Alex Leow

Publications (81) View all

• Source

  Available from: Olusola Ajilore

  Article: White Matter Tract Integrity of Anterior limb of Internal Capsule in Major Depression and Type 2 Diabetes.

  Aifeng Zhang, Olusola Ajilore, Liang Zhan, Johnson Gadelkarim, Laura Korthauer, Shaolin Yang, Alex Leow, Anand Kumar
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  ABSTRACT: A number of studies have shown an association between diabetes and depression. However, the underlying mechanisms are still unclear. Previous findings indicate a role for the prefrontal cortex and subcortical gray matter regions in type 2 diabetes and major depressive disorder (MDD). The purpose of this study was to examine the white matter integrity in the fibers that are part of the anterior limb of internal capsule (ALIC) in MDD and diabetic subjects using diffusion tensor imaging tractography. We studied 4 groups of subjects including 1) 42 healthy controls (HC), 2) 28 MDD subjects (MD), 3) 24 patients diagnosed with type 2 diabetes without depression (DC), and 4) 22 patients diagnosed with diabetes and depression (DD). Results revealed significantly decreased fractional anisotropy (FA; p=.021) and a trend towards significant increase in radial diffusivity (RD; p=.078) of the right ALIC in depressed subjects (MD+DD) compared to non-depressed subjects (HC+DC). While there were no significant diabetes effects or interactions between depression and diabetes, subjects with high depression ratings and high hemoglobin A1c levels had the lowest mean FA values in the right ALIC. In addition, we found a significant negative correlation between FA of the left ALIC with hemoglobin A1c in diabetic subjects (DC+DD; p=.016). Our study demonstrated novel findings of white matter abnormalities of the ALIC in depression and diabetes. These findings have implications for clinical manifestations of depression and diabetes as well as their pathophysiology.Neuropsychopharmacology accepted article preview online, 6 February 2013; doi:10.1038/npp.2013.41.
  Neuropsychopharmacology: official publication of the American College of Neuropsychopharmacology 02/2013; · 6.99 Impact Factor
• Article: Abnormal brain network organization in body dysmorphic disorder.

  Donatello Arienzo, Alex Leow, Jesse A Brown, Liang Zhan, Johnson Gadelkarim, Sarit Hovav, Jamie D Feusner
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  ABSTRACT: Body dysmorphic disorder (BDD) is characterized by preoccupation with misperceived defects of appearance, causing significant distress and disability. Previous studies suggest abnormalities in information processing characterized by greater local relative to global processing. The purpose of this study was to probe whole-brain and regional white matter network organization in BDD, and to relate this to specific metrics of symptomatology. We acquired diffusion-weighted 34-direction MR images from 14 unmedicated participants with DSM-IV BDD and 16 healthy controls, from which we conducted whole-brain deterministic DTI tractography. We then constructed white matter structural connectivity matrices to derive whole-brain and regional graph theory metrics, which we compared between groups. Within the BDD group, we additionally correlated these metrics with scores on psychometric measures of BDD symptom severity as well as poor insight/delusionality. The BDD group showed higher whole-brain mean clustering coefficient than controls. Global efficiency negatively correlated with BDD symptom severity. The BDD group demonstrated greater edge betweenness centrality for connections between the anterior temporal lobe and the occipital cortex, and between bilateral occipital poles. This represents the first brain network analysis in BDD. Results suggest disturbances in whole brain structural topological organization in BDD, in addition to correlations between clinical symptoms and network organization. There is also evidence of abnormal connectivity between regions involved in lower-order visual processing and higher-order visual and emotional processing, as well as inter-hemispheric visual information transfer. These findings may relate to disturbances in information processing found in previous studies.Neuropsychopharmacology accepted article preview online, 15 January 2013; doi:10.1038/npp.2013.18.
  Neuropsychopharmacology: official publication of the American College of Neuropsychopharmacology 01/2013; · 6.99 Impact Factor
• Article: Impaired Inter-Hemispheric Integration in Bipolar Disorder Revealed with Brain Network Analyses.

  Alex Leow, Olusola Ajilore, Liang Zhan, Donatello Arienzo, Johnson Gadelkarim, Aifeng Zhang, Teena Moody, John Van Horn, Jamie Feusner, Anand Kumar, Paul Thompson, Lori Altshuler
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  ABSTRACT: BACKGROUND: This represents the first graph theory-based brain network analysis study in bipolar disorder, a chronic and disabling psychiatric disorder characterized by severe mood swings. Many imaging studies have investigated white matter in bipolar disorder, with results suggesting abnormal white matter structural integrity, particularly in the fronto-limbic and callosal systems. However, many inconsistencies remain in the literature, and no study to date has conducted brain network analyses with a graph-theoretic approach. METHODS: We acquired 64-direction diffusion-weighted magnetic resonance imaging on 25 euthymic bipolar I disorder subjects and 24 gender- and age-equivalent healthy subjects. White matter integrity measures including fractional anisotropy and mean diffusivity were compared in the whole brain. Additionally, structural connectivity matrices based on whole-brain deterministic tractography were constructed, followed by the computation of both global and local brain network measures. We also designed novel metrics to further probe inter-hemispheric integration. RESULTS: Network analyses revealed that the bipolar brain networks exhibited significantly longer characteristic path length, lower clustering coefficient, and lower global efficiency relative to those of control subjects. Further analyses revealed impaired inter-hemispheric but relatively preserved intra-hemispheric integration. These findings were supported by whole-brain white matter analyses that revealed significantly lower integrity in the corpus callosum in bipolar subjects. There were also abnormalities in nodal network measures in structures within the limbic system, especially the left hippocampus, the left lateral orbitofrontal cortex, and the bilateral isthmus cingulate. CONCLUSIONS: These results suggest abnormalities in structural network organization in bipolar disorder, particularly in inter-hemispheric integration and within the limbic system.
  Biological psychiatry 10/2012; · 8.93 Impact Factor
• Source

  Available from: Johnson Johnson GadElkarim

  Conference Proceeding: Partition the human brain with binary trees using simulated annealing

  Johnson Gadelkarim, Dan Schonfeld, Olusola Ajilore, Jamie Feusner, Donatello Arienzo, Liang Zhan, Teena Moody, Anand Kumar, Alex Leow
  OHBM, China; 01/2012
• Source

  Available from: Johnson Johnson GadElkarim

  Conference Proceeding: MEASURING INTER-HEMISPHERIC INTEGRATION IN BIPOLAR AFFECTIVE DISORDER USING BRAIN NETWORK ANALYSES AND HARDI

  A Leow, L Zhan, O Ajilore, J Gadelkarim, A Zhang, D Arienzo, T Moody, J Feusner, A Kumar, P Thompson, L Altshuler
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  ABSTRACT: Bipolar disorder is characterized by extreme mood swings, including both manic and depressive episodes commonly accompanied by psychosis. Many imaging studies have investigated white matter changes in bipolar illness, and the results have suggested abnormal intra-and inter-hemispheric white matter structures, particularly in the fronto-limbic and callosal systems. However, some inconsistency remains in the literature, and no study to-date has utilized brain network analysis using graph theory. Here, we acquired 64-direction diffusion weighted imaging (DWI) on 25 euthymic bipolar I subjects and 25 gender/age matched healthy subjects. White matter integrity measures were computed and compared in 50 white matter ROIs. The results indicated impaired integrity in the corpus callosum. Guided by this, we constructed whole brain structural connectivity networks using graph theory. We devised brain network metrics (inter-hemispheric path length and efficiency) to further probe inter-hemispheric integration, and demonstrated relatively preserved intra-hemispheric but significantly impaired inter-hemispheric integration in our bipolar subjects.
  ISBI; 01/2012