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The History of the EEG

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The History of the EEG Powered By Docstoc
					The ElectroEncephaloGramm


Cognitive Neuropsychology
January 16th, 2001
                  Outline


1.   History of the EEG
2.   Biological Foundations of the EEG
3.   Measuring the EEG
4.   Analyzing the EEG
5.   Applications of the EEG
      The History of the EEG


1875 Caton records brain potentials from cortex
1883 Marxow discovers evoked potentials
1929 Berger records electrical activity from the
     skull
1936 Gray Walter finds abnormal activity with
     tumors
1957 The toposcope (imaging of electrical
     brain activity)
1980 Color brain mapping (quantitative EEG)
     Hans Berger – EEG Pioneer


In 1929, Hans Berger
• Recorded brain activity from the closed
   skull
• Reportet brain activity changes
   according to the functional state of the
   brain
     – Sleep
     – Hypnothesis
     – Pathological states (epilepsy)

First EEG recorded by Berger
      Gray Walter – Brain Imaging


                               In 1957, Gray Walter
                               • Makes recordings with
                                  large numbers of
                                  electrodes
                               • Visualizes brain activity
                                  with the toposcope
                               • Shows that brain
                                  rhythms change
                                  according to the mental
The toposcope by Gray Walter
                                  task demanded
                  Outline


1. History of the EEG
2. Biological Foundations of the EEG
  1. Brain Rhythms
  2. Information Processing in the Neocortex
  3. Summation Potentials
3. Measuring the EEG
4. Analyzing the EEG
5. Applications of the EEG
  EEG in the States of Vigilance

Frequency Ranges

Beta:    14 – 30 Hz
Alpha:   8 – 13 Hz
Theta:   5 – 7 Hz
Delta:   1 – 4 Hz
              Alpha Rhythm
Frequency:        8 – 13 Hz
Amplitude:        5 – 100 microVolt
Location:         Occipital, Parietal
State of Mind:    Alert Restfulness
Alpha blockade occurs when new stimulus is processed
Source: oscillating thalamic pacemaker neurons
               Beta Rhythm
Frequency:          14 – 30 Hz
Amplitude:          2 – 20 microVolt
Location:           Frontal
State of Mind:      Mental Activity
Reflects specific information processing between cortex
  and thalamus
               Theta Rhythm
Frequency:          5 – 7 Hz
Amplitude:          5 – 100 microVolt
Location:           Frontal, Temporal
State of Mind:      Sleepiness
Nucleus reticularis slows oscillating thalamic neurons
Therefore diminished sensory throughput to cortex
               Delta Rhythm
Frequency:          1 – 4 Hz
Amplitude:          20 – 200 microVolt
Location:           Variable
State of Mind:      Deep sleep
Oscillations in Thalamus and deep cortical layers
Usually inibited by ARAS (Ascending Reticular
  Activation System)
                  Outline


1. History of the EEG
2. Biological Foundations of the EEG
  1. Brain Rhythms
  2. Information Processing in the Neocortex
  3. Summation Potentials
3. Measuring the EEG
4. Analyzing the EEG
5. Applications of the EEG
               Cortex Structure
The neocortex consists of six
    distinct layers
I Molecular layer
II External granular layer
III External pyramidal layer
IV Internal granular layer
V Internal pyramidal layer
VI Polymorphic or
    multiform layer
        Cortex Structure Layer I
I Molecular layer
  Molekularschicht

• Apical dendrites of
  pyramidal cells
• Axons of stellate cells
  (parallel to cortex surface)
• Few cell bodies
• Local (intracortical)
  information exchange
     Cortex Structure Layer II/ III
II External granular layer
    Äußere Körnerschicht
III External pyramidal layer
    Äußere Pyramidenschicht

• Stellate & Small Pyramidal
  Cells
• Intercortical Information
  Exchange
   – Afferent fibers from other
     cortical areals enter the layers
   – Association (to the same
     hemisphere) and commisural
     (to the other hemisphere) fibers
     leave cortex (reentry at
     destination)
       Cortex Structure Layer IV
IV Internal granular layer
   Innere Körnerschicht

• Stellate cells
• Afferents from Thalamus
• Numerous and complex
  synaptic connections
• Relay of thalamic
  information to other
  cortical layers
• Information input layer
  (well developed in sensory
  cortex)
       Cortex Structure Layer V
V Internal pyramidal layer
  Innere Pyramidenschicht

• Large pyramidal cells
• Projection fibers to
  subthalamic brain areas
   – Basal ganglia
   – Brain stem
   – Spinal chord
• Information output layer
  (well developed in motor
  cortex)
       Cortex Structure Layer VI
VI Multiform layer
   Spindelzellschicht

• Neurons of various shapes
  (mainly fusiform)
• Adjacent to white matter
• Corticothalamical
  information exchang
  Cytoarchitecture Neocortex

Input layers:   II/IV (granular)
Output layers: III/V (pyramidal)
1: heterotypical agranular
   cortex
    – Mainly pyramidal layers
      (output)
    – Primary motor cortex
5: heterotypical granular
   cortex
    – Mainly granular layers
      (input)
    – Primary sensory cortex
2-4: homotypical cortex
    – Association areas
    – All layers developed
                  Outline


1. History of the EEG
2. Biological Foundations of the EEG
  1. Brain Rhythms
  2. Information Processing in the Neocortex
  3. Summation Potentials
3. Measuring the EEG
4. Analyzing the EEG
5. Applications of the EEG
      Summation Potentials
The EEG measures
• not action potentials
• not summation of
  action potentials
• but summation of
  graded Post
  Synaptic Potentials
  (PSPs)

  (only pyramidal cells:
  dipoles between
  soma and apical
  dendrites)
                Outline


1. History of the EEG
2. Biological Foundations of the EEG
3. Measuring the EEG –
   The international 10/20 system
4. Analyzing the EEG
5. Applications of the EEG
The International 10/20
        System
     Terminology: 10/20 System




Nasion:     point between the forehead and the skull
Inion:      bump at the back of the skull
Location:   Frontal, Temporal, Parietal, Occipital, Central
            z for the central line
Numbers:    Even numbers (2,4,6) right hemisphere, odd (1,3,5) left
                EEG channels




Channel: Recording from a pair of electrodes (here with a
  common reference: A1 – left ear)
Multichannel EEG recording: up to 40 channels recorded in
  parallel
   Participants with Electrodes




EEG in clinical diagnostics   EEG in scientific research
                     Outline


1.   History of the EEG
2.   Biological Foundations of the EEG
3.   Measuring the EEG
4.   Analyzing the EEG
     1. Event Related Potentials
     2. Spectral Analysis
     3. Topographical Mapping
5. Applications of the EEG
       Event Related Potentials
• Averaging of trials
  following a stimulus
• Noise reduction: The
  noise decreases by the
  squareroot of the number
  of trials
• Far field potentials require
  up to 1000 measurements

• Assumption: no
  habituation occurs
  (participants don‘t get
  used to stimulation)
           Language specific ERP
               Components
• N400: Semantic mismatch
  marker
• P600: Syntactic mismatch
  marker

Example Sentences:
Correct (Baseline): The cats won't eat
   the food Mary gives them.
Semantic mismatch: The cats won't
   bake the food Mary gives them.
Syntactic mismatch: The cats won't
   eating the food Mary gives them.
Semantic and syntactic mismatch: The
   cats won't baking the food Mary gives
   them.
       EEG Spectral Analysis
• Fast Fourier Transform seperates spontaneous EEG
  signal to component frequencies and amplitudes
• Restriction: high frequency resolution demands long
  (in the range of seconds) analysis windows
          Topographical Maps

Topographical maps plot EEG data on a map of the
  brain.
Data is interpolated between electrodes.
Usual data plotted:
• ERP maps
  – potential changes
• Spectral maps
  – frequency changes
• Statistical maps
  – comparison of
     measurements
                   Outline


1.   History of the EEG
2.   Biological Foundations of the EEG
3.   Measuring the EEG
4.   Analyzing the EEG
5.   Applications of the EEG
     Weiss, Rappelsberger (2000)
     Long-range EEG synchronization during word
     encoding correlates with successful memory
     performance
                  Methods Section 1
A set of 19 gold-cup electrodes was        After recording, the EEG data were
glued to the scalp according to the        screened for artefacts (eye blinks,
international           10/20-placement    horizontal and vertical eye movements,
system. Data were recorded against         muscle activities) by visual inspection
the average signals of both earlobes       on a monitor and on paper. These two
((A1 + A2) /2) which turned out to be      methods allowed a very reliable
the most suitable reference for            exclusion of the artefacts. Impedance
coherence            analysis.       The   did not exceed 8 kΩ and signal
electrooculogram          (EOG)      was   bandpass was 0.3 –35 Hz. Data were
recorded from two electrodes located       simultaneously monitored by an ink-
at the left later outer cantus and above   writer system and digitally sampled at
the right eye. Electrode impedance did     256 Hz to be stored on hard disk. After
not exceed 8 kΩ and signal bandpass        recording, the EEG data were
was 0.3 –35 Hz. Data were                  screened for artefacts (eye blinks,
simultaneously monitored by an ink-        horizontal and vertical eye movements,
writer system and digitally sampled at     muscle activities) by visual inspection
256 Hz to be stored on hard disk.          on a monitor and on paper. These two
                                           methods allowed a very reliable
                                           exclusion of the artefacts.
                Methods Section 2
EEG      was     recorded     during   nouns auditorily presented, 7  2
memorization of the different lists    for    recalled    nuons    visually
of nouns and during four               presented, 14  4 for not recalled
interspersed resting periods with      nouns visually presented and 198
eyes open lasting one minute            45 for the resting EEG. Then
each. According to the behavioral      averaged power spectra and
results epochs of recalled and of      cross-power        spectra     were
not recalled ones were selected for    computed for each subject.
further analysis. The beginning of     According to the 19 elctrode
each noun was marked by a trigger      positions, 19 averaged power
and the following 1 s EEG epoch        spectra were computed. Cross
was Fourier-transformed. All 1-s       power spectra were computed.
artefact-free epochs of the resting    Cross     power     spectra    were
EEG        were    also     Fourier-   computed between all possible
transformed. On the average, per       pairs, which yielded 171 values per
subject, 16  4 epochs for recalled    frequency.
nouns auditorily presented were
analysed, 28  5 for not recalled
                Methods Section 3
To reduce the large data set the        Since it has been demonstrated
adjacent spectral values vere           that, especially, lower          EEG
averaged to obtain broadband            frequencies were correlated with
parameters for the following            memory           processes,        we
frequency bands: delta-1 (1 – 2         predominantely investigated lower
Hz), delta-2 (3 – 4 Hz), theta (5 – 7   frequency bands in the present
Hz), alpha-1 (8 – 10 Hz), alpha-2       study. The division into distinct,
(11 – 12 Hz), and beta-1 (13 – 18       well-selected frequency bands was
Hz). Finally, 19 mean amplitudes        made since several studies point at
(square root of power) per              their different functional role during
frequency band were computed            cognitive processing.
and the normalization of the 171
cross-power spectra yielded 171
coherence values per frequency
band. Grand mean values were
obtained by averaging amplitude
and coherence values across
subjects.
         Coherence Map




A coherence map plots differences in
coherence between recalled and not recalled
nouns.
                  Results


• Overall increase of coherence for recalled vs.
  not recalled nouns
• Long range synchronization of frontal and
  temporal/parietal neuronal assemblies
  increases for recalled nouns.
                  Outline


1.   History of the EEG
2.   Biological Foundations of the EEG
3.   Measuring the EEG
4.   Analyzing the EEG
5.   Applications of the EEG

         Thank you for your attention!