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.

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.

Evolutionary loss of complexity in human vocal anatomy as an adaptation for speech.

Human speech production obeys the same acoustic principles as vocal production in other animals but has distinctive features: A stable vocal source is filtered by rapidly changing formant frequencies. To understand speech evolution, we examined a wide range of primates, combining observations of phonation with mathematical modeling. We found that source stability relies upon simplifications in laryngeal anatomy, specifically the loss of air sacs and vocal membranes. We conclude that the evolutionary loss of vocal membranes allows human speech to mostly avoid the spontaneous nonlinear phenomena and acoustic chaos common in other primate vocalizations. This loss allows our larynx to produce stable, harmonic-rich phonation, ideally highlighting formant changes that convey most phonetic information. Paradoxically, the increased complexity of human spoken language thus followed simplification of our laryngeal anatomy.

Neural substrates of implicit cueing effect on prospective memory.

Functional magnetic resonance imaging was used to examine the maintenance of intentions during an ongoing task involving implicit cues. Participants were required to detect target words while engaging in the ongoing task. Cues matched to the target category and cues matched to the action for targets were presented implicitly during the ongoing task. Implicit categorical target cues were found to enhance prospective memory performance, and implicit action cues accelerated responses more than irrelevant implicit cues in the prospective memory task. We found increased caudal anterior cingulate cortex (cACC) activity during the ongoing task with both implicit target and action cues, suggesting that alertness or preparatory attentional processes were strengthened by implicit cues. Implicit target cues elicited enhanced activity in the lateral anterior prefrontal cortex (Brodmann's area 10), which may be involved in dual processing of the ongoing task and the maintained intention. These results suggest that implicit cues may boost primitive attention toward an intended action and may be accessible to off-line maintenance. The facilitation of prospective target detection and the action execution by target cues were associated with increased supplementary motor area (SMA) activity. In contrast, we found enhanced premotor cortex (PMC) activation with action cue during the prospective memory task, suggesting that the PMC may be involved in stimulus-induced and rather automatic action. These results demonstrate the effectiveness of implicit cues for examining the maintenance of intention. Overall, we found that implicit target cues can facilitate prospective memory performance, and implicit action cues can accelerate responses. The above-mentioned neural underpinnings suggest that attentional and motor control processes are involved in the enhancement of prospective memory.

Neural enhancement and attenuation induced by repetitive recall.

Learning is the process of accumulating information. Repetition can make the process of retrieving information more efficient. The mechanisms by which repetition facilitates the retrieval process, however, are not yet clear. Here, we used event-related functional magnetic resonance imaging to investigate the effects of repetition on cued recall. In this study, participants were asked to encode visually presented semantically unrelated word pairs. The word presented on the left side served as the cue, and the word presented on the right side was the target. In the first test phase, participants were presented with the cue and asked to recall the associated word (target) from the study phase. The second test phase was performed 20 min later using the same method. Participants responded orally during the interval between image acquisitions, and no feedback was provided. Neural activity for identical stimuli and responses across the two tests were compared. As compared with the first test phase, the right dorsolateral prefrontal, bilateral inferior parietal, and precuneus regions showed greater activity and the left inferior frontal areas showed reduced activity during the second test phase. These shifts in neural activity that occurred with repetition may reflect the dynamics of the retrieval process.

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.

Temporal dissociation of global and local features by hierarchy of vision.

Most objects in our environment are organized hierarchically with a global whole embedding its local parts, but the way we recognize these features remains unclear. Using a visual masking paradigm, we examined the temporal dissociation between global and local feature as proposed in Reverse Hierarchy Theory, RHT (Ahissar & Hochstein, 2000), where global and local information are assumed to be processed, respectively, by feed-forward and feedback systems. We found that in a long Stimulus Onset Asynchrony (SOA) condition, both global and local information were recognized adequately. However, in a short SOA condition, global information was recognized correctly while local recognition was critically disrupted. Consistent with RHT, it is suggested that local information is processed in a feedback system; this processing is then interrupted by the mask stimulus presented later at the primary visual area. Global information, by contrast, is transferred via a feed-forward system, and is not disrupted by the mask.

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.

Configurational factors in the perception of faces and non-facial objects: an ERP study.

During the viewing of human faces, it is easier to recognize detailed features if the face is presented in an unusual configuration; for example, a split face. The present study used electroencephalography to investigate the brain activity elicited in response to a neutral, inverted, and split face and compared this to the activity produced in response to a non-facial stimulus (a clock). Results showed that the N170 response amplitude was larger and its latency longer during recognition of split and inverted faces as compared to a normal face, whereas no amplitude change was seen for the different clock configurations. However, for the P300 component, larger amplitudes were observed in both the face and the object condition. Taken together, the results suggest that unusual human face presentations are detected at earlier stages than unusual object presentations.

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.

Motion illusion activates the visual motion area of the brain: a near-infrared spectroscopy (NIRS) study.

Near-infrared spectroscopy (NIRS) enables noninvasive measurement of concentration changes of oxy- and deoxy-hemoglobin. The present study investigated cerebral representations of motion illusion by NIRS and examined several experimental procedures to determine an efficient procedure that can shorten the experimental time. We compared hemodynamic responses to figures with and without motion illusion. The number of repetitions of the tasks in the experiments and other factors were also examined. Results showed significant responses around area MT/V5 to the motion illusion from the analyses of three cycles (blocks) of presentation of illusion induction stimulus. These findings indicate that motion illusion can be detected by NIRS, and we propose a concise and efficient procedure for NIRS.

Position reversal learning in aged Japanese macaques.

We examined aged and young monkeys using a multiple position reversal task to investigate declines in cognitive functions with aging. The task consisted of an original learning task (simple position discrimination task) and a reversal learning task. While the performance of the aged monkeys was not different from that of the young monkeys in the original learning task, the aged monkeys showed a poorer performance than the young monkeys in the reversal learning task. According to our response analysis, the poor performance of aged monkeys in the reversal learning was not caused mainly by repetition of error responses, but rather by the impairment of understanding of the association between stimulus and reward. These results suggest that the prefrontal cortex, particularly the medial orbital cortex, is impaired with aging.

Experimental analyses of body image in the chimpanzee.

It is difficult to study body image in animals. In this study, it is assumed that the perception of the body of others reflects body image. The perception of the human face was examined in a series of six experiments with a chimpanzee. Delayed-matching-to-sample tasks were employed. Although the chimpanzee mastered the tasks and showed transfer of performance to new faces, subtle changes in the matching face resulted in the deterioration of performance. Responses of the chimpanzee were often controlled by factors other than the facial stimuli. Thus, although the chimpanzee has a body image as humans do, it may not be as clear and as segmented.

Identification of vocalizers by pant hoots, pant grunts and screams in a chimpanzee.

Identification of vocalizers was examined using an auditory-visual matching-to-sample task with a female chimpanzee. She succeeded in selecting the picture of the vocalizer in response to various types of vocalizations: pant hoots, pant grunts, and screams. When pant hoots by two chimpanzees were presented as a "duet", she could identify both of the vocalizers. These results suggest that researchers have underestimated the capability of vocalizer identification in chimpanzees. The chimpanzee correctly chose her own pictures in response to her vocalizations only by exclusion, and she did not show vocal self-recognition. The effect of acoustical modification (pitch shift and filtration) on the performance suggested that pitch is an important cue for the vocalizer identification.

Functional hemispheric specialization in processing phonemic and prosodic auditory changes in neonates.

This study focuses on the early cerebral base of speech perception by examining functional lateralization in neonates for processing segmental and suprasegmental features of speech. For this purpose, auditory evoked responses of full-term neonates to phonemic and prosodic contrasts were measured in their temporal area and part of the frontal and parietal areas using near-infrared spectroscopy (NIRS). Stimuli used here were phonemic contrast /itta/ and /itte/ and prosodic contrast of declarative and interrogative forms /itta/ and /itta?/. The results showed clear hemodynamic responses to both phonemic and prosodic changes in the temporal areas and part of the parietal and frontal regions. In particular, significantly higher hemoglobin (Hb) changes were observed for the prosodic change in the right temporal area than for that in the left one, whereas Hb responses to the vowel change were similarly elicited in bilateral temporal areas. However, Hb responses to the vowel contrast were asymmetrical in the parietal area (around supra marginal gyrus), with stronger activation in the left. These results suggest a specialized function of the right hemisphere in prosody processing, which is already present in neonates. The parietal activities during phonemic processing were discussed in relation to verbal-auditory short-term memory. On the basis of this study and previous studies on older infants, the developmental process of functional lateralization from birth to 2 years of age for vowel and prosody was summarized.

Magnetoencephalographic study of the neural responses in body perception.

A fundamental trait of human beings is the ability to discern information communicated by others. The human body is one of the important sources of such information. To date, several researchers have reported two body-selective regions in the brain-the extrastriate body area (EBA) and fusiform body area. As compared to the number of studies on spatial distribution, studies on the temporal processing of body perception are few. The electroencephalography (EEG) findings of a recent study indicate that observation of the human body induces a remarkable response leading to the generation of event-related-potentials that peak at 190 ms. However, source localization by using EEG has limitations. The advantage of magnetoencephalography (MEG) is that it enables localization of cortical activities and has excellent temporal resolution. In this study, we used MEG to measure the neural responses underlying the perception of the human body. Our results suggest that cortical activation induced by body images was observed in the bilateral EBA region with a latency of 190 ms and right-hemispheric dominance. Our study revealed the regions involved and the latency differences between these regions in body perception. Further, our results show the usefulness of MEG for body perception studies and suggest that like the face, the body plays a unique role in the human recognition process.

Effects of motor imagery on intermanual transfer: a near-infrared spectroscopy and behavioural study.

Intermanual transfer is the ability that previous studies by one limb promote the later learning by the other limb. This ability has been demonstrated in various effectors and types of training. Motor imagery, the mental simulation of motor execution, is believed to be strongly associated with the cognitive aspects of motor execution, and the pattern of brain activity during motor imagery is similar to that of motor execution, although the activation pattern is smaller, and the level is lower. If the cognitive component of motor execution strongly contributes to transfer, the training effect of motor imagery would be expected to transfer to the contralateral limb. In the present study, we used the tapping sequence paradigm to evaluate the occurrence of intermanual transfer through motor imagery and to compare differences of transfer effects to motor execution learning. We divided participants into three groups: an execution group, a motor imagery group and a no-training control group. Before and after a nondominant left hand training session, ipsilateral hand tests were conducted. After the post-test, a contralateral right-hand test was also conducted. In order to investigate the relationship between transfer effect and neural activation during the learning phase, we measured motor-related brain area activity using near-infrared spectroscopy (NIRS). Execution was effective especially for trained movement, imagery was effective for both trained movement and intermanual transfer. Brain activity suggesting predictive transfer differed between two groups, suggesting that motor execution and motor imagery training have different behavioural effects and neural contributions.

How do infants perceive scrambled face?: A near-infrared spectroscopic study.

Using near-infrared spectroscopy (NIRS), we recorded changes of oxy-Hb, deoxy-Hb, and total-Hb in 7- to 8-month-old infants' and adults' brains in response to canonical face and scrambled face stimuli. Using a newly developed probe for NIRS recording, which was light and soft enough to be tolerated by infants, we were able to acquire data from the very young even in the awake state. Total-Hb in response to a canonical face stimulus was greater than for scrambled face stimuli only in the right hemisphere in infants. This indicates the presence of right hemisphere dominance of brain activity in response to face images in 7- to 8-month-old infants. In adults, oxy-Hb and total-Hb were significantly increased from baseline only for the canonical face in the right hemisphere. There were greater numbers of channels showing significantly increased activity for the canonical face in the right than in the left hemisphere. These data indicate that the right hemisphere is more dominant for canonical face perception in both infants and adults. However, overall, the increase of total-Hb and oxy-Hb in adults was modest compared to infants. Although the reason for the difference between infants and adults is unclear, in addition to developmental changes influencing face perception, some methodological problems may be present. Thus, because we recorded NIRS signals in infants and adults using the same method, anatomical and physiological problems might affect the results to some degree. Although comparing the results between infants and adults is not simple, the present study is the first to indicate how 7- to 8-month-old infants perceive scrambled face stimuli and to compare such results with those of adults in order to understand developmental changes in face perception.

Motor activity and imagery modulate the body-selective region in the occipital-temporal area: a near-infrared spectroscopy study.

The extrastriate body area (EBA) lies in the occipital-temporal cortex and has been described as a "body-selective" region that responds when viewing other people's bodies. Recently, several studies have reported that EBA is also modulated when the subject moves or imagines moving their own body, even without visual feedback. The present study involved 3 experiments, wherein the first experiment was conducted to examine whether near-infrared spectroscopy (NIRS) could capture any activity in the EBA when viewing images of bodies. The second experiment was designed to elucidate whether this region also responds when the subjects move their own body, and the third to observe whether imagining carrying out a movement would activate EBA. Images of human bodies and chairs were used as the stimuli for the first experiment, simple hand movements carried out by the subject were used for the second and the act of imagining hand movements for the third. Our results confirmed that the region we defined as EBA was clearly activated when the subject viewed images of human bodies, carried out movements of their own body and imagined moving parts of their own body, thus demonstrating the usefulness of NIRS as a new brain imaging method. Moreover, we found a gender-based difference when imagining movement; male subjects showed a greater response than female subjects. This may reflect a gender difference in imagery skills; however, further research is needed to verify this hypothesis.

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.