Recent progress of non-invasive optical modality to brain computer interface: A review study

Brain activity is usually measured by non-invasive modalities. Inter alia, the electroencephalogram (EEG) is used most commonly. However, EEG is very sensitive to other biosignals, so other bio-signal detection modalities must be used as supplementary systems. Functional near-infrared spectroscopy (fNIRS) has good characteristics for use as such a supplementary modality, because brain activities can be measured by fNIRS through hemodynamic responses. Therefore, many scientists have adopted fNIRS for brain machine interface (BCI). Recently, fNIRS has become more compact and is robust to noise, so it could bring us to the development of an effective wearable BCI.

I. Outline

Brain machine interfaces use brain activities as commands, for which brain activities are usually measured by electroencephalogram (EEG). However, EEG is very sensitive to the other bio-signals: heart rate, eye movement, motion, and so on. Therefore, the use of BCI employing only EEG has limitations, so other bio-signal detection modalities are usually included as supplementary modalities, including those such as electrocardiogram (ECG), electromyography (EMG), photoplethysmography (PPG), electrooculogram (EOG), and galvanic skin reflex (GSR) [1]–[4]. However, while brain activities cannot be directly measured by such modalities, they can be directly measured by the use of functional near-infrared spectroscopy (fNIRS) through hemodynamic responses.