Abstract
Conventional techniques for the noninvasive measurement of brain activity involve critical limitations in spatial or temporal resolution. Here, we propose the method for noninvasive brain function measurement with high spatiotemporal resolution using optical signals. We verified that diffused near-infrared light penetrating through the upper jaw and into the skull, which we term as optoencephalography (OEG), leads to the detection of dynamic brain signals that vary concurrently with the electrophysiological neural activity. We measured the OEG signals following the stimulation of the median nerve in common marmosets. The OEG signal response was tightly coupled with the electrophysiological response represented by the somatosensory evoked potential (SSEP). The OEG measurement is also shown to offer rather clear discrimination of brain signals.
Highlights
The development of noninvasive techniques to allow the measurement of brain activity is imperative for revealing how the human brain functions
The event-related optical signal has a latency of up to hundreds of milliseconds introduced by the phase lag in the evoked scattering changes accessible with a conventional near-infrared spectroscopy (NIRS) [4,5], the reliability of such a signal remains a matter of debate [6,7]
The signal for neural activity measured by NIRS or functional magnetic resonance imaging (fMRI) is based on the hemodynamic response, and the attainable temporal resolution is in the range of a few seconds
Summary
The development of noninvasive techniques to allow the measurement of brain activity is imperative for revealing how the human brain functions. Conventional techniques for noninvasive measurement of brain activity such as functional magnetic resonance imaging (fMRI), near-infrared spectroscopy (NIRS), magnetoencephalography (MEG), and electroencephalography (EEG), are burdened by critical limitations in spatial or temporal resolution [1]. In order to improve the accuracy of spatiotemporal estimates of dynamic brain activity, information from multiple conventional techniques can be combined [2]. The need for techniques that allow for noninvasive measurement of brain activity accompanied by high spatial and temporal resolution is apparent. NIRS, which uses near-infrared light similar to that in this study, has been used to measure cerebral activity [3].
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