Introduction Recently there has been resurgence of attention in the pos- terior nucleus of hypothalamus (PIH) as the target for the placement of deep brain stimulation (DBS) leads [1–3] to treat trigeminal autonomic cephalalgias (TACs), such as chronic cluster headache (CCH) and short unilateral neu- ralgiform headache with conjunctival injection and tearing (SUNCT). Neuroimaging techniques have shown ipsilater- al posterior inferior hypothalamus activation during CCH and SUNCT attacks [4, 5]. This activity may be specific in these disorders as it is not reported in other painful condi- tions such as migraine. Very scanty information is available on the firing char- acteristics of PIH neurons in humans. Recently, high-fre- quency stimulation was successfully used to treat TACs by implanting stimulating leads into the PIH, ipsilateral to the side of the pain [1, 2, 6]. We thus had the opportunity to perform microrecordings in PIH, and to describe sponta- neous discharge properties of hypothalamic neurons. Methods The study was approved by the institutional review board, and the patients gave written informed consent. The operative techniques were previously reported [1]. Patients enrolled in the study did not take prophylactic drugs for one day before the implantation and remained awake throughout the surgical session. Continuous physiological recordings began as the microelec- trode reached the presumptive coordinates of the target, and were performed by means of a Medtronic Leadpoint system. The response properties of the isolated neurons were obtained with the patients fully awake. In one patient tactile stimulation at the trigeminal ophthalmic branch was performed, and the firing dis- charge recorded. Post-operative data analysis was performed by the Spike2 analysis package (CED, Cambridge, UK). Single unit events were discriminated, and confirmed to arise from a single neuron, Neurol Sci (2007) 28:93–95 DOI 10.1007/s10072-007-0793-1 R. Cordella • F. Carella • M. Leone • A. Franzini • G. Broggi • G. Bussone • A. Albanese Spontaneous neuronal activity of the posterior hypothalamus in trigeminal autonomic cephalalgias ORIGINAL Received: 6 November 2006 / Accepted in revised form: 12 February 2007 Abstract Microrecordings of three neurons were obtained at the target site in three patients with trigeminal autonom- ic cephalalgias who were implanted with deep brain stimu- lators in the posterior hypothalamus. Two patients had chronic cluster headache, one short unilateral neuralgiform headache with conjunctival injection and tearing. Average firing rate was around 24 spikes/s. All neurons were firing randomly, and for most of the recordings in tonic fashion. In one patient, tactile stimulation of the ophthalmic branch, contralateral to the recording site, decreased the firing rate. Neuronal activity in these patients was similar to that reported in animal studies of the posterior hypothalamus. Positioning deep brain stimulators in the posterior hypo- thalamus may offer a tool to better characterise the activity of this part of the brain in humans. Key words Posterior hypothalamus • Pain • Electrophysiology R. Cordella • F. Carella () • M. Leone • A. Franzini • G. Broggi G. Bussone • A. Albanese Fondazione IRCCS Istituto Nazionale Neurologico “C. Besta” Via Celoria 11, I-20133 Milan, Italy e-mail: carella@istituto-besta.it A. Albanese Università Cattolica del Sacro Cuore Milan, Italy