Optical imaging of motor cortical hemodynamic response to directional arm movements using near-infrared spectroscopy Page: 1 of 7
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International Journal of Biological Engineering 2013, 3(2): 11-17
Optical Imaging of Motor Cortical Hemodynamic
Response to Directional Arm Movements Using
Nicoladie D Taml'*, George Zouridakis2
'Department of Biological Sciences, University of North Texas, Denton, TX 76023, USA
2Departments of Engineering Technology, Computer Science, and Electrical & Computer Engineering University of Houston, Houston,
TX 77204, USA
Abstract This study aims at determining arm-movement directions from functional near-infrared spectroscopy (fNIRS)
hemodynamic signals in order to decode intentional motor commands, originating in the motor cortices of humans, which
could be implemented in neuroprosthetic assistive devices for assisting the physically disabled. Motor cortical
hemodynamic responses were recorded using 64 spatially distributed optrodes from 14 normal subjects during free arm
orthogonal movements in the x- and y-directions on a horizontal plane. The time course of oxy-(HbO2) and
deoxy-hemoglobin (Hb), and of their summation (HbO2 + Hb) and difference (HbO2 - Hb) signals, representing the
hemodynamic profiles of total oxygen delivery and extraction, respectively, were computed for the localized neuronal
populations in the motor cortices underlying the optrodes. Analysis of the above hemodynamic signals revealed that they
could be temporally, spatially, or spatiotemporally decoupled, depending on the movement direction. Thus, by analyzing
the spatiotemporal profiles of brain activation we could identify the direction of the orthogonal movements uniquely. Our
findings demonstrate that movement direction, a key feature of motor commands, can be reliably extracted in real-time
from surface recorded fNIRS signals, and support their viability in future noninvasive assistive devices.
Keywords Near-infrared Spectroscopy, Motor Cortex, Directional Arm Movements, Optical Imaging, Hemodynamic
Functional near-infrared spectroscopy (fNIRS) is a
powerful noninvasive optical imaging technique to detect
differential changes in hemodynamic response to oxygen
delivery and extraction to the underlying neural tissues.
Near-infrared (NIR) light can penetrate biological tissues up
the depth of approximately 2 cm in the cortex without
significant degradation of the optical signals. The
depth-related information on absorption variation can be
estimated by finite element simulation methods .
Hemoglobin molecules absorb light in the NIR spectral
region and can discern the difference between
oxy-hemoglobin (HbO2) and deoxy-hemoglobin (Hb) based
on the absorption spectral signature produced by the
molecular chemical bonds. This allows real-time monitoring
of the hemodynamic signals in brain tissues in a noninvasive
fashion[2-4]. The characteristic absorption spectra of HbO2
* Corresponding author:
nicoladie.tam@unt. edu (Nicoladie Tam)
Published online at http://joumal.sapub.org/ijbe
Copyright 2013 Scientific & Academic Publishing. All Rights Reserved
and Hb at the NIR region recorded on the scalp can be used
to detect the oxygen demands of the underlying brain tissues
in the cortex. This allows real-time detection of brain
activation based on metabolic events (neuro-hemodynamics)
related to oxygen consumption of the underlying neural
fNIRS has the advantage of detecting not just Hb02 but
also Hb levels in real-time. The detection and differentiation
of HbO2 and Hb levels are computed from the modified
Beer-Lambert law based on the characteristic absorption
spectra of hemoglobin molecules when incident NIR lights
are shined onto the neural tissues. In neuroimaging, the
detector records the refracted light scattered by the tissue
rather than the transmitted light as in conventional oximeter,
because both emitters and detectors reside on the same side
of the scalp surface. The depth of recording is related to the
distance between emitter and detector according to the ray
tracing of scattered-light paths from emitter to detector.
Using multichannel emitters/sensors, high-resolution
hemodynamic signals can be recorded temporally (in msec)
in the cortex together with spatial resolution in cm. Thus, it
can localize the cortical region where neural vascular
activation/deactivation occurs (as represented by the Hb02
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Tam, Nicoladie D. & Zouridakis, George. Optical imaging of motor cortical hemodynamic response to directional arm movements using near-infrared spectroscopy, article, 2013; [El Monte, California]. (digital.library.unt.edu/ark:/67531/metadc674028/m1/1/: accessed July 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT College of Arts and Sciences.