Neuronal connectivity within the mammalian brain is extensive and complex. The use of dissociated cultured neurons is valuable for investigating the cell biology of neurons and synapses, providing a relatively homogeneous population of neurons, reducing the complex three-dimensional connectivity of brain tissue to two-dimensions, and facilitating access to neurons both visually and pharmacologically. Similar to synapses in vivo, synapses in vitro are functional and can undergo various forms of synaptic plasticity. Unfortunately, the process of dissociating neurons eliminates much of the native circuitry, resulting in a disordered connectivity of neurons. To improve the organization of cultured neurons and their connections, several groups have endeavored to actively polarize cortical/hippocampal neurons using chemically patterned surfaces (Scholl et al., 2000; Stenger et al., 1998; Vogt et al., 2004; Vogt et al., 2005), soluble gradients (Dertinger et al., 2002), or physical structures that guide neuronal growth (Taylor et al., 2005; Taylor et al., 2003; Tooker et al., 2006; Tooker et al., 2004). One of the goals of these approaches is to organize cultured neurons in such a way that they more closely mimic the connectivity found in vivo, enabling them to be studied in a more physiological manner.
