View Full Version : Brain Development


Amtram
01-13-14, 12:54 PM
I was searching related to another discussion and ran across this: The Basics of Brain Development. (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2989000/)

If you want to know how your brain is built, and what it's made of, and when changes happen during prenatal and early development, plus a few things that can influence this development, this is packed full of information. Enjoy!

Conman
01-13-14, 05:46 PM
that paper inflamed my amygdalae and i felt fear at its length and rage at some larger than average words. but it was very well rounded and informative, good find!

mildadhd
01-14-14, 01:36 AM
Development of dopaminergic neurons in the mammalian brain.

Abstract
Dopaminergic neurons in the mammalian brain have received substantial attention in the past given their fundamental role in several body functions and behaviours. The largest dopaminergic population is found in two nuclei of the ventral midbrain. Cells of the substantia nigra pars compacta are involved in the control of voluntary movements and postural reflexes, and their degeneration in the adult brain leads to Parkinson's disease. Cells of the ventral tegmental area modulate rewarding and cognitive behaviours, and their dysfunction is involved in the pathogenesis of addictive disorders and schizophrenia. Because of their clinical relevance, the embryonic development and maintenance of the midbrain dopaminergic cell groups in the adult have been intensively studied in recent years. In the present review, we provide an overview of the mechanisms and factors involved in the development of dopaminergic neurons in the mammalian brain, with a special emphasis on the midbrain dopaminergic population.


http://www.ncbi.nlm.nih.gov/pubmed/16389456

janiew
01-14-14, 01:54 AM
JC, people, we read this stuff?

I am thankful to learn about scientific explanation and eventual treatment so keep me informed.

I am a Google Scholar girl when motivated...

Peace out ---

Amtram
01-14-14, 10:52 AM
Heh. Yes, janiew. Hyperfocus in action. I often wish I'd been this interested in Biology and Neuroscience back when I was in High School.

One of the reasons it's interesting is that it brings up the point of when something happens being important. This is painfully obvious when there's clear evidence of developmental interruption - missing or malformed body parts or organs that are more straightforward than the brain. Genetic abnormalities, epigenetic interruptions, consequences of deprivation of essential nutrients or oxygen or exposure to chemicals that are toxic to fetal development. . .when it comes to faces, limbs, abdominal organs, we can't ignore the evidence that something went wrong.

When that thing went wrong can often be determined by the extent of the abnormality. Someone who's born with malformed fingers obviously took a hit later in fetal development than someone with no arms, for example. People tend to forget that the brain is an organ, too, just like any other part of the body, and develops and grows in an organized fashion during gestation just like everything else. So if a fetus' brain is going to develop differently from normal, knowing the timeline of development can help pinpoint when the problem occurred. It can also help point to what caused it.

If you track what grows in the brain and when, you can get a handle on whether improper structure or function is anatomically based, whether the difference is genetic or the result of an exposure, if it's a developmental or functional disorder. . .all kinds of things. It's pretty neat stuff to know even if you're never going to be a brain surgeon!

BellaVita
01-15-14, 01:46 PM
Thank you Amtram!!! :)

Always providing the coolest stuff :)

janiew
01-17-14, 12:30 AM
This information should be made readily available to anyone who wishes to procreate - or not.

I'm a parent and did a pretty good job of managing the maternal environment when I was pregnant. Maybe not good enough...

janiew
01-20-14, 11:30 PM
Human brain development is a protracted process that begins in the third gestational week (GW) with the differentiation of the neural progenitor cells and extends at least through late adolescence, arguably throughout the lifespan. The processes that contribute to brain development range from the molecular events of gene expression to environmental input. Critically, these very different levels and kinds of processes interact to support the ongoing series of events that define brain development. Both gene expression and environmental input are essential for normal brain development, and disruption of either can fundamentally alter neural outcomes. But neither genes nor input is prescriptive or determinative of outcome. Rather brain development is aptly characterized as a complex series of dynamic and adaptive processes that operate throughout the course of development to promote the emergence and differentiation of new neural structures and functions. These processes operate within highly constrained and genetically organized, but constantly changing contexts that, over time, support the emergence of the complex and dynamic structure of the human brain (Waddington 1939 (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2989000/#CR112); Morange 2001 (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2989000/#CR70); Stiles 2008 (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2989000/#CR104)).

This paper will review some of the major events that contribute to the development of the human brain from its early embryonic state through adolescence. It begins by examining the foundational changes that occur during the embryonic period, which in humans extends through the eighth week post conception (gestational week eight, or GW8). By the end of the embryonic period the rudimentary structures of the brain and central nervous system are established and the major compartments of the central and peripheral nervous systems are defined (see Fig. 1 (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2989000/figure/Fig1/?report=objectonly)). The ensuing period of fetal development extends through the end of gestation. During this time there is rapid growth and elaboration of both cortical and subcortical structures, including the rudiments of the major fiber pathways (Kostovic and Jovanov-Milosevic 2006 (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2989000/#CR55)); (Kostovic and Jovanov-Milosevic 2006 (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2989000/#CR55)). Changes in the gross morphology of the prenatal neural system are underpinned by changes occurring at the cellular level. Neuron production in humans begins on embryonic day 42. E42, i.e. 42 days post conception (Bystron et al. 2008 (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2989000/#CR17); Stiles 2008 (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2989000/#CR104)) and is largely complete by midgestation. As they are produced neurons migrate to different brain areas where they begin to make connections with other neurons establishing rudimentary neural networks. By the end of the prenatal period major fiber pathways, including the thalamocortical pathway, are complete.



__________
Brain Development in the Postnatal Period

Though the production and migration of neurons are largely prenatal events, proliferation and migration of glial progenitors continues for an extended period after birth, and the differentiation and maturation of these cells continue throughout childhood. The full scope of neuron-glia interactions is still not fully defined, but it is clear that these interactions play an important role in functional organization of neural circuits during postnatal life. Importantly, estimates of the developmental time course in humans of the postnatal processes outlined below are derived by extrapolation from data acquired in other species, often rodents, and from very limited human postmortem material. Unfortunately, the result is much remaining uncertainty about the temporal extent of proliferation, migration, differentiation, and regression during the postnatal period in humans, and about the timing of these processes relative to each other. In vivo brain imaging of children is providing important clues about the time course of age-related biological alterations in the brain, and provides an opportunity to link these changes to evolving behavior.

__________
The Role of Experience in Brain Development

The events of the prenatal period serve to establish the core compartments of the developing nervous system from the spinal cord and hindbrain to the cortical structures of the telencephalon. These early events also provide initial patterning within each of the major subdivisions of the brain, but this early patterning, particularly in the neocortex, is both underspecified and malleable. The mature organization of the neocortex emerges over a protracted time during the postnatal period, and it requires diverse forms of input. Some of this input arises from within the organism in the form of molecular signaling and cross-regional activity. But the specific experience of the individual organism also plays an essential role in establishing the mature organization of the neocortex. The development of normal brain organization requires input via all of the major sensory systems. When specific aspects of input are lacking, alternative patterns of brain organization can and do emerge. These alternative patterns of organization reflect the effects of altered profiles of neural competition and capture a fundamental property of mammalian brain development, the capacity for plastic adaptation.
The Role of Input on Brain Development

Greenough introduced the term “experience expectant” development to capture the idea that the early experience of the organism plays an essential role in normal brain development, particularly in the early postnatal period (Greenough et al. 1987 (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2989000/#CR35)). Although cortical patterning begins in the embryonic period it remains malleable for an extended period of time. Typical, expected, postnatal experience is necessary for the emergence of normal patterns of neocortical organization. When that input is lacking brain areas develop differently, and the specific pattern of development reflects the kinds of input that the organism actually received. At later ages, the developing—and even the mature—nervous system continues to require input to acquire new knowledge and to develop functional neural systems. Greenough has termed this later phase of development “experience dependent” learning. These two important constructs suggest that throughout development experience plays an essential role in establishing and refining neural organization in ways that allow the organism to adapt to the contingences of the world in which it lives. Studies that systematically manipulate the specific experience of the young organism provide insight into the dynamic and adaptive nature of brain development.

__________
Summary and Conclusions

Over the past three decades there has been tremendous progress in our understanding of the basic principles of neural development. This progress has changed our fundamental models of how brains develop. Strongly deterministic models have given way to more dynamic and interactive models anchored in the process of development, itself. As suggested by the examples presented in this paper, the processes that underlie and guide brain development involve the ongoing interplay of genetic and environmental factors. Brains do not develop normally in the absence of critical genetic signaling and they do not develop normally in the absence of essential environmental input. Rather, at each point in development, organism intrinsic and environmental factors interact to support the increasingly complex and elaborate structures and functions of the brain. During the embryologic period the interactive processes are most prominent at the level of cell-cell interactions where gene expression in one population of cells generates molecular signals that alter the developmental course of another population of cells. However, even during this earliest period, interactions involving factors in the external environment also play essential roles in the development of the embryonic brain. During the fetal and postnatal periods, organism intrinsic factors continue to play a critical role in development, but across this extended period a wide array of factors in the external world influence the course of brain development in increasingly prominent ways.

Although nothing in neural development appears to be “predetermined”, the process of development is nonetheless orderly and follows very regular patterns over time. The regularity of developmental process arises from constraints imposed by both genetic and environmental factors. Genes provide the templates for creating particular proteins that are essential to the developmental process; the environment provides essential input that shapes and influences the direction of the emerging neural networks. A third essential constraint arises from the fact that the developmental process unfolds over time. The integrity of the developmental process depends absolutely upon the availability of the right neural elements appearing at the appropriate moment in developmental time. Often the emergence of a new element depends upon developmental events that immediately precede its appearance.


For example, the differentiation of the neural progenitor cells along the axial midline of the neural plate during gastrulation sets the stage for the formation of the ventricular zone during neurulation. Furthermore, at each point in developmental time the organism has both a state and a history that limit which factors can influence its development. Visual and auditory signals have little effect on the gastrulating embryo, but both are essential for the typical development of vision and audition in the newborn. The constructs of “progressive differentiation” and “progressive commitment” capture important aspects of the temporal nature of brain development and can account for the regularities that are observed (Stiles 2008 (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2989000/#CR104)). At all levels of the neural system, progressive differentiation of specific elements and structures coupled with progressive commitment of those elements to functional systems appear to be the governing principles of brain development.


I think it's covered. As much as it can be within the strictures of the topic.

http://www.amazon.com/What-Expect-Youre-Expecting-Edition/dp/0761148574

Like there is much you can do besides provide good genes, a positive womb experience and nutrients. After that, it's all individual make up and the environment.

Abi
01-23-14, 03:57 PM
Moderator Note:

PLEASE RETURN TO THE ORIGINAL TOPIC.

IF YOU WISH TO DISCUSS OTHER TOPICS FROM HERE ON OUT, PLEASE USE THE OPEN DISCUSSION THREAD OF THIS TOPIC:

http://www.addforums.com/forums/showthread.php?p=1605273#post1605273

Regards, me.

Luvmybully
01-23-14, 04:20 PM
The brain does, however, stop growing.

I have heard this before, but it never really sunk in JUST what it meant.


It may change, pathways activate, deactivate, or re-route, but you are born with all the brain cells you're ever going to have.

TygerSan
01-23-14, 05:14 PM
The brain is a very complicated organ, for sure, and our understanding of how it grows and develops is evolving as well.

In fact, the dogma quoted above, that the adult brain does not produce new neurons, is not entirely true. In fact, certain areas of the adult brain, including the hippocampus (very important structure involved in memory and emotional processing) do continue producing neurons in adulthood. http://www.jneurosci.org/content/22/3/612.full

In fact, there is a school of thought that says that neurogenesis in the hippocampus may be one of the ways that antidepressants work to alleviate mood symptoms (although that may still be debatable). http://www.nature.com/neuro/journal/v10/n9/abs/nn1969.html

LynneC
05-13-14, 10:16 AM
And along the same lines as Tygersan's links: (too techinical for me, but some of the discussion is quite easily understandable)
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3324277/

This, I thought, was interesting:

Intrinsically, adult neural stem cells pass through sequential developmental stages that show structurally and functionally distinct cellular properties. As noted by Holiday and Waddington, who originally coined the term ‘epigenetics’, cell differentiation during development results essentially from epigenetic changes to identical genomes through temporal and spatial control of gene activity.
The process of adult neurogenesis is therefore intrinsically under similarly choreographed epigenetic control. Extrinsically, adult neurogenesis is precisely modulated by a wide variety of environmental, physiological and pharmacological stimuli. At the interface between genes and the environment, epigenetic mechanisms naturally serve as key conduits for the regulation of adult neurogenesis by the environment, experience and internal physiological states in the form of local or systemic extracellular signaling molecules and patterns of neural circuit activity

Amtram
05-13-14, 05:18 PM
Only difference is that these cells are being created by stem cells - they are new neurons, not replacements for existing neurons. They also tend to grow in limited areas of the brain. This is epigenetic neurogenesis, not epigenetics as it applies to existing adult neurons.

Amtram
05-14-14, 07:54 PM
Oh, and I found the article I was looking for about neonatal neurogenesis that suggests what I had mentioned elsewhere about the devastating effect ongoing epigenetics in the brain would have (existing neurons developing new nuclei, cloning themselves, then apoptosing, destroying all the axonal and synaptic connections they had made to other neurons in the process).

I believe this link (https://www.sciencenews.org/article/birth-new-brain-cells-might-erase-babies%E2%80%99-memories) should be OK by forum guidelines (I do like to check) but in case it's not, it's an article called "Birth of new brain cells might erase babies’ memories" and it appears on the site sciencenews(dot)org.

Inspired by observations of their own toddler, Josselyn and her husband, study coauthor Paul Frankland, wondered why young children couldn’t retain memories of situations or events. These memories — such as what a person ate for dinner — involve the hippocampus, a skinny seahorse-shaped belt of tissue that stretches from ear to ear and houses a cell-making factory about the size of a few blueberries. This little factory is the only part of the brain that normally cranks out new neurons, which scientists believe help make memories.

(My bold)

LynneC
05-15-14, 09:26 AM
Oh, and I found the article I was looking for about neonatal neurogenesis that suggests what I had mentioned elsewhere about the devastating effect ongoing epigenetics in the brain would have (existing neurons developing new nuclei, cloning themselves, then apoptosing, destroying all the axonal and synaptic connections they had made to other neurons in the process).

I believe this link (https://www.sciencenews.org/article/birth-new-brain-cells-might-erase-babies%E2%80%99-memories) should be OK by forum guidelines (I do like to check) but in case it's not, it's an article called "Birth of new brain cells might erase babies’ memories" and it appears on the site sciencenews(dot)org.



(My bold)
You are saying that ongoing neurogenesis in the adult brain might not be such a great thing? My interpretation of that article is that neurogenesis in the adult brain may help us to forget physically and mentally painful memories. I'm thinking it may be a protective thing...

Lunacie
05-15-14, 10:35 AM
Heh. Yes, janiew. Hyperfocus in action. I often wish I'd been this interested in Biology and Neuroscience back when I was in High School.

One of the reasons it's interesting is that it brings up the point of when something happens being important. This is painfully obvious when there's clear evidence of developmental interruption - missing or malformed body parts or organs that are more straightforward than the brain. Genetic abnormalities, epigenetic interruptions, consequences of deprivation of essential nutrients or oxygen or exposure to chemicals that are toxic to fetal development. . .when it comes to faces, limbs, abdominal organs, we can't ignore the evidence that something went wrong.

When that thing went wrong can often be determined by the extent of the abnormality. Someone who's born with malformed fingers obviously took a hit later in fetal development than someone with no arms, for example. People tend to forget that the brain is an organ, too, just like any other part of the body, and develops and grows in an organized fashion during gestation just like everything else. So if a fetus' brain is going to develop differently from normal, knowing the timeline of development can help pinpoint when the problem occurred. It can also help point to what caused it.

If you track what grows in the brain and when, you can get a handle on whether improper structure or function is anatomically based, whether the difference is genetic or the result of an exposure, if it's a developmental or functional disorder. . .all kinds of things. It's pretty neat stuff to know even if you're never going to be a brain surgeon!

This thread being bumped ties in with some news I read a day or so ago, about how research found
that lack of folic acid in pregnant women seems to result in babies being born with spinal bifida or anencephaly.

Is it possible something this simple could be causing abnormal development inside the brain during fetus development?

someothertime
05-15-14, 10:45 AM
Hereditory patterns seem to negate this for most ... unless one were to go down the route of emotion hormone baseline establishment interutero...

If symptoms are present in an individual... and there are no hereditary links... then I do believe this to be a distinct possibility... In which case... i would expect hyper, short memory, attention to be much more dominant over say perseveration...

Amtram
05-15-14, 12:29 PM
What it's saying is that this happens in only certain cells. Keep in mind that neurogenesis and neuroplasticity are two completely different things. Neurons are always growing and changing, and connections are established or broken among neurons based on use and need for those connections. That is neuroplasticity.

Neurogenesis, on the other hand, means creation of new brain cells. This happens in a very limited number of cell types and cell areas, as was noted in the study you cited and many other places. Not ironically, these cells are also the most susceptible to developing cancer. Prenatally, neurogenesis is happening by cell division. Then in the third trimester, a huge number of neurons die off (unless the child is autistic, which is a new discovery) and all brain growth that follows involves neurons growing axons and dendrites and essentially getting larger.

As adults, we do not grow new neurons from existing neurons, because the way this works postnatally is that the new neurons replace the old ones, which then die. The type of neurogenesis you're looking at involves stem cells becoming neurons (or glia) and does not cause die-off. The die-off in the article about infants is a phenomenon that has only recently been documented, and has not been observed in adolescents or adults.

LynneC
05-15-14, 01:08 PM
As adults, we do not grow new neurons from existing neurons, because the way this works postnatally is that the new neurons replace the old ones, which then die. The type of neurogenesis you're looking at involves stem cells becoming neurons (or glia) and does not cause die-off. The die-off in the article about infants is a phenomenon that has only recently been documented, and has not been observed in adolescents or adults.
Yes, I understand now what you are saying... :)
But, I don't think there was actually die-off in the infants' neurons. (I could be wrong...didn't see the actual study) I think what was happening was that the rapid neurogenesis that occurs in infants/ toddlers messes up the memory circuitry. Once neurogenesis slows down, young children are able to form lasting memories. It happens in adults also, but the memory loss is not as drastic as in infants/toddlers since the interference from the new neurons is not as pervasive because there aren't as many neurons developing.
http://www.sciencemag.org/content/344/6184/598

ETA, here's a link to the full study... pretty cool stuff!
http://bms.ucsf.edu/sites/ucsf-bms.ixm.ca/files/shared/20140605.zubia_.mario_.pdf

Amtram
05-15-14, 09:09 PM
It's late for me and a cat just got sick, so I'm going to have to read later, but thanks for the link!

Amtram
05-17-14, 10:01 AM
It's a pretty dense study, and I can see a lot more to it than just the neurogenesis questions that would make it confusing to read for most people. I looked for some other information in "Neuroscience - Exploring the Brain" by Bear, Connors, and Paradiso. It's a textbook for college-level introductory courses, and therefore has illustrations that make it easier to understand.

In the very beginning, the brain develops from the inside out, with cells being produced from the fluid in the vesicles and migrating outward. This is a prenatal process, and if it's interrupted, then the outer areas of the cerebrum don't develop properly. The hippocampus is a u-shaped structure that wraps around the cerebral cortex and is close to the vesicles, and therefore closer to migrating cells.

The stem cells that remain inside the vesicles actually can produce new cells that differentiate into neurons, and it's possible for the few that are created post-natally to eventually migrate to the cortex, but they still go only a certain distance away before they're firmly connected to other neurons. (That means they don't go to the frontal cortices, where we'd really like a little more neuron power. . .in macaque monkeys, they went to the cortex area between the temporal and frontal lobes and stopped.)

You're right about the inverse correlation between neurogenesis in the hippocampus and memory - I was definitely reading that wrong. But I do believe from everything else I'm reading that it has something to do with the new neurons changing the existing connections.

LynneC
05-17-14, 11:25 AM
But I do believe from everything else I'm reading that it has something to do with the new neurons changing the existing connections.
Yes, I think so, too...