Diffusion tensor imaging and decision making in cocaine dependence

Abstract

Background: Chronic stimulant abuse is associated with both impairment in decision making and structural abnormalities in brain gray and white matter. Recent data suggest these structural abnormalities may be related to functional impairment in important behavioral processes.

Methodology/principal findings: In 15 cocaine-dependent and 18 control subjects, we examined relationships between decision-making performance on the Iowa Gambling Task (IGT) and white matter integrity as measured by diffusion tensor imaging (DTI). Whole brain voxelwise analyses showed that, relative to controls, the cocaine group had lower fractional anisotropy (FA) and higher mean of the second and third eigenvalues (lambda perpendicular) in frontal and parietal white matter regions and the corpus callosum. Cocaine subjects showed worse performance on the IGT, notably over the last 40 trials. Importantly, FA and lambda perpendicular values in these regions showed a significant relationship with IGT performance on the last 40 trials.

Conclusions: Compromised white matter integrity in cocaine dependence may be related to functional impairments in decision making.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1. Decision making performance on the Iowa Gambling Task (IGT) for the cocaine- dependent (open circle) and control (black square) subjects.

Described in detail in the experimental procedures, each trial on the IGT presents subjects with four choices represented as decks of cards. Two sets (decks C, D) return a positive net gain, and two (A, B) return a net loss. The figure shows the net score (choice of advantageous decks - disadvantageous decks) across 100 test trials, divided into five 20-trial blocks. Beginning between trial 20 and 40, control subjects shifted preference toward decks C and D (net gain), while cocaine dependent subjects continued to divide choices evenly between advantageous and disadvantageous decks, slightly favoring decks A and B (net loss). This between-group difference was statistically significant: F (1, 31)  = 4.32, p = .046.

Figure 2. Clusters that had significantly lower fractional anisotropy (FA) in cocaine-dependent compared to control subjects are overlaid in color on a montage of sagittal slices of the MNI152 standard space template T1 brain image.

Green voxels represent FA cluster 1 and blue voxels represent FA cluster 2 in Table 2. The slice in the upper left corner is in the left hemisphere; the lower right corner slice is in the right hemisphere. Note that the cluster colors were arbitrarily chosen to identify different clusters and do not represent a scale of t values.

Figure 3. Clusters that had significantly higher mean of the second and third eigenvalues (λ⊥) in cocaine-dependent subjects compared to control subjects are overlaid in color on a montage of sagittal slices of the MNI152 standard space template T1 brain image.

Green voxels represent λ⊥ cluster 1, red voxels represent λ⊥ cluster 2, blue voxels represent λ⊥ cluster 3, and black voxels represent λ⊥ cluster 4 in Table 2. The slice in the upper left corner is in the left hemisphere; the lower right corner slice is in the right hemisphere. Note that the cluster colors were arbitrarily chosen to identify different clusters and do not represent a scale of t values.

Figure 4. Graphical presentation of the relationship between performance during blocks 4 and 5 (summed) on the IGT and the DTI for λ⊥ cluster 1 (see Table 2 for X, Y, Z coordinates and Figure 3 for brain image).

Cocaine-dependent subjects are represented as white circles; control subjects as black squares. λ⊥ is expressed as 10−6 mm2/s. The solid red line shows the linear fit to the data for both the cocaine-dependent and control subjects; depicting a relationship in which λ⊥ values decline as a linear function of IGT net score on blocks 4 and 5 (R2 = .24).