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Method Article
Monitoring brain activity during upright motor tasks is of great value when investigating the neural source of movement disorders. Here, we demonstrate a protocol that combines functional near infrared spectroscopy with continuous monitoring of muscle and kinematic activity during 4 types of motor tasks.
There are several advantages that functional near-infrared spectroscopy (fNIRS) presents in the study of the neural control of human movement. It is relatively flexible with respect to participant positioning and allows for some head movements during tasks. Additionally, it is inexpensive, light weight, and portable, with very few contraindications to its use. This presents a unique opportunity to study functional brain activity during motor tasks in individuals who are typically developing, as well as those with movement disorders, such as cerebral palsy. An additional consideration when studying movement disorders, however, is the quality of actual movements performed and the potential for additional, unintended movements. Therefore, concurrent monitoring of both blood flow changes in the brain and actual movements of the body during testing is required for appropriate interpretation of fNIRS results. Here, we show a protocol for the combination of fNIRS with muscle and kinematic monitoring during motor tasks. We explore gait, a unilateral multi-joint movement (cycling), and two unilateral single-joint movements (isolated ankle dorsiflexion, and isolated hand squeezing). The techniques presented can be useful in studying both typical and atypical motor control, and can be modified to investigate a broad range of tasks and scientific questions.
Neural imaging during functional tasks has become more portable and cost-efficient using non-invasive functional near-infrared spectroscopy (fNIRS) to identify areas of brain activity by measuring blood flow dynamics at the cortex. The portability of fNIRS is especially useful in the study of upright and functional tasks such as gait1, which is not possible with other technologies such as functional magnetic resonance imaging (fMRI). This capability is critical in the fields of neurology and neuroscience, and could provide new insights into mechanisms underlying movement disorders in children and adults with cerebral palsy (CP) and other neurological conditions affecting motor control. Understanding mechanisms improves the ability to design efficacious interventions to target the source of impairments and activity limitations.
Many fNIRS studies of motor tasks to date have been with a healthy population of adults where participants are instructed to perform a certain task and monitoring of task performance is limited to visual inspection. This can be sufficient for those with typical movements and a high level of engagement, but is not acceptable when studying participants with movement disorders or those who have difficulty attending to a task for extended periods of time, including typically developing children. In order to inform the analysis of brain activation in these cases, concurrent monitoring of the motor pattern that is actually completed is required.
Comprehensive reviews of fNIRS systems and usages have been presented in the literature2-5 that guide usage and help to demonstrate the accuracy and sensitivity of these systems, but technical issues in the collection, processing and interpretation of fNIRS data still remain. Color and thickness of hair affect quality of the optical signal, with dark thick hair most likely to block or distort optical transmission3,6. This is especially relevant when studying the sensorimotor areas located on the crown area of the head where hair follicle density is the greatest, and some studies report non-responders6,7. The well established International 10/20 system can be used for placement of the optodes, but particularly in the case of those with atypical brain anatomy, co-registration of optode location to a participant’s anatomical MRI is very useful if not essential to accurately interpret the results.
The use of fNIRS to assess brain activation in childhood-onset brain injury is fairly recent, but gaining traction in the area of unilateral cerebral palsy6,8,9. In consideration of the aforementioned challenges, this protocol combines fNIRS, motion capture, and electromyographic (EMG) monitoring during a number of tasks, including simple single-joint tasks as well as more complex full-body motions. Visual and auditory guidance is used to improve attention and task performance across multiple ages of participants. The goal of the protocol is to identify differences in brain activation patterns in those with unilateral and bilateral childhood-onset brain injury compared to those who are typically developing. We explore a full body movement (gait), a bilateral lower extremity multi-joint movement (cycling), and two unilateral single-joint movements (isolated ankle dorsiflexion, and isolated hand squeezing) to illustrate the variety of applications of the methods. The same or a very similar protocol could be used to study other sensory or movement disorders or other tasks of interest.
Continuous wave near infrared light was emitted and detected at 690 nm and 830 nm over the sensorimotor cortices using the fNIRS system at a rate of 50 Hz, using a custom designed source-detector configuration. EMG data were collected wirelessly at a frequency of 1,000 Hz. Reflective marker 3-D locations were collected by an optical motion capture system at a rate of 100 Hz. Two different computers handled data acquisition, one for the fNIRS and another for the motion capture and EMG. Data were synced using a trigger pulse from a third computer that corresponds to a mouse button press to start the instructional animation for each task. For all tasks except gait, instructional animations were designed to standardize participant performance using visual guidance of the pace of a task (1 Hz), represented by a cartoon animal jumping or kicking, as well as an auditory cue.
NOTE: This protocol was approved by the Institutional Review Board of the National Institutes of Health (ClinicalTrials.gov identifier: NCT01829724). All participants are given the opportunity to ask questions and provide informed consent prior to their participation. In consideration of changes to the hemodynamic response caused by recent use of vasodilators and vasoconstrictors, participants are asked to refrain from alcohol and caffeine for 24 hr before the experiment3.These animation videos were custom made in our laboratory, but could be recorded with other sounds or images specific to alternative research questions.
1. Set Up the Room Prior to the Participant’s Arrival.
2. Basic Measures
3. Functional Near Infrared Spectroscopy (fNIRS) Setup
NOTE: This can be completed simultaneously with the setup of EMG and motion capture, if there are enough experimenters or research staff to assist, and if the participant is comfortable with several people being close to them at the same time.
4. Surface Electromyography (EMG) Setup
5. Motion Capture Setup
6. Gait Task
7. Bilateral Lower Extremity Cycling Task
8. Hand Squeezing Task
9. Ankle Dorsiflexion Task
10. Conclusion of Protocol
This protocol coordinates concurrent acquisition of 3 modalities to capture brain blood flow, electrical muscle activity, and kinematic movement of joints while a participant performs motor tasks (Figure 1).
Figure 1. Probe location. The left portion of this figure shows the approximate locations of the sensory areas (in b...
Simultaneous collection of brain activity from targeted areas of the cortex and quantitative data about how a person is moving presents tremendous potential for improving our understanding of the neural control of movement, both in a typically developing population as well as those with movement disorders. There is also broad application in terms of ages and movement tasks that could be completed, as participants are not restricted to a supine position as they would be for a functional MRI. The specific equipment items a...
The authors have nothing to disclose.
This project was funded by the Intramural Research Program at the National Institutes of Health Clinical Center. We acknowledge the helpful discussions with Dr. Thomas Bulea, PhD and Laurie Ohlrich, PT in refining the procedures presented in this protocol. Muyinat W. Osoba and Andrew Gravunder, MS assisted with the animations.
Name | Company | Catalog Number | Comments |
Name of Reagent/ Equipment | Company | Catalog Number | Comments/Description |
CW6 | TechEn | http://nirsoptix.com/ | fNIRS machine with variable number of sources and detectors, depending on the number of modules included |
MX system with ten T40-series cameras | Vicon Motion Systems Ltd., Oxford, UK | http://www.vicon.com/System/TSeries | Motion capture cameras |
reflective 4 mm markers | Vicon Motion Systems Ltd., Oxford, UK | n/a | Markers used by the motion capture cameras to locate fNIRS optodes, Ar, Al, Nz, and hand coordinates. |
reflective 9.5 mm markers | Vicon Motion Systems Ltd., Oxford, UK | n/a | Markers used by the motion capture cameras to locate arm and leg coordinates. Clusters are used for the limb segments, and markers with offsets are uses for PSIS and Iz to improve reliability in data capture. |
Trigno Wireless EMG system | Delsys, Inc. Natick, MA | http://www.delsys.com/products/wireless-emg/ | Electromyography |
Bertec split-belt instrumented treadmill | Bertec Corporation, Columbus, OH | http://bertec.com/products/instrumented-treadmills.html | Treadmill |
ZeroG body-weight support system | Aretech, LLC, Ashburn, VA | http://www.aretechllc.com/overview.html | Track and passive trolley used to support cables, harness can be used for patient safety during gait trials |
3DS Max 2013 | Autodesk, Inc., San Francisco, CA | http://www.autodesk.com/ | 3-D animation software used to animate animals for instructional videos |
Windows Movie Maker | Microsoft Corporation, Redmond, WA | http://windows.microsoft.com/en-us/windows-live/movie-maker | software used to combine animation footage with music |
Audacity | open source | http://audacity.sourceforge.net/ | Software used to alter musical beat to appropriate cadence |
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