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Dense gap-junction connections support dynamic Turing structures in the cortex
BMC Neuroscience volume 8, Article number: S2 (2007)
The recent report by Fukuda et al  provides convincing evidence for dense gap-junction connectivity between inhibitory neurons in the cat visual cortex, each neuron making 60 +/- 12 gap-junction dendritic connections with neurons in both the same and adjoining orientation columns. These resistive connections provide a source of diffusive current to the receiving neuron, supplementing the chemical-synaptic currents generated by incoming action-potential spike activity. Fukuda et al describe how the gap junctions form a dense and homogeneous electrical coupling of interneurons, and propose that this diffusion-coupled network provides the substrate for synchronization of neuronal populations.
To date, large-scale population-based mathematical models of the cortex have ignored diffusive communication between neurons. Here we augment a well-established mean-field cortical model  by incorporating gap-junction-mediated diffusion currents, and we investigate the implications of strong diffusive coupling. The significant result is the model prediction that the 2D cortex can spontaneously generate centimetre-scale Turing structures (spatial patterns), in which regions of high-firing activity are intermixed with regions of low-firing activity (see Fig. 1). Since coupling strength decreases with increases in firing rate, these patterns are expected to exchange contrast on a slow time-scale, with low-firing patches increasing their activity at the expense of high-firing patches. These theoretical predictions are consistent with the slowly fluctuating large-scale brain-activity images detected from the BOLD (blood oxygen-level-dependent) signal .
Kosaka T, Singer W, Galuske RAW: Gap junctions among dendrites of cortical GABAergic neurons establish a dense and widespread intercolumnar network. J Neurosci. 2006, 26: 3434-3443. 10.1523/JNEUROSCI.4076-05.2006.
Steyn-Ross DA, Steyn-Ross ML, Sleigh JW, Wilson MT, Gillies IP, Wright JJ: The sleep cycle modelled as a cortical phase transition. J Biol Phys. 2005, 31: 547-569. 10.1007/s10867-005-1285-2.
Fox MD, Snyder AZ, Vincent JL, Corbetta M, van Essen DC, Raichle ME: The human brain is intrinsically organized into dynamic, anticorrelated functional networks. Proc Nat Acad Sci USA. 102: 9673-9678. 10.1073/pnas.0504136102.
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Steyn-Ross, D.A., Steyn-Ross, M., Wilson, M. et al. Dense gap-junction connections support dynamic Turing structures in the cortex. BMC Neurosci 8, S2 (2007) doi:10.1186/1471-2202-8-S2-S2
- Diffusive Coupling
- Inhibitory Neuron
- Electrical Coupling
- Cortical Model
- Orientation Column