Lateral Prefrontal Cortex Contributes to Fluid Intelligence Through Multinetwork Connectivity

Abstract

Our ability to effectively adapt to novel circumstances--as measured by general fluid intelligence--has recently been tied to the global connectivity of lateral prefrontal cortex (LPFC). Global connectivity is a broad measure that summarizes both within-network connectivity and across-network connectivity. We used additional graph theoretical measures to better characterize the nature of LPFC connectivity and its relationship with fluid intelligence. We specifically hypothesized that LPFC is a connector hub with an across-network connectivity that contributes to fluid intelligence independent of within-network connectivity. We verified that LPFC was in the top 10% of brain regions in terms of across-network connectivity, suggesting it is a strong connector hub. Importantly, we found that the LPFC across-network connectivity predicted individuals' fluid intelligence and this correlation remained statistically significant when controlling for global connectivity (which includes within-network connectivity). This supports the conclusion that across-network connectivity independently contributes to the relationship between LPFC connectivity and intelligence. These results suggest that LPFC contributes to fluid intelligence by being a connector hub with a truly global multisystem connectivity throughout the brain.

Keywords: fMRI; functional connectivity; graph theory; individual differences; intelligence; prefrontal cortex; resting-state functional connectivity.

FIG. 1.

Connector versus provincial hubs. Two hypothetical networks are illustrated, with key nodes highlighted. The left highlighted node is a connector hub, which is critical for across-network communication. In contrast, the right highlighted node is a provincial hub, which is important for within-network communication, but not across-network communication. Both the connector hub and provincial hub have high global brain connectivity (GBC)/degree centrality (number of connections), while the connector hub has high betweenness centrality and a high participation coefficient. Specifically, the provincial hub has a degree of 5, betweenness of 18.7 (calculated based on 7 shortest paths through the node), and participation of 0. In contrast, the connector hub has a degree of 4, betweenness of 50 (calculated based on 24 shortest paths through the node), and participation of 0.5 (half of the node's connections are within network and half across network).

FIG. 2.

Location and graph theoretical ranking of lateral prefrontal cortex (LPFC). (A) The left hemisphere regions and network segmentations (each network is a different color) from Power et al. (2011). The left LPFC region from Cole et al. (2012) was added and highlighted with a circle. (B) A histogram of GBC values across all 265 regions, with the ranking of LPFC highlighted. (C) A histogram of betweenness, with LPFC's ranking highlighted. (D) A histogram of participation, with LPFC's ranking highlighted. LPFC was within the top ∼10% of all three graph theoretical metrics.

FIG. 3.

LPFC graph theoretical correlations with fluid intelligence. (A) The correlation between LPFC GBC and fluid intelligence. (B) The correlation between LPFC betweenness and fluid intelligence. (C) The correlation between LPFC betweenness and fluid intelligence, after regressing GBC variance out of both betweenness and fluid intelligence. The correlation remains significant, suggesting that LPFC multinetwork connectivity independently contributes to fluid intelligence.