Meta-analysis: how does posterior parietal cortex contribute to reasoning?

Abstract

Reasoning depends on the contribution of posterior parietal cortex (PPC). But PPC is involved in many basic operations-including spatial attention, mathematical cognition, working memory, long-term memory, and language-and the nature of its contribution to reasoning is unclear. Psychological theories of the processes underlying reasoning make divergent claims about the neural systems that are likely to be involved, and better understanding the specific contribution of PPC can help to inform these theories. We set out to address several competing hypotheses, concerning the role of PPC in reasoning: (1) reasoning involves application of formal logic and is dependent on language, with PPC activation for reasoning mainly reflective of linguistic processing; (2) reasoning involves probabilistic computation and is thus dependent on numerical processing mechanisms in PPC; and (3) reasoning is built upon the representation and processing of spatial relations, and PPC activation associated with reasoning reflects spatial processing. We conducted two separate meta-analyses. First, we pooled data from our own studies of reasoning in adults, and examined activation in PPC regions of interest (ROI). Second, we conducted an automated meta-analysis using Neurosynth, in which we examined overlap between activation maps associated with reasoning and maps associated with other key functions of PPC. In both analyses, we observed reasoning-related activation concentrated in the left Inferior Parietal Lobe (IPL). Reasoning maps demonstrated the greatest overlap with mathematical cognition. Maintenance, visuospatial, and phonological processing also demonstrated some overlap with reasoning, but a large portion of the reasoning map did not overlap with the map for any other function. This evidence suggests that the PPC's contribution to reasoning may be most closely related to its role in mathematical cognition, but that a core component of this contribution may be specific to reasoning.

Keywords: IPL; SPL; deductive reasoning; meta-analysis; numerical cognition; posterior parietal cortex; spatial cognition.

Figure 1

Posterior parietal ROIs from Mars et al., , including five subdivisions of IPL and five subdivisions of SPL, on the left and on the right. Subdivisions are labeled “a” through “e”, from anterior to posterior.

Figure 2

Relational reasoning tasks, including (A) matrix reasoning; (B) transitive inference; (C) relational shape matching; and (D) relational picture matching. (A) For relational matching, the given stimulus depicts a second-order problem, in which one must consider the relationships in both the bottom row and rightmost column to determine that the correct answer is #2. (B) For transitive inference, a second-order problem is shown, for which one to evaluate the validity of the probe (circled, “yellow is heavier than blue”), one must combine both the second and fourth premises (“blue is same as red” and “yellow is heavier than red”). (C) For the relational matching task, equivalent stimuli were used across conditions. The given stimulus is a texture match, because the top two shapes share the same texture, a shape mismatch, because neither pair share the same shape, and a relational match, because the same dimension of match (texture) is present for both the top and bottom pairs. (D) The semantic picture matching task follows the same logic as the relational matching task, but utilized animal vs. vehicle and land vs. water as dimensions of possible match or mismatch. The example depicts a relational match, in that the dimension of match for the top pair (land vs. water) is the same as the dimension of match for the bottom pair.

Figure 3

(A) Average % signal change for the contrast between 2nd-order and 1st-order relational reasoning, across four separate studies (matrix reasoning, transitive inference, relational matching, picture matching). Error bars are standard error of the mean across subjects. (B) Volume of the Neurosynth forward inference map associated with reasoning, for each posterior parietal ROI.

Figure 4

Relative activation volumes associated with each term, for (A) left vs. right parietal cortex, and (B) IPL vs. SPL; and (C) anterior to posterior parietal cortex. All bars add up to 100%. Terms are grouped according to the higher-level category to which they are thought to correspond.

Figure 5

Overlap metrics for reasoning (forward inference map) in relation to other functions (reverse inference maps). (A) Volume of overlap with the reasoning map, for the activation maps associated with each other term. (B) Percent of reasoning activation from the reasoning map that overlapped with each other feature, across all parietal ROIs. (C) Similarity scores comparing the reasoning map to the map associated with every other feature, across all parietal ROIs. Similarity was computed as the volume of overlap divided by the total volume of activation for both features.

Figure 6

The cluster within left mid-IPL (IPLc and IPLd) that was associated exclusively with reasoning and with no other examined term. This cluster lies on the upper part of the ventral bank of the intraparietal sulcus. Note that the image is displayed in radiological coordinates, with left and right reversed.