Brain size and folding of the human cerebral cortex

The development of gyrification in childhood and adolescence

Gyrification is the process by which the brain undergoes changes in surface morphology to create sulcal and gyral regions. The period of greatest development of brain gyrification is during the third trimester of pregnancy, a period of time in which the brain undergoes considerable growth. Little is known about changes in gyrification during childhood and adolescence, although considering the changes in gray matter volume and thickness during this time period, it is conceivable that alterations in the brain surface morphology could also occur during this period of development. The formation of gyri and sulci in the brain allows for compact wiring that promotes and enhances efficient neural processing. If cerebral function and form are linked through the organization of neural connectivity, then alterations in neural connectivity, i.e., synaptic pruning, may also alter the gyral and sulcal patterns of the brain. This paper reviews developmental theories of gyrification, computational techniques for measuring gyrification, and the potential interaction between gyrification and neuronal connectivity. We also present recent findings involving alterations in gyrification during childhood and adolescence.

Stereotactic atlas-based depth electrode localization in the human amygdala

BACKGROUND

The efficacy of stereotactic neurosurgery procedures is critically dependent on the accuracy of the device placement procedure. The first step in this process involves correctly identifying the target location in three-dimensional brain space. In some clinical applications, this targeting process cannot be accomplished using MRI images of gross anatomical structures alone. The amygdala complex is a case in point, in that it consists of multiple histologically defined subnuclei with different functional characteristics.

METHODS

In this report, we describe an elastic atlas brain-morphing method that projects amygdala subnuclear anatomical information onto the MRI volumes of individual subjects.

RESULTS

The accuracy of this method was tested in 5 representative subjects using quantitative image-matching analytical techniques. The results demonstrate a high degree of intersubject variability in medial temporal lobe anatomy, and markedly superior anatomical matching performance by the elastic morphing method compared to Affine transformation.

CONCLUSION

Nonlinear elastic morphing technique provides superior performance on fitting atlas templates to individual brain. The strengths and limitations of this and other atlas morphing methods are discussed in the context of emerging functional neurosurgery applications.

A functional polymorphism of the brain derived neurotrophic factor gene and cortical anatomy in autism spectrum disorder

Autism Spectrum Disorder (ASD) is associated with both (i) post-mortem and neuroimaging evidence of abnormal cortical development, and (ii) altered signalling in Brain Derived Neurotrophic Factor (BDNF) pathways - which regulate neuroproliferative and neuroplastic processes. In healthy controls genotype at a single nucleotide polymorphism that alters BDNF signalling (Val66met) has been related to regional cortical volume. It is not known however if this influence on brain development is intact in ASD. Therefore we compared the relationship between genotype and cortical anatomy (as measured using in vivo Magnetic Resonance Imaging) in 41 people with ASD and 30 healthy controls. We measured cortical volume, and its two sole determinants - cortical thickness and surface area - which reflect differing neurodevelopmental processes. We found “Group-by-Genotype” interactions for cortical volume in medial (caudal anterior cingulate, posterior cingulate) and lateral (rostral middle, lateral orbitofrontal, pars orbitalis and pars triangularis) frontal cortices. Furthermore, within (only) these regions “Group-by-Genotype” interactions were also found for surface area. No effects were found for cortical thickness in any region. Our preliminary findings suggest that people with ASD have differences from controls in the relationship between BDNF val66met genotype and regional (especially frontal) cortical volume and surface area, but not cortical thickness. Therefore alterations in the relationship between BDNF val66met genotype and surface area in ASD may drive the findings for volume. If correct, this suggests ASD is associated with a distorted relationship between BDNF val66met genotype and the determinants of regional cortical surface area – gyrification and/or sulcal positioning.