electroencephalography Flashcards
MEG
doesnt touch head
EEG
on scalp
ECoG
above/below dura mater
MEA
pia mater
- To find the origin of epilepsy so the tissue can be removed
- Very invasive
- High spatial and temporal resolution (low noise)
* Unfiltered by skull and scalp
- Allow measurement of high gamma activity >70Hz
SEEG
cortex
- Needles (about 10) into brain
- Less invasive than ECoG due to soft electrodes that push brain tissue to the side
- Can be used to do task to record high quality brain activity
what does EEG measure and which technique measures something else
EEG does not measure action potentials only MEA does
- The rest measure local field potentials accumulation of many individual action potentials
* IPSP
* EPSP
fMRI
- fMRI measure changes in blood flow in brain areas due to neuro-activity (NVU - neurovascular coupling)
frequency domains
- Spectral power decreases with increasing frequency
- 1Hz –> strong frontal activity (eye movement)
- 10Hz –> occipital alpha activity
- 60Hz –> power line noise (USA)
EEG-rhythms
- Neuronal oscillations = rhythmic or repetitive neuronal activity
- Synchronization of larger cortical areas lead to oscillatory activity
- Examples:
- Alpha rhythm: occurs in absence of sensory stimuli
o Occipital regions 8/13Hz - Mu rhythm: suppressed during motor and imagination activity
o Sensorimotor regions 8/13Hz - Gamma rhythm: cognitive activity
o Various regions >60Hz - Theta rhythm: hippocampal activity during memory formation
- These frequency bands are strongly person and author dependent
EEG topography
- Bad spatial resolution
- Still helpful to find out spatial patterns
event-related potentials
- An Event-Related Potential (ERP) is the brain’s electrical response shortly after an event
- Mostly measured by EEG and MEG
- Typically triggered by an external sensory stimulus
- Can be internal stimulus (e.g. associated with the execution of a motor, cognitive, or psychophysiological task)
- ERPs can provide information about brain function (clinical use)
ERP complex
- ERPs are composed of several ERP components
- Parts of the waveform called positive (P) or negative (N) according to their polarity
o Warning: Sometimes negative is upwards!! - Followed by a number indicating
o Component’s ordinal position in the waveform (e.g., P1, N1, P2, N2, P3)
o Latency in milliseconds (e.g., N100, N170, P300)
parameters ERP
- Important parameters of ERP components
- Peak amplitude in μV (often normalized to 200ms pre-stimulus interval)
- Peak latency in ms
- Mean amplitude of an ERP component (intervals more robust than peak)
- Electrode location (spatial focus)
clinical use EEG
epilepsy diagnosis (spatial)
sleep disorders –> sleep staging
brain tumours
brain damage
stroke