A new potential specifically marks the sensory thalamus in anaesthetised patients.

ABSTRACT

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 (LFPs, 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 ∼3 µV, starting time ∼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 ±â€¯66 Hz, amplitude = 5.2 ±â€¯1.8 µV starting at 17.7 ±â€¯0.5 ms, spanning 3.4 ±â€¯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.