Figure 3.

The thalamocortical system and its brainstem connections contain two antagonistic loops: one is responsible for the suppression-burst firing (red insert), and intrathalamic circuit connecting reticular inhibitory nuclei with thalamocortical relay neurons producing spindles and slow waves (sleep network); the other system is the ascending reticular system and thalamic connections (blue) conveying cholinergic arousal influences and inhibiting the reticular nuclei providing tonic thalamocortical neuronal discharge flow (blue upper insert), maintaining wake state. The right lower insert shows the excitatory postsynaptic effect of ascending cholinergic reticular neurons on the thalamocortical relay cell. The left lower insert shows the inhibitory postsynaptic effect of the cholinergic ascending arousal neurons on the thalamic reticular neurons (composed after Steriade [45], and Itier and Bertrand [46]).