The understanding of neuronal mechanisms underlying different states of sleep and epilepsy requires a detailed exposé of various neuronal types and networks in the major brain structures that generate these behavioral conditions, that is, neocortex, archicortex and related systems (rhinal cortices and amygdala), thalamus, and generalized systems that modulate the excitability of forebrain structures. Despite the innumerable neurons located in these structures and their diverse temporal patterns of repetitive firing, unifying principles can group individual neurons into a limited number of classes. This chapter deals with neuronal types and with local and distant connections among neurons, placing emphasis on peculiar neuronal features that may play a role in certain aspects of sleep and seizures.

One of the conclusions resulting from data presented in this chapter is that synaptic activities within complex neuronal networks modulate, and often overwhelm, intrinsic neuronal properties. In the absence of rich synaptic activity, as is the case in brain slices and isolated cortical slabs in vivo, neuronal properties mainly result from a host of voltage-dependent and transmitter-gated conductances. Analyses of the same neuronal types in the intact brain, under anesthesia and especially in naturally alert preparations, demonstrate that intrinsic neuronal properties display dramatic alterations with changes in membrane potential and increased synaptic activity during behavioral states.

The intrinsic properties of cortical and thalamic neurons were first revealed in brain slices.