A theoretical framework for CNS arousal

Rapid changes of state in central nervous systems (CNS), as required following stimuli that must arouse the CNS from a quiescent state in order to activate a behavioral response, constitute a particularly appropriate application of non-linear dynamics. Chaotic dynamics would provide tremendous amplification of neuronal activity needed for CNS arousal, sensitively dependent on the initial state of the CNS. This theoretical approach is attractive because it supposes dynamics that are deterministic and it links the elegant mathematics of chaos to the conception of a fundamental property of the CNS. However, a living system must be able to exit from chaotic dynamics in order to avoid widely divergent, biologically impossible outcomes. We hypothesize that, analogous to phase transitions in a liquid crystal, CNS arousal systems, having 'woken up the brain' to activate behavior, go through a phase transition and emerge under the control of orderly movement control systems.