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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

0 50 100 150 200 250 300 350 4000

0.5

0 50 100 150 200 250 300 350 4000

0.5

0 50 100 150 200 250 300 350 4000

0.5

0 50 100 150 200 250 300 350 4000

0.5

1

0 50 100 150 200 250 300 350 4000

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