Fluid intelligence and naturalistic task impairments after focal brain lesions

Verity Smith,Clara Pinasco,Jascha Achterberg,Daniel J Mitchell,Tilak Das,Maria Roca,John Duncan

doi:10.1016/j.cortex.2021.09.020

Abstract

Classical executive tasks, such as Wisconsin card-sorting and verbal fluency, are widely used as tests of frontal lobe control functions. Since the pioneering work of Shallice and Burgess (1991), it has been known that complex, naturalistic tasks can capture deficits that are missed in these classical tests. Matching this finding, deficits in several classical tasks are predicted by loss of fluid intelligence, linked to damage in a specific cortical “multiple-demand” (MD) network, while deficits in a more naturalistic task are not. To expand on these previous results, we examined the effect of focal brain lesions on three new tests–a modification of the previously-used Hotel task, a new test of task switching after extended delays, and a test of decision-making in imagined real-life scenarios. As potential predictors of impairment we measured volume of damage to a priori MD and default mode (DMN) networks, as well as cortical damage outside these networks. Deficits in the three new tasks were substantial, but were not explained by loss of fluid intelligence, or by volume of damage to either MD or DMN networks. Instead, deficits were associated with diverse lesions, and not strongly correlated with one another. The results confirm that naturalistic tasks capture cognitive deficits beyond those measured by fluid intelligence. We suggest, however, that these deficits may not arise from specific control operations required by complex behaviour. Instead, like everyday activities, complex tasks combine a rich variety of interacting cognitive components, bringing many opportunities for processing to be disturbed.

Highlights

It has long been thought that complex, open-ended tasks may capture aspects of frontal “executive” impairment that are missed in the more constrained setting of conventional neuropsychological testing
For a number of conventional tests, including card sorting, fluency, and Trails, deficits in several patient groups are largely explained by a loss of fluid intelligence; once fluid intelligence is partialled out, performance is largely equivalent for patients and controls (Roca et al 2010, 2012, 2013, Roca et al, 2014)
We have found that “executive” tasks vary widely in the degree to which deficits are explained by fluid intelligence (Roca et al, 2010, 2012; Woolgar et al, 2010)

Summary

Introduction

It has long been thought that complex, open-ended tasks may capture aspects of frontal “executive” impairment that are missed in the more constrained setting of conventional neuropsychological testing. Fluid intelligence deficits are linked to damage in a distributed cortical “multiple-demand” or MD network, incorporating specific regions of lateral frontal, dorsomedial frontal, insular and parietal cortex (Woolgar et al, 2010, Woolgar, Duncan, Manes, & Fedorenko, 2018; Barbey et al, 2012; for evidence on white matter connections see Gla€scher et al, 2010) Performance on tests such as card sorting, fluency, and Trails may largely reflect the functions of this network. For the Hotel task, we have repeatedly found that performance is only weakly related to fluid intelligence, and partialling fluid intelligence does not remove patient deficits (Roca et al 2010, 2012, 2013, Roca et al, 2014) These findings suggest less specific dependence on MD functions. The prediction would be that there is no core deficit in “complex” behaviour, reflected in shared impairments across multiple tasks; and that deficits are not well explained by damage to any one cortical region or network

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