues appeared at fixed intervals (endogenous planning), and a "random" condition where cues appeared unpredictably (exogenous planning). A control condition involved repeating a fixed stimulus-response sequence. The design ensured that working memory load and task-switching frequency were matched across conditions, isolating the variable of sequence predictability. The results revealed a double dissociation in APFC activation. The lateral APFC, particularly the frontopolar cortex (Brodmann area 10) and dorsolateral prefrontal cortex, was preferentially engaged during the random condition. This activation was associated with the dorsolateral striatum (putamen). Conversely, the medial APFC, including the anterior cingulate and medial prefrontal cortex (Brodmann areas 32/10), was preferentially active during the predictive condition, associated with the ventral striatum (caudate/accumbens). Behavioral data supported these neural findings, showing that response times increased over time in the random condition but decreased in the control condition, indicating the development of expectations in the predictive condition. The medial APFC activation in the predictive condition diminished over time as subjects anticipated the sequence, whereas lateral activation persisted throughout the random condition. These findings demonstrate that the APFC is functionally segregated along a medial-lateral axis, mirroring organizational principles observed in the premotor cortex. The lateral APFC supports the dynamic integration of intermediate tasks when sequences are contingent on unexpected environmental events, while the medial APFC supports the execution of fixed, internally driven plans. This study provides experimental evidence for the theoretical distinction between total-order and partial-order planning, suggesting that common frontal organizational principles underlie both motor control and higher-order executive functions. The results imply that the ability to adjust plans dynamically to new demands (lateral network) represents a more evolved adaptive behavior than executing learned procedures (medial network).

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• executive function