The Imaged Brain
This chapter considers how functional imaging methods work, focusing in particular on functional magnetic resonance imaging (fMRI). Whereas structural imaging measures the permanent characteristics of the brain, functional imaging is designed to measure the moment-to-moment variable characteristics of the brain that may be associated with changes in cognitive processing. Electrical and chemical activity of neurons leads to changes in the blood flow, termed the haemodynamic response. This is detected by fMRI and related techniques (e.g., fNIRS, functional near-infrared spectroscopy). The chapter focuses on methodological factors that are important in ensuring that the results obtained can indeed be meaningfully linked to cognitive theory. It discusses how functional imaging data are analyzed to find regions of activation and considers some of the pitfalls in their interpretation. It also discusses multi-voxel pattern analysis which does not rely on overall activation levels but on a pattern of activity in a given region.
Multiple Choice Questions
Flashcards
Measures of the spatial configuration of different types of tissue in the brain (principally CT and MRI)
Measures temporary changes in brain physiology associated with cognitive processing; the most common method is fMRI and is based on a hemodynamic measure
A technique for segregating and measuring differences in white matter and gray matter concentration
Voxel-based morphometry (VBM)
A technique that uses MRI to measure white matter connectivity between brain regions
Diffusion tensor imaging (DTI)
A measure of the extent to which diffusion takes place in some directions more than others
Fractional anisotropy (FA)
Blood oxygen-level dependent contrast; the signal measured in fMRI that relates to the concentration of deoxyhemoglobin in the blood
Changes in the BOLD signal over time
Hemodynamic response function (HRF)
A type of experimental design in functional imaging in which activity in a control task is subtracted from activity in an experimental task
The assumption that adding a different component to a task does not change the operation of other components
Pure insertion (also pure deletion)
The effect of one variable upon another
A motor signal used to predict sensory consequences of an action
The way in which different regions communicate with each other
A technique for measuring functional connectivity in which correlations between several regions (networks) are assessed while the participant is not performing any tasks
A set of brain regions that is more hemodynamically active during rest than during tasks
The mapping of individual differences in brain anatomy onto a standard template
Stereotactic normalization
Redistributing brain activity from neighboring voxels to enhance the signal-to-noise ratio
A volume-based unit (cf. pixels, which are 2D); in imaging research the brain is divided into many thousands of these
Locations in the brain defined relative to the atlas of Talairach and Tournoux
An approach for correcting for many statistical comparisons based on the number of tests being conducted
An approach for correcting for many statistical comparisons based on the number of positive results obtained
False Discovery Rate (FDR)
A reduction/suppression of the activity of a brain region (or a cognitive process), triggered by activity in another region/process
An increase of the activity of a brain region (or a cognitive process), triggered by activity in another region/process
An increase in physiological processing in one condition relative to some other condition(s)
A decrease in physiological processing in one condition relative to some other condition(s)
A progressive loss of information from semantic memory
Conceptually based knowledge about the world, including knowledge of people, places, the meaning of objects and words
