Date of Thesis

Spring 2018

Thesis Type

Honors Thesis

Degree Type

Bachelor of Science

Major

Neuroscience

First Advisor

Vanessa Troiani

Second Advisor

Judith Grisel

Keywords

orbitofrontal cortex, sulcogyral patterns, gray matter, white matter, diffusion tensor imaging, bipolar disorder

Abstract

Located within the frontal lobe, the human orbitofrontal cortex (OFC) is widely known for its roles in sensory integration, emotion processing, decision-making, and goal-directed behaviors. Atypical structural organization of the OFC may explain atypical social or motivational behaviors displayed by individuals with brain disorders, such as bipolar disorder patients (BP).

The human brain can be imaged using magnetic resonance imaging (MRI) to reveal interesting aspects of the underlying brain architecture. This brain is composed of different tissue types, including gray and white matter, as well as various morphological features, including sulci & gyri. Within the OFC, the sulci can be labeled and classified into a finite number of patterns based on the continuity of the most medial and most lateral sulci. Typical patterns (Type I) have previously been found at higher frequencies bilaterally in healthy populations, whereas atypical patterns (Type II and Type III) have been found at higher frequencies in relative to patients with schizophrenia (SZ).

In order to characterize differences in morphological properties of structural OFC architecture in BP patients (N=46) relative to healthy controls (N=52), we trace OFC sulcogyral patterns based on a previously established protocol, employ a voxel-based morphometry (VBM) analysis to assess OFC gray matter (GM), and implement a diffusion tensor imaging (DTI) tractography analysis to measure white matter tract microstructural properties. Chi-square analysis compared sulcogyral pattern frequency distributions between groups, and independent sample t-tests compared additional OFC properties. Based on previous work and overlap of symptoms and genetics between BP and SZ, we predict that OFC architecture in BP individuals will differ from controls.

We find that BP displayed increased atypical (Type II and Type III) sulcal pattern frequencies relative to controls in the left hemisphere (χ2= 18.6, p < 0.001). T-tests reveal that global OFC GM volumes were significantly decreased in both right (p = 0.0338) and left (p = 0.0039) hemispheres of BP relative to controls. BP also exhibit a reduced number of tracts in the uncinate fasciculus (UF) relative to controls on the left that trended toward significance (p = 0.094).

Overall, we find atypical OFC structural organization of sulcal patterns, reduced gray matter volume, and fewer white matter UF tracts in BP relative to controls, especially in the left hemisphere. Exploring and quantifying various structural brain properties within the OFC may be useful in assessing individual risk to brain dysfunction and facilitate a personalized approach for diagnosis and treatment.

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