Involvement of the trigeminal motor system in brain stem self-stimulation and stimulation-induced behavior

Anatomical and behavioral correlates of intracranial self-stimulation (ICSS) at sites in the pons suggest the involvement of the trigeminal motor system in brain stimulation reward. 90% of the electrodes terminating in or dorsal to the trigeminal motor nucleus supported ICSS. Stimulation through these ICSS electrodes was usually accompanied by a display of repetitive jaw movement in the period following brain stimulation. There appeared to be a close relation between post-stimulation jaw movement and ICSS. In the motor nucleus there was a positive linear relationship between current intensity and duration of jaw movement. Optimal current intensities for ICSS induced long periods of jaw movement. Extensive lesions of the dorsal pons which included the locus ceruleus had no effect on ICSS in the trigeminal motor system. Therefore it seems unlikely that ICSS in the trigeminal system is mediated by noradrenergic neurons located in the dorsal pontine area. These data suggest that a centripetal analysis of ICSS sites along pathways afferent to the trigeminal motor system may lead to a more complete description of the anatomical correlates of brain stimulation reward. The functional implications of a trigeminal reinforcement mechanism are discussed.