Procedimiento para realizar el diagnóstico de la comercialización en el Complejo

In this section, we show how the modular structure of the human brain is changed dur- ing schizophrenia. The results that we discuss in this section were obtained from group- averaged brain networks. For each group, the group-averaged network then thresholded on the cost-efficient density, 15%, which was obtained by analysis of individual cost-efficiency. As Figure3.8shows, the difference between the modularity index of empirical and randomised networks maximises at≈ 0.93 for both the healthy and schizophrenia group. Therefore, it suffice to examine the brain networks on this scale. Previously it was shown that the average modularity index of healthy and schizophrenia subjects is fairly close (see Figure3.4), but the group-averaged results of modularity, Figure3.8, suggest that modular- ity indexes are 0.36, 0.41 for healthy and schizophrenia subjects, respectively. In addition to the modularity index, the group-averaged brain network in schizophrenia suggest six modules, whereas, the group-average network of the healthy group suggest four modules. It is notable that the number of nodes within each of the modules in the healthy network is almost equally distributed, whereas, the modular structures in schizophrenia suggest that the size of each module can range from 10 nodes (module 1) to more than 96 nodes (module 2).

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Figure 3.8: A.Modularity index across different scales for both empirical and randomised net- works in healthy (Left). Module configurations on re-arranged group-averaged network of healthy (Right).B.Modularity index across different scales for both empirical and randomised networks in schizophrenia (Left). Module configurations on re-arranged group-averaged network of schizophre- nia (Right).

Visual inspection of the module in Figure3.9suggests that, although, the modularity algorithm was used on BOLD signals of the brain, the modules are spatially consistent. For example, the majority of nodes that were already known to be part of the Cerebrum were clustered as one module (see module 4; cyan). This effect is even more obvious in the Frontal (module 1; red), Temporal (module 2; green) and Occipital/Cerebellum (module 3) cortices. On the other hand, in schizophrenia, two extra modules, in the Frontal and

Temporal, dilute the spatial consistency across modules.

In terms of module assignments in the healthy brain network, the majority of nodes that formedModule 1are from the anterior regions such as the Paracentral, Middle Tempo- ral, Superior Parital, bilateral Insula, Postcentral and Inferior Frontal. Module 2is mainly formed by a combination of regions from the Cerebellum and Temporal lobe including: Tuber, Thalamus, Culmen, Uvula, Fusiform, Parahipocampal, Middle Temporal, Inferior Temporal and Superior Temporal. Module 3 is mainly formed from the Occipital lobe, Cerebellum and Parietal Lobe which includes Lingual gyrus, Declive, Middle Occipital, In- ferior Occipital and Pyramis. Eventually,Module 4is formed from regions mostly from the Frontal (middle, inferior, superior) and Parietal lobe which includes the Precuneus, angular gyrus, Thalamus, Caudate and Cingulate gyrus.

Module 1 Module 2 Module 3 Module 4

Module A Module B Module C Module D

Module E Module F

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Figure 3.9:Projection of individual nodes and their module assignments on a transparent surface of the human brain.

Healthy Schizophrenia

Module

s Module

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Figure 3.10:A river-plot shows the overlap between modular structure of healthy and schizophrenia subjects.

Examining the modular structure of the functional connectome in schizophrenia suggests thatmodule A, which is the smallest module with only 10 nodes, is mainly formed by regions representing the Anterior Cingulate and bilateral Caudate. Module Bis mainly formed by nodes in module 3 and module 2 of the healthy networks including parts of the Occipital lobe, Temporal lobe and a small fraction of superior Parietal lobe including Mid- dle Occipital, Inferior Occipital, Culmen, Nodule and a small portion of Precuneus.Module Cis formed by small fraction of module 2 in healthy networks which is mostly located in the Temporal Lobe including the Parahipocampal gyrus, Thalamus and Insula.Module Dhas a large overlap with module 4 of the healthy network as it is mainly formed by the Superior, Medial and Inferior Temporal Lobe as well as anterior parts of Cingulate gyrus.Module E

mostly overlaps with module 1 of the healthy networks. It mainly represents regions from the Frontal and Parietal lobes such as Precuneus, Precentral and Postcentral lobes. Eventu- ally, module F which overlaps with three modules, (1,2,4) of the healthy networks, covers the Parietal and Temporal Lobe and includes regions such as the Insula, Middle Temporal and Frontal, Inferior Parietal and Lentiform nucleus.

Using Normalised Mutual Information, we approximated the level of association between module assignments of healthy and schizophrenic brain networks and the results suggest that there is more than 59% of the nodes that overlap despite the difference in the modularity index and the block counts.

Figure 3.11: Similarity between node assignments of modularity algorithm across subjects of healthy (Left) and schizophrenia (Right)

Using the same technique, we also calculated the level of within group similarity between module assignments of each group. Figure3.11 shows the NMI score between each pair of the subjects. Hypothesis testing suggests that the mean NMI scores are not significantly different between healthy and schizophrenia subjects.