***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Recent neuroimaging studies have demonstrated that human brain networks have economic small-world topology and modular organization , enabling efficient information transfer among brain regions . However , it remains largely unknown how the small-world topology and modular organization of human brain networks emerge and develop . Using  longitudinal MRI data of 28 healthy pediatric subjects , collected at their ages of 1 month , 1 year , and 2 years , we analyzed development patterns of brain anatomical networks derived from morphological correlations of brain regional volumes . The results show that the brain network of 1-month-olds has the characteristically economic small-world topology and nonr and om modular organization . The network 's cost efficiency increases with the brain development to 1 year and 2 years , so does the modularity , providing supportive evidence for the hypothesis that the small-world topology and the modular organization of brain networks are established during early brain development to support rapid synchronization and information transfer with minimal rewiring cost , as well as to balance between local processing and global integration of information OBJECTIVE According to the stress-toxicity hypothesis of depression , hippocampal volumes may diminish as the disease progresses . We sought to examine the changes in hippocampal and amygdala volumes at baseline and at 3 years after an acute depressive episode , and the impact of reduced hippocampal volumes on the outcome . METHODS In a prospect i ve , longitudinal study , we examined the hippocampus and amygdala of 30 in patients with major depression from the Department of Psychiatry and Psychotherapy and 30 healthy participants from the community ( control group )  using high-resolution magnetic resonance images at baseline and after 3 years . Psychopathology  was assessed at baseline , weekly during the inpatient phase and then after 1 , 2 and 3 years . RESULTS During the 3-year follow-up period , neither hippocampal nor amygdala volumes changed significantly among patients or participants in the control group . However , in the subgroup of patients who took antidepressants over the full 3 years , the left hippocampal volumes increased significantly . Patients with small hippocampal volumes and previous depressive episodes had a worse clinical outcome compared with patients with large hippocampal volumes and previous depressive episodes . CONCLUSION Overall , our results suggest that a relatively small hippocampal volume may be a vulnerability factor for a bad treatment response in major depression . Subtle changes in hippocampal volumes may be detectable during continuous antidepressant therapy . Such changes may be the result of neuroplastic processes BACKGROUND Neuroimaging studies have shown that major depressive disorder ( MDD ) is accompanied by structural and functional abnormalities in specific brain regions and connections ; yet , little is known about alterations of the topological organization of whole-brain networks in MDD patients . METHODS Thirty drug-naive , first-episode MDD patients and 63 healthy control subjects underwent a resting-state functional magnetic resonance imaging scan .  The whole-brain functional networks were constructed by thresholding partial correlation matrices of 90 brain regions , and their topological properties ( e.g. , small-world , efficiency , and nodal central ity ) were analyzed using graph theory-based approaches . Nonparametric permutation tests were further used for group comparisons of topological metrics . RESULTS Both the MDD and control groups showed small-world architecture in brain functional networks , suggesting a balance between functional segregation and integration . However , compared with control subjects , the MDD patients showed altered quantitative values in the global properties , characterized by lower path length and higher global efficiency , implying a shift toward r and omization in their brain networks . The MDD patients exhibited increased nodal central ities , predominately in the cau date nucleus and default-mode regions , including the hippocampus , inferior parietal , medial frontal , and parietal regions , and reduced nodal central ities in the occipital , frontal ( orbital part ) , and temporal regions . The altered nodal central ities in the left hippocampus and the left cau date nucleus were correlated with disease duration and severity . CONCLUSIONS These results suggest that depressive disorder is associated with disruptions in the topological organization of functional brain networks and that this disruption may contribute to disturbances in mood and cognition in MDD patients OBJECTIVES Connectivity analysis was used to investigate the processing of intracutaneous stimuli and directed interactions within the pain matrix in patients with major depression ( MD ) and healthy controls ( HCs ) , by means of frequency selective generalized partial directed coherence ( gPDC ) . METHODS Eighteen patients with MD and 18 HCs underwent  stimulations consisting of moderately painful intracutaneous electrical stimuli to the right and left middle fingers . Connectivity analysis was based on nine selected EEG electrodes . RESULTS Stimulus-induced changes of the gPDC in a pre/post stimulus comparison and changes in the connectivity pattern in the post-stimulus condition were found . We could identify network changes correlating to the side stimulated , as well as differences between HCs and MD patients . CONCLUSIONS These data support the suggestion that pain processing in response to noxious stimulation in MD patients is different compared to healthy controls , suggesting aberrant functional connectivity . Generalized partial directed coherence is shown to be a promising method to detect changes in connectivity in both within- and between-subject design BACKGROUND The aim of our study was to test the hypothesis that amygdala volumes are reduced in patients with recurrent major depression compared with first episode patients . METHODS Using structural magnetic resonance imaging , we compared 30 in patients with first-episode depression and 27 in patients with recurrent major depression ( DSM-IV ) with healthy volunteer subjects from the local community matched for age , gender , and h and edness . RESULTS Patients with first-episode depression showed enlarged amygdala volumes compared with patients with recurrent major depression and healthy control subjects . No significant differences were found between patients with recurrent depression and healthy control subjects . No significant correlations were found between amygdala volumes and age of onset , illness duration , or severity of depression . CONCLUSIONS Larger amygdala volumes in patients with first-episode depression may result from higher amygdala metabolism and blood flow . Additionally , disease progression with stress-related excitotoxic processes during recurrent depressive episodes might result in decreased amygdala volumes . Prospect i ve investigations to investigate amygdala changes during the course of depression are needed 
    Output:
    
The brain regions that are most consistently affected across studies are the orbitomedial prefrontal cortex , anterior cingulate cortex , amygdala , hippocampus , cerebellum and the basal ganglia .