Development of Human Somatosensory Cortical Functions - What have We Learned from Magnetoencephalography: A Review

Inter-hemispheric somatosensory coherence and parental stress in hypersensitivity at 8 months old: An electroencephalography study

OBJECTIVE

Infant hypersensitivity affects daily challenges and parental stress. Although the crucial role of tactile sensation in infants' brain function has been highlighted, hypersensitive infants and their families lack support. Electroencephalography may be useful for understanding hypersensitivity traits. We investigated the relationship between infant perceptual hypersensitivity and parental stress, somatosensory-evoked potential (SEP), and magnitude-squared coherence (MSC) in the general population.

METHODS

Infants aged 8 months (n = 63) were evaluated for hypersensitivity and parental stress using a questionnaire and for cortical activity using electroencephalography. Vibration stimuli were applied to the infant's left foot. SEP components that peaked around 150 ms (N2) and at 200 ms (P2) after stimulus onset were evaluated by amplitude and latency at the midline electrode (Cz) and MSC between the midline electrodes (C3-C4).

RESULTS

Parental stress was associated with infant hypersensitivity. The latency of Cz was delayed, and C3-C4 delta MSC was high in infants with hypersensitivity.

CONCLUSIONS

Increasing inter-hemispheric MSC synchrony in the stimulated condition in infants with hypersensitivity suggested atypical somatosensory cortical function.

SIGNIFICANCE

These findings contribute to identifying, understanding the mechanisms of, and developing effective coping strategies for early-stage hypersensitivity.

Spatiotemporal dynamics of cortical somatosensory network in typically developing children

Sense of touch is essential for our interactions with external objects and fine control of hand actions. Despite extensive research on human somatosensory processing, it is still elusive how involved brain regions interact as a dynamic network in processing tactile information. Few studies probed temporal dynamics of somatosensory information flow and reported inconsistent results. Here, we examined cortical somatosensory processing through magnetic source imaging and cortico-cortical coupling dynamics. We recorded magnetoencephalography signals from typically developing children during unilateral pneumatic stimulation. Neural activities underlying somatosensory evoked fields were mapped with dynamic statistical parametric mapping, assessed with spatiotemporal activation analysis, and modeled by Granger causality. Unilateral pneumatic stimulation evoked prominent and consistent activations in the contralateral primary and secondary somatosensory areas but weaker and less consistent activations in the ipsilateral primary and secondary somatosensory areas. Activations in the contralateral primary motor cortex and supramarginal gyrus were also consistently observed. Spatiotemporal activation and Granger causality analysis revealed initial serial information flow from contralateral primary to supramarginal gyrus, contralateral primary motor cortex, and contralateral secondary and later dynamic and parallel information flows between the consistently activated contralateral cortical areas. Our study reveals the spatiotemporal dynamics of cortical somatosensory processing in the normal developing brain.

Altered excitation-inhibition balance in the primary sensorimotor cortex to proprioceptive hand stimulation in cerebral palsy

OBJECTIVE

Our objective was to clarify the primary sensorimotor (SM1) cortex excitatory and inhibitory alterations in hemiplegic (HP) and diplegic (DP) cerebral palsy (CP) by quantifying SM1 cortex beta power suppression and rebound with magnetoencephalography (MEG).

METHODS

MEG was recorded from 16 HP and 12 DP adolescents, and their 32 healthy controls during proprioceptive stimulation of the index fingers evoked by a movement actuator. The related beta power changes were computed with Temporal Spectral Evolution (TSE). Peak strengths of beta suppression and rebound were determined from representative channels over the SM1 cortex.

RESULTS

Beta suppression was stronger contralateral to the stimulus and rebound was weaker ipsilateral to the stimulation in DP compared to controls. Beta modulation strengths did not differ significantly between HP and the control group.

CONCLUSIONS

The emphasized beta suppression in DP suggests less efficient proprioceptive processing in the SM1 contralateral to the stimulation. Their weak rebound further indicates reduced intra- and/or interhemispheric cortical inhibition, which is a potential neuronal mechanism for their bilateral motor impairments.

SIGNIFICANCE

The excitation-inhibition balance of the SM1 cortex related to proprioception is impaired in diplegic CP. Therefore, the cortical and behavioral proprioceptive deficits should be better diagnosed and considered to better target individualized effective rehabilitation in CP.

Structural networking of the developing brain: from maturation to neurosurgical implications

Modern neuroscience agrees that neurological processing emerges from the multimodal interaction among multiple cortical and subcortical neuronal hubs, connected at short and long distance by white matter, to form a largely integrated and dynamic network, called the brain "connectome." The final architecture of these circuits results from a complex, continuous, and highly protracted development process of several axonal pathways that constitute the anatomical substrate of neuronal interactions. Awareness of the network organization of the central nervous system is crucial not only to understand the basis of children's neurological development, but also it may be of special interest to improve the quality of neurosurgical treatments of many pediatric diseases. Although there are a flourishing number of neuroimaging studies of the connectome, a comprehensive vision linking this research to neurosurgical practice is still lacking in the current pediatric literature. The goal of this review is to contribute to bridging this gap. In the first part, we summarize the main current knowledge concerning brain network maturation and its involvement in different aspects of normal neurocognitive development as well as in the pathophysiology of specific diseases. The final section is devoted to identifying possible implications of this knowledge in the neurosurgical field, especially in epilepsy and tumor surgery, and to discuss promising perspectives for future investigations.

Single-trial neuromagnetic analysis reveals somatosensory dysfunction in chronic Minamata disease

Methylmercury pollution is a global problem, and Minamata disease (MD) is a stark reminder that exposure to methylmercury can cause irreversible neurological damage. A "glove and stocking type" sensory disturbance due to injured primary sensory cortex (SI) (central somatosensory disturbance) is the most common neurologic sign in MD. As this sign is also prevalent in those with polyneuropathy, we aimed to develop an objective assessment for detecting central somatosensory disturbances in cases of chronic MD. We selected 289 healthy volunteers and 42 patients with MD. We recorded the sensory nerve action potentials (SNAPs) and somatosensory evoked magnetic fields (SEFs) to median nerve stimulation with magnetoencephalography. Single-trial epochs were classified into three categories (N20m, non-response, and P20m epochs) based on the cross-correlation between averaged sensor SEFs and individual epochs. We assessed SI responses (the appearance rate of P20m [P20m rate] and non-response epochs [non-response rate]) and early somatosensory cortical processing (N20m amplitude, reproducibility of N20m in single-trial responses [cross-correlation value], and induced gamma-band oscillations of the SI [gamma response] of single epochs excluding non-response epochs). Receiver operating characteristic curve analyses were used to examine the diagnostic accuracy of each parameter. We found that SNAPs exerted a marginal effect on the N20m. The N20m amplitude, cross-correlation value, and gamma response were significantly reduced in the MD group on either side (p < 0.0001), suggestive of altered early somatosensory cortical processing. Interestingly, the P20m rate and non-response rate were significantly increased in the MD group on either side (p < 0.0001), thereby suggesting impaired SI responses. Notably, P20m and absent N20m peaks were observed in 6 and 11 patients with MD, respectively, which may be attributed to increased numbers of P20m epochs. The cross-correlation value exhibited the highest correlation with the P20m rate or non-response rate. Thus, reduced reproducibility of N20m may play an important role in chronic MD. The cross-correlation value exhibited the highest correlation with the gamma response for both SI parameters in early somatosensory cortical processing. The area under the curve was > 0.77 (range: 0.77-0.79) for all parameters. Their confidence intervals overlapped with each other; thus, each SEF parameter likely had an approximately equivalent discrimination ability. In conclusion, chronic MD is characterized by impaired SI responses and alterations in early somatosensory cortical processing. Thus, single-trial neuromagnetic analysis of somatosensory function may be useful for detecting central somatosensory disturbance and elucidating the relevant pathophysiological mechanisms even in the context of chronic MD.

Prevalence of Phantom Phenomena in Congenital and Early-Life Amputees

Phantom limb pain (PLP) is a common consequence of the amputation of a limb. Persons with congenital limb absence (congenital amputees) or an acquired limb amputation at an early age seem to rarely experience PLP. However, the number of available studies and their sample sizes are low. In the present cross-sectional study, we assessed the presence of several phantom phenomena in a sample of 99 adult unilateral congenital amputees (con) of whom 34 had a limb correction later in life (limbc) and 153 adult participants with a unilateral amputation before the age of 6 years (subgroups: amputation between birth and 2 years (0-2y; n = 48), 3-4 years (3-4y; n = 46), and 5 to 6 years (5-6y; n = 59)). We found a higher prevalence and intensity of PLP in the 5-6y group compared to the other groups. Residual limb pain (RLP) intensity was higher in the 3 to 4 y and 5 to 6 y groups compared to the con group. Non-painful phantom limb sensation (PLS) intensity and telescoping intensity were higher in the 5 to 6 y group compared to the con and 0 to 2 y groups. Our results indicate that PLP prevalence as well as intensity is low when the limb loss happened before the age of 5 years. PERSPECTIVE: The prevalence of phantom limb pain, residual limb pain, and non-painful phantom limb sensation in congenital amputees and participants with an amputation early in life is low. This might be due to the missing or reduced nociceptive input from the residual limb to the brain and higher development-associated adaptability of the somatosensory system.

Cortical networks show characteristic recruitment patterns after somatosensory stimulation by pneumatically evoked repetitive hand movements in newborn infants

Controlled assessment of functional cortical networks is an unmet need in the clinical research of noncooperative subjects, such as infants. We developed an automated, pneumatic stimulation method to actuate naturalistic movements of an infant’s hand, as well as an analysis pipeline for assessing the elicited electroencephalography (EEG) responses and related cortical networks. Twenty newborn infants with perinatal asphyxia were recruited, including 7 with mild-to-moderate hypoxic–ischemic encephalopathy (HIE). Statistically significant corticokinematic coherence (CKC) was observed between repetitive hand movements and EEG in all infants, peaking near the contralateral sensorimotor cortex. CKC was robust to common sources of recording artifacts and to changes in vigilance state. A wide recruitment of cortical networks was observed with directed phase transfer entropy, also including areas ipsilateral to the stimulation. The extent of such recruited cortical networks was quantified using a novel metric, Spreading Index, which showed a decrease in 4 (57%) of the infants with HIE. CKC measurement is noninvasive and easy to perform, even in noncooperative subjects. The stimulation and analysis pipeline can be fully automated, including the statistical evaluation of the cortical responses. Therefore, the CKC paradigm holds great promise as a scientific and clinical tool for controlled assessment of functional cortical networks.

Early brain activity: Translations between bedside and laboratory

Neural activity is both a driver of brain development and a readout of developmental processes. Changes in neuronal activity are therefore both the cause and consequence of neurodevelopmental compromises. Here, we review the assessment of neuronal activities in both preclinical models and clinical situations. We focus on issues that require urgent translational research, the challenges and bottlenecks preventing translation of biomedical research into new clinical diagnostics or treatments, and possibilities to overcome these barriers. The key questions are (i) what can be measured in clinical settings versus animal experiments, (ii) how do measurements relate to particular stages of development, and (iii) how can we balance practical and ethical realities with methodological compromises in measurements and treatments.

The acquisition of mechanoreceptive competence by human digital Merkel cells and sensory corpuscles during development: an immunohistochemical study of PIEZO2

BACKGROUND

PIEZO2 is a transmembrane protein forming part of an ion channel required for mechanotransduction. In humans, PIEZO2 is present in axon terminals of adult Meissner and Pacinian corpuscles, as well as Merkel cells in Merkel cell-neurite complexes.

METHODS

To study the acquisition of functional capability for mechanotransduction of developing type I slowly adapting low-threshold mechanoreceptors, i.e., Merkel cell-neurite complexes, a battery of immunohistochemical and immunofluorescence techniques was performed on human skin specimens covering the whole development and growth, from 11 weeks of estimated gestational age to 20 years of life. In addition, developmental expression of PIEZO2 type I (Meissner's corpuscles) and type II (Pacinian corpuscles) rapidly adapting mechanoreceptors was studied in parallel.

RESULTS

The first evidence of Merkel cells showing the typical morphology and placement was at 13 weeks of estimated gestation age, and at this time positive immunoreactivity for PIEZO2 was achieved. PIEZO2 expression in axons terminals started at 23 WEGA in Pacinian corpuscles and at 36 WEGA in the case of Meissner corpuscles. The occurrence of PIEZO2 in Merkel cells, Meissner and Pacinian corpuscles was maintained for all the time investigated. Interestingly PIEZO2 was absent in most Aβ type I slowly adapting low-threshold mechanoreceptors that innervate MC while it was regularly present in most Aβ type I and type II rapidly adapting low-threshold mechanoreceptors that supplies Meissner and Pacinian corpuscles.

CONCLUSION

The present results provide evidence that human cutaneous mechanoreceptors could perform mechanotransduction already during embryonic development.

Infant brain imaging using magnetoencephalography: Challenges, solutions, and best practices

The excellent temporal resolution and advanced spatial resolution of magnetoencephalography (MEG) makes it an excellent tool to study the neural dynamics underlying cognitive processes in the developing brain. Nonetheless, a number of challenges exist when using MEG to image infant populations. There is a persistent belief that collecting MEG data with infants presents a number of limitations and challenges that are difficult to overcome. Due to this notion, many researchers either avoid conducting infant MEG research or believe that, in order to collect high-quality data, they must impose limiting restrictions on the infant or the experimental paradigm. In this article, we discuss the various challenges unique to imaging awake infants and young children with MEG, and share general best-practice guidelines and recommendations for data collection, acquisition, preprocessing, and analysis. The current article is focused on methodology that allows investigators to test the sensory, perceptual, and cognitive capacities of awake and moving infants. We believe that such methodology opens the pathway for using MEG to provide mechanistic explanations for the complex behavior observed in awake, sentient, and dynamically interacting infants, thus addressing core topics in developmental cognitive neuroscience.

Somatosensory Plasticity in Hemiplegic Cerebral Palsy Following Constraint Induced Movement Therapy

BACKGROUND

Children with hemiplegic cerebral palsy (HCP) experience upper limb somatosensory and motor deficits. Although constraint-induced movement therapy (CIMT) improves motor function, its impact on somatosensory function remains underinvestigated.

OBJECTIVE

The objective of this study was to evaluate somatosensory perception and related brain responses in children with HCP, before and after a somatosensory enhanced CIMT protocol, as measured using clinical sensory and motor assessments and magnetoencephalography.

METHODS

Children with HCP attended a somatosensory enhanced CIMT camp. Clinical somatosensory (tactile registration, 2-point discrimination, stereognosis, proprioception, kinesthesia) and motor outcomes (Quality of Upper Extremity Skills [QUEST] Total/Grasp, Jebsen-Taylor Hand Function Test, grip strength, Assisting Hand Assessment), as well as latency and amplitude of magnetoencephalography somatosensory evoked fields (SEF), were assessed before and after the CIMT camp with paired sample t-tests or Wilcoxon signed-rank tests.

RESULTS

Twelve children with HCP (mean age: 7.5 years, standard deviation: 2.4) participated. Significant improvements in tactile registration for the affected (hemiplegic) hand (Z = 2.39, P = 0.02) were observed in addition to statistically and clinically significant improvements in QUEST total (t = 3.24, P = 0.007), QUEST grasp (t = 3.24, P = 0.007), Assisting Hand Assessment (Z = 2.25, P = 0.03), and Jebsen-Taylor Hand Function Test (t = -2.62, P = 0.03). A significant increase in the SEF peak amplitude was also found in the affected hand 100 ms after stimulus onset (t = -2.22, P = 0.04).

CONCLUSIONS

Improvements in somatosensory clinical function and neural processing in the affected primary somatosensory cortex in children with HCP were observed after a somatosensory enhanced CIMT program. Further investigation is warranted to continue to evaluate the effectiveness of a sensory enhanced CIMT program in larger samples and controlled study designs.

Influence of dental magnets on human brain activity: A quantitative EEG analysis

PURPOSE

The magnetic field is known to attenuate mental depression, but it is not clear on the effect of dental magnets on human brain activity. Therefore, this study was to determine the influence of magnetic field from intraoral magnets on the human brain activity by analyzing the changes in alpha waves.

MATERIALS AND METHODS

Twenty complete denture male patients aged between 50 and 60 years were included after their consent. The neodymium-iron-boron sintered magnet was incorporated into the existing mandibular denture bilaterally in canine region. The participants were subjected to electroencephalogram (EEG) and the output measured alpha waves at three phases: (i) without placement of magnets (WM0), (ii) 30 days post-magnet placement in the mandibular denture (WM), and (iii) after 6 months post-removal of magnets (WM6). The data obtained was skewed (non-parametric), and hence multivariate analysis using Friedman test, and bivariate analysis using Wilcoxon signed rank test and Mann-Whitney test were done to assess the significant difference among the groups.

RESULTS

The comparison of alpha waves between different phases showed a significant difference in all the pairs (p < .05) except WM-WM6. Comparison of alpha waves between right and left hemisphere showed no statistically significant difference (p > .05).

CONCLUSION

We concluded that dental magnets had an influential effect on the alpha waves in the brain on both the left and right hemispheres. The removal of dental magnets retained the changes in brain activity even after 6 months of removal, denoting the alternative therapy to management of mental depression.

Secondary somatosensory cortex evoked responses and 6-year neurodevelopmental outcome in extremely preterm children

OBJECTIVE

We assessed in extremely preterm born (EPB) children whether secondary somatosensory cortex (SII) responses recorded with magnetoencephalography (MEG) at term-equivalent age (TEA) correlate with neurodevelopmental outcome at age 6 years. Secondly, we assessed whether SII responses differ between 6-year-old EPB and term-born (TB) children.

METHODS

39 EPB children underwent MEG with tactile stimulation at TEA. At age 6 years, 32 EPB and 26 TB children underwent MEG including a sensorimotor task requiring attention and motor inhibition. SII responses to tactile stimulation were modeled with equivalent current dipoles. Neurological outcome, motor competence, and general cognitive ability were prospectively evaluated at age 6 years.

RESULTS

Unilaterally absent SII response at TEA was associated with abnormal motor competence in 6-year-old EPB children (p = 0.03). At age 6 years, SII responses were bilaterally detectable in most EPB (88%) and TB (92%) children (group comparison, p = 0.69). Motor inhibition was associated with decreased SII peak latencies in TB children, but EPB children lacked this effect (p = 0.02).

CONCLUSIONS

Unilateral absence of an SII response at TEA predicted poorer motor outcome in EPB children.

SIGNIFICANCE

Neurophysiological methods may provide new means for outcome prognostication in EPB children.

Social interoception and social allostasis through touch: Legacy of the Somatovisceral Afference Model of Emotion

John Cacioppo and colleagues' Somatovisceral Afference Model of Emotion (SAME) highlighted the importance of interoception in emotional experience. Here we compare how the SAME and the more recent theory of constructed emotion (TCE) view the role of interoceptive signals in creating emotional experiences. We describe the characteristics of touch sensations that are carried by thin, unmyelinated fibers called C-tactile afferents (CTs) to the posterior insula, and are thus deemed interoceptive despite their typically social (external) origin. We explore how this social interoceptive input might contribute to the emotion-related effects of social touch more generally, and speculate that all social touch, with or without CT afferent stimulation, can directly influence allostasis, or the predictive regulation of short- and long-term energy resources required by the body. Finally, we describe several features of CT-optimal touch that make it a potentially useful tool to help illuminate basic interoceptive mechanisms, emotion-related phenomena, and disorders involving atypical affect or somatosensation. These proposed ideas demonstrate the long intellectual reach of John Cacioppo and Gary Berntson's highly productive scientific collaboration, which was formative for the fields of social neuroscience, social psychophysiology, and affective neuroscience.

Early Motor Differences in Infants at Elevated Likelihood of Autism Spectrum Disorder and/or Attention Deficit Hyperactivity Disorder

We investigated infant's manual motor behaviour; specifically behaviours crossing the body midline. Infants at elevated likelihood of Autism Spectrum Disorder (ASD) and/or Attention Deficit Hyperactivity Disorder (ADHD) produced fewer manual behaviours that cross the midline compared to infants with a typical likelihood of developing these disorders; however this effect was limited to 10-month-olds and not apparent at age 5 and 14 months. Although, midline crossing did not predict ASD traits, it was related to ADHD traits at 2 years of age. We rule out motor ability and hand dominance as possible explanations for this pattern of behaviour, positing that these results may be a consequence of multisensory integration abilities, and the neurobehavioural shift period, in the first year of life.

Vibration Alert to the Brain: Evoked and Induced MEG Responses to High-Frequency Vibrotactile Stimuli on the Index Finger of Dominant and Non-dominant Hand

Background: In recent years, vibrotactile haptic feedback technology has been widely used for user interfaces in the mobile devices. Although functional neuroimaging studies have investigated human brain responses to different types of tactile inputs, the neural mechanisms underlying high-frequency vibrotactile perception are still relatively unknown. Our aim was to investigate neuromagnetic brain responses to high-frequency vibrotactile stimulation, using magnetoencephalography (MEG).

Methods: We measured 152-channel whole-head MEG in 30 healthy, right-handed volunteers (aged 20–28 years, 15 females). A total of 300 vibrotactile stimuli were presented at the tip of either the left index finger or the right index finger in two separate sessions. Sinusoidal vibrations at 150 Hz for 200 ms were generated with random inter-stimulus intervals between 1.6 and 2.4 s. Both time-locked analysis and time-frequency analysis were performed to identify peak responses and oscillatory modulations elicited by high-frequency vibrations. The significance of the evoked and induced responses for dominant and non-dominant hand stimulation conditions was statistically tested, respectively. The difference in responses between stimulation conditions was also statistically evaluated.

Results: Prominent peak responses were observed at 56 ms (M50) and at 100 ms (M100) for both stimulation conditions. The M50 response revealed clear dipolar field patterns in the contralateral side with significant cortical activations in the contralateral primary sensorimotor area, whereas the M100 response was not as prominent as the M50. Vibrotactile stimulation induced significant suppression of both alpha (8–12 Hz) and beta (20–30 Hz) band activity during the mid-latency period (0.2–0.4 s), primarily in sensorimotor areas contralateral to the stimulation side. In addition, a significant alpha enhancement effect in posterior regions was accompanied with alpha suppressions in sensorimotor regions. The alpha suppression was observed in a broader distribution of cortical areas for the non-dominant hand stimulation.

Conclusion: Our data demonstrate that high-frequency tactile vibrations, which is known to primarily activate Pacinian corpuscles, elicit somatosensory M50 and M100 responses in the evoked fields and induce modulations of alpha and beta band oscillations during mid-latency periods. Our study is also consistent with that the primary sensorimotor area is significantly involved in the processing of high-frequency vibrotactile information with contralateral dominance.

Childhood Adversity and Affective Touch Perception: A Comparison of United Kingdom Care Leavers and Non-care Leavers

In the United Kingdom, the most common reasons for a child to come under the care of social services are neglect and abuse. Such early childhood adversity is a risk factor for social-isolation and poor mental health in adulthood. Touch is a key channel for nurturing interactions, and previous studies have shown links between early somatosensory input, experience dependent neural plasticity, and later life emotional functioning. The aim of the present study was to test the relationship between childhood neglect/abuse and later life experiences, attitudes, and hedonic ratings of affective touch. Here, affective touch is defined as low force, dynamic touch which C-Tactile afferents (CTs) respond optimally to. We hypothesized that a childhood lacking in early nurturing tactile stimulation would be associated with reduced sensitivity to socially relevant affective touch in adulthood. To test this, 19 care leavers (average 9.32 ± 3.70 years in foster care) and 32 non-care leavers were recruited through opportunity sampling (mean age = 21.25 ± 1.74 years). Participants completed a range of psychophysical somatosensory tests. First, they rated the pleasantness of CT-optimal (3 cm/s) and non-CT-optimal (0.3 and 30 cm/s) stroking touch applied to their forearm, both robotically and by an experimenter. They also made vicarious ratings of the anticipated pleasantness of social tactile interactions depicted in a series of videos. Finally, they filled in the Childhood Trauma Questionnaire (CTQ) and the Touch Experiences and Attitudes Questionnaire (TEAQ). As expected, care leavers reported significantly higher levels of childhood trauma than the control group. They also reported significantly lower levels of positive childhood touch compared to non-care leavers, but their attitudes and experiences of current intimate and affiliative touch did not differ. Across all psychophysical tests, care leavers showed specific reduction in sensitivity to the affective value of CT targeted 3 cm/s touch. The results of this study support the hypothesis that a lack of nurturing touch in early developmental periods leads to blunted sensitivity to the specific social value of affective touch. Future research should investigate the neural and physiological mechanisms underlying the observed effect.

Mirror-touch experiences in the infant brain

Several adult studies have proved the existence of a shared neural circuit in the somatosensory cortices that responds to both the body being touched and the sight of the body being touched. Despite the fundamental role of touch in infancy, the existence of similar visuo-tactile mirroring processes, supporting both felt and seen touch, still needs an in-depth empirical investigation. To this aim, we explored 8-month-olds mu desynchronization over somatosensory sites in response to felt and observed touch in a live experimental setting. EEG desynchronization (6-8 Hz mu frequency range) was measured during three experimental conditions: i) infants were stroked on their right hand by a parent (Touch condition); ii) infants observed a right hand being stroked (Observation Touch condition); iii) infants observed a right hand moving over the left hand without making contact (Action Control condition). Mu desynchronization of somatosensory sites contralateral to the hand being stroked emerged in response to both Touch and Observation Touch conditions, but not in the Action control condition. Further, greater mu desynchronization was found in the Touch and Observation Touch conditions as compared to the Action control condition. Our results highlight the early involvement of a shared somatosensory system, likely supporting infants' understanding of others' tactile sensations.

Importance of body representations in social-cognitive development: New insights from infant brain science

There is significant interest in the ways the human body, both one's own and that of others, is represented in the human brain. In this chapter we focus on body representations in infancy and synthesize relevant findings from both infant cognitive neuroscience and behavioral experiments. We review six experiments in infant neuroscience that have used novel EEG and MEG methods to explore infant neural body maps. We then consider results from behavioral studies of social imitation and examine what they contribute to our understanding of infant body representations at a psychological level. Finally, we interweave both neuroscience and behavioral lines of research to ground new theoretical claims about early infant social cognition. We propose, based on the evidence, that young infants can represent the bodily acts of others and their own bodily acts in commensurate terms. Infants initially recognize correspondences between self and other-they perceive that others are "like me" in terms of bodies and bodily actions. This capacity for registering and using self-other equivalence mappings has far-reaching implications for mechanisms of developmental change. Infants can learn about the affordances and powers of their own body by watching adults' actions and their causal consequences. Reciprocally, infants can enrich their understanding of other people's internal states by taking into account the way they themselves feel when they perform similar acts. The faces, bodies, and matching actions of people are imbued with unique meaning because they can be mapped to the infant's own body and behavior.

The Emergence of Hierarchical Somatosensory Processing in Late Prematurity

The somatosensory system has a hierarchical organization. Information processing increases in complexity from the contralateral primary sensory cortex to bilateral association cortices and this is represented by a sequence of somatosensory-evoked potentials recorded with scalp electroencephalographies. The mammalian somatosensory system matures over the early postnatal period in a rostro-caudal progression, but little is known about the development of hierarchical information processing in the human infant brain. To investigate the normal human development of the somatosensory hierarchy, we recorded potentials evoked by mechanical stimulation of hands and feet in 34 infants between 34 and 42 weeks corrected gestational age, with median postnatal age of 3 days. We show that the shortest latency potential was evoked for both hands and feet at all ages with a contralateral somatotopic source in the primary somatosensory cortex (SI). However, the longer latency responses, localized in SI and beyond, matured with age. They gradually emerged for the foot and, although always present for the hand, showed a shift from purely contralateral to bilateral hemispheric activation. These results demonstrate the rostro-caudal development of human somatosensory hierarchy and suggest that the development of its higher tiers is complete only just before the time of normal birth.

Pediatric Magnetoencephalography in Clinical Practice and Research

Magnetoencephalography (MEG) is a noninvasive neuroimaging technique that measures the electromagnetic fields generated by the human brain. This article highlights the benefits that pediatric MEG has to offer to clinical practice and pediatric research, particularly for infants and young children; reviews the existing literature on adult MEG systems for pediatric use; briefly describes the few pediatric MEG systems currently extant; and draws attention to future directions of research, with focus on the clinical use of MEG for patients with drug-resistant epilepsy.

The Role of Primary Motor Cortex: More Than Movement Execution

The predominant role of the primary motor cortex (M1) in motor execution is well acknowledged. However, additional roles of M1 are getting evident in humans owing to advances in noninvasive brain stimulation (NIBS) techniques. This review collates such studies in humans and proposes that M1 also plays a key role in higher cognitive processes. The review commences with the studies that have investigated the nature of connectivity of M1 with other cortical regions in light of studies based on NIBS. The review then moves on to discuss the studies that have demonstrated the role of M1 in higher cognitive processes such as attention, motor learning, motor consolidation, movement inhibition, somatomotor response, and movement imagery. Overall, the purpose of the review is to highlight the additional role of M1 in motor cognition besides motor control, which remains unexplored.

Brain Development in School-Age and Adolescent Girls: Effects of Turner Syndrome, Estrogen Therapy, and Genomic Imprinting

BACKGROUND

The study of Turner syndrome (TS) offers a unique window of opportunity for advancing scientific knowledge of how X chromosome gene imprinting, epigenetic factors, hormonal milieu, and chronologic age affect brain development in females.

METHODS

We described brain growth trajectories in 55 girls with TS and 53 typically developing girls (258 magnetic resonance imaging datasets) spanning 5 years. Using novel nonparametric and mixed effects analytic approaches, we evaluated influences of X chromosome genomic imprinting and hormone replacement therapy on brain development.

RESULTS

Parieto-occipital gray and white matter regions showed slower growth during typical pubertal timing in girls with TS relative to typically developing girls. In contrast, some basal ganglia, cerebellar, and limited cortical areas showed enhanced volume growth with peaks around 10 years of age.

CONCLUSIONS

The parieto-occipital finding suggests that girls with TS may be particularly vulnerable to altered brain development during adolescence. Basal ganglia regions may be relatively preserved in TS owing to their maturational growth before or early in typical pubertal years. Taken together, our findings indicate that particular brain regions are more vulnerable to TS genetic and hormonal effects during puberty. These specific alterations in neurodevelopment may be more likely to affect long-term cognitive behavioral outcomes in young girls with this common genetic condition.

Magnetic Source Imaging and Infant MEG: Current Trends and Technical Advances

Magnetoencephalography (MEG) is known for its temporal precision and good spatial resolution in cognitive brain research. Nonetheless, it is still rarely used in developmental research, and its role in developmental cognitive neuroscience is not adequately addressed. The current review focuses on the source analysis of MEG measurement and its potential to answer critical questions on neural activation origins and patterns underlying infants’ early cognitive experience. The advantages of MEG source localization are discussed in comparison with functional magnetic resonance imaging (fMRI) and functional near-infrared spectroscopy (fNIRS), two leading imaging tools for studying cognition across age. Challenges of the current MEG experimental protocols are highlighted, including measurement and data processing, which could potentially be resolved by developing and improving both software and hardware. A selection of infant MEG research in auditory, speech, vision, motor, sleep, cross-modality, and clinical application is then summarized and discussed with a focus on the source localization analyses. Based on the literature review and the advancements of the infant MEG systems and source analysis software, typical practices of infant MEG data collection and analysis are summarized as the basis for future developmental cognitive research.

Vibrotactile piezoelectric stimulation system with precise and versatile timing control for somatosensory research

BACKGROUND

Tactile stimulations systems are useful for studying the somatosensory system in children because they are innocuous and safe. Stimulators based on piezoelectric actuator are useful, but there is still a need for such systems capable of providing accurate and versatile control of timing and pattern of activation.

NEW METHOD

We have implemented a vibrotactile stimulating system useful for behavioral and electroencephalography (EEG) and magnetoencephalography (MEG) research. Our design goal was to create a system capable of providing up to five independently controlled mechanical stimulations with precise timing. We developed a Graphic User Interface (GUI) in LabVIEW, which controls a commercially available piezoelectric braille stimulator using an Arduino based controller. We made a customized braille stimulator based on the Metec Braille device.

RESULTS

Our system can control up to five tactile stimulators with independent timing control and negligible errors. Although it can be directly used for behavioral and EEG research, the piezoelectric stimulators in our system generate stimulus artifacts that interfere with MEG recordings. A moving averaging subtraction algorithm we developed can remove the artifact. The stimulator can be used to measure somatic evoked magnetic fields from the somatosensory cortex of a child without the artifact.

COMPARISON TO EXISTING METHODS

Our system provides an accurate independent control of one or more piezoelectric actuators using a GUI-based easy-to-control programming approach based on recent advances in embedded systems and software. Versatility and precise stimulation timing distinguish our system compared to existing somatic stimulators.

CONCLUSIONS

Our system may be useful for somatic research.

Exploring early human brain development with structural and physiological neuroimaging

Early brain development, from the embryonic period to infancy, is characterized by rapid structural and functional changes. These changes can be studied using structural and physiological neuroimaging methods. In order to optimally acquire and accurately interpret this data, concepts from adult neuroimaging cannot be directly transferred. Instead, one must have a basic understanding of fetal and neonatal structural and physiological brain development, and the important modulators of this process. Here, we first review the major developmental milestones of transient cerebral structures and structural connectivity (axonal connectivity) followed by a summary of the contributions from ex vivo and in vivo MRI. Next, we discuss the basic biology of neuronal circuitry development (synaptic connectivity, i.e. ensemble of direct chemical and electrical connections between neurons), physiology of neurovascular coupling, baseline metabolic needs of the fetus and the infant, and functional connectivity (defined as statistical dependence of low-frequency spontaneous fluctuations seen with functional magnetic resonance imaging (fMRI)). The complementary roles of magnetic resonance imaging (MRI), electroencephalography (EEG), magnetoencephalography (MEG), and near-infrared spectroscopy (NIRS) are discussed. We include a section on modulators of brain development where we focus on the placenta and emerging placental MRI approaches. In each section we discuss key technical limitations of the imaging modalities and some of the limitations arising due to the biology of the system. Although neuroimaging approaches have contributed significantly to our understanding of early brain development, there is much yet to be done and a dire need for technical innovations and scientific discoveries to realize the future potential of early fetal and infant interventions to avert long term disease.

Cortical signatures of vicarious tactile experience in four-month-old infants

The human brain recruits similar brain regions when a state is experienced (e.g., touch, pain, actions) and when that state is passively observed in other individuals. In adults, seeing other people being touched activates similar brain areas as when we experience touch ourselves. Here we show that already by four months of age, cortical responses to tactile stimulation are modulated by visual information specifying another person being touched. We recorded somatosensory evoked potentials (SEPs) in 4-month-old infants while they were presented with brief vibrotactile stimuli to the hands. At the same time that the tactile stimuli were presented the infants observed another person's hand being touched by a soft paintbrush or approached by the paintbrush which then touched the surface next to their hand. A prominent positive peak in SEPs contralateral to the site of tactile stimulation around 130 ms after the tactile stimulus onset was of a significantly larger amplitude for the "Surface" trials than for the "Hand" trials. These findings indicate that, even at four months of age, somatosensory cortex is not only involved in the personal experience of touch but can also be vicariously recruited by seeing other people being touched.

Magnetoencephalography and the infant brain

Magnetoencephalography (MEG) is a non-invasive neuroimaging technique that provides whole-head measures of neural activity with millisecond temporal resolution. Over the last three decades, MEG has been used for assessing brain activity, most commonly in adults. MEG has been used less often to examine neural function during early development, in large part due to the fact that infant whole-head MEG systems have only recently been developed. In this review, an overview of infant MEG studies is provided, focusing on the period from birth to three years. The advantages of MEG for measuring neural activity in infants are highlighted (See Box 1), including the ability to assess activity in brain (source) space rather than sensor space, thus allowing direct assessment of neural generator activity. Recent advances in MEG hardware and source analysis are also discussed. As the review indicates, efforts in this area demonstrate that MEG is a promising technology for studying the infant brain. As a noninvasive technology, with emerging hardware providing the necessary sensitivity, an expected deliverable is the capability for longitudinal infant MEG studies evaluating the developmental trajectory (maturation) of neural activity. It is expected that departures from neuro-typical trajectories will offer early detection and prognosis insights in infants and toddlers at-risk for neurodevelopmental disorders, thus paving the way for early targeted interventions.

Visual and somatosensory contributions to infant sitting postural control

There are a limited number of studies that have investigated sitting posture during infancy and the contribution of the sensory systems. The goal of this study was to examine the effects of altered visual and somatosensory signals on infant sitting postural control. Thirteen infants (mean age ± SD, 259.69 ± 16.88 days) participated in the study. Initially, a single physical therapist performed the Peabody Developmental Motor Scale to determine typical motor development. Then the child was placed onto a force platform under four randomized conditions: (a) Control (C) - sat independently on the force plate, (b) Somatosensory (SS) - Sat independently on a foam pad (low density), (c) Visual (VS) - sat independently on the force plate while the lights were turned off creating dim lighting, and (d) Combination of b and c (NVSS). Center of pressure (COP) data from both the anterior-posterior (AP) and the medial-lateral (ML) directions were acquired through the Vicon software at 240 Hz. The lights off conditions, both VS and NVSS, lead to increased Root Mean Square (RMS) and Range values in the AP direction, as well as increased Lyapunov Exponent (LyE) values in the ML direction. Altered visual information lead to greater disturbances of sitting postural control in typically developing infants than altered somatosensory information. The lights off conditions (VS and NVSS), unveiled different control mechanisms for AP and ML direction during sitting. Thus, the present findings confirm the dominance of vision during the early acquisition of a new postural accomplishment.

Social touch during development: Long-term effects on brain and behavior

In this paper, our goal is to explore what is known about the role of social touch during development. We first address the neural substrates of social touch and the role of tactile experience in neural development. We discuss natural variation in early exposure to social touch, followed by a discussion on experimental manipulations of social touch during development and "natural experiments", such as early institutionalization. We then consider the role of other developmental and experiential variables that predict social touch in adults. Throughout, we propose and consider new theoretical models of the role of social touch during development on later behavior and neurobiology.

Infant brain responses to felt and observed touch of hands and feet: an MEG study

There is growing interest concerning the ways in which the human body, both one's own and that of others, is represented in the developing human brain. In two experiments with 7-month-old infants, we employed advances in infant magnetoencephalography (MEG) brain imaging to address novel questions concerning body representations in early development. Experiment 1 evaluated the spatiotemporal organization of infants' brain responses to being touched. A punctate touch to infants' hands and feet produced significant activation in the hand and foot areas of contralateral primary somatosensory cortex as well as in other parietal and frontal areas. Experiment 2 explored infant brain responses to visually perceiving another person's hand or foot being touched. Results showed significant activation in early visual regions and also in regions thought to be involved in multisensory body and self-other processing. Furthermore, observed touch of the hand and foot activated the infant's own primary somatosensory cortex, although less consistently than felt touch. These findings shed light on aspects of early social cognition, including action imitation, which may build, at least in part, on infant neural representations that map equivalences between the bodies of self and other.

IFCN-endorsed practical guidelines for clinical magnetoencephalography (MEG)

Magnetoencephalography (MEG) records weak magnetic fields outside the human head and thereby provides millisecond-accurate information about neuronal currents supporting human brain function. MEG and electroencephalography (EEG) are closely related complementary methods and should be interpreted together whenever possible. This manuscript covers the basic physical and physiological principles of MEG and discusses the main aspects of state-of-the-art MEG data analysis. We provide guidelines for best practices of patient preparation, stimulus presentation, MEG data collection and analysis, as well as for MEG interpretation in routine clinical examinations. In 2017, about 200 whole-scalp MEG devices were in operation worldwide, many of them located in clinical environments. Yet, the established clinical indications for MEG examinations remain few, mainly restricted to the diagnostics of epilepsy and to preoperative functional evaluation of neurosurgical patients. We are confident that the extensive ongoing basic MEG research indicates potential for the evaluation of neurological and psychiatric syndromes, developmental disorders, and the integrity of cortical brain networks after stroke. Basic and clinical research is, thus, paving way for new clinical applications to be identified by an increasing number of practitioners of MEG.

Neural representations of the body in 60-day-old human infants

The organization of body representations in the adult brain has been well documented. Little is understood about this aspect of brain organization in human infancy. The current study employed electroencephalography (EEG) with 60-day-old infants to test the distribution of brain responses to tactile stimulation of three different body parts: hand, foot, and lip. Analyses focused on a prominent positive response occurring at 150-200 ms in the somatosensory evoked potential at central and parietal electrode sites. The results show differential electrophysiological signatures for touch of these three body parts. Stimulation of the left hand was associated with greater positive amplitude over the lateral central region contralateral to the side stimulated. Left foot stimulation was associated with greater positivity over the midline parietal site. Stimulation of the midline of the upper lip was associated with a strong bilateral response over the central region. These findings provide new insights into the neural representation of the body in infancy and shed light on research and theories about the involvement of somatosensory cortex in infant imitation and social perception.

The development of human digital Meissner's and Pacinian corpuscles

Meissner's and Pacinian corpuscles are cutaneous mechanoreceptors responsible for different modalities of touch. The development of these sensory formations in humans is poorly known, especially regarding the acquisition of the typical immunohistochemical profile related to their full functional maturity. Here we used a panel of antibodies (to specifically label the main corpuscular components: axon, Schwann-related cells and endoneurial-perineurial-related cells) to investigate the development of digital Meissner's and Pacinian corpuscles in a representative sample covering from 11 weeks of estimated gestational age (wega) to adulthood. Development of Pacinian corpuscles starts at 13 wega, and it is completed at 4 months of life, although their basic structure and immunohistochemical characteristics are reached at 36 wega. During development, around the axon, a complex network of S100 positive Schwann-related processes is progressively compacted to form the inner core, while the surrounding mesenchyme is organized and forms the outer core and the capsule. Meissner's corpuscles start to develop at 22 wega and complete their typical morphology and immunohistochemical profile at 8 months of life. In developing Meissner's corpuscles, the axons establish complex relationships with the epidermis and are progressively covered by Schwann-like cells until they complete the mature arrangement late in postnatal life. The present results demonstrate an asynchronous development of the Meissner's and Pacini's corpuscles and show that there is not a total correlation between morphological and immunohistochemical maturation. The correlation of the present results with touch-induced cortical activity in developing humans is discussed.

Differences in response inhibition processes between adolescents and adults are modulated by sensory processes

Response inhibition processes undergo strong developmental changes. The same is true for sensory processes, and recent evidence shows that there also within-modality differences in the efficacy to trigger motor response inhibition. Yet, modulatory effects of within-modality differences during age-related changes in response inhibition between adolescence and adulthood are still indeterminate. We investigated this question in a system neurophysiological approach combining analysis of event-related potentials (ERPs) with temporal EEG signal decomposition and source localization processes. We used the somatosensory system to examine possible within-modality differences. The study shows that differences in response inhibition processes between adolescents and adults are modulated by sensory processes. Adolescents show deficient response inhibition when stimuli triggering these mechanisms are processed via SI somatosensory areas, compared to SII somatosensory areas. Opposed to this, no differences between adolescents and adults are evident, when response inhibition processes are triggered via SII cortical regions. The EEG data suggests that specific neurophysiological subprocesses are associated with this. Adolescents seem to encounter problems assigning processing resources to integrate motor with tactile information in posterior parietal areas when this information is processed via SI. Thus, basic perceptual and age-related processes interactively modulate response inhibition as an important instance of cognitive control.

Neuromagnetic responses to tactile stimulation of the fingers: Evidence for reduced cortical inhibition for children with Autism Spectrum Disorder and children with epilepsy

The purpose of this study was to compare somatosensory responses from a group of children with epilepsy and a group of children with autism spectrum disorder (ASD), with age matched TD controls. We hypothesized that the magnitude of the tactile "P50m" somatosensory response would be reduced in both patient groups, possibly due to reduced GABAergic signaling as has been implicated in a variety of previous animal models and in vivo human MRS studies. We observed significant (~ 25%) decreases in tactile P50m dipole moment values from the source localized tactile P50m response, both for children with epilepsy and for children with ASD. In addition, the latency of the tactile P50m peak was observed to be equivalent between TD and ASD groups but was significantly delayed in children with epilepsy by ~ 6 ms. Our data support the hypothesis of impaired GABAergic signaling in both children with ASD and children with epilepsy. Further work is needed to replicate these findings and directly relate them to both in vivo measures of GABA via e.g. magnetic resonance spectroscopy and psychophysical assessments of somatosensory function, and behavioral indices.

Evaluating age-related change in lip somatosensation using somatosensory evoked magnetic fields

Somatosensory evoked fields (SEFs) to electrical stimulation on the right and left sides of the lower lip were measured using magnetoencephalography and compared in the bilateral hemispheres of 31 healthy normal young and 29 healthy normal elderly subjects to evaluate age-related change in lip somatosensation. The initial peak of the response around 13 ms, designated as N13m, and the second peak of the response, designated as P21m, were investigated. The N13m response, which was detected in 22 of 62 hemispheres in young adults and 37 of 58 hemispheres in elderly adults, showed significantly prolonged latency and increased equivalent current dipole (ECD) moment in the elderly adults. The P21m response, which was detected in 56 of 62 hemispheres in young adults and in 52 of 58 hemispheres in elderly adults, showed longer peak latency in the elderly adults. No significant difference was found in the ECD moment for P21m, which suggests that aging affected the SEFs of the lip somatosensation, but the effects of aging on N13m and P21m differed. Prolonged latency and increased ECD moment of N13m might result from decreased peripheral conduction and increased cortical excitation system associated with aging. Therefore, the initial response component might be an objective parameter for investigating change in lip function with age.

Growth of Thalamocortical Fibers to the Somatosensory Cortex in the Human Fetal Brain

Thalamocortical (TH-C) fiber growth begins during the embryonic period and is completed by the third trimester of gestation in humans. Here we determined the timing and trajectories of somatosensory TH-C fibers in the developing human brain. We analyzed the periods of TH-C fiber outgrowth, path-finding, "waiting" in the subplate (SP), target selection, and ingrowth in the cortical plate (CP) using histological sections from post-mortem fetal brain [from 7 to 34 postconceptional weeks (PCW)] that were processed with acetylcholinesterase (AChE) histochemistry and immunohistochemical methods. Images were compared with post mortem diffusion tensor imaging (DTI)-based fiber tractography (code No NO1-HD-4-3368). The results showed TH-C axon outgrowth occurs as early as 7.5 PCW in the ventrolateral part of the thalamic anlage. Between 8 and 9.5 PCW, TH-C axons form massive bundles that traverse the diencephalic-telencephalic boundary. From 9.5 to 11 PCW, thalamocortical axons pass the periventricular area at the pallial-subpallial boundary and enter intermediate zone in radiating fashion. Between 12 and 14 PCW, the TH-C axons, aligned along the fibers from the basal forebrain, continue to grow for a short distance within the deep intermediate zone and enter the deep CP, parallel with SP expansion. Between 14 and 18 PCW, the TH-C interdigitate with callosal fibers, running shortly in the sagittal stratum and spreading through the deep SP ("waiting" phase). From 19 to 22 PCW, TH-C axons accumulate in the superficial SP below the somatosensory cortical area; this occurs 2 weeks earlier than in the frontal and occipital cortices. Between 23 and 24 PCW, AChE-reactive TH-C axons penetrate the CP concomitantly with its initial lamination. Between 25 and 34 PCW, AChE reactivity of the CP exhibits an uneven pattern suggestive of vertical banding, showing a basic 6-layer pattern. In conclusion, human thalamocortical axons show prolonged growth (4 months), and somatosensory fibers precede the ingrowth of fibers destined for frontal and occipital areas. The major features of growing TH-C somatosensory fiber trajectories are fan-like radiation, short runs in the sagittal strata, and interdigitation with the callosal system. These results support our hypothesis that TH-C axons are early factors in SP and CP morphogenesis and synaptogenesis and may regulate cortical somatosensory system maturation.

Cortical Mechanisms of Tongue Sensorimotor Functions in Humans: A Review of the Magnetoencephalography Approach

The tongue plays important roles in a variety of critical human oral functions, including speech production, swallowing, mastication and respiration. These sophisticated tongue movements are in part finely regulated by cortical entrainment. Many studies have examined sensorimotor processing in the limbs using magnetoencephalography (MEG), which has high spatiotemporal resolution. Such studies have employed multiple methods of analysis, including somatosensory evoked fields (SEFs), movement-related cortical fields (MRCFs), event-related desynchronization/synchronization (ERD/ERS) associated with somatosensory stimulation or movement and cortico-muscular coherence (CMC) during sustained movement. However, the cortical mechanisms underlying the sensorimotor functions of the tongue remain unclear, as contamination artifacts induced by stimulation and/or muscle activity within the orofacial region complicates MEG analysis in the oral region. Recently, several studies have obtained MEG recordings from the tongue region using improved stimulation methods and movement tasks. In the present review, we provide a detailed overview of tongue sensorimotor processing in humans, based on the findings of recent MEG studies. In addition, we review the clinical applications of MEG for sensory disturbances of the tongue caused by damage to the lingual nerve. Increased knowledge of the physiological and pathophysiological mechanisms underlying tongue sensorimotor processing may improve our understanding of the cortical entrainment of human oral functions.

The Development of Tactile Perception

Touch is the first of our senses to develop, providing us with the sensory scaffold on which we come to perceive our own bodies and our sense of self. Touch also provides us with direct access to the external world of physical objects, via haptic exploration. Furthermore, a recent area of interest in tactile research across studies of developing children and adults is its social function, mediating interpersonal bonding. Although there are a range of demonstrations of early competence with touch, particularly in the domain of haptics, the review presented here indicates that many of the tactile perceptual skills that we take for granted as adults (e.g., perceiving touches in the external world as well as on the body) take some time to develop in the first months of postnatal life, likely as a result of an extended process of connection with other sense modalities which provide new kinds of information from birth (e.g., vision and audition). Here, we argue that because touch is of such fundamental importance across a wide range of social and cognitive domains, it should be placed much more centrally in the study of early perceptual development than it currently is.

Functional Laterality of Task-Evoked Activation in Sensorimotor Cortex of Preterm Infants: An Optimized 3 T fMRI Study Employing a Customized Neonatal Head Coil

Background

Functional magnetic resonance imaging (fMRI) in neonates has been introduced as a non-invasive method for studying sensorimotor processing in the developing brain. However, previous neonatal studies have delivered conflicting results regarding localization, lateralization, and directionality of blood oxygenation level dependent (BOLD) responses in sensorimotor cortex (SMC). Amongst the confounding factors in interpreting neonatal fMRI studies include the use of standard adult MR-coils providing insufficient signal to noise, and liberal statistical thresholds, compromising clinical interpretation at the single subject level.

Patients / methods

Here, we employed a custom-designed neonatal MR-coil adapted and optimized to the head size of a newborn in order to improve robustness, reliability and validity of neonatal sensorimotor fMRI.

Thirteen preterm infants with a median gestational age of 26 weeks were scanned at term-corrected age using a prototype 8-channel neonatal head coil at 3T (Achieva, Philips, Best, NL). Sensorimotor stimulation was elicited by passive extension/flexion of the elbow at 1 Hz in a block design. Analysis of temporal signal to noise ratio (tSNR) was performed on the whole brain and the SMC, and was compared to data acquired with an ‘adult’ 8 channel head coil published previously. Task-evoked activation was determined by single-subject SPM8 analyses, thresholded at p < 0.05, whole-brain FWE-corrected.

Results

Using a custom-designed neonatal MR-coil, we found significant positive BOLD responses in contralateral SMC after unilateral passive sensorimotor stimulation in all neonates (analyses restricted to artifact-free data sets = 8/13). Improved imaging characteristics of the neonatal MR-coil were evidenced by additional phantom and in vivo tSNR measurements: phantom studies revealed a 240% global increase in tSNR; in vivo studies revealed a 73% global and a 55% local (SMC) increase in tSNR, as compared to the ‘adult’ MR-coil.

Conclusions

Our findings strengthen the importance of using optimized coil settings for neonatal fMRI, yielding robust and reproducible SMC activation at the single subject level. We conclude that functional lateralization of SMC activation, as found in children and adults, is already present in the newborn period.

MRI and M/EEG studies of the White Matter Development in Human Fetuses and Infants: Review and Opinion

Already during the last trimester of gestation, functional responses are recorded in foetuses and preterm newborns, attesting an already complex cerebral architecture. Then throughout childhood, anatomical connections are further refined but at different rates and over asynchronous periods across functional networks. Concurrently, infants gradually achieve new psychomotor and cognitive skills. Only the recent use of non-invasive techniques such as magnetic resonance imaging (MRI) and magneto- and electroencephalography (M/EEG) has opened the possibility to understand the relationships between brain maturation and skills development in vivo. In this review, we describe how these techniques have been applied to study the white matter maturation. At the structural level, the early architecture and myelination of bundles have been assessed with diffusion and relaxometry MRI, recently integrated in multi-compartment models and multi-parametric approaches. Nevertheless, technical limitations prevent us to map major developmental mechanisms such as fibers growth and pruning, and the progressive maturation at the bundle scale in case of mixing trajectories. At the functional level, M/EEG have been used to record different visual, somatosensory and auditory evoked responses. Because the conduction velocity of neural impulses increases with the myelination of connections, major changes in the components latency are observed throughout development. But so far, only a few studies have related structural and functional markers of white matter myelination. Such multi-modal approaches will be a major challenge in future research, not only to understand normal development, but also to characterize early mechanisms of pathologies and the influence of fetal and perinatal interventions on later outcome.

Development of Proprioceptive Acuity in Typically Developing Children: Normative Data on Forearm Position Sense

This study mapped the development of proprioception in healthy, typically developing children by objectively measuring forearm position sense acuity. We assessed position sense acuity in a cross-sectional sample of 308 children (5–17 years old; M/F = 127/181) and a reference group of 26 healthy adults (18–25 years old; M/F = 12/14) using a body-scalable bimanual manipulandum that allowed forearm flexion/extension in the horizontal plane. The non-dominant forearm was passively displaced to one of three target positions. Then participants actively matched the target limb position with their dominant forearm. Each of three positions was matched five times. Position error (PE), calculated as the mean difference between the angular positions of the matching and reference arms, measured position sense bias or systematic error. The respective standard deviation of the differences between the match and reference arm angular positions (SDP_diff) indicated position sense precision or random error. The main results are as follows: First, systematic error, measured by PE, did not change significantly from early childhood to late adolescence (Median PE at 90° target: −2.85° in early childhood; −2.28° in adolescence; and 1.30° in adults). Second, response variability as measured by SDP_diff significantly decreased with age (Median SDP_diff at 90° target: 9.66° in early childhood; 5.30° in late adolescence; and 3.97° in adults). The data of this large cross-sectional sample of children document that proprioceptive development in typically developing children is characterized as an age-related improvement in precision, not as a development or change in bias. In other words, it is the reliability of the perceptual response that improves between early childhood and adulthood. This study provides normative data against which position sense acuity in pediatric patient populations can be compared. The underlying neurophysiological processes that could explain the observed proprioceptive development include changes in the tuning of muscle spindles at the spinal level, the maturation of supraspinal somatosensory pathways and the development of interhemispheric callosal connections responsible for the transfer of somatosensory information.

Beyond the N1: A review of late somatosensory evoked responses in human infants

Somatosensory evoked potentials (SEPs) have been used for decades to study the development of somatosensory processing in human infants. Research on infant SEPs has focused on the initial cortical component (N1) and its clinical utility for predicting neurological outcome in at-risk infants. However, recent studies suggest that examining the later components in the infant somatosensory evoked response will greatly advance our understanding of somatosensory processing in infancy. The purpose of this review is to synthesize the existing electroencephalography (EEG) and magnetoencephalography (MEG) studies on late somatosensory evoked responses in infants. We describe the late responses that have been reported and discuss the utility of such responses for illuminating key aspects of somatosensory processing in typical and atypical development.

Frequency of Maternal Touch Predicts Resting Activity and Connectivity of the Developing Social Brain

Previous behavioral research points to a positive relationship between maternal touch and early social development. Here, we explored the brain correlates of this relationship. The frequency of maternal touch was recorded for 43 five-year-old children during a 10 min standardized play session. Additionally, all children completed a resting-state functional magnetic resonance imaging session. Investigating the default mode network revealed a positive relation between the frequency of maternal touch and activity in the right posterior superior temporal sulcus (pSTS) extending into the temporo-parietal junction. Using this effect as a seed in a functional connectivity analysis identified a network including extended bilateral regions along the temporal lobe, bilateral frontal cortex, and left insula. Compared with children with low maternal touch, children with high maternal touch showed additional connectivity with the right dorso-medial prefrontal cortex. Together these results support the notion that childhood tactile experiences shape the developing "social brain" with a particular emphasis on a network involved in mentalizing.

Relationship between somatosensory deficit and brain somatosensory system after early brain lesion: A morphometric study

Cerebral Palsy (CP) is a group of permanent motor disorders due to non-progressive damage to the developing brain. Poor tactile discrimination is common in children with unilateral CP. Previous findings suggest the crucial role of structural integrity of the primary (S1) and secondary (S2) somatosensory areas located in the ipsilesional hemisphere for somatosensory function processing. However, no focus on the relationship between structural characteristics of ipsilesional S1 and S2 and tactile discrimination function in paretic hands has been proposed. Using structural MRI and a two-point discrimination assessment (2 PD), we explore this potential link in a group of 21 children (mean age 13 years and 7 months) with unilateral CP secondary to a periventricular white matter injury (PWMI) or middle cerebral artery infarct (MCA). For our whole sample there was a significant negative correlation between the 2 PD and the gray matter volume in the ipsilesional S2 (rho = -0.50 95% confidence interval [-0.76, -0.08], one-tailed p-value = 0.0109) and in the ipsilesional S1 (rho = -0.57, 95% confidence interval [-0.81, -0.19], one-tailed p-value = 0.0032). When studying these relationships with regard to the lesion types, we found these correlations were non-significant in the patients with PWMI but stronger in patients with MCA. According to our results, the degree of sensory impairment is related to the spared gray matter volume in ipsilesional S1 and S2 and is marked after an MCA stroke. Our work contributes to a better understanding of why some patients with CP have variable somatosensory deficit following an early brain lesion.