Neural Networks 22 (2009) 1037–1038 Contents lists available at ScienceDirect Neural Networks journal homepage: www.elsevier.com/locate/neunet 2009 Special Issue Microcircuits — Their structure, dynamics and role for brain function Vassilis Cutsuridis a,* , Thomas Wennekers d , Bruce P. Graham a , Imre Vida b , John G. Taylor c a Department of Computing Science and Mathematics, University of Stirling, Stirling FK9 4LA, UK b Division of Neuroscience and Biomedical Systems, IBLS University of Glasgow West, Medical Building Glasgow, G12 8QQ, UK c Department of Mathematics, Centre for Neural Networks, King’s College London, London, UK d Centre for Theoretical and Computational Neuroscience, University of Plymouth, Plymouth, UK Microcircuits have been characterised as functional modules that act as elementary processing units bridging single cells and systems levels (Grillner & Graybiel, 2006). The brain, from the neocortex to the spinal cord, consists of various microcircuits, each serving specific functions. Examples of such functional modules include cortical columns of the sensory cortices, glomeruli in the olfactory systems, networks for the storage and recall of memories in the hippocampus and the prefrontal cortex, and neuronal circuits generating different aspects of motor behaviour. Understanding how neurons in microcircuits interact is one of the most fundamental questions in the neurosciences today. The goal of the current special issue is to provide a snapshot and a resumé of the current state-of-the-art of ongoing experimental and computational research on design principles and computational functions of various cortical microcircuits. Tiesinga and Buia start this special issue by introducing a computational model based on the biased competition framework in order to explore the relation between V1 and V4 receptive field properties in spatial attention tasks. A number of simulations is performed that cast light on the circuits underlying stimulus selection and suppression. Results are consistent with general ideas behind biased competition, but the present work nicely demonstrates response properties for various stimulus conditions in a single network. The network also displayed a transition from more global alpha oscillations without stimuli to more localized beta/gamma range oscillations in the presence of stimuli. Schrader, Gewaltig, Koerner and Koerner present a hierarchical spiking neuron model of the ventral pathway for pattern recognition. They propose that a first wave of spikes after stimulus presentation causes a (small) number of candidate representations to be formed quickly in the top-level of the hierarchy which become confined in a subsequent recurrent phase of processing that makes use of feedback for the disambiguation at different levels. Binzegger, Douglas and Martin study the influence of neu- roanatomical connectivity on information processing in a canon- ical cortical microcircuit of cat primary visual cortex. The laminar connectivity matrix indicate that the cortical circuit is dominated * Corresponding editor. Tel.: +44 1786 467422; fax: +44 1786 464551. E-mail address: vcu@cs.stir.ac.uk (V. Cutsuridis). by strong recurrent connections within superficial layers in con- trast to deep layer structures where cells are connected more to neurons in other layers. A simple artificial linear-threshold neuron model is used to simulate and study the stability of the circuit dynamics. The simulations indicate that the recurrent con- nections in layer 2/3 dominate the circuit dynamics and move them close to the unstable regime. Stability is achieved by strong inhibition, which controls and reduces the dominance of excitatory feedback. In this simplified framework, the topology of the circuit is reconfigured dynamically by modifying the average inhibition threshold of the neurons. As the circuit becomes more active, the average inhibition becomes stronger and prunes the week connec- tions. This shifts the network from a more random topology to a more clustered small-world-like configuration. Symes and Wennekers investigate the inderdependence of local and long range connections in layer 2/3 in primary visual cortex. Their population mean field model demonstrates that the precise spatiotemporal spread of activity seen in the cortical slice results from long-range connections that target specific orientation domains while distinct regions of suppressed activity are shown to arise from local isotropic axonal projections. Distal excitatory activity resulting from long range axons is shaped by local interneurons similarly targeted by such connections. It is shown that response latencies of distal excitation are strongly influenced by frequency dependent facilitation and low threshold inhibition. Friston and Kiebel present a theoretical paper aiming at modelling perception in cortical circuits from a general point of view of Bayesian modelling and the free-energy principle. An application of their approach to song generation and recognition in song-birds is also presented. Maex and Steuber provide a very nice review of neural mechanisms underpinning retention of memory traces for periods of time from milliseconds to tens of seconds. The review is wide- ranging, providing snapshots of diverse mechanisms in different brain areas. Hajos and Paulsen offer an excellent overview of microcircuit mechanisms of cortical gamma-frequency oscillations. Focusing on experimental data obtained in an in vitro model, the authors re- view discharge pattern and synaptic interactions of various neu- ron types of the hippocampal CA3 area during gamma activity. The authors conclude that reciprocal interaction between excitatory 0893-6080/$ – see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.neunet.2009.07.006