Evoked Potentials and Neuroimaging Flashcards
What are the 2 broad classes for studying the nervous system?
1.) Electrical potentials
2.) Imaging
What is spatial resolution?
How small of a unique location in the brain you can identify
What is temporal resolution
How small of a unique unit of time you can identify
What are the 2 ways to record electrical activity?
1.) Near field
2.) Far field
What is near field?
Inserting recording electrode into the region of the brain under study
What is far field?
Placing electrodes on or under the skin
What is volume conduction?
Electrical response must be conducted from the neurons to the electrodes through fluids, brain tissues, bone, skin, etc
What are the 2 variables we can control with volume conduction?
1.) Impedance of the electrode to the skin
2.) Generate as big of a response as possible
What is Electroencephalogram (EEG)?
Measurement of synaptic and action potentials in the cortex (proximal to the skull surface)
What is a seizure?
A sudden increase in electrical activity in a discrete region of the cortex
What is Magnetoencephalography (MEG)?
A device that detects the tiny magnetic fields created by electrical currents in the brain
What is a disadvantage of EEG?
It does not allow localization of deep brain structures
What is an advantage of MEG?
It improves on spatial resolution compared to an EEG and ABR
What are evoked potentials?
Measurements of synchronous nervous system electrical activity
How to evoked potentials work?
When neurons undergo excitation, they produce small electrical activities. When a group of neurons located together all fire at the same time, the electrical activity is large enough to be measured
How do you evoke a stimulus in the sensory system?
By using the appropriate sensory stimulus
How do you evoke a stimulus in the motor system?
Typically by using an electrical stimulus
What is the problem with ABR?
The recording electrode is on the surface of the skull and you are recording from the brainstem; volume conduction is crucial
Why is ABR good for the auditory nervous system?
Auditory neurons are very good at phase-locking to a stimulus. It creates synchronized firing and increases the amplitude of the response you are recording
What are 3 advantages of EVPs?
1.) Tells you if tissue is working/sensitive to invisible lesions
2.) Typically non-invasive
3.) Portable
What is a disadvantage to EVPs?
Poor spatial resolution for deep brain structures
What does a CT scan do?
Provides static detailed images of hard bone structures along with images of soft tissue and blood vessels
What does a PET scan do?
It gives a dynamic view of the brain over time and can provide insights into areas of activation or damage that may not be visible in static CT or MRI images
What are 2 advantages of using an MRI?
1.) Better spatial resolution than a PET scan
2.) Can distinguish between different types of body tissue
How is an fMRI similar to a PET scan?
It takes a dynamic picture over time
How does an fMRI work?
1.) Hemoglobin in red blood cells change response to the MRI magnet when oxygenated or de-oxygenated
2.) Initial burst of brain activity induces de-oxygenation
3.) Blood flow is quickly increased to supply more oxygen
4.) This increase in oxygen is demonstrated on the fMRI
What do blue zones show on an fMRI?
De-oxygenation relative to baseline
What do red/yellow zones show on an fMRI?
Heavy oxygenation
What are 3 disadvantages of fMRI and PET?
1.) Changes lag behind neuron activity
2.) Use blood flow or metabolic activity to detect neural activation
3.) EEG and MEG directly test neuronal electrical activity
