The Brain Stem Reticular Core—An Integrative Matrix

Through the substance of the core of the brain stem runs a continuous column of neurons and fibers known as the reticular formation. This system bridges the gap, both spatially and phylogenetically, between spinal reflexive levels and the great telencephalic tissue masses (cerebral cortices) which apparently represent the most mature expression of neural function. Compared to the latter, the reticular core is archaic both historically and histologically. However, despite the absence of a rigorously stated structural theme and an axial location, sheltered from direct contact with any primary sensory input, the system is now known to exert a remarkable range of control upon the neuraxis and upon the organism as a whole. These functions include: determination of operational modes; gating of all sensory influx; participation at all levels of cortical function, including read out for cortical differentiative and comparative processes; gain manipulation of motor output; multilevel control over most visceral functions; and the active manipulation of a spectrum of states of consciousness from deep coma to maximal vigilance. This panoramic range of activities suggests that the reticular core serves a keystone role in brain function and combines, perhaps in larval form, the prototype of every neural process. If so, it should serve as a convenient paradigm upon which brain system models may be shaped.