Electrophysiology in vivo
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Transcript of Electrophysiology in vivo
Claus Mathiesen
Department of Neuroscience and Pharmacology
Aim: Teach you the basics of in vivo electrophysiology
!Claus Mathiesen, M.Sc. Ph.D.
Electrophysiology (Ephys) A key feature when studying neuro-vascular and
metabolic coupling
Claus Mathiesen October 2012
Outline of my talk
Core of electrophysiology !EEG !Field potentials !Contributions from different cell types !Spike (action potential) activity !Pro and Cons with types of ephys recording
Department of Neuroscience and Pharmacology
Claus Mathiesen October 2012
The core of Ephys
Ephys signal is measured in voltage (V), current (I), and resistance (R) or conductance (G=1/R) !These variables are related according to Ohm’s law:
V = I ◦ R or I = V ◦ G !Ephys signal has different frequencies !Frequency is measured as oscillation per second (Hz) !Each type of neuronal activity is located within areas in the frequency band running from 0 to 5000 Hz
Department of Neuroscience and Pharmacology Dias 3
Claus Mathiesen October 2012
The generator of the Ephys signal
Department of Neuroscience and Pharmacology (Dias 4)
Neurons are like a battery
Negative inside (-60 to -70 mV)
Generate action potentials via
voltage-gated ion-channels
Some have pacemaker activity
Claus Mathiesen October 2012
Excitatory-PostSynaptic-Potential (EPSP)
Presynaptic release of transmitter Transmitter-gated ion-channels Ion-flux Potential changes
Department of Neuroscience and Pharmacology (Dias 5)
EPSP
fEPSP
EPSP
fEPSP
Claus Mathiesen October 2012
EPSP
fEPSP
Intracellular potential changes as Synaptic events Spike activity Graded potentials
Extracellular potential changes as Evoked field excitatory-postsynaptic potentials (fEPSPs) Single unit (cell) activity (SUA) of spikes/action potentials Multi-unit activity (MUA) of spikes Non-spiking, graded potentials (EEG)
Commonly recorded Ephys signal in the in vivo brain?
SUA
MUA
EEG
Claus Mathiesen October 2012
From low frequencies to higher frequencies
Department of Neuroscience and Pharmacology (Dias 7)
Claus Mathiesen October 2012
EEG (ElectroEncephaloGraphy)
Richard Caton 1875: The electric currents of the brain. BMJ 2. 278. !Hans Berger 1929: Über das elektreenkephalogram des menschen. Arch. Psychhiatr. Nervenkr. 87, 527-570
Department of Neuroscience and Pharmacology (Dias 8)
In the beginning EEG was used as indicator for sleep stages (Slow wave, light, REM) together with recording of muscular tone (EMG) diseases like epilepsy and brain damage
Claus Mathiesen October 2012
EEG (ElectroEncephaloGraphy)
Claus Mathiesen October 2012
Brain activity and EEG
Possibly only a small proportion of nerve cells generate synchronous spikes in normal mental state !Cerebral rhythms picked up by EEG represent synchronous synaptic activity !EEG measures only a small fraction of the total brain activity due to
Dilution (distance-2 ≈ amplitude) Variability in conductivity Mixed orientation of active dendrites Lack of synchronous activity
Claus Mathiesen October 2012
Irregular activity leads to high frequency and low amplitude EEG
Synchronized activity leads to low frequency and high amplitude EEG
Claus Mathiesen October 2012
Subdivided EEG band
Delta <4 Hz (deep sleep)Theta 4-7 Hz (REM sleep, drowsy, meditation)
Alpha 8-13 Hz (eyes closed awake)
Beta 14-30 Hz (active awake, open eyes)
Gamma 30-80 Hz (memory)
Claus Mathiesen October 2012
Delta rhythms (<4 Hz EEG)
Marker for slow-wave sleep also called deep sleep. In slow-wave sleep the brain recovers
Claus Mathiesen October 2012
Theta rhythms (4-7 Hz EEG)
In rodents the theta rhythms (4-10 Hz) originate from hippocampus and is an indicator for
paradoxical sleep (rodents REM sleep) Exploration and sniffing !In humans the theta rhythms originate from cortex
and is an indicator for Drowsiness Meditation Light sleep states
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Claus Mathiesen October 2012
Alpha- (8-13 Hz) and Beta-rhythms (14-30 Hz)
Open eyesQuiet awake closed eyes
BetaAlpha
Claus Mathiesen October 2012
Gamma rhythms (30-80 Hz EEG)
Represent spike timing of a large ensemble of neurons Dependent on GABA interneurons that synchronise the spiking of pyramidal cells !Synchronous neuronal activity is a tool for dealing with information with different modalities:
Perceptual binding Attention Working memory
!Can be observed at multiple spatial scales, from single-unit recordings to MEG and scalp EEG
Gamma
Claus Mathiesen October 2012
Gamma activity
(Adapted from Sumiyoshi et al., 2012, Neuroimage)
Claus Mathiesen October 2012
Bands for different Ephys signals
Department of Neuroscience and Pharmacology
Delta <4 Hz (deep sleep)Theta 4-7 Hz (REM sleep, drowsy, meditation)
Alpha 8-13 Hz (eyes closed awake)
Beta 14-30 Hz (active awake, open eyes)
Evoked field potential 0.1-1000 Hz
Gamma 30-80 Hz (memory)
Claus Mathiesen October 2012
What generates the evoked field potential?
Department of Neuroscience and Pharmacology
Synchronic activation: •Transmembrane current flow •Extracellular current flow and the resistant properties of the extracellular media àvoltage changes in the field potential
0.5 mV
Claus Mathiesen October 2012
Shape of evoked field potentials as function of anatomy and location
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Hippocam
pus or Cerebellum
Cerebral cortex
Claus Mathiesen October 2012
Interpretation of an evoked field potentials
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Degree of excitation =
Number of open AMPA receptor
channels
Ca2+ dependent K+ current
+NMDA rec. antagonist
Claus Mathiesen October 2012
From field potentials to Current Source Density
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Jessen et al 2014 & Mathiesen et al. 2011
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Current source densityCSD Map
Claus Mathiesen October 2012
Current Source Density (CSD)
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Neuronal activity à Transmembrane current generating ensemble of current sources and sinks à Extracellular current flow à Potential differences (Field potentials) due Resistance in the extracellular media
The first spatial derivative of the Field potential is equal to Current Flow Density.
The Current Flow Density is a vector indicating the amplitude and direction of current flowing through a giving point in the extracellular medium.
The second spatial derivatives of the field potential is equal to the Current Source Density (CSD).
The Current Source Density correspond to the transmembrane current
Nicholson, Freemann 1975
Field potential
Current flow density
Current Source DensitySource
Sink
Spatial derivativeSpatial derivative
Claus Mathiesen October 2012
Contribution to Ephys from different cell type
Department of Neuroscience and Pharmacology
GliaNeurons
Principal output Relay
Cortical pyramidal
Cerebellar pyramidal
Astrocyte Oligodendrocyte MicroglialInterneurons Stellate cell
K+ buffer Blood flow House keeper Calcium waves
Myelinate Phagocyte
Major Major Middle Minor (EEG)
(Minor) (Minor) (Minor)Contribution to the field potential
Claus Mathiesen October 2012
Bands for different Ephys signals
Department of Neuroscience and Pharmacology
Evoked field potential (synaptic strenghts) 0.1-1000 Hz
Spikes /action potentials 300-3000 Hz peak 1000 Hz • Single unit activity (1-100 spikes/s) •Multi unit activity
Delta <4 Hz (deep sleep)Theta 4-7 Hz (REM sleep, drowsy, meditation)
Alpha 8-13 Hz (eyes closed awake)
Beta 14-30 Hz (active awake, open eyes)
Gamma 30-80 Hz (memory)
Adrian & Moruzzi 1939: Impulses in the pyramidal tract. J. Physiol. 97, 153-‐199
Claus Mathiesen October 2012
Spiking in respons to synaptic input
Cascades: Transmitter release Transmitter-gated channels (spatial and temporal summation) Voltage-gated channels
Calcium spikes Sodium spikes Potassium re-polarize cell
Calcium mediated potassium current !Or sodium spikes as a consequence of pacemaker activity
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Claus Mathiesen October 2012
Department of Neuroscience and Pharmacology
5 ms 5 ms
Single unit spike activity (Purkinje Cell)
0 1000 2000 3000 4000 50000.000
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
Power
Frequency
Simple spike Complex spike
Kirsten Thomsen
Claus Mathiesen October 2012
Department of Neuroscience and Pharmacology
Herrik et al. 2010
Example of single unit activity (SUA)
Event autocorrelation
InterSpikeInterval
Spike- waveform Regular
Irregular
Burst
BurstIrregularRegular
Claus Mathiesen October 2012
Methods in Multi-unit activity (MUA)
Single electrode !!!Stereotrode !!!Tetrode
Low resolution
•distance
Root-Mean-Square (RMS)
!Better resolution
•distance + location
!!Even better resolution
•Distance + 2D location
Department of Neuroscience and Pharmacology (Dias 35)
Claus Mathiesen October 2012
Pro and Cons with types of ephys recordingDepartment of Neuroscience and Pharmacology
Method Pro Cons
EEG Non-invasive, comparative to human studies, timing
Bad localisation (3-5cm), no info on cell types, or mode of actionEvoked field potentials Robust indicator of
synchronous synaptic activity
Invasive, only on evoked response, not well with non-aligned cellsCurrent source
density Robust indicator of transmembrane ion flux, better localisation
same as above
Single unit activity (SUA)
Info from one cell Only one cell
Multi unit activity (MUA)
Better overall estimation of spike activity
lack cell type information
Claus Mathiesen October 2012
Bands for different Ephys signals
Department of Neuroscience and Pharmacology
Delta <4 Hz (deep sleep)Theta 4-7 Hz (REM sleep)
Alpha 8-13 Hz (light sleep, or quit awake)
Beta 14-30 Hz (active awake)
Evoked field potential (Synaptic strengths) 0.1-1000 Hz
Spikes /action potentials 300-3000 Hz peak 1000 Hz • Single unit activity (1-100 spikes/s) •Multi unit activity
Gamma 30-80 Hz (memory)
Claus Mathiesen October 2012
THANK YOU FOR YOUR ATTENTIONDepartment of Neuroscience and Pharmacology (Dias 38)