Since about 1995, a new view of the sensory thalamus and its influence on the cortex has emphasized that thalamocortical (TC) cells are not simple relay neurons whose sole function is to transfer sensory information, without modification, from the animal’s environment to the sensory cortex. Rather, TC cells are now viewed as highly sensitive modifiers of this information that base the nature and degree of their modification upon the state of the organism (Edeline 2003; Winer et al. 2005). The effect of these state changes is brought about by the other indirect non-environmental inputs which make up more than 80% of the synapses impinging on a thalamocortical cell. Equally striking is that some TC cells may not be activated primarily by their direct inputs from the sensory environment but instead may be more strongly driven by the internal environment, that is, by neural sources such as the cerebral and cerebellar cortex that lie outside the ascending sensory pathway (Bender 1983; Diamond et al. 1992; Guillery 1995; Rouiller and Welker 2000). Thus, the information reaching the cortex by the TC system is in a continuous state-dependent flux.