Diurnal Changes of Human Cognitive Function in Response to Sound Stimuli of Different Frequencies for Evening-Type Subjects

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Abstract

In order to study cognitive function rhythms related to auditory frequency systems for people who prefer to be active at night, we conducted experiments during early evening (17:00) and after midnight (01:00) sessions. On the basis of a morningness/eveningness questionnaire, seven moderately evening-type subjects (E-types) were selected. Diurnal changes of human cognitive function under 250/500 Hz and 1000/2000 Hz conditions were assessed by auditory event-related brain potential using an oddball task. The subjects were asked to press a button when the target stimulus was detected, but to do nothing when the standard stimulus was detected. Significant diurnal changes of P300 latency and P300 amplitude were observed. The P300 latency at 17:00 was significantly shorter than at 01:00 at the Fz electrode site under the high-frequency condition [F(1,6)=6.335, P<0.05]. The P300 amplitude at 17:00 was significantly greater than at 01:00 [F(1,6)=159.964, P<0.0001]. The P300 amplitude obtained after the high-frequency stimulus was significantly smaller than that after the low-frequency stimulus at 01:00 [F(1,6)=6.258, P<0.05], but not at 17:00. These results revealed that stimulus frequency had effects on human cognitive function, and E-types' cognitive function decreased at midnight compared to that in the early evening. This study had extended previous findings of auditory P300 studies on diurnal variations in terms of time of day and stimulus parameter.

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