TABLE 2.

Glossary of the technical terms used in this review.

Gray matter
Voxel based morphometry	Neuroimaging technique that investigates voxel-wise gray or white matter differences between groups.
Volumetric analysis	An approach that processes T1-weighted images for obtaining brain structure volumes.
Cortical thickness	Brain morphometric measure derived from T1-weighted images that describes the thickness of gray matter layers in the cerebral cortex.
Tensor-based morphometry	Neuroimaging technique used to localize regions of structural differences between groups or changes over time in subjects’ repeated scans, based on deformation fields that align one image (e.g., a template) to another (e.g., individual map).
Microstructure
Tractography	Three-dimensional modeling technique used to represent neural tracts using diffusivity data collected by diffusion tensor imaging (DTI) to evaluate the presence of continuous axons that traverse multiple voxels.
Tract-based spatial statistics	Automated and observer-independent approach for a voxel-wise analysis of white matter microstructural integrity.
Fractional anisotropy	A DTI-derived measure of the diffusion of water molecules which reflects fiber density, axonal diameter, and myelination in white matter. It ranges from 0, isotropic movement of water molecules (unrestricted in all directions), to 1, anisotropic movement of water molecules (diffusion occurs only along one axis and is fully restricted along all other directions).
Mean diffusivity	DTI-derived measure of the average directionally independent amplitude of water diffusion within brain tissue.
Axial diffusivity	DTI-derived measure of water molecule diffusion parallel to the fibers within the voxel of interest.
Radial diffusivity	DTI-derived measure of water molecule diffusion perpendicular to the fibers within the voxel of interest.
ROI analysis	Approach that involves the extraction of signal from specified regions of interest.
Functional MRI
Resting state fMRI	fMRI technique based on the analysis of low-frequency fluctuations of the blood oxygenation level dependent (BOLD) signal in the absence of tasks or external stimuli (“at rest”). It is used to evaluate regional brain interactions that occur in a resting state.
Task-based fMRI	fMRI technique based on the analysis of low-frequency fluctuations of the blood oxygenation level dependent (BOLD) signal during the performance of a specific action by the patient. It is used to map regional brain activity that occurs in response of cognitive, perceptual or motor manipulations.
Dynamic causal modeling (applied to fMRI)	Bayesian scheme used to construct and compare generative models of measured blood oxygen level-dependent signals to compute neuronal effective connectivity between brain regions.
Fractional amplitude of low-frequency fluctuations	The ratio between the average value of frequency fluctuations within a specific frequency band (from 0.01 to 0.08 Hz) and the average of the whole range of frequencies. In this way, it specifically reports the spontaneous resting state activity of each region with respect to the rest of activity measured in the brain.
Effective connectivity	Effective connectivity is defined as the influence that a node exerts over another node under a network model of causal dynamics and is inferred from a model of neuronal integration, which defines the mechanisms of neuronal coupling.
Voxel-mirrored homotopic connectivity	fMRI technique to analyze the functional homotopy between the two hemispheres, by computing the connectivity between each voxel in one hemisphere and its mirrored counterpart in the other.
Graph analysis and connectome
Graph theory-based analysis	Graph theory-based approaches describe brain as a complex network represented graphically as a set of nodes and edges, where nodes indicate anatomical elements (e.g., brain regions), and edges represent the relationships between nodes (e.g., connectivity).
Connectome	Connectomics is the study of the connections in the central nervous system. The entire set of connections that constitute the brain is known as connectome.
Local efficiency	Measure that expresses the level of local connectedness of a network, with high levels of clustering interpreted as high levels of local organization of the network.
Path length	Distance between two nodes, measured as the number of edges that must be crossed to go from one node to another. It is inversely related to the global efficiency.
Clustering coefficient	The clustering coefficient describes the tendency of nodes to form local triangles, providing insights into the local organization of the network.