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measures of the spatial configuration of different types of tissue in the brain
structural imaging
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measures temporary changes in brain physiology associated with cognitive processing
functional imaging
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constructed according to the amount of x-ray absorption in different types of tissue
computerized tomography (CT) scans
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CT scans cannot distinguish between ____ ____ and ____ _____ in the same way as MRI, and it can not be adapted for
functional imaging purposes
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characteristics of this type of structural imaging device
- -is completely safe (people can be scanned multiple times)
- -provides better spatial resolution
- -better discrimination between white and gray matter
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strong magnetic field is applied across the part of the body being scanned, this strong external field is applied and a small fraction of hydrogen nuclei in water alight themselves
MRI
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strength of the magnetic field is measured in units called
tesla
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designed to measure the moment to moment variable characteristics of the brain that may be associated with changes in cognitive processing
functional imaging
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measures the change in blood flow in a region directly, the blood supply to a region increases to supply demand
PET
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sensitivity to a concentration of oxygen in the blood
fMRI
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technique for segregating and measuring differences in white matter and gray matter concentration
voxel based morphometry
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using MRI to measure white matter connectivity between brain regions
Diffusion tensor imaging (DTI)
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The basic requirement in all functional imaging studies is that
the physiological response must be compared to one or more baseline responses
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uses a radioactive tracer injected into the bloodstream. the greater the blood flow in a region, the greater the signal emitted by the tracer in that region.
Positron emission tomography (PET)
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temporal resolution refers to the accuracy with which
one can measure when a cognitive event is occuring
-
the spatial resolution refers to the accuracy with which one can measure
where a cognitive event (a physiological change) is occuring
-
the component that the fMRI is sensitive to is..
the amount of deoxyhemoglobin
-
blood oxygen level dependent contrast; the signal measured in fMRI that relates to the concentration of deoxyhemoglobin in the blood
BOLD
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three phases of hemodynamic response function
- 1. initial dip
- 2. over compensation
- 3. undershoot
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key advantages of the fMRI
- -better temporal and spatial resolution
- -does not use radioactivity
-
characteristics of PET
- -based on blood volume
- -involves radioactivity (can only be scanned once)
- -sensitive to the whole brain
- -must use a block design
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characteristics of fMRI
- -based on blood oxygen concentration
- -no radioactivity (able to scan multiple times)
- -blocked or event related design
- -some brain areas are hard to image
-
type of experimental design in functional imaging in which activity in a control task is subtracted from activity in an experimental task
cognitive subtraction
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effect of one variable on another
interaction
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ability to identify a set of tasks that has a particular component in common. the problem of interactions can be reduced
cognitive conjunction.
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measuring associations between brain activity and changes in the variables of interest
parametric design
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measuring the differences in brain activity between two or more conditions
categorical design
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in parametric design a ____ baseline condition is ______ necessary
separate; not
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implies that a region responds to a limited range of stimuli/conditions and that this distinguishes it from the responsiveness of other neighboring regions. not strictly the same as localization
functional specialization
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the way in which different regions communicate with each other. the basic approach is to model how activity in different regions is interdependent.
functional integration
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stimuli that belong together in one condition
block design
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stimuli from two or more conditions are presented randomly interspersed
event related design
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advantage of block design
the method has more power; that is, it is more able to detect significant but small effects
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advantages of even related designs over blocked ones
they enable a much wider range of experimental designs
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mapping of individual differences in brain anatomy onto a standard template
stereotactic normalization
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redistributing brain activity from neighboring voxels to enhance the signal to noise ratio
smoothing
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the most common way of dealing with individual differences is effectively to assume that ..
they dont exist. or more properly put, individual differences neednt get in the way of making claims about general brain function
-
locations in the brain defined relative to the atlas of Talairach and Tournoux
Talairach coordinates
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smoothing _____ some of the raw activation level of a given voxel to neighboring voxels
spreads
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difficulty in _____ is that the activity in each voxel is not independent, neighboring voxels tend to have similar activity
smooooothing
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functional imaging gives us a better idea of which ____ may be sufficient for performing a particular task, but not always which regions are ______ and necessary for performing a task
region; crucial
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imaging data imply that a brain region is used in a given task but lesion data suggest that this region is not essential to the task
disagreement 1 with lesion data
-
imaging data imply that a brain region is not used in a given task but lesion data suggest that this region is critical to the task
disagreement 2 with lesion data
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a progressive loss of information from semantic memory
semantic dementia
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conceptually based knowledge about the world, including knowledge of people, places, the meaning of objects and words
semantic memory
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patients with damage to the left inferior frontal gyrus do not show clinical symptoms of semantic memory impairments because
the region is involved in strategic retrieval operations from semantic memory. temporal regions may store the semantic memory and lesions produce impairments
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brain imaging can be used to infer the type of _____ and how the stimulus is _______
stimulus; evaluated
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