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Oscillatory Models of Hippocampal Activity and
MemoryRoman Borisyuk
University of Plymouth, UK
In collaboration with
Frank Hoppensteadt New York University
Outline
• Oscillatory model of Hippocampal Activity
• Memorization of sequences of events
• Theory of epineuronal memory
Publications1. Borisyuk R.M. and Hoppensteadt, F. (1998) Memorizing and recalling
spatial-temporal patterns in an oscillator model of the hippocampus. Biosystems, v.48, 3-10.
2. Borisyuk R., Denham M., Denham S. and Hoppensteadt F. (1999) Computational models of predictive and memory-related functions of the hippocampus. Reviews in the Neurosciences, v.10, pp.213-232.
3. Borisyuk R., Hoppensteadt F. (1999) Oscillatory model of the hippocampus: A study of spatio-temporal patterns of neural activity. Biological Cybernetics, v. 81, no.4, pp 359-371.
4. Borisyuk R., Denham M., Kazanovich Y., Hoppensteadt F. Vinogradova O. (2000). An Oscillatory Neural Network Model of Sparse Distributed Memory and Novelty Detection. BioSystems, 58:265-272
5. Borisyuk R., Denham M., Kazanovich Y., Hoppensteadt F., Vinogradova O., (2001). Oscillatory Model of Novelty Detection. Network: Computation in Neural System, 12: 1-20
6. Borisyuk R. and Hoppensteadt F. (2004) A theory of epineuronal memory. Neural Networks, 17:1427-1436.
Chain Model of Spatio-Temporal ActivityWe model activity of the hippocampus by a chain of interactive
oscillators corresponding to lamellas. Each oscillator has two theta modulated inputs with time shift
which controls resulting activity pattern (hippocampal bar code).
System demonstrates a wide variety of dynamics: synchronization, non-linear resonance, chaotic activity, etc.
V(t+1 ) V(t+N )
V(t+1 ) V(t+N )
Septum
Entorhinal Cortex
S1 SN . . .
Borisyuk & Hoppensteadt, 1999, Biological Cybernetics
Model Description
We study this model analytically using VCONs (Hoppeansteadt, 1975) and computationally using W-C oscillator (Wilson & Cowan, 1972).
En(t) and In(t) are average activities of excitatory and inhibitory populations; Z() is sigmoid; Rn and Vn describe interactions with neighbours; Pn and Qn are periodic inputsC –S controls patterns of activity
Gamma and Theta Rhythms of Single Oscillator
0 200 400 t
Single oscillator under influencesof two inputs can demonstrate complex behaviour with slow (theta) and fast (gamma) components
Recoding from hippocampal population(Van Quyen & Bragin, 2007)
Spatio-Temporal Patterns Hippocampal Bar Code
Borisyuk & Hoppensteadt, 1999, Biological Cybernetics
HIPPOCAMPUS
Phase deviation is a key parameter which coltrols dynamics of hippocampal
activity
TIME TIME
SEPTAL)2sin( ft
Input:EC
)2sin( ft
Input:
=5 =18
Phase/Frequency Coding and Novelty Detection
• Equations of ONN dynamics:
q
l
jk
jl
jl
n
i
jkij
jk
jk ag
q
wt
n
v
dt
d
11
10 )sin()()2sin(2
n
i
jkij
jk
jk t
nga
dt
da
10
22 )(cos
1
dt
dag
dt
d jkj
kj
k
jk
)(1
)2,1(,)/)exp((1
)/)exp(()(
ix
xxg
ii
iii
Borisyuk, Denham, Kazanovich, Hoppensteadt, Vinogradova
(2000,2001)
Model Description
Dynamics of oscillator’ frequencies is governed by the learning rule: here we do not modify connection strengths, instead we adjust natural frequency
0 500 1000 1500 2000 2500
time4
4.5
5
5.5
6
6.5
7
7.5
8
8.5
9Naturalfrequencies
Stimulation
G1
G2
G3
=5 =7 =8
Dynamics of Frequencies and Amplitudes
Am
pli
tud
e
Time
#
6,4
6,6
6,8
7
7,2
7,4
7,6
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Time
Na
tura
l fre
qu
en
cie
s
6,4
6,6
6,8
7
7,2
7,4
7,6
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Time
Nat
ura
l fre
qu
en
cie
s
Resonant state Non-Resonant state
Novelty Detection: Sparse Coding
The bar’s height is proportional to the number of resonant oscillators in the group.
The arrow indicates coincidence of resonant oscillator groups for the same symbols “O”
O
H
E
L2
L1
W
O
D
R
L
0 2000
Example of sparse coding: 10 objectare coded by 2000 groups
Oscillatory Memory of Sequences
The learning rule is temporally asymmetric, and it takes into account the activity level of pre- and post-”synaptic” neurons in two contiguous time windows.
Recall by the network is fast: All memorized patterns of sequences are reproduced in the correct order during the same time window with a short delay.
Borisyuk, Denham, Denham, Hoppensteadt (1999)
Asymmetric Learning Rule (analog of STDP)
j nw n,j
Tm+1Tm
Activity
))1(())(()(
)1()2(
maxmax
,,
hmEhmE
mwmwnj
jnjn
Time
Threshold h
Borisyuk Denham, Denham, Hoppensteadt, 1999, Rev in Neurosc.
Oscillatory Memory
0.2 0.4 0.6time
Example of ONN dynamics. Oscillator consists of 10 excitatory (RED) and 10 inhibitory (BLUE) integrate and fire units with all-to-all connections. The background activity is low. The external input is applied to some group of oscillators during time window. Three time windows are shown.
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
t
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
t
ONN Memory: Sequence of 5 Patterns
ONN Memory: Two Sequences
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 t
Reverse Replay (Wilson Lab, MIT)
Foster & Wilson, Nature, 2006
Place cell 1 fires
Place cell 2 fires
Place cell 3 fires
Reverse replay
Reverse Replay with Anti STDP
Reverse Replay with Anti STDP
Forward and Reverse ReplayA series of neuronal place-fields, which, when ordered according to the peak in-field firing rates, comprise the place-field sequence “template”.
Each neuron’s place-field is shownin a different color.
Some sample forward and reverse correlated events from these neurons (same coloring) during immobility. Forward replay
Diba & Buzsaki, Nature Neurosc 2007
Preplay and Replay
Spike trains of 13 neurons before, during, and after a single lap (CA1 local field potential shown on top; velocity of the rat shown in the lower panel). The left and right insets magnify 250-ms sections of the spike train, depicting forward preplay and reverse replay, respectively.
Forward preplay Reverse replay
Diba & Buzsaki, Nature Neurosc 2007
Epineuronal MemoryA theory of epineuronal memory includes a
hierarchical structure of variables and parameters that allows us to consider learning and memory processes as being on a variable landscape that is sculptured by reward signals.
During fast dynamics, the landscape is attractive quasi-static surface that then slowly guides the system into basin of attraction of the metastable state.
A novel mathematical model of Epineuronal Memory is developed that is based on a temporally evolving mnemonic function M, which registers information and guides the dynamics of activity patterns.
Borisyuk R & Hoppensteadt F (2004) A theory of epineuronal memory. Neural Networks
Formulas of Epineuronal Memory
).,,,(
),,,(
pxtMpp
txtfx
p
))((),(
:termreaction theof Example
)(),,(
:storageforpatterna representsterm(source)Input**
*
MMMMtg
uxupxtS
u
Variables x(t); parameters p(t); stochastic process (t).Mnemonic landscape function M(t,x,p,).
),(),,(),,,(2
,
2 MtgpxtSpxtMt
Mpx
Reaction-diffusion equation for the landscape function M(t,x,p)
Borisyuk R & Hoppensteadt F (2004) A theory of epineuronal memory. Neural Networks
Memory of 15 random mnemes
REWARD2
REWARD1
REWARD15
Recall Starting From Random Initial Data
Uniform distribution between 15 memorised mnemes. Histogram of 1000 recalls starting from random initial data
Example of recall
Recall of Five Sequential Patterns
The landscape function peak heights indicate the sequential order of recall
Epineuronal Memory: 5 Peaks Mnemonic Surface
0 1 2 3 4 5 6-20
-15
-10
-5
0
5
10
15
20
5.3 5.305 5.31 5.315 5.32 5.325 5.33 5.335 5.34 5.345-12
-11.95
-11.9
-11.85
-11.8
-11.75
-11.7
ZOOM
1D vector x
x
dx/dt
Complex dynamics
Dynamical uncertainty
Mnemonic function M(u)
x
Mnemonic Landscape and Trajectories
Borisyuk R & Hoppensteadt F (2004) A theory of epineuronal memory. Neural Networks
Conclusions• Study of chain model of the hippocampus shows that phase shift
between two inputs controls spatio-temporal patterns (hippocampal bar code)
• Phase shift, synchronization and resonance have been used to memorise signals and detect their novelty without modification of synaptic strengths
• STDP-type learning rule has been used to memorise sequences and replay them in forward and reverse order
• General theory of epineuronal memory has been developed which includes both phase-shift and STDP based memories.
• The epineuronal paradigm demonstrates mechanisms for stable and persistent memory in the presence of noisy and uncertain environments. It introduces the mnemonic landscape that governs regulation of a brain structures. This approach enables the memorization of events and sequences of events.
END
PLYMOUTH
Happy Birthday to Frank!Happy Birthday to Frank!