Brain Imaging Flashcards
What are electrophysiological techniques for monitoring neuronal activity based on?
Changes in membrane potential of activated neurons
How does brain scanning techniques work?
By monitoring changes in energy metabolism required by activating neurons
What require energy of their operation?
Electrochemical gradients that move charged ions in and out of neurons
What is the source of energy for electrochemical gradients that move charged ions in and out of neurons?
Oxidation of glucose
How are glucose and oxygen delivered to the brain?
Cerebral circulation
What causes a local increase in cerebral blood flow in active areas?
Neurovascular linl
What do modern neuroimaging devices measure?
Changes in local cerebral blood flow and use them as an index of neural activity
What is the first functional technique to be developed?
Positron Emission Tomography (PET)
What is the procedure of positron emission tomography (PET)?
Involve injection into human subject radioactive tracers that are attached to compounds of biological interest such as drugs that bind to neurotransmitter receptors
How does the positron emission tomography (PET) work?
Rings of detectors around the subject’s head record the timing and position of gamma particles emitted by the nuclear isotope as it traverses the brain and decays
What can PET be used to do?
It can be used to produce maps of changes in local cerebral blood flow (CBF)
What has PET measurement led to?
Localisation in the human brain of sensory, motor and cognitive brain functions
What are the disadvantages of PET?
- requires the injection of radioactive tracers thus many people like children and women of child-bearing age cannot have PET scan
- number of measures taken during scan are limited
What is different non-invasive technique?
Magnetic Resonance Imaging (MRI)
What can the MRI do?
Provide very fine-grained images of brain structure
What is the application of MRI that provides images of brian function?
Functional magnetic resonance imaging (fMRI)
What principle does fMRI rely on?
Difference in magnetic properties of oxyhemoglobin and deoxygenated haemoglobin in blood
What is the signal I’m fMRI called?
Blood-Oxygenation level-Dependent signal (BOLD)
How does fMRI work?
In increased neuronal activity leads to movement of ions that activate energy-requiring ion pumps, which leads to increase in energy metabolism and oxygen consumption. This leads to an increase in deoxygenated haemoglobin and decrease of magnetic signal. However, oxygen consumption is followed within seconds by an increase in local cerebral blood flow, the increase in cerebral blood flow exceeds the increase in oxygen consumption and therefore a relative increase in oxyhemoglobin and size of signal
How are fMRI studies usually carried out?
They involve measuring the BOLD signal while people are engaged in carefully controlled tasks, during a scan, subjects lie within the bore of a magnet and their behavioural responses to stimuli is monitored
What kinds of stimuli can be presented?
A wide range of stimuli, either visually which is presented to a screen for subject to view or in the auditory domain via headphones
How are task designed?
Two very similar tasks are designed with one done immediately after the other, first task should involve the brain process an experimenter is interested Jin whereas the other should not
How do they analyse the fMRI brain images?
The images obtained are subtracted from each other to yield a pixelated 2D image of what changes in activity are specifically associated with performing the critical brain process, the images are stacked up to yield an effective subtraction of image in 3D
What is event-related fMRI (efMRI) used for?
Measure very brief thoughts or brain events
How is statistical analysis used for efMRI?
It is used to test whether changes in signal during performance of a task are statically reliable
What is one widely-used analysis package standardised for processing of image data?
Statistical parametric mapping (SPM)
What colour is the hottest area of activity on SPM map?
Fiery yellow
What colour is the cooler areas of SPM map?
Blue or black
What is effective connectivity?
Mathematical techniques to look at how the neural activity of different brain region interacts and correlates during complex tasks
