Dual control of the brainstem on the spindle oscillation in humans

In human subjects, the excitability change of the brainstem was investigated over the course of the spindle oscillation. The investigation was carried out by a sequential analysis of brainstem auditory evoked potentials (BAEPs) with reference to one sequence of spindle oscillation. The method was based on the characteristics of BAEPs, i.e. far-field evoked potential. The brainstem revealed two types of excitability change: one in the lower ventral brainstem (wave-III components), and the other in the upper dorsal brainstem (wave-V components). The excitability in the dorsal brainstem showed an oscillation with one cycle period of about 1.5 s, whereas in the ventral brainstem, the excitability showed a long-range biphasic (decaying-growing) fluctuation. Both excitability changes in the brainstem preceded the spindle oscillation, and the phase was reversed during the emerging period of spindle oscillation. The results suggest a primary triggering mechanism of the brainstem for the spindle oscillation, which is independent of preceding cortical drives (K-complexes) upon the thalamus. The difference of the excitability change between the spindle oscillation and the paroxysmal discharge (spike-and-wave complex) was also discussed.