Personality Trait Aggression Influences The Second Exteroceptive Suppression Of Temporalis Muscle Activity.

Background and objective: The etiological mechanisms underlying aggression are complex and multifaceted. Neurobiological perspective of aggression operate on the assumption that certain physiological processes within the organism contribute to aggressive behavior. In human, a painful stimulation applied in the trigeminal territory induces relative or absolute suppressions of voluntary in jaw-closing muscle activities, called "exteroceptive suppressions", "silent periods", or "inhibitory reflexes", the first of which is used to avoid confusion with the proprioceptive silent periods of peripheral limb muscles. An early (ES1) and a late (ES2) exteroceptive suppressions of the temporalis of masseter muscle have been extensively studied in healthy volunteers. ES1 is assumed to be pontine di- or oligosynaptic reflex, ES2 is mediated polysynaptically by inhibitory interneurons probably located in the lateral tegmental field of the brainstem next to the trigeminal nucleus caudalis. The ES2 interneurons receive the descending control from limbic brain areas. The midbrain peraqueductal gray matter (PAG), and nucleus raphe magnus (NRM) in the lower brainstem, which are normally the source in the CNS of powerful modulation of trigeminal somatosensory trasmission, might be involved in the modulation of descending control. On the other hand, the transcranial electrical and magnetic stimulation studies indicate that the exteroceptive suppressions are also influenced by the inhibitory function of cortical of subcortical structures. From the neurobiological aspect, the inhibitory brainstem interneurons mediating ES2 receive strong input from limbic pathways, some of which are serotonergic. Besides anxiety, the aggression is also linked with...