Exam 3 Imaging EEG Other Flashcards
EEG
Electroencephalography
What is an EEG?
- •Recorded summed electrical activity from the brain
- •Reflects neuronal electrical activity in different brain regions
- •Recorded from the scalp from 21-75 electrodes
Electroencephalograms (EEGs) are Recorded from the scalp from 21-75 electrodes and Record the summed electrical activity from the brain. EEGs Reflects neuronal electrical activity in different brain regions
what does EEG reflect?
•Reflects neuronal electrical activity in different brain regions
how many electrodes does an EEG typically record from?
•Recorded from the scalp from 21-75 electrodes
what are some common diagnostic uses? (7)
- –Distinguish epileptic seizures from non-epileptic seizures, syncope & sub-cortical movement disorders
- –Characterize seizures & determine whether to wean anti-epileptic medications
- –Differentiate “organic” encephalopathy from psychiatric syndromes
- –In ICU to monitor brain function, blood flow & monitor therapeutically induced comas
- –Prognosis in some patients with coma
- –Determine where in sleep cycle during sleep studies
- –Serve as an adjunct test of brain death
what are some advantages for clinical and research uses of EEGs? (9)
•Advantages for clinical & research uses include:
- –Inexpensive equipment & analysis
- –Less sensitive to subject movement
- –Used in long term studies to follow development
- –Very high temporal resolution
- –Assess overall brain state
- –No exposure to large magnetic fields or ionizing radiation
- –Does not require motor responses
- –Useful in biofeedback studies
- –Easily combined with other techniques
What is an event related potential?
A form of EEG that has a number of issues:
- –Low spatial resolution so cannot identify specific brain locations
- –Setup time consuming and cumbersome
- –Interpretation of results can be complex
- –Lot of artifacts with low signal to noise ratio
What are some issues with Event Related Potentials? (4)
- –Low spatial resolution so cannot identify specific brain locations
- –Setup time consuming and cumbersome
- –Interpretation of results can be complex
- –Lot of artifacts with low signal to noise ratio
What are Evoked Potientials?
Evoked EEG Potentials are Electrical activity following presentation of a stimulus, as distinct from spontaneous potentials
- Evoked EEG Potentials have become Widespread in clinical use including:
- Auditory evoked potentials
- Visual evoked potentials
- Somatosensory evoked potentials
how often are evoked potentials used in the clinic?
widespread
what are three evoked potentials that enjoy widespread clinical use?
- Auditory evoked potentials
- Visual evoked potentials
- Somatosensory evoked potentials
describe auditory evoked potentials
–Auditory evoked potentials
- EEG Responses to tone or click
- Analysis: trace the signal generated by a sound through the ascending auditory pathway
Auditory evoked potentials are EEG Responses to tones or clicks. Analysis involves Tracing the signal generated by a sound through the ascending auditory pathway
describe visual evoked potentials
–Visual evoked potentials
- •Stimulus - checkerboard and grating patterns use light and dark squares and stripes
- •Electrodes over occipital area & Z line proximally
- •Potentials named for direction & magnitude
Visual evoked potentials are EEG activity stimulated by strong visual stimuli such as a checkerboard and grating patterns use light and dark squares and stripes
Electrodes over occipital area & Z line proximally
Potentials named for their direction & magnitude
SSEP
–Somatosensory evoked potentials (SSEPs)
describe Somatosensory evoked potentials (SSEPs)
–Somatosensory evoked potentials (SSEPs)
- •Electrical stimulation of tibial nerve, median nerve or ulnar nerve
- •The response is then recorded from the patient’s scalp
- •Used to assess spinal cord & brainstem function during surgery
- •Amplitude and latency of the recorded peaks from occipital cortex key to assessing damage
- •Dramatic increases in latency or decreases in amplitude are indicators of neurological dysfunction
Somatosensory evoked potentials (SSEPs) are the result of Electrical stimulation of tibial nerve, median nerve or ulnar nerve. The response is then recorded from the patient’s scalp and is used to assess spinal cord & brainstem function during surgery
Amplitude and latency of the Somatosensory evoked potentials (SSEPs) recorded peaks from occipital cortex are key to assessing damage. Dramatic increases in latency or decreases in amplitude are indicators of neurological dysfunction
Somatosensory evoked potentials: what are key to assesing damage?
what indicates neurological dysfunction?
- •Amplitude and latency of the recorded peaks from occipital cortex key to assessing damage
- •Dramatic increases in latency or decreases in amplitude are indicators of neurological dysfunction
Amplitude and latency of the Somatosensory evoked potentials (SSEPs) recorded peaks from occipital cortex are key to assessing damage. Dramatic increases in latency or decreases in amplitude are indicators of neurological dysfunction
what is another test that is being combined with EEG?
why would this be done and what kind of equipment is needed?
•Combining fMRIs with EEG recordings
- –Specially designed equipment to perform both simultaneously
- –Take advantage of the temporal accuracy of EEG and the spatial accuracy of fMRI
- –Potentially very powerful technique
As mentioned previously, Combining fMRIs with EEG recordings with Specially designed equipment to perform both simultaneously can Take advantage of the temporal accuracy of EEG and the spatial accuracy of fMRI and is a Potentially very powerful technique for both clinical and research localization o function
what is magnetoencephalography?
- a relatively new approach
- •Mapping brain activity by recording magnetic fields produced by electrical currents occurring naturally in the brain
- •Done using very sensitive magnetometers
- •About 50,000 active neurons are needed to generate a signal that is detectable
- •Very weak and must be recorded in magnetically shielded room
- •Algorithms used to determine structure
- Clinically used to localize certain seizure foci
- Experimentally used to study cognitive processes in fetuses and newborns
A relatively new approach is Magnetoencephalography which is the Mapping of brain activity by recording magnetic fields produced by electrical currents occurring naturally in the brain. This is done using very sensitive magnetometers
About 50,000 active neurons are needed to generate a signal that is detectable but these are Very weak signals and must be recorded in magnetically shielded room
Algorithms used to determine which brain structures are involved . Presently this non-invasive technique is Clinically used to localize certain seizure foci. Experimentally used to study cognitive processes in fetuses and newborns
NIRS
Near-Infrared spectroscopy
Near-Infrared Spectroscopy (6)
- •Near-infrared spectroscopy (NIRS) uses silicon-based charge-coupled devices (CCDs) to convert the IR part of the spectrum into electrical signals
- •Detects changes in hemoglobin concentrations in active neural tissues
- •Algorithms used to determine structure
- •Can only detect changes in cortex
- •Combined with MRI to elucidate structure in relationship to other structures
- •Research in this area is just developing – particularly in its application to diagnosis of magnitude of head injury
Another recently developed tehnique is Near-infrared spectroscopy (NIRS). It uses silicon-based charge-coupled devices (CCDs) to convert the IR part of the spectrum into electrical signals. It Detects changes in hemoglobin concentrations in active neural tissues and again uses complex Algorithms used to determine structure
Magnetoencephalography: how many active neurons are needed to generate a signal that is detectable?
about 50,000 active neurons
Magnetoencephalography: does it produce a weak or strong signal?
•Very weak and must be recorded in magnetically shielded room
Magnetoencephalography: what is a clinical use?
•Clinically used to localize certain seizure foci
Magnetoencephalography: what is an experimental use?
•Experimentally used to study cognitive processes in fetuses and newborns
Near-infrared spectroscopy: what does it detect changes in?
•Detects changes in hemoglobin concentrations in active neural tissues
Near-infrared spectroscopy: where can it detect changes?
•Can only detect changes in cortex
Near-infrared spectroscopy: what other test can it becombined with to elucidate structure in relationship to other structures?
•Combined with MRI to elucidate structure in relationship to other structures
Near-infrared spectroscopy: how well is it’s use developed?
•Research in this area is just developing – particularly in its application to diagnosis of magnitude of head injury
