methods Flashcards
clinical populations
researchers may examine whether degree of brain activation or deactivation shows a significant relationship with a particular characteristic of a clinically relevant group of people
neurologically intact
serve as critical reference population in lesion studies.
how are things working normally? - need to have smt to compare it to
allow researchers to determine the degree to which the performance of individuals with brain damage is compromised
lesion group and neurologically intact control group must be match as thoroughly as possible on demographic characteristics
not always ethical
everyone is difference, what is significant vs. what is natural
MRI
machines create a constant magnetic field
perturbations in this field are induced
the response of the atoms in the brain is used to derive maps of the brain structure and functions
provides info about the size and shape of different brain structures
for cortical structures, research are often examine volume, determining if it differs between groups
for subcortical structures, researchers examine volume and variations in shape
DTI diffusion tensor imaging
provides info about anatomical connectivity between different brain regions, whit matter integrity
use to find if connections between are damaged used a lot in concussions
detects the main axis along which water diffuses in nerve fibers and this indicates themain directional orientations of white-matter tracts
the degree of diffusion provides info on the structural integrity of those tracts
what can DTI be used to do
identity effect of demyelinating disorders
detect areas with partial or complete disconnection between brain regions
examine changes in diffusion during different life stages (ie water leaking out because of damage)
diffusion tractography
uses such diffusion tensor info to build an image of probable white matter tracts
positron emission tomography (PET)
works by introducing radioactive atoms into the blood supply to be carried to the brain (overtaken by MRI)
provides info about: neurotransmitter function, levels of brain metabolism - seeing where blood is going
advantages and disadvantages of PET
pros:
allows researchers to examine how the brain uses specific molecules (ie/ neurotransmitters)
provides info on absolute levels of brain metabolism
disadvantages
involves radiation, can only do 2-5 times per year safely, limited
poor temporal resolution, takes time to circulate from the area of injection
need to continually create radioactive isotope with expensive cyclotron
fMRI
BOLD (blood oxygen level dependent signal)
based on how oxygenated and deoxygenated blood have different magnetic properties
increase in oxygen rich blood in areas where the brain is active
deoxygenated blood hinders ability to get a signal, increase proportion of oxygenated to deoxygenated blood results in increase signal from that region
advantages of fMRI
machines widely available
non-invasive
multiple scans possible
safe for children and women of reproductive agen
measure brain activity over seconds
resting state approaches
examines patterns of activity while the brain is at rest
researchers found independent networks (regions that co activate during specific tasks)
advantages of resting state approaches
does not require specific cognitive ability or engagement from participant
relatively short neuroimaging session (10-15 mins)
functional connectivity
when significant relationships are observed
electromagnetic recording methods ERM
provide the best temporal resolution of brain activity
activity can be measure on a ms to ms basis
do not provide a good measure of where in the brain activity is happening
EEG electroencephalography
measures electrical activity in the brain using electrodes
specifically of cortical neurons near the electrodes on the scalp
can see different levels of activation
continuous measure of brain activity
advantages and disadvantages or EEG
pros:
high temporal resolution
non-invasive
relatively cheap
equipment is mobile and accessible
cons:
low spacial resolution
cannot reach structures deep within the brain (below cortical level)
long prep time
ERP event - related potentials
recorded in reference to a specific event
characterized by distinct components
MEG magnetoencephalography
records magnetic potentials produced by brain activity
used clinically to: localize the source of epileptic activity, locate primary sensory corticies during neurosurgical intervention
also used to understand a variety of cognitive processes
advantages and disadvantages to MEG
pros:
magnetic fields not as influenced by different tissue types as electrical currents are in EEG)
strength of magnetic field is systematic so some info about depth of source in the brain
cons:
requires a large and complicated device in a room magnetically shielded against earth’s magnetic field and other sources of electromagnetic radiation
optical recording methods
provides info about the source and time course of neural activity
a laser source of near-infrared light is positioned on the scalp
optic fiber detectors are located a few CMs away
the detectors sense how the path of light is altered by:
absorption (slow signal) in oxygenated and deoxygenated blod
scattering (fast signal) related to physiological characteristics such as the swelling of glia and neurons associated with neuronal firing
advantages and disadvantage to optical recording methods
pros:
absorption of light different for oxygenated and deoxygenated blood, can tell them apart (whereas BOLD is ratio only)
can provide info about oxygenation of the brain
system relatively small and portable
cons
cannot obtain info about subcortical regions (too much light absorbed)
does not provide precise localization of activation
TMS transcranial magnetic stimulation
can allow observation of cause and effect
a pulsed magnetic field over the scalp induces an electrical field which alter the membrane potential of neurons
when the pulsed magnetic field is discontinued, the neurons return to their previous state
can be used to increase or decrease neuronal activity depending on pulse given
method is most effective for cortical structures
transcranial direct current stimulation tDCS
a weak electrical current runs between an entrance and exit electrode to create virtual lesion and enhance activity
stimulation less intense, but less focused spatially
investigating: reduced cravings in addiction, reducing auditory hallucinations inn individuals with schizophrenia
multilevel and multimodal approaches
involve using multiple tools in tandem
researchers combine info from several measures derived from same technique
researchers can combine info from two, complimentary measures that have differing strengths
meta-analyses
determine whether similar results are obtained across multiple different studies
when a pattern is observed, there is more confidence in the conclusions drawn about brain-behaviour relationships
transcranial alternating current stimulation
easy and portable
allows for the modulation of brain oscillations
localization effect are not highly specific
