what do we measure with eeg and meg? what do we measure with eeg? xavier de tiege isabell zlobinski...
TRANSCRIPT
What do we What do we measure with measure with
EEG and MEG?EEG and MEG?What do we measure with EEG?What do we measure with EEG?
Xavier de TiegeXavier de TiegeIsabell Zlobinski Isabell Zlobinski 03/05/0603/05/06
Characteristics of the Characteristics of the EEGEEG
Localize neural electric activity using non-Localize neural electric activity using non-invasive measurementsinvasive measurements
Measures electric potential differences between Measures electric potential differences between pairs of scalp electrodespairs of scalp electrodes
Temporal precision Temporal precision
Rhythmic fluctuations in voltageRhythmic fluctuations in voltage Standard time interval: cycles per second = Standard time interval: cycles per second =
hertz (Hz)hertz (Hz) Amplitude in microvolts (Amplitude in microvolts (µV)µV)
The EEG Frequency The EEG Frequency SpectrumSpectrum
WavesWaves FrequenFrequen
cies per cies per secondsecond
AmplitudAmplitude in e in µVµV
CharacteristicsCharacteristics
Beta-Beta-waveswaves
14 - 30 5 - 50, mostly below 30
Sharp spike-waves over 35 Hz,Frontocentral, precentral & posterior Criteria of light sleep stages
Alpha-Alpha-waveswaves
8 - 13 5 - 120, mostly below 50
Posterior-dominant, awake, eyes closed, mental inactivity, physical relaxation
Theta-Theta-waveswaves
4 - 7 20 - 100 Strictly rhythmic or highly irregular Awake & drowsiness or light sleep stages
Delta-Delta-waveswaves
0,5 - 3 5 - 250 Abnormality in waking adults,Accompaniment of deep sleep
Gamma-Gamma-waveswaves
31 - 60 -10 Legality of appearance and site not well established
The EEG Frequency The EEG Frequency SpectrumSpectrum
Recording EEGRecording EEG EPSP at apical dentritic EPSP at apical dentritic
trees of pyramid cellstrees of pyramid cells Dentritic membrane Dentritic membrane
depolarizeddepolarized Potential difference Potential difference
cause a current cause a current flow flow through volume through volume conductor from the conductor from the nonexited membrane of nonexited membrane of the soma to the apical the soma to the apical dentritic treedentritic tree
Extracellular currents = Extracellular currents = secondary / volume secondary / volume currentscurrents
Recording EEGRecording EEG
The EEG machineThe EEG machine 8 – 64 identical 8 – 64 identical
channels recording channels recording simultaneously from as simultaneously from as many different pairs of many different pairs of electrodeselectrodes
Electrodes & electrode Electrodes & electrode boardboard
AmplifiersAmplifiers FiltersFilters Pen & chartdrive Pen & chartdrive
(screen)(screen)
When do we use EEG?When do we use EEG? Sleep researchSleep research Clinical diagnosis Clinical diagnosis
Epileptic patientsEpileptic patients Sleep disordersSleep disorders EncephalopathiesEncephalopathies
Biophysiologic research (e.g. evoked Biophysiologic research (e.g. evoked potentials)potentials)
Cognitive research (e.g. ERPs)Cognitive research (e.g. ERPs) ……
ArtifactsArtifacts
Physiologic artifactsPhysiologic artifacts Eye movement Eye movement Muscle activityMuscle activity ECG artifactsECG artifacts Skin artifactsSkin artifacts
Extraphysiologic Extraphysiologic artifactsartifacts
ElectrodesElectrodes Alternating current Alternating current
(60 Hz) artifact(60 Hz) artifact Movements in the Movements in the
enviromentenviroment
Event Related PotentialsEvent Related Potentials Voltage fluctuations in cortex because of cognitive Voltage fluctuations in cortex because of cognitive
procedures or stimuli responsesprocedures or stimuli responses Designed by summation & averaging of event Designed by summation & averaging of event
related EEG parts related EEG parts
Waves described after Waves described after
polarity and latency (e.g. P300), polarity and latency (e.g. P300),
method of release (mismatch negativity) method of release (mismatch negativity)
and psychophysiological correlativesand psychophysiological correlatives
ERPs – failures & limitsERPs – failures & limits
Artifacts possibleArtifacts possible Difficult to analyse high complex cognitive Difficult to analyse high complex cognitive
procedures when stimuli need more time than procedures when stimuli need more time than 100 ms 100 ms short ERP duration short ERP duration
between individuals very variablebetween individuals very variable depends on agedepends on age combined from several spacial and temporal combined from several spacial and temporal
overlapping components overlapping components low specificity low specificity
Evoked PotentialsEvoked Potentials Record of low amplitude potentials evoked by different Record of low amplitude potentials evoked by different
types of sensory stimulustypes of sensory stimulus
Voltage fluctuation is slow with a very small amplitude of Voltage fluctuation is slow with a very small amplitude of the response (about 1/100 of spontaneous EEG activity)the response (about 1/100 of spontaneous EEG activity)
high amplification is essentialhigh amplification is essential Special computer averaging technic is required Special computer averaging technic is required
clinical diagnostic, neurophysiologic & cognitive clinical diagnostic, neurophysiologic & cognitive research research
Visual evoked PotentialVisual evoked Potential Brainstem auditory evoked PotentialBrainstem auditory evoked Potential Somatosensory evoked PotentialSomatosensory evoked Potential
SourcesSources Duffy, Iyer, Surwillo (1989). Clinical Duffy, Iyer, Surwillo (1989). Clinical
Electroencephalography and Topographic Brain Electroencephalography and Topographic Brain Mapping. Springer VerlagMapping. Springer Verlag
S. Baillet, J.C. Mosher, R.M. Leahy. (2001). S. Baillet, J.C. Mosher, R.M. Leahy. (2001). Electromagnetic Brain Mapping. Electromagnetic Brain Mapping. IEEE Signal IEEE Signal Processing MagazineProcessing Magazine. P 14-30.. P 14-30.
www.dkgn.dewww.dkgn.de http://edoc.hu-berlin.de/dissertationen/eichholz-http://edoc.hu-berlin.de/dissertationen/eichholz-
stephan-2004-10-22/HTML/chapter2.htmlstephan-2004-10-22/HTML/chapter2.html http://www.emedicine.com/neuro/topic678.htmhttp://www.emedicine.com/neuro/topic678.htm