Emotional Processing in the First 2 Years of Life: A Review of Near-Infrared Spectroscopy Studies

Emotional stimuli processing during childhood helps us to detect salient cues in our environment and prepares us for our social life. In early childhood, the emotional valences of auditory and visual input are salient and relevant cues of social aspects of the environment, and it is of special interest to understand how exactly the processing ofemotional stimuli develops. Near-infrared spectroscopy (NIRS) is a noninvasive neuroimaging tool that has proven valuable in studying emotional processing in children. After conducting a systematic search of PubMed, Web of Science, and Embase databases, we examined 50 NIRS studies performed to study emotional stimuli processing in children in the first 2 years of age. We found that the majority of these studies are done in infants and the most commonly used stimuli are visual and auditory. Many of the reviewed studies suggest the involvement of bilateral temporal areas in emotional processing of visual and auditory stimuli. It is unclear which neural activation patterns reflect maturation and at what age the emotional encoding reaches those typically seen in adults. Our review provides an overview of the database on emotional processing in children up to 2 years of age. Furthermore, it demonstrates the need to include the less-studied age range of 1 to 2 years, and suggests the use of combined audio-visual stimuli and longitudinal studies for future research on emotional processing in children. Thus, NIRS might be a vital tool to study the associations between the early pattern of neural responses and socioemotional development later in life

Hemodynamic responses to emotional speech in two-month-old infants imaged using diffuse optical tomography

Emotional speech is one of the principal forms of social communication in humans. In this study, we investigated neural processing of emotionalspeech (happy, angry, sad and neutral) in the left hemisphere of 21 two-month-old infants using diffuse optical tomography. Reconstructed total hemoglobin (HbT) images were analysed using adaptive voxel-based clustering and region-of-interest (ROI) analysis. We found a distributedhappy > neutral response within the temporo-parietal cortex, peakingin the anterior temporal cortex; a negative HbT response to emotional speech (the average of the emotional speech conditions angry in the anterior superior temporal sulcus (STS), happy > angry in the superior temporal gyrus and posterior superior temporal sulcus, angry </p

An online database of infant functional near infraRed spectroscopy studies: a community-augmented systematic review

Until recently, imaging the infant brain was very challenging. Functional Near InfraRed Spectroscopy (fNIRS) is a promising, relatively novel technique, whose use is rapidly expanding. As an emergent field, it is particularly important to share methodological knowledge to ensure replicable and robust results. In this paper, we present a community-augmented database which will facilitate precisely this exchange. We tabulated articles and theses reporting empirical fNIRS research carried out on infants below three years of age along several methodological variables. The resulting spreadsheet has been uploaded in a format allowing individuals to continue adding new results, and download the most recent version of the table. Thus, this database is ideal to carry out systematic reviews. We illustrate its academic utility by focusing on the factors affecting three key variables: infant attrition, the reliability of oxygenated and deoxygenated responses, and signal-to-noise ratios. We then discuss strengths and weaknesses of the DBIfNIRS, and conclude by suggesting a set of simple guidelines aimed to facilitate methodological convergence through the standardization of reports

Auditory hemodynamic studies of newborn infants using near-infrared spectroscopic imaging

The noninvasive study of tissue blood volume and oxygenation using near-infrared light is a new and actively developing technology. We have used near-infrared spectroscopic imaging (NIRSI) to study hemodynamic responses on the auditory cortices evoked by auditory stimulation. Ten healthy newborn infants were studied. The otoacoustic emission hearing test was performed for each infant. Pulse oximetry was used to monitor the heart rate during the measurement, video recording was used to monitor motion artifacts, and the eye movements were noted in order to determine sleep stage. A 16-channel frequency-domain optical imaging system developed in our laboratory was used for NIRSI measurements. The stimuli were presented in trains of seven 1 kHz beeps with 700-ms inter-stimulus intervals. The stimulus trains were separated by 25-s silent periods in order to allow for the hemodynamic delay. In 3/8 cases, we obtained a clear bilateral increase in [HbO/sub 2/], and in two additional cases, a clear response on one hemisphere. The mean change in [HbO/sub 2/] was +0.9+/-0.9muM and the mean change in [Hb] was -0.3+/-0.4muM for those channels producing the largest response for each subject. No statistically significant response was found in 3/8 cases

Near-infrared spectroscopic imaging of stimulus-related hemodynamic responses on the neonatal auditory cortices.

We have used near-infrared spectroscopy (NIRS) to study hemodynamic auditory evoked responses on 7 full-term neonates. Measurements were done simultaneously above both auditory cortices to study the distribution of speech and music processing between hemispheres using a 16-channel frequency-domain instrument. The stimulation consisted of 5-second samples of music and speech with a 25-second silent interval. In response to stimulation, a significant increase in the concentration of oxygenated hemoglobin ([HbO2]) was detected in 6 out of 7 subjects. The strongest responses in [HbO2] were seen near the measurement location above the ear on both hemispheres. The mean latency of the maximum responses was 9.42±1.51 s. On the left hemisphere (LH), the maximum amplitude of the average [HbO2] response to the music stimuli was 0.76± 0.38 μ M (mean±std.) and to the speech stimuli 1.00± 0.45 μ± μM. On the right hemisphere (RH), the maximum amplitude of the average [HbO2] response was 1.29± 0.85 μM to the music stimuli and 1.23± 0.93 μM to the speech stimuli. The results indicate that auditory information is processed on both auditory cortices, but LH is more concentrated to process speech than music information. No significant differences in the locations and the latencies of the maximum responses relative to the stimulus type were found