Neural Networks 31 (2012) 46–52 Contents lists available at SciVerse ScienceDirect Neural Networks journal homepage: www.elsevier.com/locate/neunet Spontaneous organization of the cortical structure through endogenous neural firing and gap junction transmission Myoung Won Cho a,∗ , M.Y. Choi b a Department of Global Medical Science, Sungshin Women’s University, Seoul 142-732, Republic of Korea b Department of Physics and Center for Theoretical Physics, Seoul National University, Seoul 151-747, Republic of Korea article info Article history: Received 4 February 2011 Received in revised form 15 February 2012 Accepted 2 March 2012 Keywords: Neural network learning Spike-timing-dependent plasticity Gap junction transmission abstract We explore the effects of gap junctions, direct neural transmission between adjacent cells, on activity- dependent network formation. It is found that endogenous neural activities and weak firing correlations via gap junctions can regulate elaborately both the topographic structure in vertical connections and the radial structure in horizontal connections. Provided that pre-establishment of the lateral connection structure is required for the postnatal cortical map organization and genetic factors cannot perform such detailed regulation of synaptic connections, neural interactions via gap junctions could play an indispensable role in the brain development. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction While the major neural transmission in a vertebrate nervous system arises via flexible synapses based on axon conduction and chemical substances, gap junctions provide another type of transmission involving electrical ions. Direct diffusion of ions through these junctions allows the action potential to be transmitted without appreciable delay or distortion between adjacent neurons. There is abundant experimental evidence for gap junction couplings between inhibitory neurons, but a few instances for those between excitatory neurons (Fukuda, Kosaka, & Galuske, 2006; Galarreta & Hestrin, 1999; Gibson, Beierlein, & Conners, 1999; Hughes et al., 2004; Schmitz et al., 2001; Tamás, Buhl, Lörincz, & Somogyi, 2000; Traub, Michelson-Law, Bibbig, Buhl, & Whittington, 2004). Effects of electrical couplings on neural dynamics were investigated in networks with and without inhibitory couplings (Ermentrout, 2006; Koppel & Ermentrout, 2004; Li, Wang, & Hu, 2007; Rabinovich, Huerta, Bazhenov, Kozlov, & Abarbanel, 1998; Schmitz et al., 2001; Steyn-Ross, Steyn-Ross, & Sleigh, 2007), or with glia cells (Alvarez-Maubecin, García-Hernández, Williams, & Bockstaele, 2000; Nadarajah, Thomaidou, Evans, & Pamavelas, 1996). An important role of electrical couplings is to encourage the degree of synchronization between inhibitory neurons (Beierlein, Gibson, & Connors, 2000; Ermentrout, 2006; Galarreta & Hestrin, 1999; Gibson et al., 1999; Koppel & Ermentrout, 2004; Tamás et al., 2000; Traub et al., 2001). ∗ Corresponding author. Tel.: +82 2 958 3808; fax: +82 2 958 3870. E-mail addresses: mwcho@sungshin.ac.kr (M.W. Cho), mychoi@snu.ac.kr (M.Y. Choi). It is suggested that gap junctions may serve as the background activity to engage inhibitory oscillatory networks responsible for gamma rhythms, or generate very fast EEG oscillations preceding the onset of, and perhaps initiating, seizures (Traub et al., 2004). Gap junction coupling between excitatory cells can provide very fast electrical communications between neurons (Schmitz et al., 2001), or lead to the death of network activity (Ermentrout, 2006). In learning problems the effects of gap junctions are used to be disregarded because of their short interaction range and low flexibility. Nevertheless, gap junctions can play an important role during early brain development because gap junction transmission is fundamentally based on geometrical linkages, in contrast with synaptic transmission via (near) topological linkages. Related with the origin of early brain development, one of the most important issues in neuroscience, there have been a large number of debates on the effects of genetic and dynamic factors in the development process. It is usually assumed that early development of the ordered synaptic structure before birth is guided mostly by genetic factors although the structure would be reorganized after birth, depending on external environmental factors. Remarkable events of the early brain development involve orderly migration of billions of neurons, growth of their axons, and formation of thousands of synapses between individual axons and their target neurons. The migration and growth of neurons are dependent, at least in part, on chemical and physical influences. Growing tips of axons apparently recognize and respond to various molecular signals, which guide axons and nerve branches to their appropriate targets and eliminate those aiming at inappropriate targets (Dudek & Bear, 1989; Goodman & Shatz, 1993; Mcconnell, 1995). Nevertheless, there are several problems in the early brain development scenario led only by genetic factors. Even though 0893-6080/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.neunet.2012.03.002