Evaluation of Brain Activity in Unpleasant Emotion by Chaos Analysis

Abstract

Recently, as Japan is rapidly aging, an increase of aged people who require nursing care is expected. Especially, in case of people requiring intensive nursing care due to severe difficulty in communication by means of speech or gesture, objective evaluation of their emotional states as well as physical or mental pain is required. Therefore, it is important to establish the method for objective evaluation of feelings. Functional neuro imaging, especially near-infrared spectroscopy (NIRS), has been used so far to evaluate objective evaluation of feelings. However, there are few studies that evaluated feelings by focusing on complexity of the brain where high-level information processing is performed. There are also few studies that evaluated feeling-related responses in the prefrontal region that is known to be related to feeling processing. Unpleasant emotion is an extraneous factor of feelings. Therefore, we aimed to preliminarily evaluate unpleasant emotion quantitatively by using the lyapunov exponent that is an index of chaotic states. The lyapunov exponents calculated from temporal change of oxygenated hemoglobin concentration in the prefrontal region were compared between during the resting state and during listening to an unpleasant sound. As a result, the lyapunov exponent during listening to an unpleasant sound was significantly lower compared with that during the resting state. There was moderate correlation between the lyapunov exponent and the unpleasant psychological value measured using a visual analog scale (VAS). Especially, correlation coefficient was -0.50 at the prefrontal channel. These results suggest that our method is a useful index for emotional evaluation.