Regional limbic and somatosensory cortical thinning in adults with major depressive disorder
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Regional Limbic and Somatosensory Cortical Thinning in Adults with Major Depressive Disorder. Matthew Crawshaw. Theories of MDD. H ypothalamic -pituitary-adrenal (HPA) axis dyfunction

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Regional limbic and somatosensory cortical thinning in adults with major depressive disorder

Regional Limbic and Somatosensory Cortical Thinning in Adults with Major Depressive Disorder

Matthew Crawshaw


Theories of mdd
Theories of MDD Adults with Major Depressive

  • Hypothalamic-pituitary-adrenal (HPA) axis dyfunction

    • Hippocampus over-production of glucocorticoids, a response to stress, disruptng memory and learningand promoting dendritic atrophy in limbic areas.

  • Limbic-cortico dysregulation theory

    • failures in the coordinated interactions of limbic-frontal cortical pathways(Mayberg 1997)

    • Frontal failure to inhibit limbic activity because of abnormal activity in two pathways:

      • Dorsal: prefrontal cortex and anterior cingulate gyrus

      • Ventral: the orbitofrontal cortex and lower limbic structures


Fraught cortical volume and vbm evidence
Fraught Cortical Volume and VBM evidence Adults with Major Depressive

  • Generally support both theories, but few studies measuring volumetric changes indicate support of all the predictions of the theories

    • Hippocampal, Parahippocampal, Amygdala, Entorhinal, Frontal and Orbitofrontal cortex volume shrinkage

    • Left lateralised, sometimes

    • Sometimes Amygdala is larger

  • Perhaps other kinds of measurements may sheld light on other structural changes in MDD.


Cortical thickness analysis
Cortical Thickness Analysis Adults with Major Depressive

  • Tu et al., 2012

    • MDD patients had large areas of cortical thinning in the bilateral superior frontal gyrus, rostral and caudal middle frontal gyrus and right orbitofrontal gyrus

    • Lesser extent, cortical thinning was present in the left entorhinal cortex, and parietal, temporal and occipital lobes, postcentral gyrus.

  • Present study will similarly adopt a whole-surface analysis, and also specifically analyse cortical thickness in the main regions of interest identified by Tu and colleagues (2012).


Hypotheses
Hypotheses Adults with Major Depressive

  • Analysis 1 considers thickness measurements of the whole cortical surface.

    • H1: MDD patients will have significant cortical thinning in regions of the frontal lobe and limbic cortex, compared with healthy controls.

  • Analysis 2 adopts a regions-of-interest approach, analysing the mean thickness measurements in nine frontal lobe regions based on the main findings of Tuet al. (2012)

    • H2: MDD patients will have significant cortical thinning in the bilateral superior frontal gyrus, rostral and caudal middle frontal gyrus, precentral gyrus, and right lateral orbitofrontal gyrus, compared with healthy controls.


Participants
Participants Adults with Major Depressive


Methods
Methods Adults with Major Depressive

  • Scanning and BrainVoyager Analysis

    • Cortex-based Alignment


Methods1
Methods Adults with Major Depressive

  • Cortical Thickness Measurement

    (a) segmentation and smoothed intensities of GM, WM and CSF; (b) thickness measurement results in mm; (c) projection of thickness data onto subject’s surface mesh.


Statistical analysis
Statistical analysis Adults with Major Depressive

  • Analysis 1: Multiple subject cortical thickness measurements compared using t-tests in BVQX. Cortical thickness differences were tested throughout all vertices.

  • Analysis 2: a priori regions of interest (ROIs) were defined on the average surface mesh. Average cortical thicknesses for the ROIs were found and these were compared between healthy and MDD groups using t-tests within BrainVoyager.

    • ANCOVA also performed in SPSS 19 controlling age and verbal IQ.


Results analysis 1
Results: Analysis 1 Adults with Major Depressive

Area of significantly thinner grey matter for MDD patients in the right entorhinal cortex.


Results analysis 11
Results: Analysis 1 Adults with Major Depressive

Area of significantly thinner grey matter for MDD patients in the left postcentral gyrus. Lowered threshold for cluster size estimation.


Analysis 2 rois
Analysis 2: ROIs Adults with Major Depressive

SFG = Superior Frontal Gyrus; rMFG = Rostral middle frontal gyrus; cMFG = Caudal middle frontal gyrus; preCG = Precentral gyrus; latOFG = Lateral orbitofrontal gyrus


Analysis 2 results
Analysis 2: Results Adults with Major Depressive

  • BVQX ROI mean thickness between-group t-tests

    • No significant differences

  • SPSS 19 ANCOVA controlling for Age and Hamilton Score

    • No significant differences in mean ROI thicknesses between groups


Discussion
Discussion Adults with Major Depressive

  • Main finding: MDD patients showed cortical thinning in the right entorhinal cortex and left postcentral gyrus, but not in the frontal lobe

    • Support HPA axis theory, partial support of Fronto-cortical dysregulation theory

  • Entorhinal cortex key limbic pathway into hippocampus

  • Changes in sometosensory (post-central) gyrus observed before but not explained.

  • Lack of frontal thinning may be due to MDD not severe enough in this sample


Limitations
Limitations Adults with Major Depressive

  • Although subjects were age and gender matched, there was a gender imbalance within groups, which was not controlled for in the analysis

  • No control for the effects of medication, which is known to affect brain structure and is therefore cited as a possible reason for the often-conflicting results in the literature

  • CTA and CBA still a nascent method in MDD studies

    • Captures multiple cytoarchitectural changes in the cortex under one measure, and requires cellular studies to reveal details of what they are.


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