Imaging Flashcards
classical cognitive approach involves 3 things
- measuring observable behavior
- making inferences about underlying cognitive activity
- consider what the behavior says about how the mind works
what does imaging introduce
whole range of objectively measurable things that we can now incorporate into our investigations
Cognitive neuroscience approach involves 3 things
- measuring neural activity (and/or observable behavior)
- making inferences about underlying cognitive activity
- consider what the neural activity (and or behavior says about how the mind works
3 important considerations relevant for conducting/interpreting imaging work?
- Theoretically meaningful interpretations can be complicated
- Analyses often rely on subtractive logic, which may obscure meaningful information (e.g. what’s happening with the default network)
- Localization of function is often assumed but may sometimes be an oversimplification
within Theoretically meaningful interpretations something emerges
- Many confounds can emerge (e.g. false positive, which can become much more likely if you don’t adequately correct for multiple comparisons)
false positives can sometimes occur when
there is a large volume of data
statistical problem of multiple comparisons (what type of error)
, the more comparisons you make between various data points, the more likely you are to find a statistically significant result purely by chance (type 1)
Subtractive logic (mental chronometry) is used
used to make inferences about the differing time courses of various cognitive processes
Subtractive logic in neuro imaging (3 steps)
- measure activity at rest (baseline activation)
- measure brain activity during task (task activation)
- subtract baseline from activation
potential problem with subtractive logic
our brains are constantly active and that baseline activity may actually reflect processes that you don’t fully understand… if so, you may be ‘subtracting the background’, which doesn’t always make sense to do
default mode network (DMN)
a network of brain regions that are active at rest
properties of default mode network
Evidence for some form in many different mammals, Associated with mind wandering in humans, May have other adaptive functions (e.g. memory consolidation
localization of function
the idea that we have specific brain regions (or networks) that are specialized for certain kinds of processes
Phrenology
A belief system that attempted to relate variation in the shape of different parts of the skull with behaviour and cognition
mass action
proposed that specific functions were in fact not localized to particular parts of the brain
equipotentiality
which assumes any chunk of cortical tissue has the potential to support any brain function
plasticity
tissue in different parts of the brain can ‘take over’ for other damaged parts and effectively relocate functions, albeit there are limitations
pioneers who used EEG
Herbert Jasper
imaging methods with high spatial resolution
fMRI, PET
imaging methods with high temporal resolution
EEG/ERP, MEG
Electroencephalogram (EEG)
provides an overall measure of electrical activity emanating from the brain on the basis of the signal that reaches electrodes placed on the scalp
human brainwaves (5) from highest frequency to lowest
gamma, beta, alpha, theta, delta
application for EEG
screening for seizure activity
Event-Related Potentials (ERPs)
using EEG to measure average characteristic changes in electrical activity associated with particular psychological events (e.g. a stimulus presentation)
Calculation of ERP requires
signal averaging to form a grand average for multiple subjects across many trials that is time-locked to a specific event
ERP naming conventions have two parts
a letter and a number
The letter(s) used in ERPs
N - negative deflection P-positive deflection
The number for ERPS
1,2…100 depending on how many milliseconds after the time-locked event (e.g. stimulus presentation) before the component typically appears
application of ERPs
The presence/absence of a particular kind of ERP in response to an event can be informative, though the timing and/or magnitude of the ERP elicited is often more informative…Smaller amplitude and/or delayed onset of an ERP could indicate diminished or impaired processing
Magnetoencephalography (MEG)
maps subtle changes in the magnetic fields around the scalp caused by fluctuations in electrical activity in the brain
Magnetoencephalography (MEG) can also measure
ERPs
MEG characteristics (positive)
More sensitive to EEG
MEG characteristics negative
expensive, requires a completely magnetically shielded room, etc
Magnetic Resonance Imaging (MRI)
uses magnetic fields and radio waves to generate anatomical images of body tissue
Functional Magnetic Resonance Imaging (fMRI)
measures changes in the BOLD signal (blood-oxygen-level-dependent signal), which is correlated with cognitive activity
Remember that the BOLD signal is
simply a correlate of neural activity, it is not a direct measurement of it!
Voxles
imaginary boundaries based on three-dimensional pixels
fMRI analyses ‘draw’
what we can think of as imaginary boundaries based on three-dimensional pixels (voxels) that are superimposed onto the brain
what does the BOLD signal tell us
provides estimates for changes in the average/overall activity within specific voxels
Positron Emission Tomography (PET)
the injection of radioactive 2-DG (structurally similar to glucose) that is rapidly taken up by active cells until gradually breaking down
How does the PET use radioactive glucose to measure brain activity
can see where the radioactive dye is being used in the brain
implications of using either high spatial or high temporal imaging (the tradeoffs)
each kind of measure their own thing…there is some overlap in the modes of measurement but for the most part there is not one specific test that captures it all
seed location
brain location associated with a specific task
Diffusion Tensor Imaging (DTI)
uses MRI technology to map out major pathways (tracts: bundles of axons) in the brain
Transcranial Magnetic Stimulation (TMS)
uses a magnetic field and an electrical current to modulate brain activity at specific sites (generally decreasing or increasing firing)
what type of imaging can create a virtual leison
TMS
Repetitive TMS (rTMS)
can produce longer lasting changes in neuronal activity, though there is still some debate about the safety and efficacy of this method
Magnetic Resonance Spectroscopy (MRS
uses an MRI machine to produce estimates related to metabolic changes in the brain
what does using Magnetic Resonance Spectroscopy (MRS) allow?
estimates related to the chemical composition in particular brain regions, and has applications for both basic research and clinically relevant purposes
major advantage to using MRS
that it can be used to produce in vivo (i.e. within a living organism) estimates related to some simple neurotransmitters (e.g. GABA and glutamate)
major disadvantage to using MRS
, it is not capable of measuring more (chemically) complex neurotransmitters that are of interest of cognitive neuroscientists (e.g. serotonin, dopamine)
optogenetics
involves genetically engineering neurons that are light-sensitive (e.g. ion channels that open when exposed to a particular wavelength)
This allows neurons to be effective controlled, or turned on/off, by exposing them to light
Functional Near-Infrared Spectroscopy (fNIRS)
relatively cheap, non-invasive method for estimating changes in neural activation
How is Functional Near-Infrared Spectroscopy (fNIRS) done
measures reflected light from hemoglobin so, Changes in the relative proportion of light that is reflected back can therefore be used to estimate changes in hemoglobin concentration (which can, in turn, be used to infer changes in neural activation)
case study advantage, disadvenatage
advantage - unique research opportunities, disadvantage. cant generalize to the general public
Lesion studies
involve training a non-human animal to perform a task, damaging a part of the brain, then observing how that damage affects the organism’s ability to perform the previously learned task
Advantage and disadvantage to lesion studies
advantage - relatively straightforward causal inferences to be made about the contribution of various brain regions
disadvantage - difficulty in generalizing observations from non-human animals to humans
