Beta-Band Power Modulation in the Human Insula during a Direct Arm-Reaching Task

Introduction: The insula is a cortical structure that is mostly known for its role in viscerosomatic processing and higher-level cognition. A growing body of evidence has additionally implicated the insula in voluntary motor function, although its exact role remains unclear. In this study, we aim to characterize the role of the insula in motor function by measuring beta-band power modulation during a direct arm-reaching task.

Methods: 10 participants diagnosed with medication-resistant epilepsy were implanted with stereoelectroencephalographic (SEEG) electrodes in the insula (1 left, 7 right, 2 bilateral) for seizure localization. Local field potentials from SEEG were recorded during the Fixation and Response (movement execution) phases of a direct arm-reaching task with the right hand. Beta-band power (13-30 Hz) was compared between the Fixation and Response phases using a non-parametric cluster-based permutation test (N=1,000) with a significant p-value of < 0.05.

Results: 8 out of 10 participants (80%) showed statistically significant beta-band power modulation in the Response phase compared to Fixation phase. On an individual level, 4 participants (40%) showed decreases and 3 (30%) showed increases in beta-band power. One participant (10%) had increase in the anterior and a decrease in the posterior insula with respect to beta power. Regarding laterality, 2 out of 3 left-sided implants (66.7%) showed decreased beta-band power, while 10 out of 12 right-sided implants (83.3%) showed beta-band modulation (6 out of 10 with decreased power). 7 out of 8 anterior implants (87.5%) showed beta-band modulation (6 out of 7 with increased power), and 6 out of 7 (85.7%) posterior implants had modulation (5 out of 7 with decreased power).

Conclusion : This study demonstrates significant beta-band modulation in the insula during arm-reaching movements in the Response phase of the task. This finding suggests that the insula plays a role in voluntary motor execution.