It’s always difficult in human studies to disentangle the effects of lifestyle factors. Alcohol is a case in point, and in particular the vexed question of whether any alcohol is safe during pregnancy. A new study, however, has avoided the complication of co-occurring lifestyle and environment factors by looking directly at genetic variants.
Like us, guinea pigs can’t make vitamin C, but must obtain it from their diet. This makes them a good model for examining the effects of vitamin C deficiency.
Genetic comparisons have pinpointed a specific protein as crucial for brain size, both between and within species. Another shows how genetic regulation in the frontal lobes distinguishes the human brain from that of closely related species, and points to two genes in particular as critical.
In the light of a general increase in caesarean sections, it’s somewhat alarming to read about a mouse study that found that vaginal birth triggers the expression of a protein in the brains of newborns that improves brain development, and this protein expression is impaired in the brains of those delivered by C-section.
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.
190-million-year-old fossil skulls of Morganucodon and Hadrocodium, two of the earliest known mammal species, has revealed that even at this early stage of mammalian evolution, mammals had larger brains than would be expected for their body size. High-resolution CT scans of the skulls have now shown that this increase in brain size can be attributed to an increase in those regions dealing with smell and touch (mammals have a uniquely well developed ability to sense touch through their fur).
A study involving 725 black and Dominican pregnant women living in New York and, later, their 3-year-old children, has found that children who were more highly exposed to PBO in personal air samples taken during the third trimester of pregnancy scored 3.9 points lower on the Bayley Mental Developmental Index than those with lower exposures. This is a similar effect size to that of lead exposure.
A comparison of the brain and body size of over 500 species of living and fossilised mammals has found that the brains of monkeys grew the most over 60 million years, followed by horses, dolphins, camels and dogs. Those with relatively bigger brains tend to live in stable social groups. The brains of more solitary mammals, such as cats, deer and rhino, grew much more slowly during the same period.
Analysis of the brain sizes of 197 marsupial and 457 placental mammals has found that marsupial mammals (e.g. kangaroos, possums), had relative brain sizes that are at least as big as placental mammals. Previous belief that marsupials have relatively smaller brains appears to be produced by the inclusion of the one outlier group — primates. In both placental and marsupial groups, big brains were correlated to length of maternal care (i.e. lactation).
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.