When mothers and others speak to infants, they speak in a characteristic way called “infant-directed speech”. Fifteen middle-aged and older Japanese women read a picture book while exposed to a photograph of a non-kin infant (infant condition) or adult (adult condition). We compared the acoustic characteristics of speech between the two conditions. We analyzed three acoustic parameters and conducted principal component analysis (PCA) to summarize these three parameters into two PCA scores. Comparing the two conditions, the readings in the infant condition had significantly longer intervals between syllables, higher fundamental frequencies of the syllables, and wider fundamental frequency ranges from highest to lowest. The two PCA scores were higher in the infant condition. Both before and after the reading, the women completed an inventory assessing their affection. A significant correlation between affectional change and an acoustic parameter was found only in the infant condition. The results clarified that middle-aged and older Japanese women show the acoustic characteristics of “infant-directed speech” when speaking to non-kin infants. They also implied that the acoustic parameter in infant-directed speech is related to affection.

This study aimed to elucidate the relationship between changes in brain networks and emotional responses to additional pain-enhancing stimuli during the manifestation of cold-induced pain. We administered pain-inducing cold stimulus (6-7°C) to 15 healthy volunteers and evaluated their emotional responses using an 11-item scale, and scalp electroencephalography changes. From results of the emotion scale, factor analysis identified “arousal” and “emotional valence” as significant. Participants were categorized into groups with either high or low arousal, and high or low discomfort, based on these factors. We estimated the signal sources of the θ and low β bands, which showed changes in power values using the standardized low-resolution brain electromagnetic tomography method. Then, we calculated the composition of functional brain networks and their activity levels using constrained principal component analysis.

The present study revealed that during additional cold pain-enhancing stimuli, the main functional brain networks activated include the medial frontal cortex, associated with cognitive processes such as attention, contributing to increased arousal and discomfort levels. In contrast, decreased activity in the insular cortex contralateral to the stimulus, reflecting its regulatory role in cognitive processing of pain, helped suppress discomfort caused by cold pain.