Fig. 2.

Analogy between phases of matter and our hypothesis for CNS arousal. Upper: Schematic phase diagram for liquid crystals ranging from high temperatures and liquid phase (disordered, “random” molecules on right) to low temperatures and crystalline phase (completely ordered molecules on left). T, temperature. The liquid crystal phase is considered one of the most sensitive phases of matter because of its proximity to a phase transition to the liquid phase. Lower: In the quiescent animal at rest (depicted on right), large numbers of arousal-related neurons (the firing of a typical neuron is illustrated by the vertical lines as a function of time, t) have their rates of firing subject to chaotic dynamics, so that the effects of small perturbations from the arousing stimulus can be amplified selectively and very rapidly. When a movement in response to that stimulus is initiated, cortical and subcortical controls take over, moving the system across the nearby phase transition into the domain of orderly, high rates of firing (depicted on left). The system accrues significant advantages by not only being in the chaotic regime but also because it is poised in the vicinity of a phase transition. Adapted from ref. 34.