child development

Higher levels of omega-3 in diet associated with better sleep

A study involving 362 children with reading problems has found that 16 weeks of daily 600 mg supplements of omega-3 DHA from algal sources improved their sleep. According to a sleep questionnaire filled out by parents, 40% of these children had significant sleep problems. Monitoring of 43 of the poor sleepers found that children taking daily supplements of omega-3 had nearly one hour (58 minutes) more sleep and seven fewer waking episodes per night compared with children taking a placebo.

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Long-lasting effects of early-childhood brain injuries

January, 2012

A 10 year follow-up of children hospitalized for brain injuries in early childhood suggests that young brains are not as resilient as we thought.

I recently discussed some of the implications of head injuries and how even mild concussions can have serious and long-term consequences. A follow-up study looking at the effects of childhood traumatic brain injury ten years after the event has found that even those with mild TBI showed some measurable effects, while those with severe TBI had markedly poorer performance on a number of cognitive measures.

The study involved 40 children who were admitted to hospital with TBI in early childhood (between 2 to 7 years; average just under 5), and 16 healthy controls. The children’s cognitive functions were assessed at the time of accident, and again at 12 and 30 months and 10 years later. Of the 40 with TBIs, 7 had mild injuries, 20 had moderate, and 13 severe.

Unsurprisingly, children with severe TBI had the poorest outcomes. This group was significantly poorer (compared to controls) on full scale IQ; performance IQ; verbal IQ; verbal comprehension; perceptual organization, processing speed. Those who had moderate TBI were significantly poorer on full scale IQ and verbal comprehension only, and those with mild TBI performed more poorly than the controls on verbal comprehension only. Note the size of these effects: the average scores of the group with severe TBI were 18-26 points lower than the control group. In comparison, those with moderate TBI were around 10 points lower on the two significant measures.

These findings are in contrast to research involving adults and older children, where IQ tends to remain intact.

They also contradict the belief that young brains have greater ability to ‘bounce back’ from injury.

Interestingly, the recovery trajectory wasn’t significantly affected by severity of injury — all the groups followed a similar pattern and they all tended to plateau from 5 to 10 years after injury. In general, the findings paint a picture of a long period of disrupted development immediately after the injury, lasting perhaps as long as 30 months, before the brain has recovered sufficiently to progress relatively normally. In other words, intervention may be helpful even years after the injury.

One weakness in the study is the small number of mild TBI cases. It should also be noted that the IQ of the control group was surprisingly high (113). However, given that they had similar IQ levels to the TBI groups prior to injury, it is possible that this reflects a practice effect (but remember that all groups got the same amount of practice).

One thing I wonder about, given recent research pointing to the value of schooling in raising IQ, is the extent to which some of this is due to loss of education that may have resulted from severe injury.

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Ability to remember memories' origin develops slowly

October, 2011

A study comparing the brains of children, adolescents, and young adults has found that the ability to remember the origin of memories is slow to mature. As with older adults, impaired source memory increases susceptibility to false memories.

In the study, 18 children (aged 7-8), 20 adolescents (13-14), and 20 young adults (20-29) were shown pictures and asked to decide whether it was a new picture or one they had seen earlier. Some of the pictures were of known objects and others were fanciful figures (this was in order to measure the effects of novelty in general). After a 10-minute break, they resumed the task — with the twist that any pictures that had appeared in the first session should be judged “new” if that was the first appearance in the second session. EEG measurements (event-related potentials — ERPs) were taken during the sessions.

ERPs at the onset of a test stimulus (each picture) are different for new and old (repeated) stimuli. Previous studies have established various old/new effects that reflect item and source memory in adults. In the case of item memory, recognition is thought to be based on two processes — familiarity and recollection — which are reflected in ERPs of different timings and location (familiarity: mid-frontal at 300-500 msec; recollection: parietal at 400-70 msec). Familiarity is seen as a fast assessment of similarity, while recollection varies according to the amount of retrieved information.

Source memory appears to require control processes that involve the prefrontal cortex. Given that this region is the slowest to mature, it would not be surprising if source memory is a problematic memory task for the young. And indeed, previous research has found that children do have particular difficulty in sourcing memories when the sources are highly similar.

In the present study, children performed more poorly than adolescents and adults on both item memory and source memory. Adolescents performed more poorly than adults on item memory but not on source memory. Children performed more poorly on source memory than item memory, but adolescents and adults showed no difference between the two tasks.

All groups responded faster to new items than old, and ERP responses to general novelty were similar across the groups — although children showed a left-frontal focus that may reflect the transition from analytic to a more holistic processing approach.

ERPs to old items, however, showed a difference: for adults, they were especially pronounced at frontal sites, and occurred at around 350-450 msec; for children and adolescents they were most pronounced at posterior sites, occurring at 600-800 msec for children and 400-600 msec for adolescents. Only adults showed the early midfrontal response that is assumed to reflect familiarity processing. On the other hand, the late old/new effect occurring at parietal sites and thought to reflect recollection, was similar across all age groups. The early old/new effect seen in children and adolescents at central and parietal regions is thought to reflect early recollection.

In other words, only adults showed the brain responses typical of familiarity as well as recollection. Now, some research has found evidence of familiarity processing in children, so this shouldn’t be taken as proof against familiarity processing in the young. What seems most likely is that children are less likely to use such processing. Clearly the next step is to find out the factors that affect this.

Another interesting point is the early recollective response shown by children and adolescents. It’s speculated that these groups may have used more retrieval cues — conceptual as well as perceptual — that facilitated recollection. I’m reminded of a couple of studies I reported on some years ago, that found that young children were better than adults on a recognition task in some circumstances — because children were using a similarity-based process and adults a categorization-based one. In these cases, it had more to do with knowledge than development.

It’s also worth noting that, in adults, the recollective response was accentuated in the right-frontal area. This suggests that recollection was overlapping with post-retrieval monitoring. It’s speculated that adults’ greater use of familiarity produces a greater need for monitoring, because of the greater uncertainty.

What all this suggests is that preadolescent children are less able to strategically recollect source information, and that strategic recollection undergoes an important step in early adolescence that is probably related to improvements in cognitive control. But this process is still being refined in adolescents, in particular as regards monitoring and coping with uncertainty.

Interestingly, source memory is also one of the areas affected early in old age.

Failure to remember the source of a memory has many practical implications, in particular in the way it renders people more vulnerable to false memories.

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Brain continues to develop well into our 20s

October, 2011

A new study shows that the wiring that connects the frontal lobes to other parts of the cerebral cortex continues to develop well into young adulthood — except for a small minority that show degradation.

Brain imaging data from 103 healthy people aged 5-32, each of whom was scanned at least twice, has demonstrated that wiring to the frontal lobe continues to develop after adolescence.

The brain scans focused on 10 major white matter tracts. Significant changes in white matter tracts occurred in the vast majority of children and early adolescents, and these changes were mostly complete by late adolescence for projection and commissural tracts (projection tracts project from the cortex to non-cortical areas, such as the senses and the muscles, or from the thalamus to the cortex; commissural tracts cross from one hemisphere to the other). But association tracts (which connect regions within the same hemisphere) kept developing after adolescence.

This was particularly so for the inferior and superior longitudinal and fronto-occipital fascicule (the inferior longitudinal fasciculus connects the temporal and occipital lobes; the superior longitudinal fasciculus connects the frontal lobe to the occipital lobe and parts of the temporal and parietal lobes). These frontal connections are needed for complex cognitive tasks such as inhibition, executive functioning, and attention.

The researchers speculated that this continuing development may be due to the many life experiences in young adulthood, such as pursing post-secondary education, starting a career, independence and developing new social and family relationships.

But this continuing development wasn’t seen in everyone. Indeed, in some people, there was evidence of reductions, rather than growth, in white matter integrity. It may be that this is connected with the development of psychiatric disorders that typically develop in adolescence or young adulthood — perhaps directly, or because such degradation increases vulnerability to other factors (e.g., to drug use). This is speculative at the moment, but it opens up a new avenue to research.

Reference: 

[2528] Lebel, C., & Beaulieu C.
(2011).  Longitudinal Development of Human Brain Wiring Continues from Childhood into Adulthood.
The Journal of Neuroscience. 31(30), 10937 - 10947.

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Childhood amnesia shifts with time

August, 2011

A new study finds that the earliest memories children can recall shifts with time, providing support for the theory that children’s memories don’t consolidate in the way adults’ memories do.

Childhood amnesia — our inability to remember almost everything that happened to us when very young — is always interesting. It’s not as simple as an inability to form long-term memories. Most adults can’t remember events earlier than 3-4 years (there is both individual and cultural variability), even though 2-year-olds are perfectly capable of remembering past events (side-note: memory durability increases from about a day to a year from age six months to two years). Additionally, research has shown that young children (6-8) can recall events that happened 4-6 years previously.

Given that the ability to form durable memories is in place, what governs which memories are retained? The earliest memories adults retain tend to be of events that have aroused emotions. Nothing surprising about that. More interesting is research suggesting that children can only describe memories of events using words they knew when the experience occurred — the study of young children (27, 33 or 39 months) found that, when asked about the experimental situation (involving a "magic shrinking machine") six months later, the children easily remembered how to operate the device, but were only able to describe the machine in words they knew when they first learned how to operate it.

Put another way this isn’t so surprising: our memories depend on how we encode them at the time. So two things may well be in play in early childhood amnesia: limited encoding abilities (influenced but not restricted to language) may mean the memories made are poor in quality (whatever that might mean); the development of encoding abilities means that later attempts to retrieve the memory may be far from matching the original memory. Or as one researcher put it, the format is different.

A new study about childhood amnesia looks at a different question: does the boundary move? 140 children (aged 4-13) were asked to describe their three earliest memories, and then asked again two years later (not all could provide as many as three early memories; the likelihood improved with age).

While more than a third of the 10- to 13-year-olds described the same memory as their very earliest on both occasions, children between 4 and 7 at the first interview showed very little overlap between the memories (only 2 of the 27 4-5 year-olds, and 3 of the 23 6-7 year-olds). There was a clear difference between the overlap seen in this youngest group (4-7) and the oldest (10-13), with the in-between group (8-9) being placed squarely between the two (20.7% compared to 10% and 36%).

Moreover, children under 8 at the first interview mostly had no overlap between any of the memories they provided at the two interviews, while those who were at least 8 years old did. For the oldest groups (10-13), more than half of all the memories they provided were the same.

The children were also given recall cues for memories they hadn’t spontaneously recalled. That is, they were told synopses of memories belonging to both their own earlier memories, and other children’s earlier memories. Almost all of the false memories were correctly rejected (the exceptions mostly occurred with the youngest group, those initially aged 4-5). However, the youngest children didn’t recognize over a third of their own memories, while almost all the oldest children’s memories were recognized (90% by 8-11 year-olds; all but one by 12-13 year-olds). Their age at the time of the event didn’t seem to affect the oldest or the very youngest groups, but 6-9 year-olds were more likely to recall after cuing events that happened at least a year later than those events that weren’t recalled after cuing.

In general, the earliest memories were several months later at the follow-up than they had been previously. The average age at the time of the earliest memory was 32 months, and 39.6 months on the follow-up interview. This shift in time occurred across all ages. Moreover, for the very earliest memory, the time-shift was even greater: a whole year.

In connection with the earlier study I mentioned, regarding the importance of language and encoding, it is worth noting that by and large, when the same memories were recalled, the same amount of information was recalled.

There was no difference between the genders.

The findings don’t rule out theories of the role of language. It seems clear to me that more than one thing is going on in childhood amnesia. These findings bear on another aspect: the forgetting curve.

It has been suggested that forgetting in children reflects a different function than forgetting in adults. Forgetting in adults matches a power function, reflecting the fact that forgetting slows over time (as is often quoted, most forgetting occurs in the first 24 hours; the longer you remember something, the more likely you are to remember it forever). However, there is some evidence that forgetting in children is best modeled in an exponential function, reflecting the continued vulnerability of memories. It seems they are not being consolidated in the way adults’ memories are. This may be because children don’t yet have the cognitive structures in place that allow them to embed new memories in a dense network.

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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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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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Adults recall negative events less accurately than children

August, 2010

A word experiment shows that unpleasant or traumatic events are likely to be inaccurately remembered, and this memory distortion increases with age. The findings have implications for eyewitness testimony.

Findings that children are less likely than adults to distort memories when negative emotions are evoked has significant implications for the criminal justice system. Experiments involving children aged seven and 11, and young adults (18-23) found that when they were shown lists of closely related emotional words (e.g. pain, cut, ouch, cry, injury), they would tend to mistakenly remember a related word (e.g. hurt) although it had not been present. Despite the prevailing theory that being involved in a very negative experience focuses your mind and helps you notice and remember details, words that had negative emotional content produced the highest levels of false memory. With arousal (such as would be evoked in a traumatic experience), memory was distorted more. These tendencies increased with age.

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[1670] Brainerd, C. J., Holliday R. E., Reyna V. F., Yang Y., & Toglia M. P.
(2010).  Developmental reversals in false memory: Effects of emotional valence and arousal.
Journal of Experimental Child Psychology. 107(2), 137 - 154.

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Mothers influence how children develop advanced cognitive functions

February, 2010

A study of 80 pairs of middle-income Canadian mothers and their year-old babies has revealed conversational strategies that are associated with better executive skills among toddlers.

A study of 80 pairs of middle-income Canadian mothers and their year-old babies has revealed that children of mothers who answered their children's requests for help quickly and accurately; talked about their children's preferences, thoughts, and memories during play; and encouraged successful strategies to help solve difficult problems, performed better at a year and a half and 2 years on tasks that call for executive skills, compared to children whose mothers didn't use these techniques.

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Inner-face advantage in familiar face recognition

Journal Article: 

Campbell, Ruth, Coleman, Michael, Walker, Jane, Benson, Philip J., Wallace, Simon, Michelotti, Joanne & Baron-Cohen, Simon. 1999. When does the inner-face advantage in familiar face recognition arise and why? Visual Cognition, 6(2), 197-216.

  • Adults tend to use inner features (eyes, nose, mouth) to recognize familiar faces.
  • Children tend to use outer features (hair, hairline, jaw, ears) to recognize people they know.
  • The shift from outer to inner features does not occur until the child is 10-11 years old, and may not be reliable until mid-adolescence (14-15).
  • The shift appears to reflect developmental changes in perception rather than simply being an effect of practice.

Although we initially tend to pay attention to obvious features such as hair, it has been long established that familiar faces are recognized better from their inner (eyes, nose, mouth) rather than their outer (hair, hairline, jaw, ears) parts1. Studies have shown that this advantage of inner features does not occur in children until they’re around 10—11 years old. Children younger than this tend to use outer features to recognize people they know2.

Studies investigating the inner-face advantage have used photographs in which parts of faces have been cropped. This may be confusing to young children. It was thought that inner-face processing would be facilitated if blurring was used instead. Accordingly, in this study photographs in which either the inner face or the outer features are blurred were used.

Although it was thought that this would encourage inner-face processing, children seemed to find it harder. Extending the experiment to adolescents, it was found that the inner-face advantage typical of adults, did not appear until 14—15 years of age. A further experiment with learning-disabled adolescents, with a mental age of 5—8 years, found no shift to inner-face processing. This suggests that the shift to inner-face processing is a developmental change, rather than simply reflecting a need to gain sufficient experience in face-processing.

References

1. Ellis, H.D., Shepherd, J.W. & Davies, G.M. 1979. Identification of familiar and unfamiliar faces from internal and external features: Some implications for theories of face recognition. Perception, 8, 431-439.

2. Campbell, R. & Tuck, M. 1995. Children’s recognition of inner and outer face-features of famous faces. Perception, 24, 451-456.

Campbell, R., Walker, J. & Baron-Cohen, S. 1995. The use of internal and external face features in the development of familiar face identification. Journal of Experimental Child Psychology, 59, 196-210.

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