Partial cortical deafferentation in vivo induces an increase in intrinsic excitability that leads to seizures (Topolnik et al., 2001 SFN abstract). Immediately after the cortical undercut activity was reduced, but 2-3 hours later the intrinsic excitability of cortical neurons was enhanced, which contributed to the generation of paroxysmal discharges. In vitro evidence suggests that chronic deafferentation may induce changes in the intrinsic excitability of neurons and synaptic efficacy. Chronic blockade of activity in cultured cortical neurons results in increased Na+ and decreased K+ conductances (Desai et al., 1999) and increased efficiency of excitatory synapses between pyramidal cells (Turrigiano et al., 1998). We explored the consequences of increased excitability in computational models of neocortex including pyramidal cells (PY) and interneurons (IN). In the active state PY cells fired asynchronous spike trains. Abolition of excitatory inputs to a region of the network strongly reduced activity in t...