Statistical parametric mapping (SPM) is a

statistical Statistics (from German: ''Statistik'', "description of a state, a country") is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of data. In applying statistics to a scientific, industria ...

technique for examining differences in

brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...

activity recorded during

functional neuroimaging Functional neuroimaging is the use of neuroimaging technology to measure an aspect of brain function, often with a view to understanding the relationship between activity in certain brain areas and specific mental functions. It is primarily used a ...

experiments. It was created by

Karl Friston Karl John Friston FRS FMedSci FRSB (born 12 July 1959) is a British neuroscientist and theoretician at University College London. He is an authority on brain imaging and theoretical neuroscience, especially the use of physics-inspired stati ...

. It may alternatively refer to software created by the Wellcome Department of Imaging Neuroscience at

University College London , mottoeng = Let all come who by merit deserve the most reward , established = , type = Public research university , endowment = £143 million (2020) , budget = ...

to carry out such analyses.

Approach

Unit of measurement

Functional neuroimaging is one type of 'brain scanning'. It involves the measurement of brain activity. The measurement technique depends on the imaging technology (e.g.,

fMRI Functional magnetic resonance imaging or functional MRI (fMRI) measures brain activity by detecting changes associated with blood flow. This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area o ...

and

PET A pet, or companion animal, is an animal kept primarily for a person's company or entertainment rather than as a working animal, livestock, or a laboratory animal. Popular pets are often considered to have attractive appearances, intelligence, ...

). The scanner produces a 'map' of the area that is represented as

voxel In 3D computer graphics, a voxel represents a value on a regular grid in three-dimensional space. As with pixels in a 2D bitmap, voxels themselves do not typically have their position (i.e. coordinates) explicitly encoded with their values. Ins ...

s. Each voxel represents the activity of a specific volume in three-dimensional space. The exact size of a voxel varies depending on the technology. fMRI voxels typically represent a volume of 27 mm³ in an equilateral cuboid.

Experimental design

Researchers examine brain activity linked to a specific mental process or processes. One approach involves asking 'which areas of the brain are significantly more active when doing task A compared to task B?'. Although the tasks might be designed to be identical, except for the behaviour under investigation, the brain is still likely to show changes in activity between tasks due to factors other than task differences (as the brain coordinates many parallel functions unrelated to the task). Further, the signal may contain noise from the imaging process itself. To filter out these random effects, and to highlight the areas of activity linked specifically to the process under investigation, statistics look for the most significant differences. This involves a multi-stage process to prepare the data, and to analyse it using a

general linear model The general linear model or general multivariate regression model is a compact way of simultaneously writing several multiple linear regression models. In that sense it is not a separate statistical linear model. The various multiple linear regre ...

Image pre-processing

Images from the scanner may be pre-processed to remove noise or correct for sampling errors. A study usually scans a subject several times. To account for the motion of the head between scans, the images are typically adjusted so voxels in each image correspond (approximately) to the same site in the brain. This is referred to as ''realignment'' or ''motion correction'', see image realignment. Functional neuroimaging studies usually involve multiple participants, each of whom have differently shaped brains. All are likely to have the same gross anatomy, saving minor differences in overall brain size, individual variation in topography of the

gyri In neuroanatomy, a gyrus (pl. gyri) is a ridge on the cerebral cortex. It is generally surrounded by one or more sulci (depressions or furrows; sg. ''sulcus''). Gyri and sulci create the folded appearance of the brain in humans and other ma ...

and

sulci Sulci or Sulki (in Greek , Steph. B., Ptol.; , Strabo; , Paus.), was one of the most considerable cities of ancient Sardinia, situated in the southwest corner of the island, on a small island, now called Isola di Sant'Antioco, which is, howev ...

of the

cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting of ...

, and morphological differences in deep structures such as the

corpus callosum The corpus callosum (Latin for "tough body"), also callosal commissure, is a wide, thick nerve tract, consisting of a flat bundle of commissural fibers, beneath the cerebral cortex in the brain. The corpus callosum is only found in placental mam ...

. To aid comparisons, the 3D image of each brain is transformed so that superficial structures line up, via ''

spatial normalization In neuroimaging, spatial normalization is an image processing step, more specifically an image registration method. Human brains differ in size and shape, and one goal of spatial normalization is to deform human brain scans so one location in ...

''. Such normalization typically involves translation, rotation and scaling and nonlinear warping of the brain surface to match a standard template. Standard brain maps such as the Talairach-Tournoux or templates from the Montréal Neurological Institute (MNI) allow researchers from across the world to compare their results. Images can be smoothed to make the data less noisy (similar to the 'blur' effect used in some image-editing software) by which voxels are averaged with their neighbours, typically using a

Gaussian Carl Friedrich Gauss (1777–1855) is the eponym of all of the topics listed below. There are over 100 topics all named after this German mathematician and scientist, all in the fields of mathematics, physics, and astronomy. The English eponymo ...

filter or by

wavelet A wavelet is a wave-like oscillation with an amplitude that begins at zero, increases or decreases, and then returns to zero one or more times. Wavelets are termed a "brief oscillation". A taxonomy of wavelets has been established, based on the num ...

transformation.

Statistical comparison

Parametric statistical models are assumed at each voxel, using the general linear model to describe the data variability in terms of experimental and confounding effects, with residual variability. Hypotheses expressed in terms of the model parameters are assessed at each voxel with univariate statistics. Analyses may examine differences over

time Time is the continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future. It is a component quantity of various measurements used to sequence events, to ...

(i.e. correlations between a task variable and brain activity in a certain area) using linear

convolution In mathematics (in particular, functional analysis), convolution is a operation (mathematics), mathematical operation on two function (mathematics), functions ( and ) that produces a third function (f*g) that expresses how the shape of one is ...

models of how the measured signal is caused by underlying changes in neural activity. Because many statistical tests are conducted, adjustments have to be made to control for

type I error In statistical hypothesis testing, a type I error is the mistaken rejection of an actually true null hypothesis (also known as a "false positive" finding or conclusion; example: "an innocent person is convicted"), while a type II error is the fa ...

s (false positives) potentially caused by the comparison of levels of activity over many voxels. A type I error would result in falsely assessing background brain activity as related to the task. Adjustments are made based on the number of

resel In image analysis, a resel (from ''res''olution ''el''ement) represents the actual spatial resolution in an image or a volumetric dataset. The number of resels in the image may be lower or equal to the number of pixel/voxels in the image. In an act ...

s in the image and the theory of continuous

random field In physics and mathematics, a random field is a random function over an arbitrary domain (usually a multi-dimensional space such as \mathbb^n). That is, it is a function f(x) that takes on a random value at each point x \in \mathbb^n(or some other d ...

s in order to set a new criterion for statistical significance that adjusts for the problem of

multiple comparisons In statistics, the multiple comparisons, multiplicity or multiple testing problem occurs when one considers a set of statistical inferences simultaneously or infers a subset of parameters selected based on the observed values. The more inferences ...

Graphical representations

Differences in measured brain activity can be represented in various ways. They can be presented as a table, displaying coordinates that show the most significant differences in activity between tasks. Alternatively, differences in brain activity can be shown as patches of colour on a brain 'slice', with the colours representing the location of voxels with statistically significant differences between conditions. The color gradient is mapped to statistical values, such as t-values or z-scores. This creates an intuitive and visually appealing map of the relative statistical strength of a given area. Differences in activity can be represented as a 'glass brain', a representation of three outline views of the brain as if it were transparent. Only the patches of activation are visible as areas of shading. This is useful as a means of summarizing the total area of significant change in a given statistical comparison.

Software

SPM is software written by the Wellcome Department of Imaging Neuroscience at

University College London , mottoeng = Let all come who by merit deserve the most reward , established = , type = Public research university , endowment = £143 million (2020) , budget = ...

to aid in the analysis of functional neuroimaging data. It is written using

MATLAB MATLAB (an abbreviation of "MATrix LABoratory") is a proprietary multi-paradigm programming language and numeric computing environment developed by MathWorks. MATLAB allows matrix manipulations, plotting of functions and data, implementation ...

and is distributed as

free software Free software or libre software is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions. Free software is a matter of liberty, no ...

References

{{reflist

External links

Wikibooks Wikibooks (previously called ''Wikimedia Free Textbook Project'' and ''Wikimedia-Textbooks'') is a wiki-based Wikimedia project hosted by the Wikimedia Foundation for the creation of free content digital textbooks and annotated texts that any ...

SPM Wikibook.
fMRI guide by Chris Rorden

Introduction to fMRI: experimental design and data analysisCambridge Imagers
- Neuroimaging information and tutorials.
Buttons in SPM5
PowerPoint presentation from the SPM for dummies course
ISAS (Ictal-Interictal SPECT Analysis by SPM)
- Yale University

Biostatistics Computing in medical imaging Neuroimaging Neuroimaging software