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A Dynamical Pattern Recognition Model of Gamma Activity in
Auditory Cortex
A Dynamical Pattern Recognition Model of Gamma Activity in
Auditory Cortex
Will PennyWill Penny
Wellcome Trust Centre for Neuroimaging,Wellcome Trust Centre for Neuroimaging,University College London, UKUniversity College London, UK
Centre for Integrative Neuroscience and Neurodynamics,University of Reading, 17th March 2010
GammaActivity(>30Hz)
ComputationalNeuroscience
Imaging Neuroscience
SpikeTimeDependentPlasticity
BOLDsignal
BindingProblem
Localisation
Miller, PLOS-CB,2009
Goense et alCurr Biol, 2008
Singer,Neuron, 1999
Overview
• Bandpass filtering and feature detection• Spike Frequency Adaptation• Spike Time Dependent Plasticity • Neuronal Synchronization• Sparse Coding
Hopfield-Brody Model
Levels of Analysis Occurrence Times for Speech Recognition
Forward model of imaging data and stimulus labels
Overview
• Bandpass filtering and feature detection• Spike Frequency Adaptation• Spike Time Dependent Plasticity • Neuronal Synchronization• Sparse Coding
Hopfield-Brody Model
Levels of Analysis Occurrence Times for Speech Recognition
Forward model of imaging data and stimulus labels
Bandpass filters
Allen (1985) Cochlear Modelling IEEE ASSP
Onset Cells, Offset Cells, etc.
Hromadka et al, PLOS B, 2008Cell attached recordings from A1 in rat
Onset and offset cells with frequency adaptation
Hromadka et al, PLOS B, 2008
Overview
• Bandpass filtering and feature detection• Spike Frequency Adaptation• Spike Time Dependent Plasticity • Neuronal Synchronization• Sparse Coding
Hopfield-Brody Model
Levels of Analysis Occurrence Times for Speech Recognition
Forward model of imaging data and stimulus labels
Spike Time Dependent Plasticity
Abbott and Nelson. Nat Neuro, 2000
Pre
Post
25ms
Neuronal Synchronization
Frequencies need to be similar (Kuramoto)
With fast connections excitation causes sync (Gap Junctions)
With slow connections inhibition causes sync (Chemical synapses, PING)
Hopfield Brody – balanced excitation and inhibition
See Bartos, Van Vreeswijk, Ermentrout, Traub ….
Hopfield and Brody, PNAS 2001
Hopfield Brody Model
0.2 0.4 0.6 0.8 1-0.5
0
0.5Audio waveform
time (s) time (s)
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uenc
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Audio spectrogram
0.2 0.4 0.6
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3000
0.2 0.4 0.6 0.8 10
50
time (s)
Spikes
0.2 0.4 0.6 0.8 10
1
time (s)
In Currents
0.2 0.4 0.6 0.8 1
0.20.40.60.8
time (s)
LFP
time (s)
freq
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LFP Spectrogram
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“Add”
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time (s) time (s)
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Audio spectrogram
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time (s)
Spikes
0.2 0.4 0.6 0.8 10
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time (s)
In Currents
0.2 0.4 0.6 0.8 1
0.4
0.6
time (s)
LFP
time (s)
freq
uenc
y (H
z)LFP Spectrogram
0 0.5 1
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60
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“Add”
Word 1 Word 2
30 frequency bands x 3 types (onset,offset,peak) x 10 adaptation times=900 cells
Each word coded for by activity in an ensemble of 45 cells
Frequencies near recognition time point
Sparse Coding
Hromadka et al, PLOS B, 2008
fb
tb
k=1 k=2
j=1 j=1
j=2 j=2
Time
Frequency
fmax
Spike Time Dependent Plasticity
Overview
• Bandpass filtering and feature detection• Spike Frequency Adaptation• Spike Time Dependent Plasticity • Neuronal Synchronization• Sparse Coding
Hopfield-Brody Model
Levels of Analysis Occurrence Times for Speech Recognition
Forward model of imaging data and stimulus labels
Levels of Analysis
Algorithmic level – what algorithm is being used ?
Example – Fourier Analysis
Implementation level – how is it implemented ?
Example – FFT if you have digital storage, adders, multipliers Holography if you have a laser and photographic plates
See eg. Marr and Poggio, AI Memo, 1976
Levels of Analysis
Algorithmic level – what algorithm is being used ?
Similarity of Occurrence Times
Implementation level – how is it implemented ?
Transient Synchronisation
Recognising Patterns
Bandpassfilteringat multiple spatial scales
Spatial configurationof Features
Leveldetection
Bandpassfilteringat multiple temporal scales
Temporal configurationof Features
Leveldetection
Fukushima, Rolls etc.
Overview
• Bandpass filtering and feature detection• Spike Frequency Adaptation• Spike Time Dependent Plasticity • Neuronal Synchronization• Sparse Coding
Hopfield-Brody Model
Levels of Analysis Occurrence Times for Speech Recognition
Forward model of imaging data and stimulus labels
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F (
Hz)
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f (H
z)Occurrence Times
y=[t1, t2, t3, ……, t45]
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0
0.5
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x
t
F (
Hz)
-0.2 -0.1 0 0.1 0.2 0.3 0.4 0.50
1000
2000
-0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.60
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f (H
z)Autoregressive features
K frames
)()(...)2()1()( 21 teptxatxatxatx p EachFrame:
1 2 3 4 5 6 7 8 9 10
1
2
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5
6
7
8
9
10
0
1
2
3
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9
Confusion matrix from one cross-validation run
Truth
Cla
ssifi
catio
n
HB spokendigit database
FirstNearestNeighbourClassifier
Occurrence TimesAutoregressive Parameters
Single shot learning results
Results on single subject
Overview
• Bandpass filtering and feature detection• Spike Frequency Adaptation• Spike Time Dependent Plasticity • Neuronal Synchronization• Sparse Coding
Hopfield-Brody Model
Levels of Analysis Occurrence Times for Speech Recognition
Forward model of imaging data and stimulus labels
ECOG recordings over fronto-temporal cortex
Canolty et al. Front. Neuro, 2007
Subject listened to words and “nonwords”
• Task: press button if word is a persons name (this data not analysed)
• Each nonword was created by taking a word, computing the spectrogram and removing ripple sound components corresponding to formants. The spectrogram was then inverse transformed (Singh and Theunissen, 2003)
• Each nonword matched one of the words in duration, intensity, power spectrum, and temporal modulation.
Time (ms)
Fre
quen
cy (
Hz)
Words
-200 0 200 400 600 80060
80
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160
2.5
3
3.5
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4.5
5
5.5
Time (ms)
Fre
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cy (
Hz)
NonWords
-200 0 200 400 600 80060
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2.5
3
3.5
4
4.5
5
5.5
Time (ms)
Fre
quen
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Hz)
Difference
-200 0 200 400 600 800
20
40
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-0.2
0
0.2
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0.8
Time (ms)
Fre
quen
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Hz)
T-score
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160
-2
0
2
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14
ECOG recordings over STS
u y
x
u yu y
Encoding
Symmetric
Decoding
u yStimulusLabels
LocalField
x
tk
s
f(x,t)
AuditoryInput Pattern
BandpassFilters
Onset, offsetand peak responsetimes
Input-dependentFrequencies
Weakly-coupledOscillators Pattern
Recognition
FeatureExtraction
WCO-TS Model
)]()(sin[),()( ttwtxft ijj
ijii
Input-pattern dependent frequencies
LateralConnectivity:Uniform (A)
Sync is stablestate
j
j tty )(cos)(
LFP
WCO-TS
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20
20
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60
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20
20
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0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2-20
0
20
f(x,t)
cos (t)
y(t)
fb
tb
k=1 k=2
j=1 j=1
j=2 j=2
Time
Frequency, fi(x,t)
fmax
Minimal model with four parameters: ={A, fmax, fb, tb }
Time (ms)
Fre
quen
cy (
Hz)
Words
-200 0 200 400 600 80060
80
100
120
140
160
2.5
3
3.5
4
4.5
5
5.5
Time (ms)
Fre
quen
cy (
Hz)
NonWords
-200 0 200 400 600 80060
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100
120
140
160
2.5
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5
5.5
Time (ms)
Fre
quen
cy (
Hz)
Difference
-200 0 200 400 600 800
20
40
60
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100
120
140
160
-0.2
0
0.2
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0.6
0.8
Time (ms)
Fre
quen
cy (
Hz)
T-score
-200 0 200 400 600 800
20
40
60
80
100
120
140
160
-2
0
2
4
6
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14
ECOG recordings over STS
Word
30 frequency bands x 3 types (onset,offset,peak) x 10 adaptation times=900 cells
Each word coded for by activity in an ensemble of 45 cells
Frequencies near recognition time point
For each of 96trials look at response to wordversus nonword
Computational saving:only look at those cells activated by both word and nonword stimuli
Model fitting
• EN: ECOG spectra-model spectra
• EC: Word versus non word
)exp()|( ECENyp
Uniform priors, Metropolis Hastings estimation of posterior densities
Training Testing
Minimal Model
Testing Training
Augmented Model
SummaryLevels of Analysis Occurrence Times for Speech Recognition
Forward model of imaging data and stimulus labels
FUTURE:
Lack of direct evidence for TS mechanism
Can STDP rules synchronize multiple spikes ?
Have modelled activity in single region only.
GammaActivity(>30Hz)
ComputationalNeuroscience
Imaging Neuroscience
SpikeTimeDependentPlasticity
BOLDsignal
BindingProblem
Localisation
Miller, PLOS-CB,2009
Goense et alCurr Biol, 2008
Singer,Neuron, 1999
Melissa Zavaglia & Mauro UrsinoDEIS, Cesena, Italy
LIF network simulations
Rich Canolty & Bob Knight,UCSF, San Francisco.
ECOG data and analysis
Tom Schofield & Alex Leff,UCL, London.
Cognitive neuroscience of language
Acknowledgements
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time (s)fr
eque
ncy
(Hz)
Word 6, Ex 9
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Sensitivity
FN
time (s)
freq
uenc
y (H
z)
Word 1, Ex 1
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time (s)fr
eque
ncy
(Hz)
Word 9, Ex 1
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Specificity
FP
Optical Imaging
Harrison et al. Acta Oto, 2000
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