2006/2007In the last decade there has been new interest in the posterior nucleus of the hypothalamus (PIH) as the target for the placement of deep brain stimulation to improve pain and psychiatric symptoms. This has brought the possibility to study single-unit acitvity from PIH. Very scanty information is available regarding the firing discharge of human’s PIH neurons. The aim of this study is to describe the firing discharge properties of PIH neurons in neurological and psychiatric disorders. Continuous physiological extracellular recordings were obtained in awake and sedated humans. Firing rate analysis, time domain and frequency domain analyses were used to characterize the firing pattern of PIH neurons. 19 PIH neurons from 7 patients were further studied (5 patients with Trigeminal Autonomic Cephalalgias, 1 aggressive behavior associated with epilepsy, and 1 aggressive behavior associated with head injury). During wakefulness PIH neurons displays tonic firing discharge at around 25Hz, while during sedation the firing rate is 12Hz and the firing pattern more variable. In aggressive behaviour and epilepsy the firing discharge is phasic and rhythmic with oscillations locked at around 7-8Hz. Regular and irregular tonic discharge is noticed in aggressive behaviour and head injury. Spontaneous activity in awake TACs patients is similar to what has been reported in animal models. Interestingly, in aggressive behaviour with epilepsy the observed pattern is bursting and rhythmic at around 7-8Hz. In the patient with head injury no specific pattern is found in PIH neurons. At this stage of knowledge these data are a novelty in the literature, thus it is not possibile to exclude that all these observations represent normal features of PIH neurons. However the differences noticed between pathologies may suggest that PIH neurons discharge rates and patterns are associated to the underlying neurological and psychiatric condition.XX Ciclo197