Executive function and fluid intelligence after frontal lobe lesions

Abstract

Many tests of specific 'executive functions' show deficits after frontal lobe lesions. These deficits appear on a background of reduced fluid intelligence, best measured with tests of novel problem solving. For a range of specific executive tests, we ask how far frontal deficits can be explained by a general fluid intelligence loss. For some widely used tests, e.g. Wisconsin Card Sorting, we find that fluid intelligence entirely explains frontal deficits. When patients and controls are matched on fluid intelligence, no further frontal deficit remains. For these tasks too, deficits are unrelated to lesion location within the frontal lobe. A second group of tasks, including tests of both cognitive (e.g. Hotel, Proverbs) and social (Faux Pas) function, shows a different pattern. Deficits are not fully explained by fluid intelligence and the data suggest association with lesions in the right anterior frontal cortex. Understanding of frontal lobe deficits may be clarified by separating reduced fluid intelligence, important in most or all tasks, from other more specific impairments and their associated regions of damage.

Figure 1

Potential relationships between fluid intelligence and deficits in specific executive tests X and Y. Higher values on each scale indicate better performance. (A) Deficit fully explained by g. (B) Deficit in specific function unrelated to g. (C and D) Predictions for model with fluid intelligence a joint function of separate executive processes X and Y.

Figure 2

Lesion overlaps for patients with predominantly inferior medial, superior medial, left lateral and right lateral lesions. Colour scales show numbers of affected patients for each brain voxel.

Figure 3

Experiment 1. Regressions of Wisconsin Card Sorting Test and verbal fluency on Culture Fair IQ. Points show data for single patients (coloured) and controls (empty); regression line is calculated on combined patient and control data.

Figure 4

Experiment 2. Regressions on fluid intelligence for all tasks showing significant difference between patients and controls. Symbols and regressions as Fig. 3.

Figure 5

Experiment 2. Lesion overlap for 6 patients with worst average residual (performance adjusting for fluid intelligence) across Go–no go, Proverbs, Hayling, Hotel and Faux Pas tests. Left: overlap projected to brain surface; colour scale shows number of affected patients. Right: slice illustrating maximum overlap; coordinates in MNI space.