Prediction of Aggression
Our hypotheses centered on large-scale networks in the functional connectome that predict severity of aggressive behavior in children. Therefore, we first trained and tested a predictive model for aggression in a transdiagnostic sample of children. The overall CPM model revealed that patterns of brain-wide connectivity predicted severity of aggressive behavior (combined positive and negative networks: r=0.31, RMSE = 9.05, p=0.005 via permutation testing) (Fig. 1). Follow-up comparisons controlling for potential covariates were conducted for age, IQ, sex, motion, and psychotropic medication use, which demonstrated similar model performance (r>0.25 and p<0.03 for all models). The CPM model also remained significant after accounting for internalizing behaviors, social behavior impairments, and ADHD diagnosis (r>0.22 and p<0.05 for all models). Further details are provided in the Supplemental Results. Analyses were also repeated using 10-fold cross-validation and similar results were observed although, as expected with 10-fold versus leave-one-out cross-validation, the correlation coefficient was smaller (r=0.24, RMSE=9.30, p= 0.01).
Network Anatomy and Localization of Circuits
Consistent with previous CPM work18, 19, the predictive edges were distributed throughout the brain, particularly for positive networks, and included connections between frontal, parietal, occipital, and temporal lobes (Fig. 2a). The spatial extent of both positive and negative networks together included 396 edges (369 positive, 27 negative) or less than 1.1% of possible connections that predicted severity of aggressive behavior. Further inspection of these dense networks revealed that were 126 ipsilateral connections in the right hemisphere, 98 ipsilateral connections in left hemisphere, and 172 connections between the right and left hemispheres. Networks predictive of aggression included significantly more long- than short-range connections (168 long-range; 95 short-range, c2 = 10, p=0.002). Highest-degree nodes (i.e., nodes with the most connections) for the positive network included: a bilateral dlPFC node with connections to limbic, temporal-parietal, sensorimotor, and other prefrontal nodes; a temporal node with connections to limbic, parietal, insula, subcortical, sensorimotor, and prefrontal nodes (Fig. 2b). Other high degree nodes for the positive network included nodes in the bilateral vmPFC, right vlPFC, and bilateral temporal poles. Highest-degree nodes for the negative network included a temporal-parietal node in the supramarginal gyrus with connections to limbic, parietal, and prefrontal nodes as well as with connections to cerebellar and subcortical nodes (Fig. 2b).
At the network level, Fig. 2c summarizes connectivity based on the number of connections within and between neural networks (e.g., frontoparietal, default mode, salience). For positive connectivity, within network connections were observed for several networks including the frontoparietal, default mode, medial prefrontal, and salience networks. Several large-scale, between network connections were observed: between frontoparietal and salience networks, which contributed the majority of edges to the positive network; between the medial frontal and default mode, sensorimotor, and salience networks; between the frontoparietal and default mode, salience, sensorimotor, and subcortical networks; and between default mode and salience, sensorimotor, and visual networks. The negative network included relatively more connections between the cerebellum and sensorimotor and salience networks. Overall between network connectivity was further characterized by within-network connections in frontoparietal networks and between network connections with the salience network (Fig. 2c).
Sensitivity Analyses
Virtual Lesioning Analysis. To test the hypothesis of ventral and lateral prefrontal involvement, we used a virtual lesioning analysis to evaluate the sensitivity of edges within and between the dlPFC versus edges from every other node. However, to explore other regions that contributed to the model but were not included in our a priori hypotheses, we also examined the robustness of other high-degree nodes (i.e., most predictive) that were identified in the CPM model. Because these nodes were also predictive of aggression, we reasoned that this could be informative for developing biomarkers. Thus, we selected regions that emerged as high degree nodes, including the dlPFC, that occurred in all iterations of the connectome predictive model. First, we retained only high-degree nodes and all edges connected to these nodes, performing CPM using only these edges. The CPM predictive model remained significant even when restricted to each of the following high-degree nodes and related edges: bilateral dlPFC (r=0.27, RMSE=9.0 p=0.002), bilateral temporal pole (r=0.22, RMSE=9.18, p=0.01), right vlPFC (r=0.21, RMSE=9.20, p=0.02), bilateral parietal cortex (r=0.23, RMSE=9.12, p=0.009), bilateral occipital cortex (r=0.24, RMSE=9.08, p=0.006), and the right cerebellum (r=0.25, RMSE=9.03, p=0.004) (Fig. 3). Next, to check model robustness, we systematically removed each of the high-degree nodes (i.e., retaining all other edges). We found that the model predicting aggressive behavior remained significant across each of the high-degree nodes for the bilateral dlPFC (r=0.21, RMSE=9.18, p=0.03), bilateral temporal pole (r=0.30, RMSE= 9.06, p=0.0005), right vlPFC (r=0.30, RMSE= 9.05, p=0.0004), bilateral parietal cortex (r=0.29, RMSE= 9.12, p=0.0009), bilateral occipital cortex (r=0.29, RMSE= 9.07, p=0.0006), and the right cerebellum (r=0.28, RMSE= 9.12, p=0.0009)—indicating the complexity of the functional connectome and contribution of nodes across the brain in the prediction of aggression. However, it is important to note that the predictive model retaining only the dlPFC nodes showed the greatest effect size while the predictive model lesioning the dlPFC nodes showed the smallest effect size, indicating the contribution of this region to predicting aggression.
Construct Specificity. We then tested the construct specificity of high-degree nodes in predicting aggression. Therefore, we conducted post-hoc tests retaining these high-degree nodes and all related edges (i.e., removing all other edges) to evaluate the robustness of nodes in predicting aggression in subgroups with high severity of co-occurring behaviors (internalizing symptoms, ADHD symptoms, and social impairments). A cut-off T score of >65 was used on standardized continuous measures (CBCL Internalizing Behaviors and CBCL Attention Problems scores, SRS-2 SCI total) to form subgroups because this represents the cut-off for a clinically significant level of psychopathology. The CPM model predicting aggression from dlPFC and its associated nodes remained significant with the dlPFC emerging as a high degree node despite co-occurring symptoms in subgroups with high severity of internalizing (r=0.38, RMSE = 6.46, p=0.005), ADHD (r=0.27, RMSE = 6.54, p=0.03), and social impairments (r=0.26, RMSE = 6.76, p=0.05) (Fig. 4a-c). Other high-degree nodes did not demonstrate similar performance as the dlPFC across each of the co-occurring symptom subgroups (all other Ps > 0.06) and are therefore less robust and not further discussed in the main article. However, for the interested reader, we present these findings for other high-degree nodes in Table S3.
To further assess construct specificity of the dlPFC nodes, we then tested whether the CPM model predicted internalizing and ADHD in the total sample (N=129). Even when dlPFC network connectivity predicted aggression (Fig. 4), it did not predict internalizing behaviors (r=-0.015, RMSE=9.94, p=0.86) or ADHD (r=-0.29, RMSE=5.42, p=1), or social behavior impairments (r=-0.48, RMSE=27.1, p=1)—note that negative correlations indicate CPM model failure.
External Replication and Validation: Aggression Prediction
Out-of-Sample Replication. We then tested the replication of findings from the transdiagnostic sample indicating an association between the functional connectome and aggressive behavior in an independent sample of children from the ABCD study22. Therefore, we trained and tested a model in the ABCD sample to predict aggressive behavior using task-based fMRI from 1,701 children (920 females) using the stop signal task (SST) and from 1,791 children (958 females) using the emotional n-back task (EN-back) (age range 9-10 years). These tasks were selected for external replication and validation purposes because we reasoned that the SST and EN-back tasks tap frontoparietal and fronto-amygdala circuitry that are relevant to aggressive behavior22-24 and, similar to current study, the EN-back task stimuli included a set of happy, fearful, and neutral expressions drawn from the NimStim Stimulus Set25. In addition, the SST taps the construct of response inhibition23, which is implicated in disruptive behavior disorders in youths26. For both tasks (EN-back, SST), the CPM model predicted aggressive behavior in the independent sample (EN-back: rs=0.10, RMSE=3.98, p < 0.001; SST: rs=0.07, RMSE=4.01, p=0.002) (Fig. 5a). Follow-up comparisons controlling for potential covariates were conducted for age, IQ, and sex demonstrated similar model performance for both the SST and EN-back tasks (r>0.1 and p<0.01 for all models). The CPM models also remained significant after accounting for ADHD and internalizing symptoms (r>0.7 and p<0.01 for all models). For completeness, model performance when including these covariates is provided in the Supplemental Results. Similar to the CPM model predicting aggression in the discovery transdiagnostic sample (Fig. 1), highest-degree nodes in ventral and lateral prefrontal regions as well as temporal-parietal regions emerged as highly predictive in the independent sample (EN-back task: bilateral dlPFC, right temporal pole, right frontal eye fields, right vmPFC; SST task: bilateral dlPFC, left temporal pole, bilateral supramarginal gyrus, right vmPFC) (Fig. 5b-d). At the network level, Fig. 5e summarizes connectivity within and between large-scale neural networks for the SST and EN-back tasks, which demonstrated similar patterns to the CPM model from the discovery sample. Overall, between-network connectivity was characterized by connections between medial frontal and frontoparietal, sensorimotor, default mode, and salience networks, which contributed the majority of edges to the positive network, as well as between the frontoparietal and subcortical, cerebellum, and salience networks.
Out-of-Sample Validation. We also tested the generalizability of findings by testing the ability of the identified networks in the transdiagnostic sample (Fig. 1) to predict aggressive behavior in an independent sample of children from the ABCD study and vice versa. First, we found that aggression network strength in the current, transdiagnostic sample predicted aggression severity in the independent sample (ABCD) for the EN-back (rs=0.06, p=0.007), but not the SST (rs=-0.002, p=0.9). Next, we tested the generalization of the aggression model developed in the independent dataset (ABCD study) to the current study’s discovery sample. We found that models developed using the EN-back and SST tasks both generalized to the current sample (EN-back: rs=0.18, p=0.03; SST: rs=0.24, p=0.005).