LECTURE 2- MEASURES OF THE BRAIN Flashcards
what is functional specialisation and function integration?
function specilisation= where?
functional integration=how?
how does MRI work?
strong magnetic field causes hydrogen atoms to align in the same orientation, when radio wave passes through the head, atoms emit electromagnetic energy as they relax. MRI detects emitted radiation. Different types of tissue produce different signals, the computer then reconstructs the image.
How does fMRI work?
measures dynamic physiological changes in the brain and associate them with different patterns of mental processes. It does not measure neuronal activation directly but the downstream consequence of neural activation such as increased blood flow/blood oxygen in a certain brain region. BOLD signal is measured in FMRI studies- BOLD signals indicate oxygen is consumed which indicates neural activity in that area.
- Good spatial resolution
and its safe and non-invasive - Poor temporal resolution
How do PET scans work?
a radioactive tracer is injected to the blood stream and the amount of radioactivity in each voxel of the brain is measured
explain two methods in fMRI
subtraction method (difference in activation tasks) used to show which specific area is related to which process. Conjunction method (joint activation tasks)
what is DTI?
diffusion tensor imaging=
aims at specifying fibre tracts with white matter connecting cortex/ subcortical areas. Important to investigate network architecture of the brain- so not just activated grey matter areas. Looks at the diffusion of water molecules across the brain/neural tracts.
What is an EEG?
records electrical signals generated by the brain through electrodes placed at different points on the scalp.
Used for event related potentials= presenting stimuli and measuring the brain activity.
* To gain an EEG measure you must compare the voltage between 2 or more different sites. E.g. a reference point (a common reference point is the mastoid bone)
- Poor spatial
What is a single cell recording?
- Single-cell recordings can be obtained by implanting a very small electrode either into the axon itself (intracellular recording) or outside the membrane (extracellular recording) and counting the number of times that an action potential is produced (spikes per second) in response to a given stimulus
- Experiment on animals only as it is invasive
what is multi cell recording?
- Multi cell recording- simultaneously recording from 100 neurons
What is an ERP?
An EEG in a particular stimuli or cognitive task
- EEG produces a waveform reflecting neural activity
- Good temporal resolution
- Poor spatial resolution
What are Hemodynamic methods?
PET and fMRI
* Doesn’t measure neurons directly but the changes in blood flow/ blood oxygen
* Good spatial resolution
what is the BOLD response?
- blood oxygen-level dependent. BOLD signal reduces when neurons consume energy as they convert oxyhaemoglobin to deoxyhaemoglobin
what is HRF
what are the 3 phases
hemodynamic response function- BOLD signals increase in neural activity.
* HRF has 3 phases- initial dip, overcompensation, undershoot
* Initial dip= small rise in deoxyhaemoglobin, reducing the BOLD signal
* Overcompensation= in response blood flow to the region increases- causing BOLD to increase dramatically (the component measured in fmri)
* Undershoot- blood flow and oxygen consumption dip
What is TMS and tDCS?
Transcranial Magnetic Stimulation (TMS) Non-invasive stimulation of the brain caused by a rapidly changing electrical current in a coil held over the scalp
Transcranial Direct Current Stimulation (tDCS) Non-invasive stimulation of the brain caused by passing a weak electrical current through it
Methods of MRI- voxel based Morphometry
A technique for segregating and measuring differences in white matter and gray matter concentration
