Investigation on Deep Layer Measurements in the Cerebral Cortex within the Adult Head by near Infrared Spectroscopy Using an Absorbance Difference Technique

Recent reports on modeled simulation of near infrared photons' paths in the adult head have shown that the cerebrospinal fluid functions as an optical guide, suggesting that non-invasive haemodynamic measurement of the deep layer of the cerebral cortex is difficult. Thus, the authors investigated the volume of the cortex measured by near infrared spectroscopy with the absorbance difference technique. This technique uses two radiation detector probes to yield short and long photon paths in order to realise selective measurement of the cortex by minimising the interference from the superficial layers covering the cortex. The results show that the volume of the cortex measured by this technique is larger in the temporal area than in the frontal area. Therefore, it is concluded that the photons' path in the temporal area reaches the deep layer of the cortex and that it is possible to measure the haemodynamic response of the auditory cortex in the deep temporal area of the adult head to sound stimuli.