Specialization of the rostral prefrontal cortex for distinct analogy processes

Abstract

Analogical reasoning is central to learning and abstract thinking. It involves using a more familiar situation (source) to make inferences about a less familiar situation (target). According to the predominant cognitive models, analogical reasoning includes 1) generation of structured mental representations and 2) mapping based on structural similarities between them. This study used functional magnetic resonance imaging to specify the role of rostral prefrontal cortex (PFC) in these distinct processes. An experimental paradigm was designed that enabled differentiation between these processes, by temporal separation of the presentation of the source and the target. Within rostral PFC, a lateral subregion was activated by analogy task both during study of the source (before the source could be compared with a target) and when the target appeared. This may suggest that this subregion supports fundamental analogy processes such as generating structured representations of stimuli but is not specific to one particular processing stage. By contrast, a dorsomedial subregion of rostral PFC showed an interaction between task (analogy vs. control) and period (more activated when the target appeared). We propose that this region is involved in comparison or mapping processes. These results add to the growing evidence for functional differentiation between rostral PFC subregions.

Figure 1.

Experimental design and tasks. Experimental design consisted of 2 different tasks: Match and Analogy, with the latter subdivided into crossdimension and intradimension conditions.

Figure 2.

Significant signal change between conditions in 4 distinct analyses (P < 0.001 uncorrected, minimum extent: 10 voxels): (a) the contrast “analogy versus match” during source (in orange) is superimposed with the contrast analogy versus match during target (in red); (b) greater period effect (target–source) in the analogy than in the match task (obtained from a task by period interaction with exclusion of regions more activated in match than analogy task); and (c) the contrast match versus analogy.

Figure 3.

Differential activities within the rostral PFC for 3 identified subregions. On the left, activation obtained in the whole-brain analyses is superimposed on a frontal slice (y = 58) on a standard MRI brain and on a canonical surface brain in the MNI space. In orange: analogy versus match activating the lateral rostral PFC (maxima = −44, 50, −4); in blue: task by period interaction, activating a more dorsal and medial part of the rostral PFC (maxima = 18, 62, and 22); in green: match versus analogy, activating a ventral and medial frontopolar subregion (maxima = 0, 44, −16). On the right, graphs represent parameter estimates for the rostral prefrontal ROIs defined independently from the whole-brain analysis: lateral ROI (MNI coordinates = −39, 50, 2), dorsomedial ROI (MNI coordinates = 8, 59, 19), and ventromedial ROI (MNI coordinates = 0, 48, −16). A schematic representation of each of these ROIs is shown on frontal slices of a standard brain (ch2.nii template provided by MRIcron in the MNI space), at the upper part of the figure. Parameter estimates were extracted for each task (analogy and match) and period (source and target) and averaged between subjects. On the y axis are the values of the mean parameter estimates across subjects and trials. This shows qualitative differences in activation profile of the 3 rostral prefrontal regions. Stars represent significant condition by ROI interactions. In black are schematized the condition by ROI interaction for the “source analogy” versus “source match” conditions. In white are schematized the condition by ROI interaction for the “target analogy” versus “target match” conditions. In orange is schematized the condition by ROI interaction for the “target analogy” versus “source analogy” conditions.