Global Perturbation of Initial Geometry in a Biomechanical Model of Cortical Morphogenesis

Cortical folding pattern is a main characteristic of the geometry of the human brain which is formed by gyri (ridges) and sulci (grooves). Several biological hypotheses have suggested different mechanisms that attempt to explain the development of cortical folding and its abnormal evolutions. Based on these hypotheses, biomechanical models of cortical folding have been proposed. In this work, we compare biomechanical simulations for several initial conditions by using an adaptive spherical parameterization approach. Our approach allows us to study and explore one of the most potential sources of reproducible cortical folding pattern: the specification of initial geometry of the brain.Comment: 4 pages 2 columns (IEEE style), 41st EMB Conferenc

Simulating local deformations in the human cortex due to blood flow-induced changes in mechanical tissue properties: Impact on functional magnetic resonance imaging

Investigating human brain tissue is challenging due to the complexity and the manifold interactions between structures across different scales. Increasing evidence suggests that brain function and microstructural features including biomechanical features are related. More importantly, the relationship between tissue mechanics and its influence on brain imaging results remains poorly understood. As an important example, the study of the brain tissue response to blood flow could have important theoretical and experimental consequences for functional magnetic resonance imaging (fMRI) at high spatial resolutions. Computational simulations, using realistic mechanical models can predict and characterize the brain tissue behavior and give us insights into the consequent potential biases or limitations of in vivo, high-resolution fMRI. In this manuscript, we used a two dimensional biomechanical simulation of an exemplary human gyrus to investigate the relationship between mechanical tissue properties and the respective changes induced by focal blood flow changes. The model is based on the changes in the brain’s stiffness and volume due to the vasodilation evoked by neural activity. Modeling an exemplary gyrus from a brain atlas we assessed the influence of different potential mechanisms: (i) a local increase in tissue stiffness (at the level of a single anatomical layer), (ii) an increase in local volume, and (iii) a combination of both effects. Our simulation results showed considerable tissue displacement because of these temporary changes in mechanical properties. We found that the local volume increase causes more deformation and consequently higher displacement of the gyrus. These displacements introduced considerable artifacts in our simulated fMRI measurements. Our results underline the necessity to consider and characterize the tissue displacement which could be responsible for fMRI artifacts

Morphology And Mechanics Of Cortical Folding Associated With Auditory Deprivation

Hearing loss is increasingly becoming a common disabling condition that affects the global population. Functional and structural changes occur in the developing auditory cortex after the onset of auditory deprivation. This study aims at measuring and modeling these changes, which can help understand the pathology of hearing loss and support research on treatment. Specifically, it describes a pipeline of automatically extracting inner and outer cortical surfaces from MRI images and measuring morphological metrics. Then, a two-component finite element mechanical model mimicking gray matter and white matter is used to investigate the causes of measured structural differences between cats with normal hearing and hearing loss. Mechanical parameters, such as shear and bulk modulus, are varied with a view to studying their influence on cortical folding patterns. Compared to hearing cats, cats with hearing loss have decreased cortical curvature and folding index, and increased thickness. By varying the shear modulus and bulk modulus of the gray and white matter at different locations, the mechanical model reveals distinct stable folding patterns. Specific combinations of parameters and locations lead to changes in curvature, folding index, and thickness. The methods used in this study can also be extended to examine cortical morphological characteristics associated with other abnormalities in the developing brain