UH Biocomputation Group - Sam Sutton

Signal Propagation and Logic Gating in Networks of Integrate-and-Fire Neurons

2018-06-20T15:35:20+01:00

Sam Sutton's journal club session where he discusses the paper "Signal Propagation and Logic Gating in Networks of Integrate-and-Fire Neurons (Vogels and Abbott, 2005)".

Transmission of signals within the brain is essential for cognitive function, but it is not clear how neural circuits support reliable and accurate signal propagation over a sufficiently large dynamic range. Two modes of propagation have been studied: synfire chains, in which synchronous activity travels through feedforward layers of a neuronal network, and the propagation of fluctuations in firing rate across these layers. In both cases, a sufficient amount of noise, which was added to previous models from an external source, had to be included to support stable propagation. Sparse, randomly connected networks of spiking model neurons can generate chaotic patterns of activity. We investigate whether this activity, which is a more realistic noise source, is sufficient to allow for signal transmission. We find that, for rate-coded signals but not for synfire chains, such networks support robust and accurate signal reproduction through up to six layers if appropriate adjustments are made in synaptic strengths. We investigate the factors affecting transmission and show that multiple signals can propagate simultaneously along different pathways. Using this feature, we show how different types of logic gates can arise within the architecture of the random network through the strengthening of specific synapses.

Date: 22/06/2018
Time: 16:00
Location: LB252

Inhibitory plasticity balances excitation and inhibition in sensory pathways and memory networks

2017-08-30T11:06:27+01:00

Cortical neurons receive balanced excitatory and inhibitory synaptic currents. Such a balance could be established and maintained in an experience-dependent manner by synaptic plasticity at inhibitory synapses. We show that this mechanism provides an explanation for the sparse firing patterns observed in response to natural stimuli and fits well with a recently observed interaction of excitatory and inhibitory receptive field plasticity. The introduction of inhibitory plasticity in suitable recurrent networks provides a homeostatic mechanism that le ads to asynchronous irregular network states. Further, it can accommodate synaptic memories with activity patterns that become indiscernible from the background state but can be reactivated by external stimuli. Our results suggest an essential role of inhibitory plasticity in the formation and maintenance of functional cortical circuitry.

The full paper can be found here: http://www.sciencemag.org/content/334/6062/1569.short

Date: 01/09/2017
Time: 16:00
Location: LB252

Improving the performance of spatial searching in BTMORPH: An investigation into the implementation of R-tree spatial indexing

2017-02-08T15:56:46+00:00

In order to improve BTMORPH’s spatial querying capabilities, an implementation of Guttman’s (1984) R-tree and an investigation to determine the best parameters for performance was conducted. This presentation will discuss:

the precursory improvements to work flow
the implementation of forest structures that were a necessary to the addition of spatial indexing into BTMORPH
the effects on the R-tree of the parameter M
the method of node splitting during R-tree construction
the BTMORPH forest handling strategy

All of which were used to produce a 400% reduction in average search time on a 130,000 node search.

Date: 10/02/2017
Time: 16:00
Location: LB252