Tracking gaze position from EEG: Exploring the possibility of an EEG-based virtual eye-tracker.

INTRODUCTION: Ocular artifact has long been viewed as an impediment to the interpretation of electroencephalogram (EEG) signals in basic and applied research. Today, the use of blind source separation (BSS) methods, including independent component analysis (ICA) and second-order blind identification (SOBI), is considered an essential step in improving the quality of neural signals. Recently, we introduced a method consisting of SOBI and a discriminant and similarity (DANS)-based identification method, capable of identifying and extracting eye movement-related components. These recovered components can be localized within ocular structures with a high goodness of fit (>95%). This raised the possibility that such EEG-derived SOBI components may be used to build predictive models for tracking gaze position. METHODS: As proof of this new concept, we designed an EEG-based virtual eye-tracker (EEG-VET) for tracking eye movement from EEG alone. The EEG-VET is composed of a SOBI algorithm for separating EEG signals into different components, a DANS algorithm for automatically identifying ocular components, and a linear model to transfer ocular components into gaze positions. RESULTS: The prototype of EEG-VET achieved an accuracy of 0.920° and precision of 1.510° of a visual angle in the best participant, whereas an average accuracy of 1.008° ± 0.357° and a precision of 2.348° ± 0.580° of a visual angle across all participants (N = 18). CONCLUSION: This work offers a novel approach that readily co-registers eye movement and neural signals from a single-EEG recording, thus increasing the ease of studying neural mechanisms underlying natural cognition in the context of free eye movement.

A resting-state network for novelty: Similar involvement of a global network under rest and task conditions.

Neuroimaging research provides converging evidence in support of functional networks active under rest conditions. While these networks are typically locally-distributed, a globally-distributed resting-state network (gRSN) was recently identified. The gRSN component is characterized by a scalp topography similar to that of the widely-studied P3 component of the event related potential, thought to represent the brain's response to novelty. In this study, we investigate similarities between the neural generators underlying these two networks to test the hypothesis that the gRSN is a resting-state network for novelty. By using the second-order blind identification (SOBI) algorithm, which works with temporal information, we show that (1) a resting-state component resembling the topography of the P3 can be recovered in all participants; (2) this gRSN component can be modeled with a set of ECDs with high goodness of fit; (3) ECD locations of the gRSN correspond to a network of globally-distributed brain structures overlapping heavily with the networking underlying the P3; and, (4) structures underlying these two networks are similarly involved during task and resting-state conditions. We interpret this as evidence in support of a resting-state network for detection and response to novelty.

Validation of SOBI-DANS method for automatic identification of horizontal and vertical eye movement components from EEG.

Neurophysiological investigation of neural processes are hindered by the presence of large artifacts associated with eye movement. Although blind source separation (BSS)-based hybrid algorithms are useful for separating, identifying, and removing these artifacts from EEG, it remains unexamined to what extent neural signals can remain mixed with these artifact components, potentially resulting in unintended removal of critical neural signals. Here, we present a novel validation approach to quantitatively evaluate to what extent horizontal and vertical saccadic eye movement-related artifact components (H and V Comps) are indeed ocular in origin. To automate the identification of the H and V Comps recovered by the second-order blind identification (SOBI), we introduced a novel Discriminant ANd Similarity (DANS)-based method. Through source localization, we showed that over 95% of variance in the SOBI-DANS identified H and V Comps' scalp projections were ocular in origin. Through the analysis of saccade-related potentials (SRPs), we found that the H and V Comps' SRP amplitudes were finely modulated by eye movement direction and distance jointly. SOBI-DANS' component selection was in 100% agreement with human experts' selection and was 100% successful in component identification across all participants indicating a high cross-individual consistency or robustness. These results set the stage for future work to transform the to-be-thrown-away artifacts into signals indicative of gaze position, thereby providing readily co-registered eye movement and neural signal without using a separate eye tracker.

English spoken word segmentation activates the prefrontal cortex and temporo-parietal junction in Chinese ESL learners: A functional near-infrared spectroscopy (fNIRS) study.

A direct measure of spoken lexical processing based on neuroimaging technology would provide us useful information to understand the neural mechanisms underlying speech or auditory language processing. The neural mechanisms of spoken word segmentation for English as a second language (ESL) learners remain elusive. The present study, using functional near-infrared spectroscopy (fNIRS), addresses this issue by measuring hemodynamic responses in the temporo-parietal junction (TPJ) and the prefrontal cortex (PFC) in a word-spotting task, designed with two task conditions (easy vs. difficult). Thirty participants, divided into a high listening proficiency group (HLG) and a low listening proficiency group (LLG), were tested. Results revealed significantly less TPJ activation in the HLG than in the LLG. Further analyses supported this result by showing that activation in the TPJ was in a negative correlation with listening proficiency. This association appears to be related to the more efficient use of processing resources in a bottom-up fashion for accurate and efficient sensory representations in high proficient language learners. In contrast, cortical activation in the PFC increased with listening proficiency and was stronger in the difficult task condition than in the easy task condition, implying that recruitment of top-down cognitive control functions might play a role in word segmentation. Our results suggest that the combination of the functions mediated via bottom-up sensory input processing (demonstrated in the TPJ activation) and top-down cognitive processing (demonstrated in the PFC activation) are crucial for ESL listeners' spoken word segmentation.

Normalized Cortisol Reactivity Predicts Future Neuropsychological Functioning in Children With Mild/Moderate Asthma.

Cortisol reactivity to adrenocorticotropic hormone (ACTH) has been associated with neuropsychological processes including attention and memory in children with asthma. While cortisol reactivity to a psychological stressor is often considered a measure of current neuroendocrine functioning, this study examines the association of the cortisol reactivity and subsequent neuropsychological functioning. Using prospective data from the Childhood Asthma Management Program (CAMP), we explored the predictive ability of cortisol reactivity to ACTH and children's later attention and memory using traditional and an alternative cortisol reactivity (normalized cortisol) measures. Cortisol reactivity was assessed at study entry and 1-year follow-up, and neuropsychological functioning was assessed at 3-year follow-up. Cortisol reactivity was assessed through plasma cortisol concentrations collected at baseline (CORTBASELINE) and 30 min post-ACTH challenge (CORTPOST-A CTH). An alternative measure of cortisol reactivity was developed through post-ACTH stimulation cortisol, normalized by cortisol by baseline (CORTNORM -ACTH). CORT B ASELINE positively predicted year 3 attention, while CORTNORM -ACTH negatively predicted attention, suggesting convergence of cortisol variables in prediction of neuropsychological function. Year 1 CORTACTH positively predicted child memory at year 3; Year 1 CORTNORM-ACTH negatively predicted year 3 sustained attentions. These findings demonstrate that HPA reactivity, including the application of normalized cortisol reactivity, can predict subsequent neuropsychological functioning of children with mild to moderate asthma.

Enhancing offspring hypothalamic-pituitary-adrenal (HPA) regulation via systematic novelty exposure: the influence of maternal HPA function.

In the rat, repeated brief exposures to novelty early in life can induce long-lasting enhancements in adult cognitive, social, emotional, and neuroendocrine function. Family-to-family variations in these intervention effects on adult offspring are predicted by the mother's ability to mount a rapid corticosterone (CORT) response to the onset of an acute stressor. Here, in Long-Evans rats, we investigated whether neonatal and adulthood novelty exposure, each individually and in combination, can enhance offspring hypothalamic-pituitary-adrenal (HPA) regulation. Using a 2 × 2 within-litter design, one half of each litter were exposed to a relatively novel non-home environment for 3-min (Neo_Novel) daily during infancy (PND 1-21) and the other half of the litter remained in the home cage (Neo_Home); we further exposed half of these two groups to early adulthood (PND 54-63) novelty exposure in an open field and the remaining siblings stayed in their home cages. Two aspects of HPA regulation were assessed: the ability to maintain a low level of resting CORT (CORTB) and the ability to mount a large rapid CORT response (CORTE) to the onset of an acute stressor. Assessment of adult offspring's ability to regulate HPA regulation began at 370 days of age. We further investigated whether the novelty exposure effects on offspring HPA regulation are sensitive to the context of maternal HPA regulation by assessing maternal HPA regulation similarly beginning 7 days after her pups were weaned. We found that at the population level, rats receiving neonatal, but not early adulthood exposure or both, showed a greater rapid CORTE than their home-staying siblings. At the individual family level, these novelty effects are positively associated with maternal CORTE. These results suggest that early experience of novelty can enhance the offspring's ability to mount a rapid response to environmental challenge and the success of such early life intervention is critically dependent upon the context of maternal HPA regulation.

Synchronized network activity as the origin of a P300 component in a facial attractiveness judgment task.

Many studies have used the P300 as an index for cognitive processing and neurological/psychiatric disorders. Here, we combined the source separation and source localization methods to investigate the cortical origins of the P300 elicited in a facial attractiveness judgment task. For each participant, we applied second-order blind identification (SOBI) to continuous EEG data to decompose the mixture of brain signals and noise. We then used the equivalent current dipole (ECD) models to estimate the centrality of the SOBI-recovered P300. We found that the ECD models, consisting of dipoles in the frontal and posterior association cortices, account for 96.5 ± 0.5% of variance in the scalp projection of the component. Given that the recovered dipole activities in different brain regions share the same time course with different weights, we conclude that the P300 originates from synchronized activity between anterior and posterior parts of the brain.

On the causes of early life experience effects: evaluating the role of mom.

Early life experiences are thought to have long-lasting effects on cognitive, emotional, and social function during adulthood. Changes in neuroendocrine function, particularly the hypothalamic-pituitary-adrenal (HPA) axis, contribute to these systems-level behavioral effects. In searching for causal mechanisms underlying these early experience effects, pioneering research has demonstrated an important role for maternal care in offspring development, and this has led to two persistent ideas that permeate current research and thinking: first, environmental impact on the developing infant is mediated through maternal care behavior; second, the more care that a mother provides, the better off her offspring. While a good beginning, the reality is likely more complex. In this review, we critically examine these ideas and propose a computationally-motivated theoretical framework, and within this framework, we consider evidence supporting a hypothesis of maternal modulation. These findings may inform policy decisions in the context of child health and development.

Intensive training induces longitudinal changes in meditation state-related EEG oscillatory activity.

The capacity to focus one's attention for an extended period of time can be increased through training in contemplative practices. However, the cognitive processes engaged during meditation that support trait changes in cognition are not well characterized. We conducted a longitudinal wait-list controlled study of intensive meditation training. Retreat participants practiced focused attention (FA) meditation techniques for three months during an initial retreat. Wait-list participants later undertook formally identical training during a second retreat. Dense-array scalp-recorded electroencephalogram (EEG) data were collected during 6 min of mindfulness of breathing meditation at three assessment points during each retreat. Second-order blind source separation, along with a novel semi-automatic artifact removal tool (SMART), was used for data preprocessing. We observed replicable reductions in meditative state-related beta-band power bilaterally over anteriocentral and posterior scalp regions. In addition, individual alpha frequency (IAF) decreased across both retreats and in direct relation to the amount of meditative practice. These findings provide evidence for replicable longitudinal changes in brain oscillatory activity during meditation and increase our understanding of the cortical processes engaged during meditation that may support long-term improvements in cognition.

Reducing behavioral inhibition to novelty via systematic neonatal novelty exposure: the influence of maternal hypothalamic-pituitary-adrenal regulation.

BACKGROUND: Behavioral inhibition (BI) to novelty is thought to be a stable temperament type that appears early in life and is a major risk factor for anxiety disorders. In the rat, habituation of such inhibition can be facilitated via neonatal novelty exposure (NNE), thus reducing BI to novelty. Here, we tested the hypothesis that this early intervention effect is modulated by the context of maternal self-stress regulation. METHODS: The NNE was carried out during postnatal days 1-21, in which one half of each litter was exposed to a relatively novel nonhome environment for 3-min daily while the remaining one half stayed in the home cage. After weaning, BI to novelty was assessed in an open field with a measure of disinhibition defined as a greater increase in exploration across two brief trials. Maternal context was characterized by trait measures of hypothalamic-pituitary-adrenal (HPA) axis reactivity, including basal and stress-evoked corticosterone (CORT) responses. RESULTS: Family-to-family variations in the NNE effect were associated with variations in maternal HPA function-a low-basal CORT and high-evoked CORT response profile constituting the context for a novelty-induced facilitation of disinhibition (i.e., a greater increase in exploratory activity over repeated trials) and an opposite HPA profile constituting the context for a novelty-induced reduction of disinhibition. CONCLUSIONS: This result is consistent with the hypothesis that maternal self-stress regulation modulates the effect of early life intervention on BI to novelty and suggests that effective interventions should include strategies to help mothers improve their self-stress regulation.

Maternal modulation of novelty effects on physical development.

Familiarity to the mother and the novelty afforded by the postnatal environment are two contrasting sources of neonatal influence. One hypothesis regarding their relationship is the maternal modulation hypothesis, which predicts that the same neonatal stimulation may have different effects depending on the maternal context. Here we tested this hypothesis using physical development, indexed by body weight, as an endpoint and found that, among offspring of mothers with a high initial swim-stress-induced corticosterone (CORT) response, neonatal novelty exposure induced an enhancement in early growth, and among offspring with mothers of a low initial CORT response, the same neonatal stimulation induced an impairment. At an older age, a novelty-induced increase in body weight was also found among offspring of mothers with high postnatal care reliability and a novelty-induced reduction found among offspring of mothers with low care reliability. These results support a maternal modulation of early stimulation effects on physical development and demonstrate that the maternal influence originates from multiple instead of any singular sources. These results (i) significantly extend the findings of maternal modulation from the domain of cognitive development to the domain of physical development; (ii) offer a unifying explanation for a previously inconsistent literature regarding early stimulation effects on body weight; and (iii) highlight the notion that the early experience effect involves no causal primacy but higher order interactions among the initial triggering events and subsequent events involving a multitude of maternal and nonmaternal influences.

Functional specificity in the modulation of novelty exposure effects by reliability of maternal care.

Using the within-litter neonatal novelty exposure procedure, we manipulated newborn pups' environmental novelty independently from natural variations in maternal care. To better translate animal models to human development studies, we introduce a measure for maternal care reliability. We examined how this reliability modulates novelty-exposure-induced effects on offspring cognitive, social, and emotional development and show that maternal care reliability acts in a function-specific manner. We discuss our results within the framework of a maternal reliability-based modulation model.

Dissociation between neonatal novelty-induced preferential maternal care and enhancement in cognitive, social, and emotional functions.

Early life stimulation is known to produce long-lasting changes in the brain and behavior. One such early stimulation method is the neonatal novelty exposure procedure which allows the isolation of the novelty effect from several prominent confounding factors inherent to the neonatal handling procedure. In two previous studies, we found long-lasting novelty effects on different sets of functional measures without accompanying preferential maternal care, even when the observation was made immediately after the novelty manipulation, a time when such preferential care is most likely to be expressed. Here, within a single cohort of Long-Evans male rats, we demonstrate that novelty exposure leads to enhancements across several functional domains, including increased disinhibition to novelty, enhanced spatial and social memory, and reduced aggression, again without the accompaniment of preferential maternal care. These findings extend novelty exposure effects to aggression and replicate previously known novelty exposure effects on spatial and social memory with extension to new developmental stages. Most importantly, these findings do not support the hypothesis that preferential maternal care towards novelty-exposed pups mediates the observed novelty effects. We discuss the possibility that the effects of neonatal novelty exposure are mediated via repeated activation of the hypothalamic-pituitary-adrenal (HPA) axis that serves to inoculate pups for future exposures to novelty and novelty-induced HPA activation and that maternal influence is likely to be expressed via its modulatory role-the mother sets the individual-family specific behavioral and hormonal context to allow the same early life experience to have a family-specific effect.

Neonatal novelty-induced persistent enhancement in offspring spatial memory and the modulatory role of maternal self-stress regulation.

Development of spatial memory in the rat is influenced by both maternal and nonmaternal aspects of the postnatal environment. Yet it remains poorly understood how these two aspects of the postnatal environment interact to program offspring cognitive development. By considering the joint influence of neonatal environmental novelty and maternal self-stress regulation on the development of spatial memory function in Long-Evans hooded rats, we show a persistent neonatal novelty-induced enhancement in spatial reference and working memory functions among the same individual offspring from juvenility to adulthood and a contrasting transient maternal modulatory influence on this novelty-related enhancement present during only juvenility. Specifically, at and only at juvenility, for mothers with good self-stress regulation as indexed by a low circulating basal corticosterone level, offspring showed a novelty-induced enhancement in spatial memory function, whereas for mothers with poor self-stress regulation, indexed by a high basal corticosterone level, offspring showed little enhancement or even small impairments. These findings indicate that maternal and nonmaternal postnatal environments exert separate but interacting influences on offspring cognitive development and support a maternal modulation model of cognitive development that considers maternal self-stress regulation as an important factor among the multitude of maternal influences.

Converging influence of neonatal novelty experience and maternal self-stress regulation on the plasticity of offspring acoustic startle response latency.

Behavioral and brain development is influenced by both maternal and non-maternal aspects of the postnatal environment and the precise nature of their interaction is the topic of an ongoing debate. Here, we consider the joint influence of neonatal environmental novelty and maternal self-stress regulation on the development of acoustic startle reflex (ASR), an extensively investigated model system for learning and neural plasticity. We test the hypothesis in the rat that brief repeated neonatal exposures to novelty can affect ASR in late adulthood and that this influence is sensitive to postnatal context of maternal self-stress regulation. We carried out the neonatal and early adulthood novelty exposure (PND 1-21 and PND 54-63 respectively), obtained measures of maternal self-stress regulation after weaning (PND 25-26), and evaluated in the male rats, ASR and ASR plasticity at adulthood (ASR1 and ASR2, one week apart, at 13.5 months of age). During ASR1, offspring, whose mothers had poor self-stress regulation as indexed by a high circulating basal corticosterone (CORT) concentration, showed a novelty-induced decrease of ASR latency. Offspring whose mothers had good self regulation as indexed by a low CORT, showed a novelty-induced increase in ASR latency. From ASR1 to ASR2, offspring whose mothers had poor self-stress regulation, showed a novelty-induced ASR latency habituation (increase in latency) while offspring whose mothers had good self regulation showed no novelty effect. These findings support a novel framework in which maternal and non-maternal postnatal environments exert interacting influences on the neonates, with maternal individual differences in self-stress regulation providing a critical context to enable bidirectional novelty-induced influence across different rat families.

Functional brain asymmetry in adult novelty response: on fluidity of neonatal novelty exposure effects.

Novelty and surprises differentially modify the left and right sides of the brain. Here we show that repeated brief exposures to the novelty of a non-home environment during infancy and early adulthood lead to long-lasting changes in adulthood in the global bi-lateralization organization of the brain as indexed by a transiently detectable right-sided orientating bias upon the initial encounter with the novel environment. Most surprisingly, we show that in the same individuals, the short-term effect of the combined neonatal and adulthood novelty exposures on functional brain asymmetry measured at young adulthood (5 months of age) is distinctively different from the long-term effect measured at late adulthood (15 months of age). These results suggest that long-lasting, cumulative effects of early life experience on brain and behavior organization are not necessarily permanent, but continue to unfold, presumably via interactions with a multitude of unmonitored intervening life events.

Novelty-induced enhancement in spatial memory: is infancy a critical period?

Development of many psychological functions is known to occur within a limited time window and beyond such a critical period, environmental stimulation has little or no effect. With a split-litter 2×2 factorial design in which neonatal and early adulthood novelty exposure were two within-litter factors, we examined whether infancy is a critical period for novelty exposure experience to induce a long-lasting functional enhancement in spatial memory and whether the known enhancement effect induced by early life experience can be further augmented by later adult experience. Spatial memory performance was evaluated in a three-day moving platform Morris water maze task. We found that the animals deprived of novelty exposure during infancy could nevertheless benefit from a delayed adult exposure and that the magnitude of this enhancement was comparable to the enhancement induced by neonatal exposure. This finding indicates that infancy is not a critical period beyond which novelty exposure will have little effect on enhancing spatial memory. Surprisingly, although both neonatal and adult experience alone produced enhancement in spatial memory performance, animals that experienced both neonatal and adult exposures showed no statistically significant difference from those who had none. This finding indicates that the cumulative effect of neonatal and early adulthood experience of novelty is not additive but a result of non-linear interaction and that knowing the effect of a single-stage-intervention does not allow one to predict the final developmental outcome without taking into consideration events occurring before or after.

Social competitiveness and plasticity of neuroendocrine function in old age: influence of neonatal novelty exposure and maternal care reliability.

Early experience is known to have a profound impact on brain and behavioral function later in life. Relatively few studies, however, have examined whether the effects of early experience remain detectable in the aging animal. Here, we examined the effects of neonatal novelty exposure, an early stimulation procedure, on late senescent rats' ability to win in social competition. During the first 3 weeks of life, half of each litter received daily 3-min exposures to a novel environment while the other half stayed in the home cage. At 24 months of age, pairs of rats competed against each other for exclusive access to chocolate rewards. We found that novelty-exposed rats won more rewards than home-staying rats, indicating that early experience exerts a life-long effect on this aspect of social dominance. Furthermore, novelty-exposed but not home-staying rats exhibited habituation of corticosterone release across repeated days of social competition testing, suggesting that early experience permanently enhances plasticity of the stress response system. Finally, we report a surprising finding that across individual rat families, greater effects of neonatal novelty exposure on stress response plasticity were found among families whose dams provided more reliable, instead of a greater total quantity of, maternal care.

An epigenetic induction of a right-shift in hippocampal asymmetry: selectivity for short- and long-term potentiation but not post-tetanic potentiation.

In humans, it is well established that major psychological functions are asymmetrically represented between the left and right cerebral cortices. The developmental origin of such functional lateralization remains unknown. Using the rat as a model system, we examined whether exposing neonates briefly to a novel environment can differentially affect synaptic plasticity in the left and right hippocampi during adulthood. During the first 3 weeks of life, one half of the pups from a litter spent 3 min daily away from their familiar home environment (Novel) while their littermates remained in that familiar environment (Home). At adulthood (7-months old), post-tetanic potentiation (PTP) of excitatory post-synaptic potentials (EPSPs), a very short-lasting form of plasticity, was greater among the Novel than the Home rats in both left and right hippocampi. In contrast, the novelty-induced increases in short- and long-term potentiation (STP, LTP), two relatively longer-lasting forms of plasticity, were found only in the right hippocampus. These findings demonstrate that a phase-selective asymmetry in hippocampal synaptic plasticity can be induced epigenetically by seemingly small systematic differences in early life environment. The selectivity of this asymmetry for the longer-lasting forms of synaptic plasticity suggests that the observed asymmetry in plasticity may contribute specifically to an asymmetric learning process which, in turn, may contribute to a functional asymmetry in the neocortex.

Programming social, cognitive, and neuroendocrine development by early exposure to novelty.

Mildly stressful early life experiences can potentially impact a broad range of social, cognitive, and physiological functions in humans, nonhuman primates, and rodents. Recent rodent studies favor a maternal-mediation hypothesis that considers maternal-care differences induced by neonatal stimulation as the cause of individual differences in offspring development. Using neonatal novelty exposure, a neonatal stimulation paradigm that dissociates maternal individual differences from a direct stimulation effect on the offspring, we investigated the effect of early exposures to novelty on a diverse range of psychological functions using several assessment paradigms. Pups that received brief neonatal novelty exposures away from the home environment showed enhancement in spatial working memory, social competition, and corticosterone response to surprise during adulthood compared with their home-staying siblings. These functional enhancements in novelty-exposed rats occurred despite evidence that maternal care was directed preferentially toward home-staying instead of novelty-exposed pups, indicating that greater maternal care is neither necessary nor sufficient for these early stimulation-induced functional enhancements. We suggest a unifying maternal-modulation hypothesis, which distinguishes itself from the maternal-mediation hypothesis in that (i) neonatal stimulation can have direct effects on pups, cumulatively leading to long-term improvement in adult offspring; and (ii) maternal behavior can attenuate or potentiate these effects, thereby decreasing or increasing this long-term functional improvement.