Summary of the Development & Validation Study:

People who tend to impulsively choose smaller, sooner rewards over larger, later rewards are at increased risk for addiction and psychiatric disorders. A neurobiological measure of the tendency to overvalue immediate gratification could facilitate the study of individuals who are susceptible to these mental disorders. In this study, published in Psychological Medicine, our objective was to develop a cortical assay of impulsive choice for immediate rewards. We created a cortex-based assay of impulsive choice using 1105 healthy adults from the Human Connectome Project, and then cross-validated the score in two independent samples of adults with elevated rates of psychiatric disorders. In Study 1, we developed the cortical delay discounting (C-DD) using a multivariate additive model of gray matter thickness across both hemispheres (to calculate this score, see the instructions below). We found that higher C-DD corresponded to thinner cortex and greater impulsive choice for immediate rewards. It also predicted cannabis use beyond established risk factors for drug use, including familial substance use, childhood conduct problems, personality traits, and cognitive functioning. In Study 2, we replicated the association between C-DD and delay discounting performance from study 1. Structural equation modeling also showed C-DD covaried with symptoms of externalizing, but not internalizing disorders. In Study 3, we found the C-DD positively predicted future delay discounting behavior (6–34 months later). Together, these studies demonstrate a cortical assay of impulsive choice evidenced consistent associations with drug use and delay discounting task performance. It was also uniquely associated with psychiatric disorders that share impulsivity as a core feature. The findings support the utility of C-DD as a neurobiological assay of impulsive decision-making and a possible biomarker of externalizing disorders.

Citation: 

Sadeh, N., Miglin, R., Bounoua, N., Sheehan, A., & Spielberg, J. (2021). Development of a cortical delay discounting assay: A potential biomarker of externalizing disorders. Psychological Medicine, 1-8. doi:10.1017/S003329172100252X

To calculate the Cortical Delay Discounting (C-DD) Score:

1.  Z-score the cortical thickness in each region, defined by the FreeSurfer Destrieux Atlas.
2.  Multiply each region by the value indicated in the list below (RH = right hemisphere. LH = left hemisphere. G = gyrus. S = sulcus.).
3.  Sum the values.

LIST OF FREESURFER DESTRIEUX ATLAS REGIONS & ASSOCIATED WEIGHTS:

• RH Fronto-marginal gyrus (of Wernicke) and sulcus*-0.012+
• RH Inferior occipital gyrus (O3) and sulcus*-0.039+
• RH Paracentral lobule and sulcus*-0.052+
• RH Subcentral gyrus (central operculum) and sulci*-0.046+
• RH Transverse frontopolar gyri and sulci*0.007+
• RH Anterior part of the cingulate gyrus and sulcus (ACC)*0.022+
• RH Middle-anterior part of the cingulate gyrus and sulcus (aMCC)*-0.031+
• RH Middle-posterior part of the cingulate gyrus and sulcus (pMCC)*-0.092+
• RH Posterior-dorsal part of the cingulate gyrus (dPCC)*-0.128+
• RH Posterior-ventral part of the cingulate gyrus (vPCC, isthmus of the cingulate gyrus)*-0.031+
• RH Cuneus*0.006+
• RH Opercular part of the inferior frontal gyrus*-0.005+
• RH Orbital part of the inferior frontal gyrus*-0.007+
• RH Triangular part of the inferior frontal gyrus*0.017+
• RH Middle frontal gyrus *0.005+
• RH Superior frontal gyrus*-0.023+
• RH Long insular gyrus and central sulcus of the insula*-0.047+
• RH Short insular gyri*-0.070+
• RH Middle occipital gyrus (O2, lateral occipital gyrus)*-0.049+
• RH Superior occipital gyrus (O1)*-0.002+
• RH Lateral occipito-temporal gyrus (fusiform gyrus, O4-T4)*-0.089+
• RH Lingual gyrus, lingual part of the medial occipito-temporal gyrus (O5)*-0.027+
• RH Parahippocampal gyrus, *-0.053+
• RH Orbital gyri*-0.054+
• RH Angular gyrus*-0.008+
• RH Supramarginal gyrus*-0.013+
• RH Superior parietal lobule (lateral part of P1)*0.006+
• RH Postcentral gyrus*-0.025+
• RH Precentral gyrus*-0.001+
• RH Precuneus (medial part of P1)*0.002+
• RH Straight gyrus*-0.038+
• RH Subcallosal area, subcallosal gyrus*0.036+
• RH Anterior transverse temporal gyrus (of Heschl)*-0.036+
• RH Lateral aspect of the superior temporal gyrus*-0.023+
• RH Planum polare of the superior temporal gyrus*-0.020+
• RH Planum temporale of the superior temporal gyrus*-0.013+
• RH Inferior temporal gyrus (T3)*-0.025+
• RH Middle temporal gyrus (T2)*-0.054+
• RH Horizontal ramus of the anterior segment of the lateral sulcus*0.045+
• RH Vertical ramus of the anterior segment of the lateral sulcus*0.0305+
• RH Posterior ramus of the lateral sulcus*-0.044+
• RH Occipital pole*-0.051+
• RH Temporal pole*-0.060+
• RH Calcarine sulcus*-0.011+
• RH Central sulcus (Rolando’s fissure)*-0.047+
• RH Marginal branch of the cingulate sulcus*-0.018+
• RH Anterior segment of the circular sulcus of the insula*-0.058+
• RH Inferior segment of the circular sulcus of the insula*0.017+
• RH Superior segment of the circular sulcus of the insula*-0.056+
• RH Anterior transverse collateral sulcus*-0.022+
• RH Posterior transverse collateral sulcus*-0.071+
• RH Inferior frontal sulcus*-0.017+
• RH Middle frontal sulcus*-0.001+
• RH Superior frontal sulcus*-0.034+
• RH Sulcus intermedius primus (of Jensen)*-0.013+
• RH Intraparietal sulcus and transverse parietal sulci*-0.012+
• RH Middle occipital sulcus and lunatus sulcus*-0.020+
• RH Superior occipital sulcus and transverse occipital sulcus*-0.012+
• RH Anterior occipital sulcus and preoccipital notch*-0.048+
• RH Lateral occipito-temporal sulcus*-0.014+
• RH Medial occipito-temporal sulcus and lingual sulcus*-0.058+
• RH Lateral orbital sulcus*-0.001+
• RH Medial orbital sulcus (olfactory sulcus)*0.008+
• RH Orbital sulci (H-shaped sulci)*-0.004+
• RH Parieto-occipital sulcus*-0.008+
• RH Pericallosal sulcus (S of corpus callosum)*-0.021+
• RH Postcentral sulcus*-0.001+
• RH Inferior part of the precentral sulcus*-0.037+
• RH Superior part of the precentral sulcus*-0.029+
• RH Suborbital sulcus*0.019+
• RH Subparietal sulcus*-0.023+
• RH Inferior temporal sulcus*-0.023+
• RH Superior temporal sulcus*-0.037+
• RH Transverse temporal sulcus*-0.089 + 
• LH Fronto-marginal gyrus (of Wernicke) and sulcus*-0.044+
• LH Inferior occipital gyrus (O3) and sulcus*-0.058+
• LH Paracentral lobule and sulcus*-0.076+
• LH Subcentral gyrus (central operculum) and sulci*-0.033+
• LH Transverse frontopolar gyri and sulci*-0.024+
• LH Anterior part of the cingulate gyrus and sulcus (ACC)*0.030+
• LH Middle-anterior part of the cingulate gyrus and sulcus (aMCC)*0.015+
• LH Middle-posterior part of the cingulate gyrus and sulcus (pMCC)*-0.045+
• LH Posterior-dorsal part of the cingulate gyrus (dPCC)*-0.119+
• LH Posterior-ventral part of the cingulate gyrus (vPCC, isthmus of the cingulate gyrus)*0.047+
• LH Cuneus*-0.049+
• LH Opercular part of the inferior frontal gyrus*-0.000+
• LH Orbital part of the inferior frontal gyrus*-0.047+
• LH Triangular part of the inferior frontal gyrus*0.003+
• LH Middle frontal gyrus (F2)*0.007+
• LH Superior frontal gyrus (F1)*-0.0253+
• LH Long insular gyrus and central sulcus of the insula*-0.036+
• LH Short insular gyri*-0.0422+
• LH Middle occipital gyrus (O2, lateral occipital gyrus)*-0.018+
• LH Superior occipital gyrus (O1)*0.001+
• LH Lateral occipito-temporal gyrus (fusiform gyrus, O4-T4)*-0.088+
• LH Lingual gyrus, lingual part of the medial occipito-temporal gyrus (O5)*-0.024+
• LH Parahippocampal gyrus*-0.056+
• LH Orbital gyri*-0.068+
• LH Angular gyrus*0.003+
• LH Supramarginal gyrus*-0.024+
• LH Superior parietal lobule (lateral part of P1)*0.014+
• LH Postcentral gyrus*-0.030+
• LH Precentral gyrus*-0.008+
• LH Precuneus (medial part of P1)*-0.024+
• LH Straight gyrus*-0.040+
• LH Subcallosal area, subcallosal gyrus*0.048+
• LH Anterior transverse temporal gyrus (of Heschl)*-0.054+
• LH Lateral aspect of the superior temporal gyrus*-0.017+
• LH Planum polare of the superior temporal gyrus*0.003+
• LH Planum temporale of the superior temporal gyrus*0.003+
• LH Inferior temporal gyrus (T3)*-0.045+
• LH Middle temporal gyrus (T2)*-0.031+
• LH Horizontal ramus of the anterior segment of the lateral sulcus*-0.046+
• LH Vertical ramus of the anterior segment of the lateral sulcus*0.041+
• LH Posterior ramus of the lateral sulcus*-0.056+
• LH Occipital pole*-0.051+
• LH Temporal pole*-0.029+
• LH Calcarine sulcus*-0.013+
• LH Central sulcus*-0.033+
• LH Marginal branch of the cingulate sulcus*0.045+
• LH Anterior segment of the circular sulcus of the insula*-0.070+
• LH Inferior segment of the circular sulcus of the insula*0.001+
• LH Superior segment of the circular sulcus of the insula*-0.080+
• LH Anterior transverse collateral sulcus*-0.016+
• LH Posterior transverse collateral sulcus*-0.016+
• LH Inferior frontal sulcus*-0.020+
• LH Middle frontal sulcus*0.025+
• LH Superior frontal sulcus*-0.023+
• LH Sulcus intermedius primus (of Jensen)*-0.054+
• LH Intraparietal sulcus and transverse parietal sulci*0.013+
• LH Middle occipital sulcus and lunatus sulcus*-0.025+
• LH Superior occipital sulcus and transverse occipital sulcus*-0.022+
• LH Anterior occipital sulcus and preoccipital notch*0.006+
• LH Lateral occipito-temporal sulcus*-0.007+
• LH Medial occipito-temporal sulcus and lingual sulcus*-0.078+
• LH Lateral orbital sulcus*-0.019+
• LH Medial orbital sulcus (olfactory sulcus)*-0.030+
• LH Orbital sulci (H-shaped sulci)*-0.017+
• LH Parieto-occipital sulcus*-0.026+
• LH Pericallosal sulcus (S of corpus callosum)*-0.01+
• LH Postcentral sulcus*0.007+
• LH Inferior part of the precentral sulcus*-0.017+
• LH Superior part of the precentral sulcus*-0.024+
• LH Suborbital sulcus*0.030+
• LH Subparietal sulcus*-0.022+
• LH Inferior temporal sulcus*-0.046+
• LH Superior temporal sulcus*-0.023+
• LH Transverse temporal sulcus*-0.018