P67. The spectral and spatial profile of high frequency oscillations in the human thalamus

Abstract

Objective To clarify whether high frequency oscillations (HFOs, >150 Hz) exist in the thalamus. So far, HFOs have only been observed in the basal ganglia. Methods Local field potentials from the ventral intermediate nucleus of the thalamus were recorded during implantation of electrodes for deep brain stimulation in 22 patients with different tremor syndromes: Essential Tremor (N = 16), Parkinsonian Tremor (N = 3), Holmes Tremor (N = 2), and Dystonic Tremor (N = 1). Recordings were performed with up to five electrodes featuring both micro- and macroelectrode contacts. These combined micro/macro-electrodes were simultaneously advanced to the predetermined stereotactic target. 11 patients were implanted under local anaesthesia and 11 under general anaesthesia. Results HFOs were found in all investigated tremor syndromes. An in-depth analysis of the Essential Tremor sub-group revealed that medial channels recorded HFOs more frequently than other channels, and that the highest HFO peaks were observed 4 mm above target. Furthermore, macro- and microelectrode channels differed in their sensitivity to HFOs: both detected peaks in the fast HFO range (>300 Hz) but only macroelectrodes additionally detected slow HFO peaks (150–300 Hz), which were stable across several depths and channels. We did not observe significant beta-HFO phase-amplitude coupling or a modulation of HFOs by anaesthesia. Conclusion HFOs exist in the human thalamus and are not specific to any of the tremor syndromes investigated here. Their spatial distribution is focal, and they have a different appearance on micro- and macroelectrodes. Significance Our results tally with converging evidence from other studies demonstrating that HFOs occur in various disorders and subcortical areas. While data from healthy controls are not available, such an unspecific occurrence suggests that HFOs might play a role in normal brain physiology.