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Summary

Reaching is a fundamental skill that allows humans to interact with the environment. Several studies have aimed to characterize reaching behavior using a variety of methodologies. This paper offers an open-source application of transcranial magnetic stimulation to assess the state of corticospinal excitability in humans during reaching task performance.

Abstract

Reaching is a widely studied behavior in motor physiology and neuroscience research. While reaching has been examined using a variety of behavioral manipulations, there remain significant gaps in the understanding of the neural processes involved in reach planning, execution, and control. The novel approach described here combines a two-dimensional reaching task with transcranial magnetic stimulation (TMS) and concurrent electromyography (EMG) recording from multiple muscles. This method allows for the noninvasive detection of corticospinal activity at precise time points during the unfolding of reaching movements. The example task code includes a delayed response reaching task with two possible targets displayed ± 45° off the midline. Single pulse TMS is delivered on the majority of task trials, either at the onset of the preparatory cue (baseline) or 100 ms prior to the imperative cue (delay). This sample design is suitable for investigating changes in corticospinal excitability during reach preparation. The sample code also includes a visuomotor perturbation (i.e., cursor rotation of ± 20°) to investigate the effects of adaptation on corticospinal excitability during reach preparation. The task parameters and TMS delivery can be adjusted to address specific hypotheses about the state of the motor system during reaching behavior. In the initial implementation, motor evoked potentials (MEPs) were successfully elicited on 83% of TMS trials, and reach trajectories were recorded on all trials.

Introduction

Goal-directed reaching is a fundamental motor behavior that allows humans to interact with and manipulate the external environment. The study of reaching in the fields of motor physiology, psychology, and neuroscience has produced rich and extensive literature that includes a variety of methodologies. Early studies of reaching used direct neural recordings in non-human primates to investigate neural activity at the level of single neurons1,2. More recent studies have investigated reaching using behavioral paradigms that employ sensorimotor adaptation to explore the nature of motor learning and control

Protocol

All methods detailed here were performed in compliance with IRB protocol and approval (University of Oregon IRB protocol number 10182017.017). Informed consent was obtained from all subjects.

1. Reaching apparatus

  1. Place a large graphics tablet flat on a desktop.
  2. Use an adjustable 80-20 aluminum frame to position the task monitor 6-8 in above the tablet in parallel, with the screen facing upward (for a blueprint, check here: https://github.com/greenhousela.......

Representative Results

Successful execution of the described methods includes the recording of tablet data, EMG traces, and reliable elicitation of MEPs. An experiment was completed that included 270 test trials with TMS delivered on 4/5 of the trials (216 trials).

Data were collected from 16 participants (eight females; eight males) aged 25 ± 10 years, all of whom self-reported as right-handed. We assessed the effectiveness of the visual perturbation on behavioral performance by deriving a learning function fo.......

Discussion

The methods outlined above offer a novel approach to studying motor preparation in the context of reaching behaviors. Although reaching represents a popular model task in the study of motor control and learning, there is a need for precisely evaluating the CS dynamics associated with reaching behavior. TMS offers a noninvasive, temporally precise method of capturing CS activity at discrete time points during reaching. The approach described here combines two independent subfields-TMS and reaching-into a .......

Acknowledgements

This research was made possible in part by the generous funding of the Knight Campus Undergraduate Scholars program and the Phil and Penny Knight Foundation

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Materials

NameCompanyCatalog NumberComments
2-Port Native PCI Express StarTech.comRS232 Card with 16950 UART Must be compatible with desktop computer
Adjustable 80-20 aluminum frameany
Alcohol prep padsanyEMG preparation
Bagnoli Bipolar ElectrodesDelsysDE 2.1
Bagnoli Reference ElectrodeDelsysUSX20002” (5cm) Round
Bagnoli-8 EMG SystemDelsys
Chairany
Computer monitor for EMG/TMSn/a
Deskany
Desktop ComputerDellxps 8930RAM: 16 GB, Storage: 1TB, Graphics: 1060 6GB 
EMG electrodesDelsysSensor Adhesive Interface
Fine grain sandpaperanyEMG preparation
Graphics tabletWacomIntuos-4 XL
Handle of paint rolleranyto be used as stylus handle, hollowed out center must be large enough for stylus to sit securely inside 
Medical tapeanyTo secure EMG electrodes
PCI-6220 card DAQNational InstrumentsTo interface EMG system
Photodiode SensorVishayBPW21RTo record timing of task events into EMG trace.
Rear TMS portMagstimIncluded with TMS machine
Right-handed polyethylene gloveanyCut out thumb and index finger of glove to expose FDI muscle
Sensory Adhesive Interface, 2-slotDelsysSC-F01
StylusWacomIntuos-4 grip pen
Tablet-to-Computer USB cable anyIncluded in Tablet purchase
Task MonitorAsusVG248
TMS coilMagstimD70 Remote Coil7cm diameter, figure-of-eight coil
TMS machineMagstim200-2
TMS-to-Computer DB9 cableanyConnects to PCIe Serial Card
VelcroanyTo be placed on glove and stylus handle

References

  1. Georgopoulos, A. P., Kalaska, J. F., Caminiti, R., Massey, J. T. On the relations between the direction of two-dimensional arm movements and cell discharge in primate motor cortex. The Journal of Neuroscience. 2 (11), 1527-1537 (1982).
  2. Georgopoulous, A. P., Schwartz, A. B., Kettner, R. E.

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