Control Pathways from the Subcortical Limbic Structures to the Trigeminal Motor System in the Lower Brainstem: A Hodological Review

The organization of the emotion-related somatic motor behavior, including jaw movements, is governed not only by the cortical limbic system but also by the subcortical limbic system including the amygdala and hypothalamus. GABAergic neurons in the central amygdaloid nucleus (CeA) and glutamatergic neurons in the posterior lateral hypothalamus (PLH) exert inhibitory and excitatory influences, respectively, upon premotor neurons for the motor trigeminal nucleus (Vm) in the parvicellular reticular formation (RFp) of the medulla oblongata. The CeA also has an inhibitory influence on non-dopaminergic (probably GABAergic) neurons in the retrorubral field of the midbrain that send their axons to the RFp. Furthermore, the CeA and lateral hypothalamus including the PLH may also modulate Vm neurons via projections to the mesencephalic trigeminal nucleus which contains the cell bodies of primary afferent neurons conveying inputs from the masticatory muscle spindles or the periodontal ligament receptors to jaw closing motoneurons within the Vm. These pathways from the subcortical limbic structures to the trigeminal motor system in the lower brainstem underlie the regulation of emotional jaw movements.