Noninvasive optical evaluation of low frequency oscillations in prefrontal cortex hemodynamics during verbal working memory
2014
The low frequency oscillation (LFO) around 0.1 Hz has been observed recently in cerebral hemodynamic signals during
rest/sleep, enhanced breathing, and head- up-tilting, showing that cerebral autoregulation can be accessed by LFOs.
However, many brain function researches require direct measurement of LFOs during specified brain function activities.
This pilot study explored using near-infrared spectroscopy/imaging (NIRS) to noninvasively and simultaneously detect
LFOs of prefrontal cerebral hemodynamics (i.e., oxygenated/deoxygenated/total hemoglobin concentration: △[oxy-Hb]/
△[deoxy-Hb]/ △[tot-Hb]) during N-back visual verbal working memory task. The LFOs were extracted from the
measured variables using power spectral analysis. We found the brain activation sites struck clear LFOs while other sites
did not. The LFO of △[deoxy-Hb] acted as a negative pike and ranged in (0.05, 0.1) Hz, while LFOs of △[oxy-Hb] and
△[tot-Hb] acted as a positive pike and ranged in (0.1, 0.15) Hz. The amplitude difference and frequency lag between
△[deoxy-Hb] and △[oxy-Hb]/ △[tot-Hb] produced a more focused and sensitive activation map compare to
hemodynamic amplitude-quantified activation maps. This study observed LFOs in brain activities and showed strong
potential of LFOs in accessing brain functions.
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