Random Forest Classification of Alcohol Use Disorder Using fMRI Functional Connectivity, Neuropsychological Functioning, and Impulsivity Measures.

Seed regions of the DMN consisting of 6 regions in the left hemisphere (blue beads) and 6 homologous regions in the right hemisphere (red beads), as listed in Table 1. Axial (top), coronal (front), and sagittal (left side) views are shown. (PCC–Posterior cingulate cortex; ACC–Anterior cingulate cortex; IPL–Inferior parietal lobule; PFC–Prefrontal cortex; LTC–Lateral temporal cortex; PHG–Parahippocampal gyrus; L–Left; R–Right; A–Anterior; P–Posterior; S–Superior; I–Inferior).

The multi-way importance plot showing the top significant variables (labelled and marked with black circles) that contributed to the classification of AUD from CTL individuals based on the following measures: the Gini decrease, the number of trees, and the p-values. Fourteen DMN connections, two neuropsychological variables, and all four impulsivity scores were significant (circled and labelled red and green dots). BIS–Barratt Impulsivity Scale; MI–Motor impulsivity; NP–Non-planning; AI–Attentional impulsivity; Tot–Total; Span_Fw–Span forward; TotCor_Fw–Total correct forward; s1-s12–DMN seeds 1-12 as listed in Table 2.

The distribution of minimal depth among the trees of the forest for the significant variables is shown in different colors for each level of minimal depth. The mean minimal depth in the distribution for each variable is marked by a vertical black bar overlapped by its value inside a box. A lower mean minimal depth of a functional connectivity (FC) variable represents a higher number of observations (participants) categorized in a specific group on the basis of the variable. The top significant variables (14 DMN connections, two neuropsychological scores, and all four BIS scores) followed the same rank in the plot as in Table 3, which is ordered based on p-values.

Illustration of rankings of variables based on any of the two RF parameters of importance (inside the left and bottom panels showing distribution of the rankings of all predictor variables marked with black dots along a blue trend line) as well as the respective correlation coefficients across rankings of any two parameters (inside the right and top panels). It is shown that all RF parameters of importance were found to have very high correlations among each other, suggesting that these parameters are highly reliable at ranking the importance of variables in group classification.

Significant DMN connections that contributed to the Random Forest classification of AUD from CTL individuals based on importance parameters including the p-value (p < 0.01), as listed in Table 3. These connections (i.e., edges) across the seed regions (i.e., nodes) within an anatomical brain template are shown: (A) axial (top) view; (B) coronal (front) view; and (C) sagittal (left side) view. The blue and red beads represent left and right-sided nodes, respectively, and the edges in orange and cyan lines represent hyper- and hypo-connectivity, respectively, in the AUD compared to the CTL group.

Correlation matrix showing associations among the top significant variables. The values within each cell represent the bivariate Pearson correlation between the variable on its vertical axis and the variable on its horizontal axis. The correlation values are color coded (red/pink shades represent negative r-values, blue/cyan shades indicate positive r-values, darker shades represent relatively higher magnitudes) and significant correlations have been marked with asterisks (*p < 0.05; **p < 0.01; and ***p < 0.001).