Linking motor-related brain potentials and velocity profiles in multi-joint arm reaching movements

Abstract

The study of the movement related brain potentials (MRPBs) needs accurate technical approaches to disentangle the specific patterns of bran activity during the preparation and execution of movements. During the last forty years, synchronizing the electromyographic activation (EMG) of the muscle with electrophysiological recordings (EEG) has been commonly ussed for these purposes. However, new clinical approaches in the study of motor diseases and rehabilitation suggest the demand of new paradigms that might go further into the study of the brain activity associated with the kinematics of movements. As a response to this call, we have used a 3-D hand-tracking system with the aim to record continuously the position of an ultrasonic sender attached to the hand during the performance of multi-joint self-paced movements. We synchronized time-series of position and velocity of the sender with the EEG recordings, obtaining specific patterns of brain activity as a function of the fluctuations of the kinematics during natural movement performance. Additionally, the distribution of the brain activity during the preparation and execution phases of movements was similar that reported previously using the EMG, suggesting the validity of our technique. We claim that this paradigm could be usable in patients because of its simplicity and the potential knowledge that can be extracted from clinical protocols.

Keywords: 3-D movement analyser; kinematics; motor activity; motor related brain potentials; self-paced movement; time-series analysis.

Figure 1

(A) Configuration of the experimental setup. Parcitipants sat in a confortable position in front of a table. An ultrasonic sender was located on the index finger of the active hand. A 3-D movement analyzer recorded the position of the sender during self-paced movements to the target position (red arrow). (B) Time-line of one representative trial. Each picture corresponds to different time points during movement (preparation, achievement of the maximum height and reaching the target). Movements were performed as multi-joint arm reaching through elbow-extensions. (C) Three-dimensional representation of the averaged time series of all movements performed by one representative participant. (D) Projections over the three planes are represented. Continuous black lines correspond to the forward movement, whereas black dashed lines correspond to the backward movement towards the initial position.

Figure 2

Movement-related ERPs (A) and their laplacian-transformed CSD waveforms (B) at the locations C3, C4, and Cz time-locked to the onset of the movement for merged left and right movements. Before merging, electrodes were flipped from one hemisphere to the other for left movements. Below, mean 2-D time series of the trajectory (y-coordinate) of the movement registered with the ultrasound sender (gray). The time series of velocity (black) is represented as the numerical differentiation of the displacement time series. Vertical squares (time-intervals) correspond to different components of the movement-related ERPs that were related with different stages of the movement preparation and execution. Bellow, the topographical distribution of the scalp activity in each of these time-intervals is shown. Warm colors indicate positive activation and cold colors indicate negative activation.

Figure 3

Movement-related ERPs (A) and their laplacian-transformed CSD waveforms (B) at the locations C3, C4, and Cz time-locked to the peak-velocity. Before merging, electrodes were flipped from one hemisphere to the other for left movements. Below, mean 2-D time series of the trajectory (y-coordinate) of the movement registered with the ultrasound sender (gray). The time series of velocity (black) is represented as the numerical differentiation of the displacement time series. Vertical square include the time-interval (centered at the 0) that corresponds to the topographic representation. Warm colors indicate positive activation and cold colors indicate negative activation. To note, there is a clear degree of similarity between the component (−50 to 50 ms) and its distribution than the observed in Figure 2.

Figure 4

Grand average traces of mu (8–13 Hz) ERD/ERS extracted from voltage (A) and CSD-transformed signal (B) for electrodes C3, C4, and Cz time-locked to the onset of the movement. Values are in percentages of the base-line period (−2250 to −2000 ms). Before merging, electrodes were flipped from one hemisphere to the other for left movements. Below, mean 2-D time series of the trajectory (y-coordinate) of the movement registered with the ultrasound sender (gray). The time series of velocity (black) is represented as the numerical differentiation of the displacement time series. Vertical squares (time-intervals) correspond to different components of the ERD/S that were related with different stages of the movement preparation and execution. Bellow, the topographical distribution of the power synchronization and desynchronization is shown. Warm colors indicate increases of synchronization and cold colors indicate increases of desynchronization.

Figure 5

Grand average traces of beta (18–24 Hz) ERD/ERS extracted from voltage (A) and CSD-transformed signal (B) for electrodes C3, C4, and Cz time-locked to the onset of the movement. Values are in percentages of the base-line period (−2250 to −2000 ms). Before merging, electrodes were flipped from one hemisphere to the other for left movements. Below, mean 2-D time series of the trajectory (y-coordinate) of the movement registered with the ultrasound sender (gray). The time series of velocity (black) is represented as the numerical differentiation of the displacement time series. Vertical squares (time-intervals) correspond to different components of the ERD/S that were related with different stages of the movement preparation and execution. Bellow, the topographical distribution of the power synchronization and desynchronization is shown. Warm colors indicate increases of synchronization and cold colors indicate increases of desynchronization.