Natural Frequencies of Human Corticothalamic Circuits

TLDR

Natural frequency of a system can be determined by perturbing it and observing the resulting oscillations, a method applied in physics, geology, and musical tuning. The study aims to demonstrate that natural frequency can be directly measured across cortical areas to serve as a bedside probe of thalamocortical circuit state. The authors used transcranial magnetic stimulation of Brodmann areas 19, 7, and 6 combined with high‑density EEG to record the resulting oscillations. TMS evoked alpha, beta, and fast beta/gamma oscillations in occipital, parietal, and frontal cortex respectively, with each area maintaining its characteristic frequency across intensities and individuals, demonstrating that human corticothalamic modules are tuned to specific rates.

Abstract

The frequency tuning of a system can be directly determined by perturbing it and by observing the rate of the ensuing oscillations, the so called natural frequency. This approach is used, for example, in physics, in geology, and also when one tunes a musical instrument. In the present study, we employ transcranial magnetic stimulation (TMS) to directly perturb a set of selected corticothalamic modules (Brodmann areas 19, 7, and 6) and high-density electroencephalogram to measure their natural frequency. TMS consistently evoked dominant α-band oscillations (8–12 Hz) in the occipital cortex, β-band oscillations (13–20 Hz) in the parietal cortex, and fast β/γ-band oscillations (21–50 Hz) in the frontal cortex. Each cortical area tended to preserve its own natural frequency also when indirectly engaged by TMS through brain connections and when stimulated at different intensities, indicating that the observed oscillations reflect local physiological mechanisms. These findings were reproducible across individuals and represent the first direct characterization of the coarse electrophysiological properties of three associative areas of the human cerebral cortex. Most importantly, they indicate that, in healthy subjects, each corticothalamic module is normally tuned to oscillate at a characteristic rate. The natural frequency can be directly measured in virtually any area of the cerebral cortex and may represent a straightforward and flexible way to probe the state of human thalamocortical circuits at the patient9s bedside.