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Hardware/Software Models of Brain Like Self-Repair
Liam McDaid, Jim Harkin & Muhammad Naeem (Ulster)
John Marsland (Liverpool)
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SNN based Brain Model
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Endocannabinoid Mediated Self Repair
DSE is very local: 2-AG travels ~20nM.
e-SP is local and far reaching: astrocyte releases glutamate at all contacted synapses.
e-SP signalling pathway: proposed mechanism of self repair for damaged or low PR synapses.
If neuron does not fire due to damaged synapse no 2-AG emitted (No DSE). However, PR increased via astrocyte stimulation by neighbouring neurons releasing 2-AG.
Axon
Dendrite
Astrocyte Process
ER
Glu2-AG
Ca2+
IP3
2-AGDirect
Indirect
CB1Rs
CB1Rs
mGluRs
Glu
Navarrete, M., & Araque, A (2010). Endocannabinoids Potentiate Synaptic Transmission Through Stimulation of Astrocytes, Neuron, 68(1), 113-126.
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Endocannabinoid Mediated Self Repair
2-AG (DSE)
2-AG (DSE)
e-SP2-AG
2-AG (DSE)
e-SP 2-AG
Healthy State After Damage
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Endocannabinoid Mediated Self Repair
2-AG (DSE)
e-SP 2-AG
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Endocannabinoid Mediated Self Repair
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0.5
0 50 100 150 200 250 300 350 4000
0.5
0 50 100 150 200 250 300 350 4000
0.5
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0.5
1
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0.5
1
Self-repair in a Bi-directionally Coupled Astrocyte-Neuron (AN) System based on Retrograde Signalling, Special Topic: Frontiers in Computational Neuroscience, 26 September 2012
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Network with induced fault in 80% of synapses (PR =0 after 200s) of N2 (Red). No synapses connected to N1 (Blue) have a fault. (A) Firing rate of N2 falling off at 200s and increasing thereafter due to repair . Please note a moving average over 10 s has been plotted (B) Calcium signal (C) PR of the synapse connected to N1 (D) PR of the healthy and damaged synapse connected to N2 (E) Cumulative IP3 signal (F) Cumulative signal of 2-AG (G) e-SP signal (H) Dse signals showing reduced suppression in the case of
synapse associated with N2
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Need to consider Probability of Release in STDP rule - used the BCM rule for now but need to re-visit this again
δω
δt
ωp
ωd
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Firing rates of N1 (Blue) and N2 (Red). A moving average of 10 s has been plotted. Column 1-5 from left-to-right represents 0-80 % fault in neuron N2 of the network. Please note to the averaging some of the spectacular effects are nor visible: after 200s in a narrow
temporal window (width proportional to the fault) rates actually fall close to zero
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M. Goldberg, M. De Pittà, V. Volman, H. Berry and E. Ben-Jacob, “Nonlinear Gap Junctions Enable Long-Distance Propagation of Pulsating Calcium Waves in Astrocyte Networks”, PloS Comput. Biology, Aug 26, 2010
Distributed Self Repair
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Firing rates of 5-Astrocytes in a ring network with BCM-STDP module (Red) and without (Blue). Row 1: A1 (N1, N2) - N1 is healthy and N2 is 80 % damaged. Row 2: A2 (N3, N4) - both 80 % damaged. Row 3: A3 (N5, N6) - both 80 % damaged. Row 4: A4 (N7, N8) - both 80 % damaged. Row 5: A5 (N9, N10) - both 80 % damaged
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X
VP N1
10V
FG1
VR
VDD
N2FG2 FGn
Cluster C2
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Conclusion Implemented an self-repairing SNN
Based on an “astro-centric” topology
Targeting IEEE TNNLS plus a conference paper (ICANN 2014)
Next step is a demonstrator of Self-Repair: EPSRC bid
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Acknowledgements
Dr. John Wade (Ulster)
eFuturesXD