Magnetic resonance imaging (MRI)
uses magnetic fields and radio waves to generate anatomical images of body tissue
functional magnetic resonance imaging (fMRI)
MRI application that measures changes in the BOLD (blood oxygen level dependent) signal, which is correlated with cognitive activity.
as neurons become more active they require/use oxygen, which changes magnetic properties of the surrounding blood.
fMRI analyses draw what we can think of as imaginary boundaries based on three dimensional pixels (Voxels) that are superimposed onto the brain
BOLD Signal
Blood oxygen level dependent signal.
changes measured by fMRI.
does not tell us anything about the activity of individual neurons, but rather estimate changes in the average activity within specific voxels
Para hippocampal place area (PPA)
in the temporo-occipital cortex.
responds specifically to places (ex. indoor/ outdoor scenes)
damage to this area can disrupt the ability to perceive scenes
extrastriate body area (EBA)
in the occipital lobe.\
responds specifically to pictures/ parts of bodies
Transcranial magnetic stimulation (TMS)
uses a magnetic field and an electrical current to modulate brain activity at specific sites. can create virtual lesion
virtual lesion
a temporary and reversible disruption of normal brain activity in a specific cortical area, induced by TMS
Repetitive TMS (rTMS)
can produce longer lasting changes in neuronal activity , though there is still debate about safety and efficacy
distributed representation
many complex behaviours involve coordinated activity across different parts of the brain
semantic memories
refer to factual information (ex. knowing what the capital of Alberta is)
episodic memories
refer to complex memories for events in a persons life (ex. remembering what you did on the weekend)
multidimensional in nature
distributed representation compatibility with localization of function
these two things may appear to be contradictory but are actually complimentary.
fMRI data demonstrates both localization of function and distributed representation:
-specific areas of the brain are responsible for perception of specific stimuli
-max. activity occurs in separate areas of cortex
- however, data also indicates widespread activity that stretched across cortex for the processing of various stimuli
high spatial resolution vs high temporal resolution
as a generalization, we can contrast imaging methods that have high spatial resolution with those that have high temporal resolution.
-High Spatial (low temporal): fMRI, PET
-High temporal (low spatial): EEG, MEG
Both approaches can be important for more fully understanding cognitive and neurological phenomena
Position Emission Tomography (PET)
early functional brain imaging method. involved the injection of radioactive 2-DG (structurally similar to glucose) that is rapidly taken up by active cells until gradually breaking down. This allows a map to be produced showing where the radioactive dye goes, which correlates with neural activity.
it is a high spatial resolution imaging technique
Electroencephalogram (EEG)
a high temporal resolution imaging technique.
provides an overall measure of electrical activity emanating from the brain on the basis of the signal that reaches electrodes placed on the scalp.
this electrical activity fluctuates between different characteristic frequencies , which are associated with particular states of consciousness
event related potentials (ERPS)
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 2 parts:
1. the letter : N (for negative deflection, i.e., decrease in voltage) or P (for positive deflection, i.e., increase in voltage)
2. the number: depending on how many milliseconds after the time locked event (e.g. stimulus presentation) before the component typically appears
go/ no go task
press space bar every time number appears on screen, except you need to withhold response for one specific number (e.g., 7).
Participants are periodically interrupted and asked to report on mental state (either on task or mind wandering)
amplitude of p1 reduced when participants report mind wandering , relative to when they report being on task.
this suggests attentional mechanisms affect early stages of sensory processing
4 principles of neural networks
- complex structural pathways called networks form the brains info highway
- within these structural pathways are functional pathways that serve different functions
- these networks operate dynamically , mirroring the dynamic nature of cognition
- there is a resting state of brain activity , so parts of the brain are active all the time, even where there is no (/limited) cognitive activity
structural connectivity
relates to physical connections . various methods of measurement . including DTI/ TWI
functional connectivity
can be inferred based on the extent to which activity in multiple areas is correlated.
resting state functional connectivity
a specified procedure for determining whether two areas are functionally connected
diffusion tensor imaging (DTI)
uses MRI technology to map out major pathways in the brain.
aka track weighted imaging (TWI)
useful for understanding how differences in structural connectivity between different regions in the brain are related to different factors.
produce maps called connectomes
assessing functional connectivity
- Use task related fMRI to determine brain location associated with a specific task (these data are referred to as seed location)
- measure the resting state fMRI at the seed location
- measure the resting state fMRI at another location (referred to as the test location)
- calculate the correlation between the seed and test location responses to assess the degree of functional connectivity
