EP 67. Charakterization of thalamic nuclei and somatosensory evoked potentials in anesthetized humans

Abstract

Question The centro-median thalamic nucleus (Ce) must be correctly identified for deep brain stimulation (DBS). We have analysed the properties of Ce and surrounding nuclei in anaesthetized humans. Methods We recorded with microelectrodes in 6 patients bilaterally operated for intractable epilepsy, starting 10 mm from the target (coordinates x = 8, y = −10, z = 0 mm). The ventro-caudal thalamic nucleus (V.c.) is defined by the presence of somato-sensory evoked potentials recorded through microelectrodes (SSEPm). Then, the real trajectory through the thalamus is reconstructed considering the depth where SSEPm were obtained. We have analysed these properties: density (number of units), amplitude (μV), duration at the half amplitude (μs), maximum and minimum value of first derivative (Dmax/Dmin, V/s) and frequency (Hz) from fasciculoso medial/lamina medialis (Mf) c/lm, Zentro-oralis (Z.o.e/Z.o.i), Ventral oralis posterior (V.o.p), V.c, Ventralis intermedius (V.im.i), Ce magnocelullar (Ce.mc) and parvocellular (Ce.pc). Results SSEPm (see below for its definition) were obtained only in 4 trajectories from 3 patients, from which we have obtained all the results. The properties of spikes from different nuclei are shown in the next table. In relation to SSEP, we have obtained two kind of responses: i) low amplitude ( 1300 Hz, termed HFO) and ii) High Amplitude (>25 μV) and lowest frequency ( Conclusions (1) It’s easy differentiate between cells from Ce and the other surrounding thalamic nuclei by the properties of its action potentials. (2) However, it’s not so easy to discriminate the Ce.mc and Ce.pc. (3) SSEPm (HAO) are extremely valuable in the identification of the somato-sensory part of thalamus. (4) However, they are very restricted spatially and not always can be recorded during the trajectory. (5) SSEPm must be differentiated from HFO which are broader represented in several nuclei, unlike than V.c.