A model of the electrocortical effects of general anaesthesia.

In an attempt to describe how reduction in synaptic efficiency by general anaesthetic agents results in loss of consciousness, we examined the behaviour of a two-dimensional (a lattice of 80 x 80 cellular elements) cellular automaton (CA) computer model as the connectivity between cellular elements was altered. The lattice was taken to represent cortical elements with variable connectivity to their neighbours. The summation of the active elements of the CA lattice was taken to represent a simulated "EEG" signal. If cellular automation elements had a high probability of connectivity, the simulated EEG showed high frequency predominance and low amplitudes, similar to the desynchronized pattern in an alert person. As connectivity was decreased, median frequency in the simulated EEG decreased and amplitude increased, similar to that in anaesthetized patients. As in our model, we believe it is possible that the human central nervous system in the conscious resting state exists above a critical threshold of synaptic efficiency; awareness is associated with an increase in synaptic efficiency and anaesthesia with a decrease that sharply reduces cortical information transfer.