Functional cortical localization of tongue movements using corticokinematic coherence with a deep learning-assisted motion capture system

Abstract

Corticokinematic coherence (CKC) between magnetoencephalographic and movement signals using an accelerometer is useful for the functional localization of the primary sensorimotor cortex (SM1). However, it is difficult to determine the tongue CKC because an accelerometer yields excessive magnetic artifacts. Here, we introduce a novel approach for measuring the tongue CKC using a deep learning-assisted motion capture system with videography, and compare it with an accelerometer in a control task measuring finger movement. Twelve healthy volunteers performed rhythmical side-to-side tongue movements in the whole-head magnetoencephalographic system, which were simultaneously recorded using a video camera and examined using a deep learning-assisted motion capture system. In the control task, right finger CKC measurements were simultaneously evaluated via motion capture and an accelerometer. The right finger CKC with motion capture was significant at the movement frequency peaks or its harmonics over the contralateral hemisphere; the motion-captured CKC was 84.9% similar to that with the accelerometer. The tongue CKC was significant at the movement frequency peaks or its harmonics over both hemispheres. The CKC sources of the tongue were considerably lateral and inferior to those of the finger. Thus, the CKC with deep learning-assisted motion capture can evaluate the functional localization of the tongue SM1.

Figure 1

(A) Raw data of movement signals obtained through motion capture and an accelerometer (ACC), and magnetoencephalographic (MEG) signal from the contralateral (left) Rolandic sensor for the right finger movement condition of a single participant (Subject 2). Cyclical rhythms are observed at a specific frequency band of finger movements using both the motion capture and ACC. (B) Power spectra of movement signals obtained through motion capture and the ACC for the right finger movement condition of a single participant (Subject 2). The scale of the x-axis is 10 Hz. Note that the peak frequency occurs in the same frequency band of finger movement, i.e., at 3.3 Hz, in both the motion capture and ACC results (indicated by arrows). (C) Corticokinematic coherence (CKC) waveform from a representative channel over the contralateral hemisphere for the right finger movement condition of a single participant (Subject 2) using motion capture and the ACC. The scale of the x-axis is 10 Hz. The horizontal dashed line indicates a significance level of 99%. The CKC peak is observed at 7.0 Hz in the motion capture (CKC value: 0.61) and ACC (CKC value: 0.60) results around the harmonic frequency band of the finger movements.

Figure 2

(A)[1,2] Corticokinematic coherence (CKC) waveform for the tongue from a representative channel over the left [1] and right [2] hemispheres of a single participant (subject 1). The scale of the x-axis is 10 Hz. The horizontal dashed line indicates a significance level of 99%. The CKC peak is observed at 3.3 Hz in the left hemisphere (CKC value: 0.43) and right hemisphere (CKC value: 0.46). [3–5] Spatial distribution of the 1-s-long cross-correlogram for the tongue of a single participant (subject 1). The largest peaks of the cross-correlogram occurred in the Rolandic sensors of the left [4] and right [5] hemispheres for the tongue CKC. B. Isocontour maps and dipole locations for the tongue (B) and finger (C) of Subject 1. The time points that showed the cross-correlation peaks were used to obtain the contour map. The incoming and outgoing magnetic fluxes are denoted by the blue and red lines, respectively (B[1],C[1]). The green arrows denote the directions and locations of the equivalent current dipoles (ECDs), which were projected onto the surface of the skull. The arrowheads indicate the negative poles of the ECDs. The ECDs (blue dots) of the tongue (B[2]) and finger (C(2]) are superimposed on magnetic resonance image slices of the participant. The directions of the blue lines represent the negative poles of the ECDs. Both ECDs are located at the central sulcus (B[2],C[2]). The locations of the ECDs of the tongue are estimated to be more lateral, anterior, and inferior to those of the finger. Lt left side.

Figure 3

Average locations of the ECDs of the tongue and finger CKCs on the x-, y-, and z-axes, considering all participants. The data points represent the means ± SEM values. The locations of the ECDs of the tongue are considerably lateral and inferior to those of the finger. The x-axis intersects the preauricular points from left to right; the y-axis passes through the nasion; the z-axis is perpendicular to the plane determined by the x- and y-axes. Asterisks indicate statistically significant differences (p < 0.0167).