All participants involved in experimentation undergo informed consent procedures approved by the West Virginia University Institutional Review Board (IRB).
1. Overall System Characteristics, Design, and General Experimental Task
Note: The complete setup is comprised of the following major components: EMG equipment and associated digital acquisition (DAQ) equipment; a motion capture system (this protocol incorporates an active LED system); a TMS unit with a figure-of-eight coil and stereotaxic localization equipment; a VR headset and associated computer and software; and a custom synchronization circuit. Figure 1 schematically outlines the connectivity between the protocol components.
Figure 1: Connectivity of entire setup. This layout describes the general connectivity between the elements of our system. The synchronization circuit is described elsewhere in the text in more detail. The blue trace corresponds to the signal that starts both motion capture and EMG data streams. This event is the source of the temporal delay of up to 190 msec using the equipment described in this protocol. The red trace corresponds to the VR-initiated synchronization event that is concomitantly recorded by the motion capture and EMG systems and subsequently used for temporal alignment of the respective data streams. Please click here to view a larger version of this figure.
2. General Details of System Integration and Synchronization
Note: Synchronization of the separate data acquisition systems in this protocol (motion capture and EMG) is accomplished through the use of an event signal that is common to all recording streams. Using a common event, all of the signals can be temporally realigned after data collection to minimize real-time recording discrepancies (upwards of 190 msec using the equipment in this protocol). In this protocol, the common signal originates from the VR system as a parallel port signal. The common signal is routed to a circuit that permits synchronization of the separate data streams through direct recording with EMG signals and by simultaneously turning off a motion capture LED. The circuit is constructed using basic tools and techniques for building electronic components, similar to circuits described elsewhere9.
Figure 2: Trial flowchart. This flowchart outlines the stimulus and signal events that occur during a typical experimental trial that includes TMS stimulation. Parallel port codes that occur throughout a trial are shown in the DB25 schematic symbols (light blue).
Figure 3: Synchronization Circuit. This schematic displays the layout of our custom synchronization circuit. The default output of the NAND gate is a high voltage state; this voltage output is sent to the gate of a transistor through which the sync LED’s circuit is routed. This default state renders the circuit closed, which maintains the LED in a lighted state. Upon receiving a sync trigger parallel port signal (red trace in inset), an internal state of the 555 device is flipped rendering the output into a high state, shutting off the LED (blue trace). When this occurs, the voltage on C1 (green trace) builds up to a voltage that resets the internal state of the 555, reactivating the LED. The parallel port sync trigger signal is also directly routed to a BNC connector that is connected to the TMS input trigger port. Note: The direction of this trigger signal may have to be reversed (from positive- to negative-going or vice-versa) depending on an investigator’s specific equipment requirements. The addition of an “inverter” chip on this trigger output would easily accomplish this task. Please click here to view a larger version of this figure.
3. Experimental Procedures
Synchronization of the numerous data streams in this setup allows one to record the kinematics, continuous muscle activity (EMG), and instantaneous neuromuscular activity (MEPs) that occur during movements of the upper limb. Repeated trials of a given movement are required to reconstruct MEP response profiles over an entire movement. Figure 4 displays data collected from one subject. Figure 4A shows an example of these data streams during a single trial with the corresponding synchronization signals and events. Temporal alignment of the signals with respect to the synchronization event is a simple post-hoc procedure using signal analysis software (the signals are “shifted” in time using the synchronization event as a common temporal anchor). Signals can then be time-normalized by the duration of each movement trial. Without synchronization, the EMG and motion capture data streams can have a temporal discrepancy as great as 160-190 msec. However, by utilizing synchronization in addition to widely used TTL signaling, users should expect to minimize temporal errors between data streams to the limit of the sampling frequencies of their signals (approximately one msec in this example). Figure 4B shows average angular kinematics and dynamics across 24 trials for a single movement, the long head of the biceps EMG profile from trials without TMS during the same movements, and the corresponding reconstructed MEP profiles from trials with single-pulse TMS during movement to the same targets.
Figure 4: Alignment of EMG and Motion Capture. (A) Representative signals that are recorded during an experimental trial are displayed in the left column of charts. The blue and red circles correspond to the same VR-generated synchronization event recorded by two separate pieces of equipment (illustrated by dividing black line). These time points and respective data are later temporally aligned using custom software. The difference between these two time points can be upwards of 190 msec using when using the equipment described in this protocol; other investigators using different equipment may experience different delays. (B) After temporal alignment, averaged data can be created to describe the physiological, kinematic, and dynamic features of a movement. These data represent 24 trials of the same movement; the bars on the Bicep MEPs graph and the shaded areas on other graphs represent standard deviation. These data can subsequently be used to describe potential descending motor control signals with respect to muscle activity and movement kinematics and dynamics.
Transcranial magnetic stimulator | Magstim | N/A | TMS stimulator and coils |
Impulse X2 | PhaseSpace | N/A | Motion capture system |
MA300 Advanced Multi-Channel EMG System | Motion Lab Systems | MA300-28 | EMG pre-amplifier and amplifier |
Norotrode EMG electrodes | Myotronics | N/A | EMG electrodes |
BNC-2111 Single-Ended, Shielded BNC Connector Block | National Instruments | 779347-01 | BNC Connector Block |
NI PXI-1033 5-Slot PXI Chassis with Integrated MXI-Express Controller |
National Instruments | 779757-01 | DAQ chassis |
NI PXI-6254 16-Bit, 1 MS/s (Multichannel), 1.25 MS/s (1-Channel), 32 Analog Inputs |
National Instruments | 779118-01 | DAQ card |
SHC68-68-EPM Cable (2m) | National Instruments | 192061-02 | Shielded cable |
DK1 or DK2 | Oculus VR | N/A | Ocuclus Rift headset |
Vizard 5 Lite | WorldViz | N/A | Virtual reality software |
C1 and C2 capacitors | varied | N/A | Adjust values to suit |
R1 and R2 resistors | varied | N/A | Adjust values to suit |
CD4011 NAND gate | varied | N/A | NAND gate |
2N2222 transistor | varied | N/A | Transistor |
NE555 timer circuit | varied | N/A | Timer circuit |
DB25 and USB connectors | varied | N/A | parallel and USB connectors |
The study of neuromuscular control of movement in humans is accomplished with numerous technologies. Non-invasive methods for investigating neuromuscular function include transcranial magnetic stimulation, electromyography, and three-dimensional motion capture. The advent of readily available and cost-effective virtual reality solutions has expanded the capabilities of researchers in recreating “real-world” environments and movements in a laboratory setting. Naturalistic movement analysis will not only garner a greater understanding of motor control in healthy individuals, but also permit the design of experiments and rehabilitation strategies that target specific motor impairments (e.g. stroke). The combined use of these tools will lead to increasingly deeper understanding of neural mechanisms of motor control. A key requirement when combining these data acquisition systems is fine temporal correspondence between the various data streams. This protocol describes a multifunctional system’s overall connectivity, intersystem signaling, and the temporal synchronization of recorded data. Synchronization of the component systems is primarily accomplished through the use of a customizable circuit, readily made with off the shelf components and minimal electronics assembly skills.
The study of neuromuscular control of movement in humans is accomplished with numerous technologies. Non-invasive methods for investigating neuromuscular function include transcranial magnetic stimulation, electromyography, and three-dimensional motion capture. The advent of readily available and cost-effective virtual reality solutions has expanded the capabilities of researchers in recreating “real-world” environments and movements in a laboratory setting. Naturalistic movement analysis will not only garner a greater understanding of motor control in healthy individuals, but also permit the design of experiments and rehabilitation strategies that target specific motor impairments (e.g. stroke). The combined use of these tools will lead to increasingly deeper understanding of neural mechanisms of motor control. A key requirement when combining these data acquisition systems is fine temporal correspondence between the various data streams. This protocol describes a multifunctional system’s overall connectivity, intersystem signaling, and the temporal synchronization of recorded data. Synchronization of the component systems is primarily accomplished through the use of a customizable circuit, readily made with off the shelf components and minimal electronics assembly skills.
The study of neuromuscular control of movement in humans is accomplished with numerous technologies. Non-invasive methods for investigating neuromuscular function include transcranial magnetic stimulation, electromyography, and three-dimensional motion capture. The advent of readily available and cost-effective virtual reality solutions has expanded the capabilities of researchers in recreating “real-world” environments and movements in a laboratory setting. Naturalistic movement analysis will not only garner a greater understanding of motor control in healthy individuals, but also permit the design of experiments and rehabilitation strategies that target specific motor impairments (e.g. stroke). The combined use of these tools will lead to increasingly deeper understanding of neural mechanisms of motor control. A key requirement when combining these data acquisition systems is fine temporal correspondence between the various data streams. This protocol describes a multifunctional system’s overall connectivity, intersystem signaling, and the temporal synchronization of recorded data. Synchronization of the component systems is primarily accomplished through the use of a customizable circuit, readily made with off the shelf components and minimal electronics assembly skills.