Molecular Mechanisms for Changing Brain Connectivity in Mice and Humans.

The goal of this study was to examine commonalities in the molecular basis of learning in mice and humans. In previous work we have demonstrated that the anterior cingulate cortex (ACC) and hippocampus (HC) are involved in learning a two-choice visuospatial discrimination task. Here, we began by looking for candidate genes upregulated in mouse ACC and HC with learning. We then determined which of these were also upregulated in mouse blood. Finally, we used RT-PCR to compare candidate gene expression in mouse blood with that from humans following one of two forms of learning: a working memory task (network training) or meditation (a generalized training shown to change many networks). Two genes were upregulated in mice following learning: caspase recruitment domain-containing protein 6 (Card6) and inosine monophosphate dehydrogenase 2 (Impdh2). The Impdh2 gene product catalyzes the first committed step of guanine nucleotide synthesis and is tightly linked to cell proliferation. The Card6 gene product positively modulates signal transduction. In humans, Card6 was significantly upregulated, and Impdh2 trended toward upregulation with training. These genes have been shown to regulate pathways that influence nuclear factor kappa B (NF-κB), a factor previously found to be related to enhanced synaptic function and learning.

Decision Making as a Learned Skill in Mice and Humans.

Attention is a necessary component in many forms of human and animal learning. Numerous studies have described how attention and memory interact when confronted with a choice point during skill learning. In both animal and human studies, pathways have been found that connect the executive and orienting networks of attention to the hippocampus. The anterior cingulate cortex, part of the executive attention network, is linked to the hippocampus via the nucleus reuniens of the thalamus. The parietal cortex, part of the orienting attention network, accesses the hippocampus via the entorhinal cortex. These studies have led to specific predictions concerning the functional role of each pathway in connecting the cortex to the hippocampus. Here, we review some of the predictions arising from these studies. We then discuss potential methods for manipulating the two pathways and assessing the directionality of their functional connection using viral expression techniques in mice. New studies may allow testing of a behavioral model specifying how the two pathways work together during skill learning.

Increasing the amplitude of intrinsic theta in the human brain.

In a mouse study we found increased myelination of pathways surrounding the anterior cingulate cortex (ACC) following stimulation near the theta rhythm (4-8 Hz), and evidence that this change in connectivity reduced behavioral anxiety. We cannot use the optogenetic methods with humans that were used in our mouse studies. This paper examines whether it is possible to enhance intrinsic theta amplitudes in humans using less invasive methods. The first experiment compares electrical, auditory and biofeedback as methods for increasing intrinsic theta rhythm amplitudes in the Anterior Cingulate Cortex (ACC). These methods are used alone or in conjunction with a task designed to activate the same area. The results favor using electrical stimulation in conjunction with a task targeting this region. Stimulating the ACC increases intrinsic theta more in this area than in a control area distant from the site of stimulation, suggesting some degree of localization of the stimulation. In Experiment 2, we employed electrical stimulation with the electrodes common to each person, or with electrodes selected from an individual head model. We targeted the ACC or Motor Cortex (PMC). At baseline, intrinsic theta is higher in the ACC than the PMC. In both areas, theta can be increased in amplitude by electrical stimulation plus task. In the PMC, theta levels during stimulation plus task are not significantly higher than during task alone. There is no significant difference between generic and individual electrodes. We discuss steps needed to determine whether we can use the electrical stimulation + task to improve the connectivity of white matter in different brain areas.

Relation of FTO to BOLD response to receipt and anticipated receipt of food and monetary reward, food images, and weight gain in healthy weight adolescents.

Although the fat mass and obesity-associated gene (FTO) correlates with elevated body mass, it is unclear how it contributes to overeating. We tested if individuals with the A allele show greater reward region responsivity to receipt and anticipated receipt of food and money and palatable food images. We also tested if these individuals show greater future weight gain. Initially healthy weight adolescents (Study 1, N = 162; Study 2, N = 135) completed different functional magnetic resonance imaging paradigms and had their body mass measured annually over 3 years. Adolescents with the AA or AT genotypes showed less precuneus and superior parietal lobe response and greater cuneus and prefrontal cortex response to milkshake receipt and less putamen response to anticipated milkshake receipt than those with the TT genotype in separate analyses of each sample. Groups did not differ in response to palatable food images, and receipt and anticipated receipt of money, or in weight gain over 3-year follow-up. Results suggest that initially healthy weight adolescents with vs without the FTO A allele show differential responsivity to receipt and anticipated receipt of food but do not differ in neural response to palatable food images and monetary reward and do not show greater future weight gain.

Influence of the SLC6A3-DAT1 Gene on Multifaceted Measures of Self-regulation in Preschool Children.

Development of self-regulation, the capacity to voluntarily modulate thoughts, emotions and actions is strongly related to the maturation of the dopamine-mediated executive attention network (EAN). The attention control processes associated with the EAN greatly overlap with efficiency of the executive functions and are correlated with measures of effortful control. Regulation of dopamine levels within the EAN, particularly in the basal ganglia is carried out by the action of dopamine transporters. In humans, the SLC6A3/DAT1 gene carries out the synthesis of the DAT protein. The 10-repeat allele has been associated with an enhanced expression of the gene and has been related to ADHD symptoms. Little is known about the impact of DAT1 variations on children's capacity to self-regulate in contexts that impose particular demands of regulatory control such as the school or home. This study defines a multi-domain phenotype of self-regulation and examines whether variations of the DAT1 gene accounts for individual differences in performance in 4-5 year old children. Results show that presence of the 10r allele is related to a diminished ability to exert voluntary regulation of reactivity. These findings shed light on the neurobiological mechanisms underlying individual differences in self-regulation during childhood.

Methylation polymorphism influences practice effects in children during attention tasks.

Epigenetic mechanisms mediate the influence of experience on gene expression. Methylation is a principal method for inducing epigenetic effects on DNA. In this paper, we examine alleles of the methylenetetrahydrofolate reductase (MTHFR) gene that vary enzyme activity, altering the availability of the methyl donor and thus changing the efficiency of methylation. We hypothesized that alleles of the MTHFR gene would influence behavior in an attention-related task in conjunction with genes known to influence attention. We found that seven-year-old children homozygous for the C allele of MTHFR in interaction with the catechol O-methyltransferase (COMT) gene showed greater improvement in overall reaction time (RT) and in conflict resolution with practice on the Attention Network Test (ANT). This finding indicates that methylation may operate on or through genes that influence executive network operation. However, MTHFR T allele carriers showed faster overall RT and conflict resolution. Some children showed an initial improvement in ANT RT followed by a decline in performance, and we found that alleles of the dopamine beta-hydroxylase (DBH) gene were related to this performance decline. These results suggest a genetic dissociation between improvement while learning a skill and reduction in performance with continued practice.

White matter and reaction time: Reply to commentaries.

We appreciate the many comments we received on our discussion paper and believe that they reflect a recognition of the importance of this topic worldwide. We point out in this reply that there appears to be a confusion between the role of oscillations in creating white matter and other functions of oscillations in communicating between neural areas during task performance or at rest. We also discuss some mechanisms other than the enhancement of white matter that must influence reaction time. We recognize the limited understanding we have of transfer and outline some future directions designed to improve our understanding of this process.

How changes in white matter might underlie improved reaction time due to practice.

Why does training on a task reduce the reaction time for performing it? New research points to changes in white matter pathways as one likely mechanism. These pathways connect remote brain areas involved in performing the task. Genetic variations may be involved in individual differences in the extent of this improvement. If white matter change is involved in improved reaction time with training, it may point the way toward understanding where and how generalization occurs. We examine the hypothesis that brain pathways shared by different tasks may result in improved performance of cognitive tasks remote from the training.

Developing brain networks of attention.

PURPOSE OF REVIEW: Attention is a primary cognitive function critical for perception, language, and memory. We provide an update on brain networks related to attention, their development, training, and pathologies. RECENT FINDINGS: An executive attention network, also called the cingulo-opercular network, allows voluntary control of behavior in accordance with goals. Individual differences among children in self-regulation have been measured by a higher order factor called effortful control, which is related to the executive network and to the size of the anterior cingulate cortex. SUMMARY: Brain networks of attention arise in infancy and are related to individual differences, including pathology during childhood. Methods of training attention may improve performance and ameliorate pathology.

Developing Attention: Behavioral and Brain Mechanisms.

Brain networks underlying attention are present even during infancy and are critical for the developing ability of children to control their emotions and thoughts. For adults, individual differences in the efficiency of attentional networks have been related to neuromodulators and to genetic variations. We have examined the development of attentional networks and child temperament in a longitudinal study from infancy (7 months) to middle childhood (7 years). Early temperamental differences among infants, including smiling and laughter and vocal reactivity, are related to self-regulation abilities at 7 years. However, genetic variations related to adult executive attention, while present in childhood, are poor predictors of later control, in part because individual genetic variationmay have many small effects and in part because their influence occurs in interaction with caregiver behavior and other environmental influences. While brain areas involved in attention are present during infancy, their connectivity changes and leads to improvement in control of behavior. It is also possible to influence control mechanisms through training later in life. The relation between maturation and learning may allow advances in our understanding of human brain development.

Control networks and neuromodulators of early development.

In adults, most cognitive and emotional self-regulation is carried out by a network of brain regions, including the anterior cingulate, insula, and areas of the basal ganglia, related to executive attention. We propose that during infancy, control systems depend primarily upon a brain network involved in orienting to sensory events that includes areas of the parietal lobe and frontal eye fields. Studies of human adults and alert monkeys have shown that the brain network involved in orienting to sensory events is moderated primarily by the nicotinic cholinergic system arising in the nucleus basalis. The executive attention network is primarily moderated by dopaminergic input from the ventral tegmental area. A change from cholinergic to dopaminergic modulation would be a consequence of this switch of control networks and may be important in understanding early development. We trace the attentional, emotional, and behavioral changes in early development related to this developmental change in regulative networks and their modulators.

The Dopamine Receptor D4 Gene 7-Repeat Allele Interacts with Parenting Quality to Predict Effortful Control in Four-Year-Old Children.

The dopamine receptor D4 gene (DRD4) 7-repeat allele has been found to interact with environmental factors such as parenting in children and peer attitudes in adults to influence aspects of behavior such as risk taking. We previously found that in toddlers, lower-quality parenting in combination with the 7-repeat allele of the DRD4 gene was associated with greater parent-reported Sensation Seeking (SS), but was unrelated to Effortful Control (EC). We now report findings from a followup assessment with the same sample of children showing that parenting quality interacts with the presence of the 7-repeat allele to predict EC in 3-to 4-year-old children. The change in these patterns of results may reflect the increased role of the executive attention network in older children and adults. However, due to the small sample size (N = 52) and the novelty of the results, these findings should be treated with caution and considered preliminary until they are replicated in an independent sample.

Genetic variation influences on the early development of reactive emotions and their regulation by attention.

INTRODUCTION: Individual differences in temperament and attention provide an important link between normal and pathological development. Previous studies suggest that during infancy, orienting of attention is associated with higher levels of positive affect and lower levels of negative affect. For older children and adults, self-regulation, as measured by ratings of effortful control, is consistently associated with lower levels of negative affect such as sadness and distress. METHODS: In the current paper we use a longitudinal study of children at ages 6-7 months (Time 1) and 18-20 months (Time 2) to examine how variations in candidate genes relate to emotional and self-regulatory aspects of temperament. RESULTS: In accord with previous findings, parent ratings of orienting were positively related to positive affect only during infancy. Genetic variation in COMT was related to positive affect at Time l but not Time 2. Negative affect at both Time 1 and Time 2 was related to genetic variation in SNAP25. Genetic variation in CHRNA4 was related to Effortful Control at Time 2. CONCLUSIONS: These findings lend support to the early modulation of emotion by aspects of orienting (Time 1) and executive attention (Time 2), and indicate that emotional reactivity and its regulation are modulated by different genes.

Parenting quality interacts with genetic variation in dopamine receptor D4 to influence temperament in early childhood.

We examined the influence of a common allelic variation in the dopamine receptor D4 (DRD4) gene and caregiver quality on temperament in early childhood. Children 18-21 months of age were genotyped for the DRD4 48 base pair tandem repeat polymorphism, which has been implicated in the development of attention, sensation seeking, and attention-deficit/hyperactivity disorder. The children also interacted with their caregiver for 10 min in a laboratory setting, and these videotaped interactions were coded for parenting quality using an observational rating procedure. The presence of the DRD4 7-repeat allele was associated with differences in the influence of parenting on a measure of temperamental sensation seeking constructed from caregiver reports on children's activity level, impulsivity, and high-intensity pleasure. Children with the 7-repeat allele were influenced by parenting quality, with lower quality parenting associated with higher levels of sensation seeking; children without the 7-repeat allele were uninfluenced by parenting quality. Differences between alleles were not related to the child's self-regulation as assessed by the effortful control measure. Previous studies have indicated that the 7-repeat allele is under positive selective pressure, and our results are consistent with the hypothesis that the DRD4 7-repeat allele increased children's sensitivity to environmental factors such as parenting. This study shows that genes influence the relation between parenting and temperament in ways that are important to normal development and psychopathology.

A pentatricopeptide repeat protein facilitates the trans-splicing of the maize chloroplast rps12 pre-mRNA.

The pentatricopeptide repeat (PPR) is a degenerate 35-amino acid repeat motif that is widely distributed among eukaryotes. Genetic, biochemical, and bioinformatic data suggest that many PPR proteins influence specific posttranscriptional steps in mitochondrial or chloroplast gene expression and that they may typically bind RNA. However, biological functions have been determined for only a few PPR proteins, and with few exceptions, substrate RNAs are unknown. To gain insight into the functions and substrates of the PPR protein family, we characterized the maize (Zea mays) nuclear gene ppr4, which encodes a chloroplast-targeted protein harboring both a PPR tract and an RNA recognition motif. Microarray analysis of RNA that coimmunoprecipitates with PPR4 showed that PPR4 is associated in vivo with the first intron of the plastid rps12 pre-mRNA, a group II intron that is transcribed in segments and spliced in trans. ppr4 mutants were recovered through a reverse-genetic screen and shown to be defective for rps12 trans-splicing. The observations that PPR4 is associated in vivo with rps12-intron 1 and that it is also required for its splicing demonstrate that PPR4 is an rps12 trans-splicing factor. These findings add trans-splicing to the list of RNA-related functions associated with PPR proteins and suggest that plastid group II trans-splicing is performed by different machineries in vascular plants and algae.