Nobuyoshi Harada

Oxidative stress is involved in fatigue induced by overnight deskwork as assessed by increase in plasma tocopherylhydroqinone and hydroxycholesterol.

In this study, we examined the relationship between fatigue and plasma concentrations of antioxidants and lipid peroxidation products. Fourteen healthy volunteers performed overnight desk work for 18h then took a nap for 4h. Participants answered questionnaires of subjective symptoms of fatigue (QSSF) and completed a self-assessment of fatigue using a visual analog scale (VAS). At each test time, they underwent a critical flicker frequency (CFF) test and blood samples were collected. Plasma levels of α-tocopherol (αT) decreased and α-tocopherylquinone (αTQ), the oxidation product of αT, increased. The ratio of 7β-hydroxycholesterol (7β-OHCh), the oxidation product of cholesterol, against total cholesterol increased until the end of experiment. αTQ levels correlated with VAS and QSSF scores. The ratio of 7β-OHCh to total cholesterol and the value of CFF showed a significant correlation. From these results, plasma levels of αTQ and 7β-OHCh are useful and objective indicators of fatigue induced by overnight deskwork.

The effect of 1/f fluctuation in inter-stimulus intervals on auditory evoked mismatch field

This study focused on the effect of regularity of environmental stimuli on the informational order extracting function of human brain. The regularity of environmental stimuli can be described with the exponent n of the fluctuation 1/f(n). We studied the effect of the exponent of the fluctuation in the inter-stimulus interval (ISI) on the elicitation of auditory evoked mismatch fields (MMF) with two sounds with alternating frequency. ISI times were given by three types of fluctuation, 1/f(0), 1/f(1), 1/f(2), and with a fixed interval (1/f(infinity)). The root mean square (RMS) value of the MMF increased significantly (F(3/9)=4.95, p=0.027) with increases in the exponent of the fluctuation. Increments in the regularity of the fluctuation provoked enhancement of the MMF, which reflected the production of a memory trace, based on the anticipation of the stimulus timing. The gradient of the curve, indicating the ratio of increments between the MMF and the exponent of fluctuation, can express a subjects capability to extract regularity from fluctuating stimuli.

The effect of 1/f fluctuation in inter-stimulus interval of visual stimulus on flicker fusion threshold

computational V1 model is equivalent to the dynamics of the Kalman filter. In short, this model adaptively changes the weights of input stimulus and of internal estimates according to the contrast level of the input signal. The temporal receptive field of the proposed model changed from biphasic to monophasic as the noise level increased. Moreover, the model naturally explained contrast-dependency of the preferred velocity. These results support our computational theory that V1 neurons equivalently execute the Kalman filter, and that the above-mentioned temporal properties are the neural substrates to execute the Kalman filter.

Objective Detection of the Flicker Fusion Threshold with Pupil Diameter and Visual Evoked Magnetic Field

Objective detection of a flicker fusion threshold was investigated by examining the differences in responses of pupil diameter and the visual evoked magnetic field (VEF) for flickering visual stimulation with a frequency over or under the flicker fusion threshold. The pupil diameter increment was larger and the decrement was smaller in frequencies over 7.5 Hz. The amplitude of OFF responses increased with an increase in the frequency of flickering. Differences in pupil diameter and OFF responses for VEF demonstrated the frequency of the flicker fusion threshold in a non-arbitrary way.

Non-arbitrary detection of the flicker fusion threshold with pupil diameter and visual evoked magnetic field

The progressive diminution of frequency of the flicker fusion threshold was observed in the process of the development of the fatigue stage. Non-arbitrary detection of a flicker fusion threshold was investigated from differences in the responses of pupil diameter and the visual evoked magnetic field (VEF) for flickering visual stimulation with a frequency over or under the flicker fusion threshold. Pupil diameter in periods of omission, and VEF of ON and OFF responses were observed for flickering visual stimulus durations with a frequency under or over 2.5 Hz or 7.5 Hz from the threshold. The pupil diameter increment was larger and decrement was smaller in the over 7.5 Hz flickering condition than in the under 7.5 Hz condition. The amplitude of OFF responses increased with the increment of the frequency of flicker. Differences in pupil diameter and OFF responses for VEF could show the frequency of the flicker fusion threshold in a non-arbitrary way.

Effects of regularity, familiarity and congruity of stimuli on auditory and visually evoked magnetic fields

Effects of regularity, familiarity, and congruity of stimuli were investigated on Auditory and Visually Evoked Magnetic Fields. Regularity was controlled by exponent n on a fluctuation of 1/fn, Familiarity was controlled by the score of word familiarity in a database of Lexical Properties of Japanese. Congruity was controlled by the semantic distance of the components of the constructed stimulus. Decrement of these three factors of stimuli enhanced the amplitude and prolonged the latency of the AEF activity of the N100m component of primary auditory aria. The increment of the three factors of visual stimuli enhanced the VEF of the 150 ms and 220 ms components. The three factors of stimuli play similar roles for activity enhancement of the auditory and visual cortex, and provoked expectation of auditory stimuli and figure ground segmentation for visual stimuli. The activities of the cortex reflected the basic function of the conventionalization of the pattern of a repetitive experience unit in the process of the emergence of linguistic structure.