Biophotonic Methods for Brain-Computer Interfaces

A brain-computer interface (BCI) is a system that allows a user to communicate with the external world through thought processes alone. A Near-Infrared Spectroscopy (NIRS) based BCI or Optical BCI (OBCI) intends to detect volitional mental states non-invasively, in-vivo, via optical interrogation methods. NIR light pervades to a depth of ~2cm, successfully penetrating the scalp, skull, further cranial layers, and cortical tissue. Under the influence of volitional neuronal excitation, the cortical tissue’s optical properties serve to absorb and scatter the impending incident light, which can be detected and classified as an ‘attempt’ by the subject to control some augmentative device. The absorption and scattering of most intermediate layers and chromophores are assumed constant and therefore do not affect the qualitative varying haemodynamic concentrations of interest. Overall, the BCI research field is attempting to mitigate the affects of such neurodegenerative diseases such as Amyotrophic Lateral Sclerosis. Construction of the device can be broken into hardware, software, ambient control and subject preparation. Each of these modules is further broken into pre-processing and post-processing. Finally, visual feedback aids in improving performance over time as subjects learn to control their cranial haemodynamics. Indeed, such control has been used over the last decade for the purpose of relieving the affects of such disorders as ADD. Hemoencephalography (HEG) has been used in biofeedback, also having its origins in NIRS, to essentially teach the subjects to control the haemodynamics of their frontal lobe.