Basics of Neuronal Activity and EEG Measurements

Jan Heysel

15 June 2015

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Motivation: How can we see this flower?

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The Protagonists: Neurons

1011 neurons in brain

106 km of ’wires’ (≈ 2.5 · dEarth−Moon)

103 − 104 synapses per neuron

102 − 103 ion channels per neuron

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Neurons: Electricity

in cell:K+, negative molecules, total: -

outside cell:Na+, Cl−, total: +

voltage between in and out:’membrane potential’ Um

in rest state:Um = Urest ≈ −80mV

kept by:

membrane withion pumps (active)ion channels(voltage or chemically gated)

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Signal Generation and Transmission: Action Potential

voltage on input(s) overthresholdNa+ ion channels openNa+ ions flow inUm increases furthermore channels open ...all channels are openUm = 0K+ channel openK+ ions flow outUm decreasesend: Um < Urest

pumps recreate initial state

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Action Potential Hops along an Axon

generating action potential: 200ms → too slow

in real: transmission faster: < 7ms

energy saving

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Junktions between Neurons: Synapses

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Biological Neuronal Networks: Signal Processing (Idea)

each neuron couples to manyother neurons→ neuronal network

excite or inhibit next neuron

information: sequence of actionpotentials (?)

idea: logical circuit

Example: Stone in front of me, if:

eye 1: signal

hand : signal

nose : no signal

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How are Brains Wired?

We found:

neurons are the protagonists for biological signal transmission andprocessing

transmission: action potentials in axons

processing: neuronal network

How does such a network look like? To investigate this (try):

Do: measure (and plot) electricity in the headGreek: graphy electro en kephalikos

→ Electroencephalography (EEG)

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EEG - Principle:

measure voltage between (headclose to) brain and reference(e.g. ear)

plot voltage versus time

Figure: first EEG (1924): H. Berger, Uber das Elektrenkephalogramm desMenschen, Archives fur Psychiatrie. 1929; 87:527-70.

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What Does EEG Measure?

action potentials:change charge distribution inhead

measure potential differences

each electrode:’macroscopic output’(superposition) of actionpotentials of 108 neurons

consider each neuron as dipole:superposition of E-fields is notlinear!

resistance of skull, skin, ...

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What Does EEG Measure?

EEG:

Differences in electricpotentials on variouspositions on the head.These arise from a hugenumber of action potentialsin a complex neural network(brain).

Heuristic:

We do not know exactly,what EEG measures,but it is still very useful.

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EEG Recording, Epileptic Seizure

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EEG: Applications

levels of consciousness

epilepsy

sleep (disorders)

...

make appropriate choise of

number of electrodes

position of electrodes

example: 10-20 system

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EEG - Problem/Summary:

microscopic, assume:network of neuronseach neuron transmitts/processesvoltage signals (action potentials)

macroscopic, measure:

EEG - effective voltage signalin/around head

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Literature, Image SourcesBooks:

Carl Schoonover, Portraits of the Mind, Abrams Books, New York, 2010

R. Phillips et al., Physical Biology of the cell, 2nd edition, Garland Science, London NewYork, 2013

R. Cooper et al., Elektroenzephalographie - Technik und Methoden, 3.Auflage, Gustav Fischer Verlag, Stuttgart

NewYork, 1984Image Sources:-slide-

2 , Eye: http://images.wisegeek.com/anatomy-of-the-human-eye.jpg, 10.6.15

2 , Head: http://thumbs.dreamstime.com/z/human-brain-simple-head-silhouette-19224141.jpg, 10.6.15

2 , Flower: http://cliparts.co/cliparts/kc8/ok9/kc8ok9LEi.png, 10.6.15

3 , schematic: [Phillips]

3 , photo of neuron: Thomas Deerinck and Mark Ellisman, 2009, originally from [Schoonover], found on:http://www.newscientist.com/gallery/scenes-of-thought-the-brain-in-pictures/4, 11.6.15

5 , action potential: http://www.dummies.com/how-to/content/understanding-the-transmission-of-nerve-impulses.html,11.6.15

7 , synapse: http://www.sinpos.com/wp-content/uploads/2012/04/synapse.jpg, 11.6.15

8 , real neurons: http://www.alanturing.net/turing archive/graphics/realneurons.gif, 11.6.15

10 , time series: http://en.wikipedia.org/wiki/Electroencephalography#/media/File:1st-eeg.png, 11.6.15

13 , EEG recording: http://en.wikipedia.org/wiki/Electroencephalography, 12.6.15

14 , Cap: http://www.ternimed.de/WebRoot/Store2/Shops/62826360/4DE0/7D0E/09EC/0DBB/1F14/C0A8/2936/3EC3/Links-web.jpg, 14.6.15

14 , 10-20 system: https://en.wikipedia.org/wiki/10-20 system %28EEG%29, 14.6.15

11 , potential: K. Lehnertz, Electroencephalography - An Introduction, lecture at the University of Bonn, Summer Term2014

10 , setup: [Lehnertz], see above.

15 : All pictures cited before.

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Thank you for your attention.

Questions?

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