In this study, we identified 8 clusters of brain heatmap patterns across patients with recent onset depression or recent onset psychosis, that showed differential associations to symptom clusters, functionality and age; i.e., clinical heterogeneity in transdiagnostic psychopathology was reflected in homogeneous clusters of contrast texture brain changes. The brain regions contributing most to the decision of our classifier included key areas implicated in psychotic and depressive disorders in studies that have assessed grey and white matter changes in patients. We used the contrast feature map and the LRP method suggested by Bach et al.54 to train and explain a classifier for identification of the transdiagnostic psychopathology. The model showed good accuracy in classifying a combined group of ROD and ROP patients against healthy controls in the training sample, which decreased in the external validation sample. However, the innovative finding of this study is the creation of the homogeneous clusters which are associated with clinical severity and outcome profiles.
Brain alterations in hippocampus, insula, and lateral prefrontal cortex have been suggested to be critical both for emotional processing and for emergence of psychotic symptoms21. Changes in these areas have been observed in ROD (e.g., volume decrease in medial temporal regions)28 and ROP (e.g., volume deficit in the anterior hippocampus)58, which emphasizes the implication of brain alterations in early stages of both illnesses. GM analysis in transdiagnostic psychopathology using our method showed brain changes in regions which are reported in other studies, e.g., cerebellum22, frontal59, temporal regions60, cingulum61, precuneus62, rectus63, insula64, heschl65, lingual7 and putamen left66. The explained classification results using texture feature maps indicate posterior cingulate cortex, gyrus rectus and third ventricle (consistent with our previous results in patients with schizophrenia and major depressive disorder16), insular (consistent with previous study for clinical high risk who transitioned to psychosis and first-episode psychosis38,67) as key regions for the transdiagnostic classification of psychopathology using the contrast feature map (further details in Table S3).
In patients with mental problems, there is mounting evidence of decreased WM function resulting in problems of synchronization and connectivity68, with fractional anisotropy (FA) evaluated using diffusion tensor imaging being the most extensively used measure (DTI). Throughout the phases and progression of psychosis, neural alterations, particularly changes in WM connectivity, could be seen69. There are consistent findings of significantly lower FA in the left genu of the corpus callosum, the left anterior corona radiata (ACR) and the right superior longitudinal fasciculus in ROP patients relative to healthy controls34,70,71. Functional dysconnectivity in dorsal anterior cingulate cortex revealed in major depression72. Third ventricle expansion has been reported in recent onset of psychosis73. Other studies have reported WM integrity abnormalities as measured by FA in major depressive disorders35. The above findings are in line with our results regarding the WM changes in frontal gyrus, gyrus rectus, dorsal anterior, corpus callosum. 3rd and 4th ventricle have been reported as regions that contribute to the identification of the transdiagnostic psychopathology using the contrast texture map.
The brain relevance calculated by the LRP algorithm resulted in clusters that showed differential associations with age, positive, negative and depressive symptom clusters, and functionality. Previous studies performed sMRI-based prediction models determined social functioning in the patients with ROD28. In some clusters, mean relevance values and/or relevance of voxels significantly contributing to the classification decision significantly predicted PANSS sum scores, functionality and change in functionality over time. Significant contributing voxels were located in regions that have been previously associated with these scores. In previous studies on schizophrenia and ROD, the FA of the temporal part and the temporolombic GM was positively correlated with GAF score, in consistance with findings in Cluster 6, which includes 17 ROP and 14 ROD patients at baseline28,74. Reduction of GM in fusiform and temporal lobe were associated with PANSS scores in schizophrenia75, as we observed in Cluster 3 which includes mainly ROP patients. Improvement of functionality has also been associated with increased GM volume in temporal lobes at baseline in a previous study76. Our proposed method yielded further, new findings, which should be further validated in different datasets, e.g., right hemisphere calcarine, lingual and precuneus for the prediction of the functionality at follow-up, fusiform gyrus and insula for the prediction of PANSS scores at baseline and occipital and fusiform gyrus for the prediction of the GAF scores at baseline.
The innovation of this study is the development and validation of individualized transdiagnostic models which give insights regarding the relation of brain changes to clinical symptoms and functional outcome. Given that heterogeneity of the mental disorders has hindered the search for biomarkers so far5,27,28, we created homogeneous clusters based on brain relevance patterns. We found groups with different brain alteration profiles, which a) corresponded to different transdiagnostic clinical profiles while also b) showing distinct association profiles between clinical symptom clusters and anatomy. Larger studies are warranted to investigate the optimal number of stable clusters; for the purposes of this study, it is important to show that MRI can be potentially used to form clinical categorization into more homogeneous groups than those offered by categorical classification systems3,77,78. Distinct psychopathological profiles might be established to help distinguish patients with different syndromes, independent of other diagnostic considerations, and relate these to symptoms and clinical outcomes. Models that emphasize the role of changeable transdiagnostic illness mechanisms can help further these efforts, promoting generalizability of evidence-based treatments to routine care settings by accommodating comorbidities.
Texture feature map extraction from non-segmented brain images provides insight into voxel interrelationships of different modalities. To our knowledge, non-segmented images have never been used to detect the examined disorders due to the lack of interaction between GM, WM and CSF as an indicator of diagnosis, suggesting a novel biomarker. The main advantages of the proposed method are the interpretability of the results and the use of non-segmented images, which eliminate segmentation errors. It considers that contrast reveals microstructure changes when calculated in small 3D cubes and image intensities interrelations between GM, WM and CSF. The radiomic texture feature maps were extracted in MNI space from a registered masked T1-weighted image. The radius of the cubes and the topology of the neural network, for example, should be investigated further. For replication of results, we used the same cube size and pre-processing methods as in previous papers16,38. Future studies should investigate a range of textural qualities, as each one reflects a different component of brain diversity. Finally, diverse methodological techniques should be examined further to acquire a better understanding of neurobiological variations across disorders and to make results useful for targeted interventions and treatment alternatives. Future studies should investigate whether several neuroimaging modalities may be combined and used for more accurate prediction.
Limitations
Results must be interpreted with a clear understanding of limitations, such as the cross-sectional and longitudinal nature of our data, which is important in interpretation because there may be dynamic and changing symptom cluster profiles that are not captured. The texture feature extraction is impacted by the variation in MRI intensity standardization. Another methodological drawback of the proposed method lies in the present lack of consensus regarding the applied image normalization method within the texture features extraction process.