Some Mechanisms for a Theory of the Reticular Formation

Throughout the life of the vertebrates, the core of the central nervous system, sometimes called the reticular formation, has retained the power to commit the whole animal to one mode of behavior rather than another. Its anatomy, or wiring diagram, is fairly well known, but to date no theory of its circuit action has been proposed that could possibly account for its known performance. Its basic structure is that of a string of similar modules, wide but shallow in computation everywhere, and connected not merely from module to adjacent module, but by long jumpers between distant modules. Analysis of its circuit actions heretofore proposed in terms of finite automata or coupled nonlinear oscillators has failed. We propose a radical set of nonlinear, probabilistic hybrid computer concepts as guidelines for specifying the operational schemata of the above modules. Using the smallest numbers and greatest simplifications possible, we arrive at a reticular formation concept consisting of 12 anastomatically coupled modules stacked in columnar array. A simulation test of its behavior shows that despite its 800-line complexity, it still behaves as an integral unit, rolling over from stable mode to stable mode according to abductive logical principles, and as directed by its succession of input 60-tuples. Our concept employs the following design strategies: modular focusing of input information; modular decoupling under input changes; modular redundancy of potential command (modules having the most information have the most authority); and recruitment and inhibition around reverberatory loops. Presently we are augmenting these strategies to enable our model to condition, habituate, generalize, discriminate, predict, and generally follow a changing environment. Our program is epistemological. We are trying to develop reticular formation concepts which are complex, precise, and valid enough to inspire reasonable experiments on the functional organization of this progenitor of all vertebrate central nervous tissues.