Functional Brain Signal
Processing: Current Trends and
Future Directions
Kaushik Majumdar
Indian Statistical Institute
Bangalore Center
kmajumdar@isibang.ac.in
National Conference on Brain and Consciousness, 20 – 21 September 2013, ISI Kolkata
Functional Brain Signals
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• Two Photon Microscopy
EEG
ECoG
LFP
Single Cell Electrophysiology
MEG
fMRI
PET
SPECT
Functional Brain Regions
By fundamental premise of deductive science it
is to be determined how each area works and
how different areas work together, that is, how
the areas couple and decouple among
themselves.
The gold-standard signals are
electrophysiological signals from
single cells to scalp EEG.
http://spot.colorado.edu/~dubin/talks/brodmann/br
odmann.html
Electrophysiological Signals at
Different Scales
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Single cell recording
Local filed potential (LFP)
Electrocorticogram (ECoG)
Electroencephalogram (EEG)
Buzsaki et al., Nat. Rev. Neurosci., 13: 407 – 420, 2012
EEG, LFP, Spikes
Buzsaki et al., Nat. Rev. Neurosci., 13: 407 – 420, 2012
Information Richness
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EEG – least informative, source ambiguous,
full of artifacts.
ECoG – mainly excitatory postsynaptic
potential in layer VI of the cortex, has less
artifacts and more informative than EEG.
LFP – is the most information rich brain
signal, superposition of almost all sorts of
membrane potentials.
Oscillation and Synchrony: Two
Major Paradigms for Studying
Brain Functions
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Oscillating band components in EEG are
delta (0 – 4 Hz), theta (4 – 8 Hz), alpha (8 –
12 Hz), beta (12 – 30 Hz) and gamma (30 –
80 Hz).
LFP in mammalian forebrain can oscillate
between 0.05 to 500 Hz (Buzsaki & Draguhn,
2004).
Power of oscillation of frequency ƒ varies as
ƒ-2.
Brain Oscillations (cont.)
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The higher the frequency the more confined
the oscillation is locally.
The lower the frequency the more
widespread the oscillation is.
Canolty et al., Science., 313: 1626 – 1628, 2006
Neuronal Oscillation: Functions
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Modulates synaptic plasticity.
Influence reaction time.
Correlates with attention.
Modulates perceptual binding.
Coordinate among brain regions far apart.
Consolidate memory.
Cortical Oscillation: Frequency
Bands
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Delta (0 – 4 Hz)
Theta (4 – 8 Hz)
Alpha (8 – 12 Hz), Mu (8 – 12 Hz)
Beta (12 – 30 Hz)
Gamma (30 – 80 Hz)
High gamma (80 – 150 Hz)
Canolty et al., Science., 313: 1626 – 1628, 2006
Task Specific Theta – High Gamma
Coupling
Passive listening to predictable tones
Two back phoneme working memory
Canolty et al., Science., 313: 1626 – 1628, 2006
Theta – High Gamma Coupling
Phase of 4 – 8 Hz (theta)
modulates amplitude of 80
– 150 Hz (high gamma).
Gray et al., Nature, 338: 334 – 337, 23 March 1989
Neuronal Synchronization
linguisticsandbeyond.wordpress.com
Broadmann’s Areas
Engel et al. Nat. Rev. Neurosci., 2: 704-716, 2001
Binding Problem
Phase Synchronization
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amplitude
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0
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time
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Rodriguez et al., Nature, 397: 430 – 433, 1999
Phase Synchronization in Face
Perception
Future Challenges
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Human depth EEG acquisition.
Different paradigms of cortical computation:
a) Neural computation.
b) Synaptic computation.
c) Dendritic computation.
d) Glial computation.
Membrane computation.
Brain-body integration.
References
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G. Buzsaki, C. A. Anastassiou and C. Koch,
The origin of extracellular fields and currents
– EEG, ECoG, LFP and spikes, Nat. Rev.
Neurosci., 13: 407 – 420, 2012.
X.-J. Wang, Neurophysiological and
computaitonal principles of cortical rhythms
in cognition, Physiological Rev., 90(3): 1195
– 1268, 2010.
THANK YOU
This lecture is available at http://www.isibang.ac.in/~kaushik