L8: Neuroimaging Flashcards
What are neuroimaging techniques used for?
Able to get a well rounded idea about behaviour from the brain
Developed by Hans Berger., 1873: first EEG recordings were developmental
When do biological processes begin?
First few weeks of life (in utero)
Central NS starts developing week 16
Once the CNS begins developing environmental influences impact the baby e.g., Fetal Alcohol Syndrome
What is synaptogenesis?
For babies after birth there is rapid brain growth
Formation of synapses (inhibitory or excitatory)
Peaks between birth and 30 months old
What is synaptic pruning?
Brain eliminates extra synapses
Gogtay: Gray matter volume shows brain becomes more efficient & set in its day to day process
What is myelination?
Myelin sheath is the fatty tissue around axon - speeds up communication process
Myelination occurs rapidly in development
Usually around sensory & motor development to improve 5 senses
As we gain more speed of processing these motor movements we are able to begin developing more complex motor movement
How do neurons communicate?
Through synaptic transmission either chemically or electrically
Summary of biological development
Most rapid growth in first 30 months
Increase in gray matter volume & overproduction of synapses
Decrease in gray matter volume as adult- pruning of non-functional connections & neuron death
Our brain has plasticity which occurs over lifespan as well as synaptogenesis
Past 30 months plasticity occurs w/ much slower & with greater effort
What are electrophysiology measures?
Electroencephalogram (EEG) records electrical activity in the brain
Magnetoencephalography (MEG) imaging technique that identifies brain activity and measures small magnetic fields produced in the brain
Strengths of MEG
High temporal resolution
Is not affected by human tissue resulting in better resolution
Sensitive & Accurate
Weaknesses of MEG
Requires ppt’s to sit very still (is this ideal for infants?)
Very expensive
Limited look at deeper structures as it’s analyzing magnetic fields produced by electrical currents
Poor spatial resolution
Strengths of EEG
Good temporal resolution
Measures real time electrical activity
What waves are measured in electrophysiology techniques?
Theta: 4-7HZ
Alpha: 8-12 HZ
Beta: 13-30 HZ
Beta EEG are present when a person is alert/attentive and thinking actively
Resting EEG (Marshall et al., 2002) - The 6-9 HZ band is a useful alpha range band from the end of the 1st year of life into early childhood
What are event related potentials? (ERP)
Measure brain response that’s directly a result of cognitive, sensory or motor event
We have streams of event related potentials
Able to present stimuli to ppts & time lock them to when event occurs to create ERP’s
Written as N= negative, P = positive, number is seconds when it happens e.g., N= 100
What did Davies et al., (2004) observe from the ERP’s and blinker task?
Gave ppts blinker task
Observed process of maturation in ppts
General differences were found in the amplitude and time course of event-related potentials (ERPs) between children and adults that are consistent with their differences in reaction time
What is a optically pumped magnetometer? (OPM)
Wearable MEG
Able to test different populations
Wearable system which records neuronal activity
What are hemodynamics?
Neuroimaging technique which measures blood flow
What is an fMRI?
Functional magnetic resonance imaging
Measures small changes in blood flow that occur with brain activity
What is an fNIRS?
Functional near-infrared spectroscopy
Technique based upon changes of absorption of light emitted shined onto the skull
Strengths of fMRI?
Can evaluate brain function safely, noninvasively and effectively
Easy to use
Objective
Good spatial resolution- able to see gray & white matter
Weaknesses of fMRI?
Poor temporal resolution
Expensive
Ppt must remain still - may be difficult for younger ppts
Strengths of fNIRS?
Infants have less hair & thinner skulls which means this is a good way of measuring in infants as more light gets through to their skull
Inexpensive
Non-invasive
Less motion restriction
Can be used throughout lifetime
Weaknesses of fNIRS?
Limited to surface and frontal regions analysis
Low spatial resolution (centimeters)
Difficult to distinguish neural responses cortical areas
Weaknesses of EEG
Poor spatial resolution
Does not specify where in the brain the activity is coming from
Does not show a clear link between brain structure and function
fNIRS/fMRI Task structure
Responses are measured differently but stimuli presented is similar
Lines presented are areas of interest in an fMRI or channel of activity
Stimuli is blocked together in a way that requires cognitive activity
Repeated hemodynamic responses are induced due to cognitive activity
Congruent block: Task if easier (less blood flow activity)
Incongruent block: Task is harder causing more inhibitory flow
Take each response and avg. them for response
How did Perez- Edgar et al., 2007 use fMRI to measure face perception in adolescents?
Sample: Were behaviorally inhibited infants or not behaviorally inhibited infants
Asked q’s about faces presented e.g., “How hostile is this face?”
-Used fMRI during this
Findings:
Behaviorally inhibited infants amygdala was more active
Issues with fMRI: You can’t localize activity to specific brain areas with fMRI meaning findings ARE NOT critical
What did Hashmi et al., (2020) measure using fNRIS in infants?
Captured infant’s brain activities as they were playing games as normal
Coded children’s speech
Captured sentences related to thoughts & desires
Results:
Children were using language when the PFC & posterior superior temporal sulcus was active
Eval: fNIRS can be problematic to measure deep brain activity
BUT the fNIRS cap allows infants to move
Contrasting stimuli in neuroimaging
To gather a final neuroimaging technique result you need multiple presentations of stimuli due to lots of noise (signal to noise ratio)
Subtraction method: Stimuli - Control - Difference
Summary of L8:
Face processing = more right hemisphere
These techniques must be fit for the right developmental populations
Neuroimaging techniques are rich data sets
EEG/MEG: Measure fast electrical neural activity - measures WHEN
MRI/fNIRS: measure slow neural activity - measures WHERE
