Vorlesung: EEG: Entstehung und funktionelle Bedeutung Univ' Prof' Dr' Wolfgang Klimesch

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VorlesungEEG Entstehung und funktionelle
BedeutungUniv. Prof. Dr. Wolfgang Klimesch

• Einführungs-VO zum Modul
• EEG und Kognition

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Termine für Klausur oder mündl Prüfung 26. 1. 09
Inhalte A Entstehung des EEGs und
Dipole B1 ERPs frühe Komponenten,
Quellen-Lokalisation und kognitive
Bedeutung B2 Gedächtnisrelevante
ERP-Komponenten C1 Alpha Oszillation, kognitive
Bedeutung und physiologischer Hintergrund
C2 Theta Oszillationen, kognitive Bedeutung und
physiologischer Hintergrund D ERPs und
evozierte Oszillationen E EEG und kognitive
Leistung
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EPSP
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Input from contralateral hemisphere
Thalamocortical input

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Dipole
Dipole
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• The Nature of the EEG
• The contribution of single neuron activity to the
  EEG can be understood by examining a simplified
  cortical circuit and some basic electrical
  principles. Pyramidal neurons are the major
  projection neurons in the cortex. The apical
  dendrites of pyramidal cells, which are oriented
  perpendicular to the cell surface, receive a
  variety of synaptic inputs. Synaptic activity in
  the pyramidal cells is the principle source of
  EEG activity.
• To understand the contribution of a single neuron
  to the EEG, consider the flow of current produced
  by an excitatory synaptic potential (EPSP) on the
  apical dendrite of a cortical pyramidal neuron
  (Figure 46-2). Current flows into the dendrite at
  the site of generation of the EPSP, creating a
  current sink. It then must complete a loop by
  flowing down the dendrite and back out across the
  membrane at other sites, creating a current
  source. The size of the voltage created by the
  synaptic current is approximately predicted by
  Ohms Law (V IR where V is voltage, I is
  current, and R is resistance). Because the
  membrane resistance (Rm) is much larger than that
  of the salt solution that constitutes the
  extracellular medium (Re), the voltage recorded
  across the membrane with an intracellular
  electrode (electrode 1) is also larger than at an
  extracellular electrode positioned near the
  current sink (electrode 2).
• At the site of generation of an EPSP the
  extracellular electrode detects current flowing
  away from the electrode into the cytoplasm as a
  downward deflection. However, an extracellular
  electrode near the source has an opposite
  polarity (compare electrodes 2 and 3, Figure
  46-2). The situation is reversed if the site of
  the EPSP generation is on a proximal dendrite. In
  the cortex excitatory inputs from the
  contralateral hemisphere contact the pyramidal
  neurons primarily on distal parts of the dendrite
  in layers 2 and 3, whereas thalamocortical inputs
  terminate in layer 4. The activity measured at a
  surface EEG electrode will have opposite
  polarities for these two inputs, even though the
  basic electrical event, membrane depolarization,
  is the same. EPSPs in superficial layers and
  inhibitory postsynaptic potentials (IPSPs) in
  deeper layers appear as upward (negative)
  potentials, whereas EPSPs in deeper layers and
  IPSPs in superficial layers have downward
  (positive) potentials (Figure 46-3). Thus
  cortical synaptic events cannot be unambiguously
  determined from EEG recordings alone.
• From Westbrook, G.L.. Seizures and Epilepsy. In
  Kandel, E.R., Schwartz, J.H. Jessell, T.M.
  (Eds.) (2000). Principles of Neural Science (P.
  914-915). New York Mc-Graw-Hill

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Scalp EEG positive polarity
Scalp EEG negative polarity
EPSP
IPSP

• Note
• At a surface electrode, both positive and
  negative polarity may
• indicate depolarization (EPSPs) depending on
  the orientation of
• the dipole.
• EPSPs in superficial layers and IPSPs in deeper
  layers appear
• (at a surface electrode) as a negative
  potential.

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From Bragin et al. (1995). Gamma (40-100 Hz)
oscillation in the hippocampus of the behaving
rat. The Journal of Neuroscience, 15(1), 47-60.
CSD maps
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Figure 1. Results for V4. A, Schematic of the
multielectrode with 14 equally spaced (200m)
contacts. B, A short segment (200 ms) of LFPs. C,
PRAT-CSD displayed as a color-coded plot, which
is the second spatial derivative of
phase-realigned and averaged PRAT-LFPs (smooth
traces, blue). The y-axis is electrode contacts
from 2 to 13. The contacts used for bipolar (bip)
derivations are shown to the left (see Fig. 4 and
Results, Interaction of alpha current
generators). A single epoch ofMUAfrom three
contacts is superimposed (black). D, Laminar
distribution of the peak (10 Hz) LFP power across
all penetrations in both monkeys.E, CSDMUA
coherence spectra for the penetration shown in C.
The horizontal line corresponds to p0.01. From
Bollimunta, A. et al. (2008). Neural mechanisms
of cortical alpha oscillations in awake-behaving
macaques. The Journal of Neuroscience, 28 (40),
9976-9988.
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The P1-N1 complex
From Mangun, Hillyard Luck, 1993
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Example for a polarity reversal of the P1 and
N1 Continuous Recognition Task
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90º
Data from Clark, Fan Hillyard (1995)
0º
Horizontal Median
- 90º
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Early components of the visually evoked potential
(VEP)Data on the next pages from Di Russo et
al.(2001)
Early components are the C1 and C2 ( P1)
C1
P1 Onset latency 40 - 70 ms 65 80 ms
Peak latency 60 - 100 ms 100 130 ms
Source area 17 areas
18/19 Polarity reversal yes
no
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C1 P1 N1 for upper quadrant stimulation
lower bank of calcarine fissure
Missing P1 due to polarity overlap with C1?
Thin line Lower quadrant of left visual
field Thick line Upper quadrant of left visual
field
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EEG Experiment Checkerboard stimuli with mean
luminance isoluminant to gray background.
Exposure time 50ms randomized presentation of
four quadrants with 1400 trials/quadrant. fMRI
Experiment Same stimuli and exposure time but
blocks of 20 secs for each quadrant
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Dipole 1 C1 Dipoles 2-3 Early P1 Dipoles
4-5 N 180 Dipoles 6-7 N 155
Upper Left
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Dipole 1 C1 Dipoles 2-3 Early P1
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