Brain morphometry

This article uses direct referencing.

As a subfield of both morphometry and the brain sciences, brain morphometry is concerned with the quantification of anatomical patterns in the brain. These include whole-brain parameters like brain mass or brain volume, encephalization quotient, the distribution of grey matter and white matter as well as cerebrospinal fluid but also derived parameters like gyrification and cortical thickness or quantitative aspects of substructures of the brain, e.g. the volume of the hippocampus, or the amount of neurons in the optic tectum.

Biological background

The morphology and function of a complex organ like the brain are the result of numerous biochemical and biophysical processes interacting in a highly complex manner across multiple scales in space and time. Most of the genes known to control these processes during brain development, maturation and aging are highly conserved (Holland, 2003), whereas pronounced differences at the cognitive level abound even amongst closely related species, or between individuals within a species (Roth and Dicke, 2005).

In contrast, variations in macroscopic brain anatomy (i.e. at a level of detail still discernable by the naked human eye) are sufficiently conserved to allow for comparative analyses, yet diverse enough to reflect variations within and between individuals and species: As morphological analyses that compare brains at different ontogenetic or pathogenetic stages can reveal important information about the progression of normal or abnormal development within a given species, cross-species comparative studies have a similar potential to reveal evolutionary trends and phylogenetic relationships, though the concept of progression has to be used with caution here, especially when considering contemporary species.

Methodologies

Though the extraction of some morphometric parameters like brain mass or liquor volume may be relatively straightforward in post mortem samples, studies in living subjects normally use an indirect approach: First, a spatial representation of the brain or its components is obtained by some appropriate neuroimaging technique, and from such datasets, the parameters of interest can then be extracted.

Technically, several approaches exist for in vivo brain morphometric analyses: Voxel-based morphometry, deformation-based morphometry, surface-based morphometry and tract-based morphometry. All four are usually performed based on Magnetic Resonance Imaging data, the former three using T1-weighted pulse sequences, the latter diffusion-weighted ones.

Applications

Currently, most applications of brain morphometry have a clinical focus, i.e. they serve to diagnose and monitor neuropsychiatric disorders, in particular neurodevelopmental disorders (like schizophrenia) or neurodegenerative diseases (like Alzheimer), but brain development and aging as well as brain evolution can also be studied this way.