Neurophysiological Characterization of Posteromedial Hypothalamus in Anaesthetized Patients

Abstract

Deep brain stimulation (DBS) requires a precise localization, which is especially difficult at the hypothalamus, because it is usually performed in anesthetized patients. We aimed to characterize the neurophysiological properties posteromedial hypothalamus (PMH), identified by the best neurophysiological response to electrical stimulation. We obtained microelectrode recordings from four patients with intractable aggressivity operated under general anesthesia. We pooled data from 1.5 mm at PMH, 1.5 mm upper (uPMH) and 1.5 mm lower (lPMH). We analyzed 178 units, characterized by the mean action potential (mAP). Only 11% were negative. We identified the next types of units: P1N1 (30.9%), N1P1N2 (29.8%), P1P2N1 (16.3%), N1P1 and N1N2P1 (6.2%) and P1N1P2 (5.0%). Besides, atypical action potentials (amAP) were recorded in 11.8%. PMH was highly different in cell composition from uPMH and lPMH, exhibiting also a higher percentage of amAP. Different kinds of cells shared similar features for the three hypothalamic regions. Although features for discharge pattern did not show region specificity, the probability mass function of inter-spike interval were different for all the three regions. Comparison of the same kind of mAP with thalamic neurons previously published demonstrate that most of cells are different for derivatives, amplitude and/or duration of repolarization and depolarization phases and also for the first phase, demonstrating a highly specificity for both brain centers. Therefore, the different properties described for PMH can be used to positively refine targeting, even under general anesthesia. Besides, we describe by first time the presence of atypical extracellular action potentials.

Atypical Extracellular Action Potentials from Posteromedial Hypothalamus in Anesthetized Humans

“…Recently, it has been shown that the types of mAPs in the hypothalamus are similar to those described in the thalamus [19,20], with the majority of cells showing three phases. Despite the similar morphology in both brain structures, the properties of the mAPs were different, showing that mAP morphology is region specific.…”

“…Despite the similar morphology in both brain structures, the properties of the mAPs were different, showing that mAP morphology is region specific. However, in the thalamus, we did not record the amAPs that were recorded in the hypothalamus [20]. This fact adds another element of regional specificity regarding the structure of action potentials.…”

“…We more deeply analysed the structure of the mAPs, defined as the arrangement of the components composing each of the waveforms [20]. Excluding atypical mAPs (amAPs), most of the mAPs were positive, 260/295 (81.1%), and fewer were negative, 25/290 (19.9%).…”

“…Most brain regions used for DBS have been described in terms of discharge patterns [9][10][11][12][13][14][15][16], but less attention has been devoted to the analysis of extracellular action potentials (EAPs), with the exception of the pedunculopontine nucleus [17,18] in a very limited way and some nuclei in the thalamus [19] and hypothalamus [20].…”

“…Descriptions of discharge patterns have been recently provided [21]. However, it have been described, for the first time, features of EAPs from the posteromedial hypothalamus (PMH) and adjacent regions [20]. In that work, it was described for the first time a type of cell with a highly anomalous EAP morphology, which was referred to as atypical (i.e., atypical mean action potential or amAP).…”