Hybrid Optical–Electrical Brain Computer Interfaces, Practices and Possibilities

Abstract

In this chapter we present an overview of the area of electroencephalographyfunctional near infrared spectroscopy (EEG-fNIRS) measurement as an activity monitoring technology for brain computer interfacing applications. Our interest in this compound neural interfacing technology is motivated by a need for a motor cortical conditioning technology suitable for use in a neurorehabilitation setting [15,50]. Specifically we seek BCI technology that allows a patient with a paretic limb (as a consequence of stroke) to engage in movement-based rehabilitation exercises which will, we hope, encourage neuroplastic processes in the brain so that recovery and function is ultimately restored [38]. As we are interested in rehabilitation following stroke haemodynamic signatures of motor cortical activity coupled with the corresponding direct measures of the electrical activity of the neurons involved could be a rich source of new information on the recovering brain areas. While most neural engineers will be familiar with the concepts underpinning the electroencephalogram (EEG), the same cannot be said for fNIRS. Consequently this chapter will discuss much of the foundational concepts underlying this measurement before describing an EEG-fNIRS probe and early experiments which illustrate the concept and highlight aspects of the utility of this hybrid BCI approach. The Underlying Physiological Origins of EEG and fNIRSIt is appropriate at this juncture to consider the physical basis of the measurements generated during both electroencephalography and fNIRS. While both measurement

Near-Infrared Optical Technologies in Brain-Computer Interface Systems

“…Inevitably on the path from source to detector, a portion of radiation will be lost in tissues and will never get in the detector. The other portion diffusely reflected from target volume will be weakened and get in to detector, where it can be quantitatively estimated [17,18].…”

“…Layout of sources and detectors in a manner, when the distance between them is approximately 3 cm on the scalp surface, allows ensuring probing depth of 3-5 cm, sufficient for detecting an activation of human brain cortical areas, although this occurs indirectly, through metabolic effects. Intensive neural activity (usually well differs from background activity) is a process accompanied by oxygen delivery, its absorption by neurons, and evacuation of metabolic products [18][19][20]. Interpretation of such activity is practically basic of any BCI.…”