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Kids' Temporary Hearing Loss Can Lead to 'Lazy Ear'

Scientists have gained new insight into why a relatively short-term hearing deprivation during childhood may lead to persistent hearing deficits, long after hearing is restored to normal.

Research published in the March 11 issue of the journal Neuron, reveals that development of the auditory cortex is quite vulnerable if it does not receive the correct stimulation at just the right time.

It is well established that poor sensory intake during critical periods of childhood development can have detrimental effects on the brain and behavior. A classic example, amblyopia - or lazy eye - can arise when balanced visual signals are not transmitted from each eye to the brain during a critical period in the development of the visual cortex.

"An analogous problem may exist in the realm of hearing, in that children commonly experience a buildup of viscous fluid in the middle ear cavity, called otitis media with effusion, which can degrade the quality of acoustic signals reaching the brain and has been associated with long-lasting loss of auditory perceptual acuity," explains senior study author, Dr. Daniel Polley from the Massachusetts Eye and Ear Infirmary.

Dr. Polley and his colleague Dr. Maria Popescu from Vanderbilt University implemented a method to block hearing in one ear in infant, juvenile, and adult rats, then they looked at how auditory brain areas were impacted by this temporary hearing loss.

They observed that the temporary hearing loss in one ear distorted auditory patterning in the brain, weakening the deprived ear's representation and strengthening the open ear's representation.

The scope of reorganization was most striking in the cortex and was more pronounced when hearing deprivation began in infancy. It appears that the lack of plasticity in the developing auditory cortex might underlie "amblyaudio," in a similar way to the visual cortex plasticity in amblyopia.

"The good news about amblyaudio is that it is unlikely to be a permanent problem for most people", concludes Dr. Polley. "Even if the acoustic signal isn't improved within the critical period, the mature auditory cortex still expresses a remarkable degree of plasticity. We know that properly designed visual training can improve visual acuity in adult amblyopia patients. We are gearing up now to study whether auditory perceptual training may also be a promising approach to accelerate recovery in individuals with unresolved auditory processing deficits stemming from childhood hearing loss."

Pregnant Moms with Metal-on-Metal Hip Implants Pass Metal Ions to Offspring

Women with metal-on-metal hip implants, where both the ball of the joint and the surface of the socket are made of metal, pass metal ions to their offspring during pregnancy, according to a study by researchers at Rush University Medical Center. The ions are the result of wear and corrosion as the metal parts rub against one another.

The data showed a correlation between levels of cobalt and chromium – components of metal implants – in mothers and their babies at the time of delivery.

The study will be presented March 9 at the 2010 Annual Meeting of the American Academy of Orthopaedic Surgeons in New Orleans.

"We don't know whether metal ions pose any health risks for pregnant women and their babies," said Dr. Joshua Jacobs, professor and chairman of orthopedic surgery at Rush, "but as metal-on-metal implants increase in popularity and use, especially among young, active patients, women of child-bearing age and their doctors need to be aware of these findings when considering options for hip replacements."

Jacobs and his colleagues evaluated three women who had metal-on-metal hip implants and gave birth two to six years after their surgeries.

Maternal and umbilical cord blood was gathered at the time of delivery and tested for blood serum concentrations of titanium, nickel, cobalt and chromium using inductively coupled plasma mass spectrometry, a highly sensitive technique that can detect trace amounts of metals in biological samples.

Researchers found that mothers with metal-on-metal implants and their offspring had significantly higher levels of chromium and cobalt compared with a control group of seven women and their offspring who were also tested at the time of delivery. The levels of these metals in the blood of mothers with implants correlated with the levels found in the umbilical cords. Cobalt levels in newborns were about half that in the mothers' blood, while chromium levels were about 15 percent of the mothers' chromium levels. In the control group, no correlation existed.

The lower levels in the umbilical cords indicated that the placenta provided at least some barrier to the transfer of metal ions from mother to fetus, but not a complete barrier, Jacobs said.

Levels of titanium or nickel showed no significant difference between the two groups.

It is unknown whether metal ions in the bloodstream – for pregnant mothers, developing fetuses or newborns – pose any significant health risk. According to Jacobs, medical device companies are working to improve the wear and corrosion properties of metal implants to reduce the release of metal ions.

THURSDAY March 11---------News Archive
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Behavior Problems in Childhood Doubles Risk of Chronic Pain in Adulthood

Bad behaviour in childhood is associated with long-term, chronic widespread pain in adult life, according to the findings of a study following nearly 20,000 people from birth in 1958 to the present day.

Chronic widespread pain is a common complaint that can have a major adverse effect on quality of life, often requiring referral to a hospital specialist for investigation and treatment. The research, published online in the journal Rheumatology (March 10, 2010), found that children with severe behaviour disturbances had approximately double the risk of chronic widespread pain by the time they reached the age of 45 than children who did not.

The association was not explained by social class, early reporting of symptoms or an already-known link between adult psychological distress and chronic widespread pain (CWP). Instead, scientists believe that a dysfunction in the interaction between the nervous system and hormones, occurring in early life, may have long-term consequences for adult health.

"We know already that severe adverse events in childhood such as hospitalization after a road traffic accident and separation from mothers are linked to CWP in adulthood. In addition, aspects of childhood behaviour are strongly related to children reporting CWP. However, until now, it was unknown whether maladjusted behaviour in children was a long-term marker for CWP in adulthood. Our study shows that it is." said Dr Dong Pang, an epidemiologist at the University of Aberdeen (UK).

"We are not sure what underlying biological mechanism underpins this relationship, but one possible explanation might be that both the childhood behaviour and the adult CWP are due to a long-term neuroendocrine dysfunction beginning in early life."

"The hypothalamic-pituitary-adrenal (HPA) axis, the primary neuroendocrine stress response system, has been shown to be associated with childhood behaviour. Similarly, altered HPA axis function has been reported to be associated with CWP. Early life experience, such as emotional stress due to past trauma, may have a lifelong impact on the neuroendocrine system (HPA axis), which in turn leads to behavioural problems in childhood and CWP in adulthood as well as other mental problems. Further research at molecular and genetic level are needed to clarify this." continued Dr. Pang.

A group of 18,558 children who were born in one week in 1958 in England, Scotland and Wales, and an additional 920 children who were born in the same week overseas and who came to the UK before the age of 16 were followed for the research.

Information was collected at the ages of 7, 11 and 16, and at 42 and 45 in adulthood. Parents and teachers independently assessed the children's behaviour on aspects of restlessness, worrying, solitariness, ability to make friends, obedience, stealing, sucking thumbs and biting nails, lying, bullying, truanting etc. At the age of 42 the participants completed a questionnaire asking about psychological distress in adult life, and at the age 45 they completed another questionnaire about pain.

The study found that CWP was slightly more common in women than in men (12.9% versus 11.7%).

Children whose teachers had reported severe persistent behaviour problems at all ages (7, 11 and 16) had more than double the risk of CWP in adulthood compared with children without behaviour problems at all ages. If the children had severe behaviour problems at 11 and 16, then they had nearly double the risk of CWP in later life.

Similar, but weaker associations were shown for parent-reported behaviour, which the researchers believe is because teachers tend to be better at providing objective assessments of behaviour as they have more children to compare.

The researchers saw not just CWP associated with bad behaviour in childhood. Other adult problems include long-term depression and anxiety, suicidal behaviour, substance abuse and treatment for psychiatric illness. The researchers suggest that all these problems may be outcomes of the chain of events set in motion by the dysfunctioning neuroendocrine system.

If further research proves this correct, then it might be possible to intervene in early life to prevent these problems occurring later in adulthood.

Professor Gary Macfarlane, the leader of the research group, said: "This study helps us to understand the factors in childhood that can lead someone to get on a trajectory of ill-health, including chronic pain. The disruption to the hypothalamic-pituitary-adrenal (stress-response) axis is one biological marker of the effect of such experiences and this could help to identify persons at higher risk of chronic pain. Interventions would be lifestyle focussed and would include identification and treatment of behavioural and emotional factors, but would also address lifestyle factors such as increased physical activity.

"We plan to undertake some studies in children to understand what range of factors cause a disturbance to the stress-response axis; such work can then inform what intervention studies may be appropriate."


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