Voxel wise comparison (Voxel Based Morphometry or VBM) across subjects in fMRI studies?

What is a voxel-based morphometry study?

Voxel-based morphometry (VBM) is a neuroimaging technique that investigates focal differences in brain anatomy. The core process of VBM is segmenting the brain into grey matter, white matter, and cerebrospinal fluid, warping the segmented images to a template space and smoothing.

What is a voxel-wise comparison?

At its simplest, voxel-based morphometry (VBM) involves a voxelwise comparison of regional gray matter ‘density’ between two groups of subjects. Density here refers to the relative amount of gray matter and should not be confused with cell packing density (number of cells per unit volume of neuropil).

What does voxel-based morphometry measure?

Voxel-based morphometry is a computational approach to neuroanatomy that measures differences in local concentrations of brain tissue, through a voxel-wise comparison of multiple brain images.

What is a whole brain voxel-wise analysis?

The whole brain white matter was defined as voxels within the brain that had FA values larger than 0.2 from the average of the FA maps from the two time points, and that were not contaminated by CSF (defined by segmenting b=0 image using an automated segmentation tool (FAST) (Zhang et al., 2001)).

What is deformation based morphometry?

Deformation-based morphometry (DBM) is a method for identifying macroscopic anatomical differences among the brains of different populations of subjects. The method involves spatially normalizing the structural MR images of a number of sub- jects so that they all conform to the same stereotaxic space.

What is voxel based lesion symptom mapping?

VLSM is an imaging analysis technique that establishes a relationship between precise lesion location and clinical deficit. A group of patients with a symptom (e.g. aphasia) is analyzed; every voxel on each patient’s MRI is evaluated for lesion presence or absence.

What is surface based morphometry?

In neuroimaging, surface-based morphometry (often abbreviated SBM) is a group of brain morphometric techniques used to construct and analyze surfaces that represent structural boundaries within the brain.

What is voxel based registration?

Voxel-based registration uses the intensities throughout the entire selected volume and therefore uses the image content as the basis of the registration and is useful were it is difficult to detect distinct surface topography features.

What are voxels MRI?

An MRI image is composed of a number of voxels; the voxel size is the spatial resolution of the image. A voxel is a 3D unit of the image with a single value, just as for digital photographs a pixel is a 2D unit of the image with a single value.

What is grey matter?

Grey matter (or gray matter) makes up the outermost layer of the brain and is pinkish grey in tone, hence the name grey matter. It gets its grey tone from the high concentration of neuronal cell bodies in contains. Grey matter also contains unmyelinated axons.

How many neurons are in a voxel?

three million neurons

Georgiou points out that a typical voxel corresponds to roughly three million neurons, each with several thousand connections with its neighbors.

How does fMRI measure brain activity?

fMRI detects brain activity by measuring the changes in both the amount of oxygen in the blood and the amount of blood flow [4, 5]. This measurement is known as blood-oxygen-level-dependent activity (BOLD activity).

What is the key principle of bold fMRI?

To summarise, let’s consider three key principles: 1) neural activity is systematically associated with changes in the relative concentration of oxygen in local blood supply (figure 3); 2) oxygenated blood has different magnetic susceptibility relative to deoxygenated blood; 3) changes in the ratio of oxygenated/de- …

What are electroencephalograms used for?

The EEG is used to evaluate several types of brain disorders. When epilepsy is present, seizure activity will appear as rapid spiking waves on the EEG. People with lesions of their brain, which can result from tumors or stroke, may have unusually slow EEG waves, depending on the size and the location of the lesion.

What is reverse inference?

Reverse inference in cognitive neuropsychology has been characterized as inference to ‘psychological processes’ from ‘patterns of activation’ revealed by functional magnetic resonance or other scanning techniques. Several arguments have been provided against the possibility.

What is reverse inference fMRI?

Reverse inference, i.e. the use of brain activation (fMRI) data to infer the engagement of a certain mental function, is heavily criticised (e.g., Poldrack 2011, Neuron).

What is double dissociation in memory?

a research process for demonstrating the action of two separable psychological or biological systems, such as differentiating between types of memory or the function of brain areas. One experimental variable is found to affect one of the systems, whereas a second variable affects the other.