A new potential specifically marks the sensory thalamus in anaesthetised patients

Objective: During deep brain stimulation (DBS) surgery, we analysed somatosensory evoked potentials (SSEPs) using microelectrode recordings (MERs) in patients under general anaesthesia. Methods: We obtained MERs from 5 patients with refractory epilepsy. Off-line analysis isolated local field potentials (LFFs, 2-200 Hz) and high frequency components (HFCs, 0.5-5 kHz). Trajectories were reconstructed off-line. Results: The ventral caudate (V.c.) nucleus was most frequently recorded from (171 mm). Very high frequency oscillations (VHFOs) were recorded up to 8 mm in length from all 4 electrodes but were most frequently recorded from the V.c. The properties of VHFOs were similar among all nuclei (frequency >1500 Hz, amplitude similar to 3 mu V, starting time similar to 14 ms, duration 8-9 ms). Consecutive recordings did not show any synchronization or propagation, but a new kind of potential (high frequency oscillation, HFO) appeared abruptly inside the V.c. (frequency = 848 +/- 66 Hz, amplitude = 5.2 +/- 1.8 mu V starting at 17.7 +/- 0.5 ms, spanning 3.4 +/- 0.3 ms). Conclusions: VHFOs are widely extending and cannot be ascribed to the V.c. HFOs in patients under general anaesthesia can serve as a landmark to identify the V.c. in thalamic DBS surgery. Significance: Thalamic processing involves nuclei other than the V.c, and HFO can be used to improve DBS surgery. (C) 2019 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.