Synaptic rewiring for topographic map formation (PhD 2005-2009)

For my PhD at the University of Edinburgh I worked on an alternative method for delivering events within neuromorphic systems made of many silicon chips.The events represent spikes (the electrical pulses that brain cells use to communicate with each other). These events were broadcast across each chip and could be received simultaneously by many synapses (the connections between neurons) - this reduced a speed bottleneck present in other designs.

I also implemented the formation and elimination of synapses (a process which happens continuously in our brains, known as "synaptic rewiring" or "structural plasticity"). I then used synaptic rewiring to model the development of topographic maps (ordered sets of connections between different brain areas).

As a learning rule, the model used a type of spike-timing-dependent plasticity (STDP). I created an analogue silicon circuit to emulate this learning rule, which allowed some control of the weight-dependence of the plasticity. A serendipitous result that emerged was that the learning rule automatically provided some compensation for inhomogenities in the chip design.

Follow-up

It's been rewarding to see a small trail of newer implementations following my modelling. Specifically, Bogdan et al used Spinnaker, and Senk et al used GeNN framework.

Publications

• "Silicon synapses self-correct for both mismatch and design inhomogeneities", Bamford SA, Murray AF, Willshaw DJ. Electronics Letters, 2012, vol. 48, no. 7, pp. 360-361. pdf
• "A learning process" (Editorial for the above article), H. Dyball, Electronics Letters, 29th Mar 2012, pdf
• "Spike-timing-dependent plasticity with weight dependence evoked from physical constraints", Bamford SA, Murray AF, Willshaw DJ. IEEE Transactions on Biomedical Circuits and Systems, 2012, vol. 6, no. 4, pp. 385-398. pdf
• "Large Developing Receptive Fields Using a Distributed and Locally Reprogrammable Address-Event Receiver", Bamford SA, Murray AF, Willshaw DJ. IEEE Transactions on Neural Networks, 2010, vol. 21, no. 2, pp. 286-304. pdf
• "Synaptic Rewiring for Topographic Map Formation and Receptive Field Development", Bamford SA, Murray AF, Willshaw DJ. Neural Networks, 2010, vol. 23 pp. 517-527. pdf
• "Large Developing Axonal Arbors Using a Distributed and Locally-Reprogrammable Address-Event Receiver", Bamford SA, Murray AF, Willshaw DJ. IEEE International Joint Conference on Neural Networks (IJCNN), 2008, pp. 1464-1471. pdf
• "Synaptic Rewiring for Topographic Map Formation", Bamford SA, Murray AF, Willshaw DJ. International Conference on Artificial Neural Networks (ICANN), 2008, pp. 218-227. pdf
• "Synaptic Rewiring in Neuromorphic VLSI for Topographic Map Formation", PhD Thesis, University of Edinburgh, 2009. pdf
• This work by the Spinnaker team has followed up my modelling approach: "Structural Plasticity on the SpiNNaker Many-Core Neuromorphic System", Bogdan PA, Rowley AGD, Rhodes O, Furber SB Frontiers in Neuroscience, 2018, https://doi.org/10.3389/fnins.2018.00434 pdf