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Abstract:
The advantages of Near Infrared Spectroscopy (NIRS) as a
non-invasive neuroimaging technique include its excellent temporal
resolution and its ability to provide spectroscopic measurement
from adult human cortex. In addition, it offers great promise for
functional neuroimaging in young children. However, the specificity
of the technique remains to be fully validated. Using the MGH-NIRS
system, we examined neural activity during a verb generation task
that is known to consistently activate the left inferior prefrontal
cortex. Subjects underwent NIRS testing while generating verbs
related to presented nouns, compared to visual fixation as a
baseline task. Subjects were reclined to reduce the influence of
the Mayer wave. One source optode was placed over the frontal pole
while another source was placed putatively over the left inferior
frontal gyrus. Each source was surrounded by 4 detectors with an
interoptode distance of 3 cm. Concentrations of oxyhemoglobin and
deoxyhemoglobin were estimated for each source-detector pair using
the modified Beer-Lambert law, and were compared between verb
generation and baseline periods. Experience with this apparatus
indicates that signals from lateral prefrontal cortex are
relatively weak compared to those from primary sensory cortices.
However, results indicate that NIRS activity (increased
oxyhemoglobin and decreased deoxyhemoglobin) was greater at the
lateral prefrontal location than at the frontal pole. These data
suggest that localized language-related activation may be
identified with NIRS.
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