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Module 2
Local Field Potential
Supratim Ray
[email protected]
References
Buzsaki, Anastassiou and Koch, 2012, The origin of
extracellular fields and currents – EEG, ECoG, LFP
and Spikes, Nature Reviews Neuroscience
Einevoll, Kayser, Logothetis and Panzeri, 2013,
Modeling and analysis of local field potentials for
studying the function of cortical circuits, Nature
Reviews Neuroscience
Local Field Potential - Outline

Contributors
Mainly Synaptic Activity
Contribution from spikes, oscillations, AHP

Spatial Spread
~250 micro-mm for uncorrelated activity
increase when activity is correlated

Relationship with Spikes
Spike-related transients can be observed in the LFP above ~50
Hz and its contribution increases with increasing frequency
Local field potential (LFP)
Raw Signal
Micro-electrode
Spikes
Local field
Potential (LFP)
LFP and other measures (EEG/ECoG) have
fundamentally similar traces
Figure 1, Buzsaki et al., 2012,
Nature Reviews Neuroscience
Contributors to the LFP
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Synaptic activity
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Spikes
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Intrinsic membrane oscillations

Spike afterhyperpolarization (AHP)
Neuronal Structure
Figure 2-8, Kandel, Schwartz and Jessell
Four functional regions - Input, Integrative, Conductile and Output
Synaptic Transmission
Wikipedia.org
Synaptic activity
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Extracellular currents from many individual compartments must overlap in
time to induce a measurable signal.
Such overlap is easily achieved for relatively slow events, such as synaptic
currents.
The influx of cations from the extracellular into the intracellular space gives
rise to a local extracellular sink.
To achieve effective electroneutrality within the time constants of relevance
for systems neuroscience, the extracellular sink needs to be 'balanced' by
an extracellular source, that is, an opposing ionic flux from the intracellular
to the extracellular space, along the neuron.
Depending on the location of the sink current(s) and its distance from the
source current(s), a dipole or a higher-order n-pole is formed.
Buzsaki et al., 2012, Nature Reviews Neuroscience
Modeling LFPs from trans-membrane
currents
Einevoll et al., 2013, Nature Reviews Neuroscience
Pyramidal Cells
Cells in the cortex form columns. In this
image the red neurons, called
pyramidal cells, are revealed to be
entwined by blue fibers from other,
inhhibitory neurons that slow their firing.
The layers of the column are indicated
by the numerals to the left: L1, at the
surface of the brain, through L6, the
deepest cortical layer. Pyramidal cells,
which receive messages along their
extensively branched fibers, and send
long fibers out to other brain areas or
down to the spinal cord, are crucial in
movement control and in cognition.
They have their cell bodies in layer 5 of
the cortex, and the main receiving fiber,
the apical dendrite, rises up to the
surface, layer 1. ©BBP/EPFL
http://biomedicalcomputationreview.org/
content/reverse-engineering-brain
Synaptic activity
Kajikawa and Schroeder, 2011, Neuron
Fast action potentials
Fast (Na+) action potentials generate the strongest currents across the
neuronal membrane and can be detected as 'unit' or 'spike' activity in the
extracellular medium.
Although Na+ spikes generate large-amplitude deflections near the soma, until
recently they were thought not to contribute substantially to the traditionally
considered LFP band (<100 Hz) or to the scalp-recorded EEG because the
strongest fields they generate are of short duration (<2 ms) and nearby
neurons rarely fire synchronously in such short time windows under
physiological conditions.
However, synchronous action potentials from many neurons can contribute
substantially to high-frequency components of the LFP.
Buzsaki et al., 2012, Nature Reviews Neuroscience
Calcium Spikes
Other non-synaptic events that can contribute prominently to the extracellular
field are the long-lasting (10–100 ms) Ca2+-mediated spikes.
Because voltage-dependent regenerative Ca2+ spikes are often triggered by
NMDA receptor-mediated excitatory postsynaptic potentials (EPSPs),
separating them from EPSPs in extracellular recordings is not
straightforward.
Because dendritic Ca2+ spikes are large (10–50 mV) and long lasting, their
share in the measured extracellular events can be substantial under certain
circumstances.
Buzsaki et al., 2012, Nature Reviews Neuroscience
Membrane Oscillations
Some voltage-gated currents contribute to intrinsic resonance and oscillation
of the membrane potential. Several neuron types possess resonant
properties.
When intracellular depolarization is sufficiently strong, the resonant property of
the membrane can give way to a self-sustained oscillation of the voltage.
Voltage-dependent resonance and oscillations at theta frequency have been
described in principal neurons of several cortical regions. By contrast,
perisomatic inhibitory interneurons have a preferred resonance in the
gamma frequency (30–90 Hz) range.
To contribute substantially to the LFP, resonant membrane potential
fluctuations must occur synchronously in nearby neurons, a feature that
most often occurs in inhibitory interneurons.
Buzsaki et al., 2012, Nature Reviews Neuroscience
Spike afterhyperpolarization
Elevation of the intracellular concentration of a certain ion may trigger influx of
other ions through activation of ligand-gated channels, and this will in turn
contribute to Ve. For example, bursts of fast spikes and associated dendritic
Ca2+ spikes are often followed by hyperpolarization of the membrane,
owing to activation of a Ca2+-mediated increase of K+ conductance in the
somatic region.
The amplitude and duration of such burst-induced afterhyperpolarizations
(AHPs) can be as large (and last as long as) synaptic events, particularly
when bursting of nearby neurons occurs in a temporally coordinated
fashion.
In the intact brain, responses to unexpected stimuli or movement initiation are
often associated with relatively long-lasting (0.5–2 s) LFP shifts, which
might be mediated by synchronized AHPs.
Buzsaki et al., 2012, Nature Reviews Neuroscience
Local Field Potential - Outline

Contributors
Mainly Synaptic Activity
Contribution from spikes, oscillations, AHP

Spatial Spread
~250 micro-mm for uncorrelated activity
ncreases when activity is correlated

Relationship with Spikes
Spike-related transients can be observed in the LFP above ~50
Hz and its contribution increases with increasing frequency
Local Field Potential - Outline


Contributors
–
Mainly Synaptic Activity
–
Contribution from spikes, oscillations, AHP
Spatial Spread
~250 micro-mm for uncorrelated activity
ncreases when activity is correlated

Relationship with Spikes
Spike-related transients can be observed in the LFP above ~50
Hz and its contribution increases with increasing frequency
Spatial Spread of LFP
is a topic of much debate!
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200-400 µm:
Xing et al., Katzner et al., 2009
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600-1000 µm:
Berens et al., 2009
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~3 mm:
Kreiman et al., 2006
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several mm vertical: Kajikawa and Schroeder, 2011
LFP Spread (Katzner et al., 2009)
V1, Anesthetized Cats
Voltage Sensitive Dyes
(VSD)+implanted microelectrodes
Optimum integration radius:
~100 µm
LFP Spread (Xing et al., 2009)
V1, Anesthetized Monkeys
Compared visual spreads of LFP and MUA
LFP Spread = ~250 µm
LFP Spread (Kajikawa and Schroeder, 2011)
A1, awake monkeys
LFP Spread (Kajikawa and Schroeder, 2011)
Vertical spread observable at ~18 mm
Volume conduction explains the large spread
LFP Spread (Linden et al., 2011)
The spatial reach of the LFP is activity dependent
Spatial reach of local field potential is 200–300 μm with uncorrelated synapses
For correlated synaptic inputs the reach is set by spatial extent of correlations
In vivo-like network model mimicking sensory column is in correlated regime
Correlated
Uncorrelate
d
Local Field Potential - Outline


Contributors
–
Mainly Synaptic Activity
–
Contribution from spikes, oscillations, AHP
Spatial Spread
~250 micro-mm for uncorrelated activity
ncreases when activity is correlated

Relationship with Spikes
Spike-related transients can be observed in the LFP above ~50
Hz and its contribution increases with increasing frequency
Local Field Potential - Outline



Contributors
–
Mainly Synaptic Activity
–
Contribution from spikes, oscillations, AHP
Spatial Spread
–
~250 micro-mm for uncorrelated activity
–
Increases when activity is correlated
Relationship with Spikes
Spike-related transients can be observed in the LFP above ~50
Hz and its contribution increases with increasing frequency
LFP during stimulus presentation
Firing rate
Gamma rhythm
Evoked LFP
LFP during stimulus presentation
Firing rate
Gamma rhythm
Evoked LFP
LFP during stimulus presentation
Firing rate
Gamma rhythm
Evoked LFP
Compare spiking with LFP power at different frequencies
Compare spiking with LFP power at different frequencies
Firing rate
Compare spiking with LFP power at different frequencies
Firing rate
Compare spiking with LFP power at different frequencies
Firing rate
Compare spiking with LFP power at different frequencies
Firing rate
Ray and Maunsell, PLoS Bio, 2011
high-gamma (>80 Hz) power is correlated with firing rate
Ray and Maunsell, PLoS Bio, 2011
high-gamma (>80 Hz) power is correlated with firing rate
Ray and Maunsell, PLoS Bio, 2011
high-gamma (>80 Hz) power is correlated with firing rate
Trial-by-trial correlation
STA analysis during spontaneous activity
STA analysis during spontaneous activity
STA analysis during spontaneous activity
STA analysis during spontaneous activity
STA analysis during spontaneous activity
high-gamma (>80 Hz) power is correlated with firing rate
Local Field Potential - Outline



Contributors
–
Mainly Synaptic Activity
–
Contribution from spikes, oscillations, AHP
Spatial Spread
–
~250 micro-mm for uncorrelated activity
–
Increases when activity is correlated
Relationship with Spikes
Spike-related transients can be observed in the LFP above ~50
Hz and its contribution increases with increasing frequency
Local Field Potential - Outline



Contributors
–
Mainly Synaptic Activity
–
Contribution from spikes, oscillations, AHP
Spatial Spread
–
~250 micro-mm for uncorrelated activity
–
Increases when activity is correlated
Relationship with Spikes
–
Spike-related transients can be observed in the LFP above
~50 Hz and its contribution increases with increasing
frequency
Rhythms of the brain
Oscillations at different frequencies are
often observed in brain signals
The oscillations are associated with
various cognitive states
Brain signals obey a “1/f” power law: low
frequency oscillations have large
amplitude
alpha
hi-gamma/sigma
http://www.scholarpedia.org/w/images/b/ba/Thalcortx_oscillations.gif
Alpha Rhythm (8-12 Hz)
Discovered by German neurologist Hans Berger, most famous for his invention
of the EEG (Berger, 1929).
This alpha activity is centered in the occipital lobe, and is presumed to originate
there, although there has been recent speculation that it instead has a
thalamic origin.
The amplitude of alpha-frequency band activity in the human
electroencephalogram is suppressed by eye opening, visual stimuli and
visual scanning, and by attentive processing.
An ‘idling’ rhythm that characterizes an alert-but-still brain state
Recent studies have shown that there might be other alpha oscillations at
different parts of the brain, associated with different functions.
Stimulus/attention suppresses alpha rhythm
Attend-out
Pre-stimulus
Attend-in
Stimulation
Frequency
Frequency
Fries et al., 2008, J Neurosci
Gamma Oscillations (30-80 Hz)
Discovered by Wolf Singer and colleagues in 1989.
Neural assemblies oscillate at gamma frequencies (3080 Hz), such that the spiking activity of the neurons are
synchronized.
Binding by synchrony hypothesis
Auto-correlation
Cross-correlation
Engel et al., 1991, PNAS
Attention increases Gamma power and
synchronization in higher visual areas (V4)
Fries et al., 2008, J Neurosci