school-age child

Physical fitness improves memory in children

October, 2010

More evidence for the benefits of physical exercise for cognition, this time involving 9-10 year old children.

Brain imaging of 49 children aged 9-10 has found that those who were physically fit had a hippocampus significantly bigger (around 12%) than those who were not fit. Animal studies and those with older adults have shown that aerobic exercise increases the growth of new brain cells in the hippocampus. Physical fitness was measured by how efficiently the children used oxygen while running on a treadmill. Fitter children also did better on tests of relational (but not item) memory, and this association was directly mediated by hippocampal volume.

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Manganese in drinking water may impair children's intellectual abilities

October, 2010

The ‘safe’ levels of manganese in water may need to be revisited after a study finds school-age children with high levels of manganese in their tap water have significantly lower IQs.

Manganese exposure in the workplace is known to have neurotoxic effects, but manganese occurs naturally in soil and sometimes in groundwater. One region where the groundwater contains naturally high levels of manganese is Quebec. A study involving 362 Quebec children, aged 6-13, has measured both the concentrations of metals (manganese, iron, copper, lead, zinc, arsenic, magnesium and calcium) in their tap water, and their cognitive abilities.

Although manganese concentrations were well below current guidelines, the average IQ of those whose tap water was in the upper 20% was 6.2 points below children whose water contained little or no manganese. The association was more marked for Performance IQ than Verbal IQ (Performance IQ reflects perceptual organization and processing speed). The analysis took into account factors such as family income, maternal intelligence, maternal education, and the presence of other metals in the water. No association was found between manganese in their food and IQ.

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Childhood cancer survivors show sustained benefit from common ADHD medication

October, 2010

Ritalin helps some survivors of childhood cancer with attention problems.

Many survivors of childhood cancer experience cognitive problems as a result of their treatment. The drug methylphenidate (marketed under several names, the best known of which is Ritalin) has previously been shown to help attention problems in such survivors in the short term. Now a new study demonstrates that it can also be of benefit in the long term.

The study tested attention, social skills and behavior in survivors who had been on the drug for a year, comparing them to a similar group of unmedicated survivors. Although the drug did not lead to a significant gain in measured academic skills in math, reading and spelling, many did show improvements to attention that put them back in the normal range.

Nevertheless, the results also emphasize the need for other approaches, given that many did not benefit from the drug, and some may not be good candidates for medical or other reasons. The treatment group included 35 survivors of brain tumors and 33 of acute lymphoblastic leukemia (ALL). Any who suffered from ADHD before their cancer were excluded from the study.

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Low grades in adolescence linked to dopamine genes

October, 2010

A large American study of middle- and high-school students has found lower academic performance in core subjects was associated with three dopamine gene variants

Analysis of DNA and lifestyle data from a representative group of 2,500 U.S. middle- and high-school students tracked from 1994 to 2008 in the National Longitudinal Study of Adolescent Health has revealed that lower academic performance was associated with three dopamine gene variants. Having more of the dopamine gene variants (three rather than one, say) was associated with a significantly lower GPA.

Moreover, each of the dopamine genes (on its own) was linked to specific deficits: there was a marginally significant negative effect on English grades for students with a specific variant in the DAT1 gene, but no apparent effect on math, history or science; a specific variant in the DRD2 gene was correlated with a markedly negative effect on grades in all four subjects; those with the deleterious DRD4 variant had significantly lower grades in English and math, but only marginally lower grades in history and science.

Precisely why these specific genes might impact academic performance isn’t known with any surety, but they have previously been linked to such factors as adolescent delinquency, working memory, intelligence and cognitive abilities, and ADHD, among others.

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White noise improves memory in inattentive schoolchildren

October, 2010

Adding to research suggesting type of background noise affects whether it impairs learning or not, a new study indicates white noise has different effects depending on whether the students have attention problems.

Five years ago I reported on a finding that primary school children exposed to loud aircraft noise showed impaired reading comprehension (see below). Now a small Norwegian study has found that playing white noise helped secondary school children with attention problems, but significantly impaired those who were normally attentive.

The adolescents were asked to remember as many items as possible from a list read out either in the presence or absence of white noise (78dB). The results were consistent with a computational model based on the concepts of stochastic resonance and dopamine related internal noise, postulating that a moderate amount of external noise would benefit individuals in hypodopaminergic states (such as those with ADHD). The results need to be verified with a larger group, but they do suggest a new approach to helping those with attention problems.

The previous study referred to involved 2844 children aged 9-10. The children were selected from primary schools located near three major airports — Schiphol in the Netherlands, Barajas in Spain, and Heathrow in the UK. Reading age in children exposed to high levels of aircraft noise was delayed by up to 2 months in the UK and by up to 1 month in the Netherlands for each 5 decibel change in noise exposure. On the other hand, road traffic noise did not have an effect on reading and indeed was unexpectedly found to improve recall memory. An earlier German study found children attending schools near the old Munich airport improved their reading scores and cognitive memory performance when the airport shut down, while children going to school near the new airport experienced a decrease in testing scores.

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Change in our understanding of memory development

September, 2010

Children’s slowly developing memory for past events may not be due to the slow development of the prefrontal cortex, as was thought, but to changes in the hippocampus.

Children’s ability to remember past events improves as they get older. This has been thought by many to be due to the slow development of the prefrontal cortex. But now brain scans from 60 children (8-year-olds, 10- to 11-year-olds, and 14-year-olds) and 20 young adults have revealed marked developmental differences in the activity of the mediotemporal lobe.

The study involved the participants looking at a series of pictures (while in the scanner), and answering a different question about the image, depending on whether it was drawn in red or green ink. Later they were shown the pictures again, in black ink and mixed with new ones. They were asked whether they had seen them before and whether they had been red or green.

While the adolescents and adults selectively engaged regions of the hippocampus and posterior parahippocampal gyrus to recall event details, the younger children did not, with the 8-year-olds indiscriminately using these regions for both detail recollection and item recognition, and the 10- to 11-year-olds showing inconsistent activation. It seems that the hippocampus and posterior parahippocampal gyrus become increasingly specialized for remembering events, and these changes may partly account for long-term memory improvements during childhood.

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Prenatal exposure to pesticides linked to attention problems

September, 2010

In a study of young Mexican-American children, higher prenatal exposure to pesticides was significantly associated with ADHD symptoms at age 5.

A study following over 300 Mexican-American children living in an agricultural community has found that their prenatal exposure to organophosphate pesticides (measured by metabolites in the mother’s urine during pregnancy) was significantly associated with attention problems at age 5. This association was stronger among boys, and stronger with age (at 3 ½ the association, although present, did not reach statistical significance — perhaps because attention disorders are much harder to recognize in toddlers). Based on maternal report, performance on attention tests, and a psychometrician’s report, 8.5% of 5-year-olds were classified as having ADHD symptoms. Each tenfold increase in prenatal pesticide metabolites was linked to having five times the odds of scoring high on the computerized tests at age 5. The child’s own level of phosphate metabolites was not linked with attention problems.

Organophosphate pesticides disrupt acetylcholine, which is important for attention and short-term memory. While the exposure of these children to pesticides is presumably higher and more chronic than that of the general U.S. population, food is a significant source of pesticide exposure among the general population.

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Marks AR, Harley K, Bradman A, Kogut K, Barr DB, Johnson C, et al. 2010. Organophosphate Pesticide Exposure and Attention in Young Mexican-American Children. Environ Health Perspect :-. doi:10.1289/ehp.1002056
Full text available at http://ehp03.niehs.nih.gov/article/fetchArticle.action?articleURI=info%3...

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New ways of assessing connectivity establish a "brain age" measure of child development

September, 2010

A new way of analyzing brain scans reveals exactly what changes in the brain, in terms of connectivity, as it matures.

Last year I reported on a study involving 210 subjects aged 7 to 31 that found that in contrast to the adult brain, most of the tightest connections in a child's brain are between brain regions that are physically close to each other. As the child grows to adulthood, the brain switches from an organization based on local networks based on physical proximity to long-distance networks based on functionality. Now the same researchers, using five-minute scans from 238 people aged 7 to 30, have looked at nearly 13,000 functional (rather than structural) connections and identified 200 key ones. On the basis of these 200 connections, the brains could be identified as belonging to a child (7-11) or an adult (25-30) with 92% accuracy, and adolescents or adults with 75% accuracy. Moreover, the most important factor in predicting development (accounting for about 68%) was the trimming of the vast number of childhood connections.

Apart from emphasizing the importance of pruning connections in brain development, the main value of this research is in establishing an effective analytic method and baseline measurements for normal development. It is hoped that this will eventually help researchers work out indicators for various developmental disorders.

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Are some ADHD-labeled kids just young for their grade?

September, 2010

Two studies suggest that ADHD is being over-diagnosed among students who are the youngest in their classes.

Two independent studies have found that students whose birthdays fell just before their school's age enrollment cutoff date—making them among the youngest in their class—had a substantially higher rate of ADHD diagnoses than students who were born later. One study, using data from the Early Childhood Longitudinal Study-Kindergarten cohort, found that ADHD diagnoses among children born just prior to their state’s kindergarten eligibility cutoff date are more than 60% more prevalent than among those born just afterward (who therefore waited an extra year to begin school). Moreover, such children are more than twice as likely to be taking Ritalin in grades 5 and 8. While the child’s school starting age strongly affects teachers’ perceptions of ADHD symptoms, it only weakly affects parental perceptions (who are more likely to compare their child with others of the same age, rather than others in the same class). The other study, using data from the 1997 to 2006 National Health Interview Survey, found that 9.7% of those born just before the cutoff date were diagnosed with ADHD compared to 7.6% of those born just after.

The two findings suggest that many of these children are mistakenly being diagnosed with ADHD simply because they are less emotionally or intellectually mature than their (older) classmates.

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Rehearsing so as not to forget

August, 2010

A new study shows that verbal rehearsal develops considerably between the ages of six and eight.

A study involving 117 six year old children and 104 eight year old children has found that the ability to preserve information in working memory begins at a much younger age than had previously been thought. Moreover the study revealed that, while any distraction between learning the words and having to recall them hindered recall, having to perform a verbal task was particularly damaging. This suggests that their remembering was based on “phonological rehearsal”, that is, verbally repeating the names of the items to themselves. Consistent with the research suggesting children begin to phonologically rehearse at around 7 years of age, the verbal task hindered the 8 year olds more than the 6 year olds.

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