Brain development

What are the facts about the left-brain/right-brain characterizations?

gettingwell4 4-5 stars Advanced knowledge, Brain development, Brain hemispheres

This 2013 human study added to the existing understanding of how our brain hemispheres work.

“The main contribution of our study is to demonstrate, at a whole-brain scope, the qualitative differences between the hemispheres in their within- and between-hemisphere interactions. The correlations with behavioral ability really hammer this distinction home, since one needed to use the appropriate metric – that is, segregation versus integration – to see these correlations.

..the left hemisphere showing a preference to interact more exclusively with itself, particularly for cortical regions involved in language and fine motor coordination. In contrast, right-hemisphere cortical regions involved in visuospatial and attentional processing interact in a more integrative fashion with both hemispheres.

The degree of lateralization present in these distinct systems selectively predicted behavioral measures of verbal and visuospatial ability, providing direct evidence that lateralization is associated with enhanced cognitive ability.”

A paraphrase of this last sentence may be that our overall cognitive ability is enhanced when we develop the functional specializations of both brain hemispheres.

http://www.pnas.org/content/110/36/E3435.full “Two distinct forms of functional lateralization in the human brain”

Sex hormone exposure to the developing female fetus causes infertility in adulthood

gettingwell4 4-5 stars Advanced knowledge, Brain development, Epigenetics, Hypothalamus, Limbic system, Testosterone ,

This 2014 rodent study was of polycystic ovarian syndrome, which is the leading cause of human female infertility.

The researchers could reliably induce this disease in mice while they were still fetuses, but effects didn’t manifest until adulthood! The inducement method exposed the developing female fetuses to androgens such that their testosterone concentration was significantly increased.

Comparing this study with How mothers-to-be program lifelong low testosterone into their unborn male children, we can see that in early development:

  • too much testosterone for a female fetus and
  • too little testosterone for a male fetus

both have lifelong ill effects.

http://www.pnas.org/content/112/2/596.full “Enhancement of a robust arcuate GABAergic input to gonadotropin-releasing hormone neurons in a model of polycystic ovarian syndrome”

Why do researchers title their study the cortex vs. the limbic system or lower brain?

gettingwell4 2-3 stars Required further work, Brain development, Brainstem, Cerebrum, Limbic system, Lower brain, Stress ,

This 2012 review of 89 studies was ostensibly of the prefrontal cortex. The review title showed how researchers characterize their work as studying the cerebrum, even when they primarily deal with the limbic system and lower brains.

For example, the reviewer discussed rodent studies of the developing pup fetus regarding:

  • Sensory/motor – Paternal complex housing, maternal complex housing
  • Stress – Mild stress, bystander stress, moderate stress
  • Psychoactive drugs – Stimulants
  • Adult stimulants – Ethanol

The active brain areas of the rodent fetus are the brainstem and the limbic system, and those areas were primarily what was studied. The cerebrum of the developing pup is a tiny strip that has little cognitive function.

http://www.pnas.org/content/109/Supplement_2/17186.full “Experience and the developing prefrontal cortex”

Maternal depression and antidepressants epigenetically change infant language development

gettingwell4 4-5 stars Advanced knowledge, Brain development, Epigenetics, Neurochemicals, Serotonin , , , , ,

This 2012 human study found that infant language development accelerated when the depressed mother-to-be took antidepressants:

“Language acquisition reflects a complex interplay between biology and early experience.

Psychotropic medication exposure has been shown to alter neural plasticity and shift sensitive periods in perceptual development.”

Infant language development was delayed when the depressed mother-to-be didn’t take serotonin reuptake inhibitor medication:

“Prenatal depressed maternal mood and (S)SRI exposure were found to shift developmental milestones bidirectionally on infant speech perception tasks.”

Contrast this study with Problematic research with telomere length, which pretended that maternal depression had negligible epigenetic effects on the developing fetus, infant, and child.

http://www.pnas.org/content/109/Supplement_2/17221.full “Prenatal exposure to antidepressants and depressed maternal mood alter trajectory of infant speech perception”

Early human brain development can be greatly modified by environmental factors

gettingwell4 4-5 stars Advanced knowledge, Brain development, Brain hemispheres, Epigenetics , , ,

This 2014 Brazilian human study found that the brains of people born without the corpus callosum, the major connection between brain hemispheres, adapted to this loss:

“The authors believe that the development of alternative pathways results from the brain’s ability for long-distance plasticity and occurs in the utero during embryo development, which indicates that connections formed in the human brain early in development can be greatly modified, and most likely by environmental or genetic factors.”

BRAVO! MORE STUDIES LIKE THIS ONE!

People have limited capability to adapt later in life to corpus callosum injuries or to brain hemisphere disconnection.

http://www.pnas.org/content/111/21/7843.full “Structural and functional brain rewiring clarifies preserved interhemispheric transfer in humans born without the corpus callosum”

Face-selective neurons maintain consistent visual responses across months

gettingwell4 2-3 stars Required further work, Brain development, Memory

This 2014 primate study provided additional details on the specialized brain circuits for recognizing faces:

“The current finding that neurons commonly give similar responses upon seeing the same faces months apart raises the possibility that some neurons might respond the same way to the same individual faces over most of the animal’s lifespan.”

But the finding could also have been:

“Another example of a biological system maintaining its complex organization as the constituent components are exchanged.”

http://www.pnas.org/content/111/22/8251.full “Face-selective neurons maintain consistent visual responses across months”

Both sexes can be skilled child caregivers when we put time and effort into it

gettingwell4 2-3 stars Required further work, Amygdala, Brain development, Cerebrum, Limbic system

My POV of this 2014 Israeli study’s findings, at the risk of being dragged into the politically-correct quagmire:

  • Mothers (heterosexual primary-caregiving) mainly used areas of their limbic systems to care for children;
  • Fathers (heterosexual secondary-caregiving) mainly used areas of their cerebrums to care for children;
  • Fathers (homosexual primary-caregiving) mainly used both their limbic systems and cerebrums to care for children.

Findings of the “duh” variety:

  • Women have a built-in capacity to care for children before they have children;
  • Men can learn to care for children;
  • Both sexes can be skilled child caregivers when we put time and effort into it.

“Although only mothers experience pregnancy, birth, and lactation, and these provide powerful primers for the expression of maternal care via amygdala sensitization, evolution created other pathways for adaptation to the parental role in human fathers, and these alternative pathways come with practice, attunement, and day-by-day caregiving.”

http://www.pnas.org/content/111/27/9792.full “Father’s brain is sensitive to childcare experiences”

Problematic research on hardwired differences in human male and female brains

gettingwell4 < 0 Detracted from science, Brain development, Brain hemispheres, Epigenetics

At the risk of wading into a quagmire, it’s hard to take this 2013 Pennsylvania study’s findings seriously, that there were new and significant hardwired differences in human male and female brains in addition to what we already knew. The authors didn’t explain all the factors involved in why they found what they did.

For example, can we raise kids in our culture along typical gender roles and biases, then at ages 12-14, say that the differences in their brains are solely due to their genders? To do so would be to ignore what’s known about epigenetic and environmental influences in shaping the brain.

Here’s an ancient (2011), 90-minute, poor-quality-of-science panel discussion of the subject that included the author of Is the purpose of research to define opportunities for interventions?

Kevin Mitchell had the last word in his 2017 post Debunking the male-female brain mosaic where he both exposed this and other conceptual fallacies, and explained how framing and data cherry-picking can mislead accurate analysis. Feel free to apply what he said to the above video and to the below study.

http://www.pnas.org/content/111/2/823.full “Sex differences in the structural connectome of the human brain”

Our early experiences are maintained and unconsciously influence us for years, if not indefinitely

gettingwell4 4-5 stars Advanced knowledge, Brain development, Brain hemispheres, Memory , , , ,

This 2014 Montreal study provided more evidence of critical periods during human development:

“Clearly illustrates that early acquired information is maintained in the brain and that early experiences unconsciously influence neural processing for years, if not indefinitely.

We show that internationally adopted children (aged 9–17 years) from China, exposed exclusively to French since adoption (mean age of adoption, 12.8 mo), maintained neural representations of their birth language despite functionally losing that language and having no conscious recollection of it.

We show that neural representations are not overwritten and suggest a special status for language input obtained during the first year of development.”

YES! GIVE US MORE STUDIES LIKE THIS ONE!

http://www.pnas.org/content/111/48/17314.full “Mapping the unconscious maintenance of a lost first language”

Chronic stress changes the architecture of the hippocampus, leading to depression and cognitive impairment

gettingwell4 4-5 stars Advanced knowledge, Brain development, Cortisol, Epigenetics, Hippocampus, Limbic system, Memory, Neurochemicals, Stress ,

This 2014 rodent study gave further details that:

“Chronic stress, which can precipitate depression, induces changes in the architecture and plasticity of apical dendrites that are particularly evident in the CA3 region of the hippocampus.”

Other studies on the hippocampus CA3 region include:

http://www.pnas.org/content/111/45/16130.full “Role for NUP62 depletion and PYK2 redistribution in dendritic retraction resulting from chronic stress”

Improvements in tracking and predicting single cell epigenetic changes during embryonic development

gettingwell4 2-3 stars Required further work, Brain development, Epigenetics, Immune system

This 2014 Harvard rodent study demonstrated improvements in tracking and predicting how, during embryonic development, a cell’s environment epigenetically changed the cell’s genetic expression. The researchers stated applicability to human B-cell development in the immune system.

http://www.pnas.org/content/111/52/E5643.full “Bifurcation analysis of single-cell gene expression data reveals epigenetic landscape”

Treating the father’s symptoms of an inherited disease can epigenetically treat the son

gettingwell4 4-5 stars Advanced knowledge, Brain development, Epigenetics , , ,

This 2014 La Jolla rodent study showed that treating the symptoms of an inherited disease can, through epigenetic DNA methylation, positively treat the symptoms in the subjects’ offspring.

The disease studied was Huntington’s, which is the most common inherited neurodegenerative disease:

  • The treatment induced epigenetic changes in the expression of genes on the male Y chromosome.
  • The treated male subjects were bred, and their sperm carried both the Huntington’s disease and the epigenetic changes that reduced the symptoms.
  • The male offspring showed both delayed onsets of Huntington’s disease and reductions of specific symptoms when compared with both the treated subjects’ female offspring and the control group non-treated subjects’ male offspring.

Per the definitions in A review of epigenetic transgenerational inheritance of reproductive disease and Transgenerational effects of early environmental insults on aging and disease, for the term in the study’s title “transgenerational effects” to apply, the researchers needed to provide evidence in at least the next 2 male and/or 3 female generations of:

“Altered epigenetic information between generations in the absence of continued environmental exposure.”

The study instead provided evidence for intergenerational effects.

http://www.pnas.org/content/112/1/E56.full “HDAC inhibition imparts beneficial transgenerational effects in Huntington’s disease mice via altered DNA and histone methylation”

Problematic research: Feigning naivety of the impact of prenatal, infancy and early childhood experiences

gettingwell4 < 0 Detracted from science, Brain development, Epigenetics, Hippocampus, Limbic system, Memory, Stress

What I found curious in this 2012 UK review of 82 studies was the reviewer’s reluctance to highly regard a human’s life before birth, during infancy, and in early childhood.

There was no lack in 2012 of animal studies to draw from to inferentially hypothesize how a human fetal environment causes the fetus to adapt with enduring epigenetic changes.

To take just one study that I won’t curate on this blog because it’s too old:

Weinstock M (2008) The long-term behavioural consequences of prenatal stress. Neurosci Biobehav Rev 32:1073–1086, “Stress, [to the pregnant mother] in rodents as well as nonhuman primates, produces behavioral abnormalities [in the pup], such as

  • an elevated and prolonged stress response,
  • impaired learning and memory,
  • deficits in attention,
  • altered exploratory behavior,
  • altered social and play behavior, and
  • an increased preference for alcohol.”

Yet the reviewer posed the question:

“There is a need to determine just what epigenetic changes do and do not account for. Put succinctly, do they explain individual differences in response to adversity and do they account for variations in health and behavior outcomes?”

I suspect that the cause of this feigned naivety was the political incorrectness of adequately placing importance in the human fetus’ experience of the development environment provided by their mother.

The PC view would have us pretend that there aren’t lasting adverse effects from human prenatal, infancy, and early childhood experiences.

The follow-on pretense to this PC view would be that later-life consequences aren’t effects, but are instead, mysteries due to “individual differences.”

http://www.pnas.org/content/109/Supplement_2/17149.full “Achievements and challenges in the biology of environmental effects”

This post has somehow become a target for spammers, and I’ve disabled comments. Readers can comment on other posts and indicate that they want their comment to apply here, and I’ll re-enable comments.

A mother’s care affects the infant’s hippocampus structure and function through epigenetic regulation of genes

gettingwell4 4-5 stars Advanced knowledge, Brain development, Epigenetics, Glutamate, Hippocampus, Limbic system, Memory, Neurochemicals, Stress

This 2012 McGill University rodent study found:

“Variations in maternal care in the rat affect hippocampal morphology and function as well as performance on hippocampal-dependent tests of learning and memory in the offspring.

Thus, in the rat, as in humans, social influences operate during early life to influence the structure and function of brain regions critical for cognitive capacity.

Variations in maternal care can influence hippocampal function and cognitive performance through the epigenetic regulation of genes.”

http://www.pnas.org/content/109/Supplement_2/17200.full “Variations in postnatal maternal care and the epigenetic regulation of metabotropic glutamate receptor 1 expression and hippocampal function in the rat”

The effects of early-life stress are permanent alterations in the child’s brain circuitry and function

gettingwell4 4-5 stars Advanced knowledge, Amygdala, Brain development, Cortisol, Limbic system, Memory, Neurochemicals, Stress ,

The sobering application of this 2013 rodent study’s finding was that if the limbic systems of human children weren’t already permanently damaged before they entered an orphanage, the orphanage experience would probably do that to them:

“The current study manipulates the type and timing of a stressor and the specific task and age of testing to parallel early-life stress in humans reared in orphanages.

The results provide evidence of both early and persistent alterations in amygdala circuitry and function following early-life stress.

These effects are not reversed when the stressor is removed nor diminished with the development of prefrontal regulation regions.”

http://www.pnas.org/content/110/45/18274.full “Early-life stress has persistent effects on amygdala function and development in mice and humans”