Infants' Prefrontal Hemodynamic Responses and Functional Connectivity During Joint Attention in an Interactive-Live Setting.

The present study examined cerebral hemodynamic responses and functional connectivity during joint attention either initiated by infants (Initiating Joint Attention, IJA condition) or by their partner (Responding to Joint Attention, RJA condition). To capture responses to natural social cues in infants aged 7-12 months using functional near-infrared spectroscopy (fNIRS), we employed an interactive-live paradigm for IJA and RJA. During the measurement, an adult sat facing an infant, and objects, such as small stuffed animals, paired with sound toys were presented to the right or left side of the screen. In the RJA condition, the adult gazed at the infants' eyes and then to the objects to encourage the infants to follow the adult's gaze. On the other hand, in the IJA condition, the adult followed the infant's gaze as it shifted to the presented object. Our results indicate that the concentration of oxy-Hb in the bilateral ventral prefrontal region had significantly decreased, then followed by an increase in the right dorsal prefrontal region in the RJA. In addition, a selective activation in the bilateral dorsal prefrontal region was seen in the IJA condition. Moreover, the infants exhibited increased functional connectivity especially within the right ventral prefrontal region during RJA condition when compared with IJA conditions. These findings suggest that RJA and IJA recruit specific brain networks localized in the prefrontal cortex of infants.

Prefrontal Responses to Odors in Individuals With Autism Spectrum Disorders: Functional NIRS Measurement Combined With a Fragrance Pulse Ejection System.

Individuals with autism spectrum disorders (ASD) are impaired not only in social competencies but also in sensory perception, particularly olfaction. The olfactory ability of individuals with ASD has been examined in several psychophysical studies, but the results have been highly variable, which might be primarily due to methodological difficulties in the control of odor stimuli (e.g., the problem of lingering scents). In addition, the neural correlates of olfactory specificities in individuals with ASD remain largely unknown. To date, only one study has investigated this issue using functional magnetic resonance imaging (fMRI). The present study utilized a sophisticated method-a pulse ejection system-to present well-controlled odor stimuli to participants with ASD using an ASD-friendly application. With this advantageous system, we examined their odor detection, identification, and evaluation abilities and measured their brain activity evoked by odors using functional near-infrared spectroscopy (fNIRS). As the odor detection threshold (DT) of participants with ASD was highly variable, these participants were divided into two groups according to their DT: an ASD-Low DT group and an ASD-High DT group. Behavioral results showed that the ASD-High DT group had a significantly higher DT than the typically developing (control) group and the ASD-Low DT group, indicating their insensitivity to the tested odors. In addition, while there was no significant difference in the odor identification ability between groups, there was some discrepancy between the groups' evaluations of odor pleasantness. The brain data identified, for the first time, that neural activity in the right dorsolateral prefrontal cortex (DLPFC) was significantly weaker in the ASD-High DT group than in the control group. Moreover, the strength of activity in the right DLPFC was negatively correlated with the DT. These findings suggest that participants with ASD have impairments in the higher-order function of olfactory processing, such as olfactory working memory and/or attention.

Interactive live fNIRS reveals engagement of the temporoparietal junction in response to social contingency in infants.

Live social interaction is the dominant form of human social activity, but it remains unclear if brain processing of live interactive social stimuli differs substantially from processing of non-interactive social stimuli, mainly because of technical difficulties measuring brain activity during natural social interactions. This distinction is particularly important during infancy considering the importance of real-life interactions for various forms of learning. To assess the impact of live social interaction accompanied by ostensive social signals on infant cortical processing, the present study measured the cortical activities of 6-8-month-old and 10-12-month-old infants using functional near-infrared spectroscopy under contingent and non-contingent conditions (appropriately timed versus delayed responsiveness). We found greater activation over the right temporoparietal junction region in response to contingent interactions relative to non-contingent interactions in 6-8-month-old and 10-12-month-old infants. Our study indicates a critical role of contingent responsiveness for differential processing of live interactive social stimuli.

Infant word segmentation recruits the cerebral network of phonological short-term memory.

Segmenting word units from running speech is a fundamental skill infants must develop in order to acquire language. Despite ample behavioral evidence of this skill, its neurocognitive basis remains unclear. Using behavioral testing and functional near-infrared spectroscopy, we aimed to uncover the neurocognitive substrates of word segmentation and its development. Of three age-groups of Japanese infants (5-6, 7-8, and 9-10months of age), the two older age-groups showed significantly larger temporo-parietal (particularly supramarginal gyrus) responses to target words repeatedly presented for training, than to control words. After the training, they also exhibited stronger inferior frontal responses to target words embedded in sentences. These findings suggest that word segmentation largely involves a cerebral circuit of phonological (phonetic) short-term memory. The dorsal pathway involved in encoding and decoding phonological representation may start to function stably at around 7months of age to facilitate the growth of the infant's vocabulary.

Effects of preterm birth on intrinsic fluctuations in neonatal cerebral activity examined using optical imaging.

Medical advancements in neonatology have significantly increased the number of high-risk preterm survivors. However, recent long-term follow-up studies have suggested that preterm infants are at risk for behavioral, educational, and emotional problems. Although clear relationships have been demonstrated between preterm infants and developmental problems during childhood and adolescence, less is known about the early indications of these problems. Recently, numerous studies on resting-state functional connectivity (RSFC) have demonstrated temporal correlations of activity between spatially remote cortical regions not only in healthy adults but also in neuropathological disorders and early childhood development. In order to compare RSFC of the cerebral cortex between preterm infants at term-equivalent ages and full-term neonates without any anatomical abnormality risk during natural sleep, we used an optical topography system, which is a recently developed extension of near-infrared spectroscopy. We clarified the presence of RSFC in both preterm infants and full-term neonates and showed differences between these groups. The principal differences were that on comparison of RSFC between the bilateral temporal regions, and bilateral parietal regions, RSFC was enhanced in preterm infants compared with full-term neonates; whereas on comparison of RSFC between the left temporal and left parietal regions, RSFC was enhanced in full-term neonates compared with preterm infants. We also demonstrated a difference between the groups in developmental changes of RSFC related to postmenstrual age. Most importantly, these findings suggested that preterm infants and full-term neonates follow different developmental trajectories during the perinatal period because of differences in perinatal experiences and physiological and structural development.

Decreased right temporal activation and increased interhemispheric connectivity in response to speech in preterm infants at term-equivalent age.

Preterm infants are at increased risk of language-related problems later in life; however, few studies have examined the effects of preterm birth on cerebral responses to speech at very early developmental stages. This study examined cerebral activation and functional connectivity in response to infant-directed speech (IDS) and adult-directed speech (ADS) in full-term neonates and preterm infants at term-equivalent age using 94-channel near-infrared spectroscopy. The results showed that compared with ADS, IDS increased activity in larger brain areas such as the bilateral frontotemporal, temporal, and temporoparietal regions, both in full-term and preterm infants. Preterm infants exhibited decreased activity in response to speech stimuli in the right temporal region compared with full-term infants, although the significance was low. Moreover, preterm infants exhibited increased interhemispheric connectivity compared with full-term controls, especially in the temporal and temporoparietal regions. These differences suggest that preterm infants may follow different developmental trajectories from those born at term owing to differences in intrauterine and extrauterine development.

Prosody discrimination by songbirds (Padda oryzivora).

In human verbal communication, not only lexical information, but also paralinguistic information plays an important role in transmitting the speakers' mental state. Paralinguistic information is conveyed mainly through acoustic features like pitch, rhythm, tempo and so on. These acoustic features are generally known as prosody. It is known that some species of birds can discriminate certain aspects of human speech. However, there have not been any studies on the discrimination of prosody in human language which convey different paralinguistic meanings by birds. In the present study, we have shown that the Java sparrow (Padda oryzivora) can discriminate different prosodic patterns of Japanese sentences. These birds could generalize prosodic discrimination to novel sentences, but could not generalize sentence discrimination to those with novel prosody. Moreover, unlike Japanese speakers, Java sparrows used the first part of the utterance as the discrimination cue.

Broad cortical activation in response to tactile stimulation in newborns.

Tactile sensation, which is one of the earliest developing sensory systems, is very important in the perception of an individual's body and the surrounding physical environment, especially in newborns. However, currently, only little is known about the response of a newborn's brain to tactile sensation. The objective of the present study was to determine the response of a newborn's brain to tactile sensation and to compare the brain responses to various sensory stimuli. Ten healthy newborns, 2-9 days after birth, were enrolled. A multichannel near-infrared spectroscopy system was used to measure brain responses. The probe array covered broad cortical areas, including the parietal, temporal, and occipital areas. We measured cortical hemodynamic changes in response to three different types of stimuli: tactile, auditory, and visual. Activated areas were analyzed by t-tests, and the number of activated channels among the three different stimuli was compared by χ²-tests. The results showed that when the brain responded to each type of stimulation, the corresponding primary sensory area was activated, and tactile stimuli induced broader areas of brain activation than the other two types of stimuli (auditory or visual). Thus, broad brain areas, including the temporal and parietal areas, were activated by tactile stimuli in early newborn periods. These results suggest that there are differences in newborns' reactions to various types of sensory stimuli, which may reflect the importance of tactile sensation in the early newborn period.

Cerebral responses to infant-directed speech and the effect of talker familiarity.

A number of behavioral studies suggest that infant-directed speech (IDS) plays a more important role in facilitating both: a) speech perception, and b) adult-infant social interactions than does adult-directed speech (ADS), and hence that IDS contributes to subsequent social and language development. However neural substrates that may underlie these IDS functions have not been examined. The present study examined cerebral hemodynamic responses to IDS in 48 infants (4-13 months of age) using near-infrared spectroscopy (NIRS). Japanese sentences uttered by the infants' own mothers and by unfamiliar mothers were used to record activations in temporal and frontal area separately. Increased activations were observed predominantly in infants' left and right temporal areas when they listened to IDS rather than to ADS when both involved voices of their own and unfamiliar mothers. In contrast, significantly greater activations were observed in the frontal area when infants listened to IDS produced by their own mothers, not when IDS arose from unfamiliar mothers. Furthermore, the present results indicate that responses to IDS do vary as a function of the infant's age and the talker familiarity. These findings suggest a differential function for frontal and temporal areas in processing infant-directed speech by the different speakers.

Cerebral laterality for phonemic and prosodic cue decoding in children with autism.

This study examined the cerebral functional lateralization, from a phonological perspective, in children with autism spectrum disorder (ASD) and typically developing children (TDC). With near infrared spectroscopy, we measured auditory evoked-responses in the temporal areas to phonemic and prosodic contrasts in word contexts. The results of TDC showed stronger left-dominant and right-dominant responses to phonemic and prosodic differences, respectively. Furthermore, although ASD children displayed similar tendencies, the functional asymmetry for phonemic changes was relatively weak, suggesting less-specialized left-brain functions. The typical asymmetry for the prosodic condition was further discussed in terms of acoustic-physical perceptual ability of ASD children. The study revealed differential neural recruitment in decoding phonetic cues between ASD children and TDC and verified the applicability of near infrared spectroscopy as a suitable neuroimaging method for children with developmental disorders.

Prefrontal activation associated with social attachment: facial-emotion recognition in mothers and infants.

Attachment between mothers and infants is the most primitive and primary form of human social relationship. Many reports have suggested that the orbitofrontal cortex (OFC) plays a significant role in this attachment; however, only a select few provide experimental neurophysiological evidence. In the present study, to determine the neural substrates underlying the social and emotional attachment between mothers and infants, we measured their prefrontal activation by using near-infrared spectroscopy. We used movie stimuli that could robustly induce a positive affect, and the results for viewing own versus unfamiliar infants showed that own-infant viewing elicited increased activations around the anterior part of the orbitofrontal cortex (OFC) in the mothers. Their response magnitude in that area was also correlated with the behavioral rating of the pleasant mood of infants. Furthermore, our study revealed that the infants' prefrontal activation around the anterior OFC is specific to viewing their mothers' smile. These results suggest the OFC's role in regulating and encoding the affect in attachment system and also show that infants share similar neuronal functions with mothers, associated with their bonds at 1 year of age. We further discussed infants' prefrontal activations and their implications for the development of the social brain network.

Functional training for initiating joint attention in children with autism.

The present study aimed to examine the controlling variables for initiating joint attention (IJA) in three children with autism. During the baseline, target objects were presented in a location where the child could see them, but the adult could not, and the emergence of IJA was assessed. Children with autism showed some IJA skills during the baseline, but none initiated pointing. In training, the motivating operation for IJA was manipulated by using each child's preferred materials as targets of joint attention. It was found that more frequent and functional joint attention behaviors were emitted following training. The present study suggests that difficulties in IJA in children with autism could be partly explained by restricted interests in children with autism.

Neural attunement processes in infants during the acquisition of a language-specific phonemic contrast.

To elucidate the developmental neural attunement process in the language-specific phonemic repertoire, cerebral hemodynamic responses to a Japanese durational vowel contrast were measured in Japanese infants using near-infrared spectroscopy. Because only relative durational information distinguishes this particular vowel contrast, both first and second language learners have difficulties in acquiring this phonemically crucial durational difference. Previous cross-linguistic studies conducted on adults showed that phoneme-specific, left-dominant neural responses were observed only for native Japanese listeners. Using the same stimuli, we show that a larger response to the across-category changes than to the within-category changes occurred transiently in the 6- to 7-month-old group before stabilizing in the groups older than 12 months. However, the left dominance of the phoneme-specific response in the auditory area was observed only in the groups of 13 months and above. Thus, the durational phonemic contrast is most likely processed first by a generic auditory circuit at 6-7 months as a result of early auditory experience. The neural processing of the contrast is then switched over to a more linguistic circuit after 12 months, this time with a left dominance similar to native adult listeners.