Tongue as a Wire? Glossokinetic Artifact and Insights From Intracranial EEG

Glossokinetic artifact (GKA) is a well-known scalp EEG artifact characterized by deflections within the delta to low-theta frequency bands and dynamic polarity typically attributed to the direction of tongue movement. This study aims to investigate intracranial EEG correlations of scalp-GKA. If the tongue is a dipole, per the conventional view, then volume-conducted deflections are expected in the nearest frontal intracranial EEG contacts.

Simultaneous scalp and intracranial EEG recordings were evaluated in five consecutive medically resistant epilepsy patients at Yale Epilepsy Center in 2017 and 2018, who had classic GKA deflections on scalp EEG. The EEG was sampled at 2,048 to 4,096 Hz and analyzed visually, using a reference placed in the diploic space or over the convexity, and confirmed quantitatively by a statistical framework. Ten GKA deflections were analyzed per case.

The medians of age at the time of recording, contacts per case, and amplitude of scalp GKA deflections were 35 years (range: 20-41 years), 171 contacts (range: 165-241 contacts), and 56 μV (range: 51-72 μV), respectively. There were no slow discharges in the frontal intracranial EEG contacts synchronized with the scalp GKA, either in the delta (1-3 Hz) or in the sub-delta (0.1-1 Hz) bands. However, the expected physiologic attenuation of alpha and beta rhythms and the emergence of high-gamma activity were observed over the peri-Rolandic regions in the invasive recordings.

The traditional view of the tongue as a dipole generator of scalp GKA is simplistic and does not account for the findings reported herein. The tongue most probably shunts other scalp and soft-tissue currents. Knowledge of tongue potentials is of interest in the education and the design of tongue-computer interfaces.