Timeline of human brain development

{{Short description|When the human brain ceases to make new neurons and stops developing in humans}}The '''human brain development timeline''' encompasses the sequential, overlapping phases in which the central nervous system forms, matures, and reorganizes from conception through adolescence and into early adulthood.<ref name="Tau20102">{{cite journal |last=Tau |first=G.Z. |author2=Peterson, B.S. |date=2010 |title=Normal Development of Brain Circuits |journal=Neuropsychopharmacology |volume=35 |issue=1 |pages=147–168 |doi=10.1038/npp.2009.115 |pmc=3055433 |pmid=19794405}}</ref><ref name="Springer2024">{{cite journal |last1=Moore |first1=Andrew |year=2024 |title=Development and Maturation of the Human Brain, from Infancy to Adolescence |journal=Handbook of Developmental Neuroscience |series=Current Topics in Behavioral Neurosciences |volume=68 |pages=327–348 |doi=10.1007/7854_2024_514 |pmid=39138744 |isbn=978-3-031-70136-8 }}</ref><ref name="NCBI2000">{{Cite journal |last=Volpe |first=Joseph J. |date=2000 |title=Overview: Normal and abnormal human brain development |url=https://onlinelibrary.wiley.com/doi/abs/10.1002/%28SICI%291098-2779%282000%296%3A1%3C1%3A%3AAID-MRDD1%3E3.0.CO%3B2-J |journal=Mental Retardation and Developmental Disabilities Research Reviews |language=en |volume=6 |issue=1 |pages=1–5 |doi=10.1002/(SICI)1098-2779(2000)6:1<1::AID-MRDD1>3.0.CO;2-J |pmid=10899791 |issn=1098-2779|url-access=subscription }}</ref> This process starts in the third gestational week with the differentiation of neural progenitor cells and progresses through neurogenesis, cell migration, synaptogenesis, myelination, and synaptic pruning.<ref name="Springer2024" /><ref name="NeuroStages">{{cite web |date=2024-06-22 |title=What are the 7 Stages of Brain Development? |url=https://www.neurocenternj.com/blog/what-are-the-7-stages-of-brain-development/ |website=NeuroCenterNJ}}</ref><ref name="NCBI1999">{{cite book |url=https://www.ncbi.nlm.nih.gov/books/NBK225562/ |title=From Neurons to Neighborhoods |publisher=National Academies Press |year=1999 |chapter=The Developing Brain}}</ref>

Many foundational structures of the brain, including the forebrain, midbrain, and hindbrain, emerge by the sixth week of gestation, with further differentiation resulting in secondary regions like the telencephalon, diencephalon, and metencephalon in subsequent weeks.<ref name="Kim20082">{{cite journal |last=Kim |first=M.S. |author2=Jeanty, P. |author3=Turner, C. |author4=Benoit, B. |year=2008 |title=Three-dimensional sonographic evaluations of embryonic brain development |journal=J Ultrasound Med |volume=27 |issue=1 |pages=119–124 |doi=10.7863/jum.2008.27.1.119 |pmid=18096737}}</ref> Structural milestones, including the formation of cortical folds and the appearance of commissural fibers, occur rapidly during prenatal development.<ref name="Budday2014">{{cite journal |last=Budday |first=Silvia |author2=Raybaud, Charles |author3=Kuhl, Ellen |year=2014 |title=A mechanical model predicts morphological abnormalities in the developing human brain |journal=Scientific Reports |volume=4 |issue=5644 |article-number=5644 |doi=10.1038/srep05644 |pmc=4090617 |pmid=25008163 |bibcode=2014NatSR...4.5644B }}</ref><ref name="Ashwell19962">{{cite journal |last=Ashwell |first=K.W. |author2=Waite, P.M. |author3=Marotte, L. |year=1996 |title=Ontogeny of the projection tracts and commissural fibres in the forebrain of the tammar wallaby (Macropus eugenii): timing in comparison with other mammals |journal=Brain, Behavior and Evolution |volume=47 |issue=1 |pages=8–22 |doi=10.1159/000113225 |pmid=8834781}}</ref>

Postnatally, white matter volume and grey matter architecture undergo significant changes, with cortical regions maturing at different rates.<ref name="Blakemore20122">{{cite journal |last=Blakemore |first=S.J. |date=2012 |title=Imaging brain development: the adolescent brain |journal=NeuroImage |volume=61 |issue=2 |pages=397–406 |doi=10.1016/j.neuroimage.2011.11.080 |pmid=22178817}}</ref><ref name="NCBI2018">{{cite journal |last=Ouyang |first=Ming |author2=Jeon, Tae Hyun |author3=Chung, Sungmin |author4=Kim, Ji Hye |author5=Huang, Hao |year=2018 |title=Delineation of early brain development from fetuses to infants with diffusion MRI and beyond |journal=Front Neurosci |volume=12 |pages=538 |doi=10.3389/fnins.2018.00538 |doi-access=free |pmc=6185831 |pmid=29997493}}</ref> The frontal and parietal lobes tend to mature earlier than temporal regions, with synaptic pruning and myelination continuing into the fourth decade of life.<ref name="Springer2024" /><ref name="Blakemore20122" /><ref name="Shafee2014">{{cite journal |last=Shafee |first=R. |author2=Buckner, R. L. |author3=Fischl, B. |year=2014 |title=Gray matter myelination of 1555 human brains using partial volume corrected MRI images |journal=NeuroImage |volume=105 |pages=473–485 |doi=10.1016/j.neuroimage.2014.10.054 |pmc=4262571 |pmid=25449739}}</ref> Experience and environmental factors dynamically shape neural connectivity, influencing lifelong cognitive, affective, and behavioral outcomes.<ref name="NCBI2010">{{cite journal |last=Stiles |first=Joan |author2=Jernigan, Terry L. |year=2010 |title=The Basics of Brain Development |journal=Neuropsychology Review |volume=20 |issue=5 |pages=327–348 |doi=10.1007/s11065-010-9148-4 |pmc=2989000 |pmid=20544222}}</ref><ref name="NCBI2009">{{Cite journal |last1=Knickmeyer |first1=Rebecca C. |last2=Gouttard |first2=Sylvain |last3=Kang |first3=Chaeryon |last4=Evans |first4=Dianne |last5=Wilber |first5=Kathy |last6=Smith |first6=J. Keith |last7=Hamer |first7=Robert M. |last8=Lin |first8=Weili |last9=Gerig |first9=Guido |last10=Gilmore |first10=John H. |date=2008-11-19 |title=A Structural MRI Study of Human Brain Development from Birth to 2 Years |url=https://www.jneurosci.org/content/28/47/12176 |journal=Journal of Neuroscience |language=en |volume=28 |issue=47 |pages=12176–12182 |doi=10.1523/JNEUROSCI.3479-08.2008 |issn=0270-6474 |pmid=19020011|pmc=2884385 }}</ref>

Advances in magnetic resonance imaging and the study of brain organoids have enhanced understanding of neurological disorders and critical periods of vulnerability, enabling new approaches for early diagnosis and intervention.<ref name="Hindawi2021">{{cite journal |last1=Xu |first1=Jie |last2=Wen |first2=Zhexing |year=2021 |title=Brain Organoids: Studying Human Brain Development and Diseases in a Dish |journal=Stem Cells International |pages=1–16 |doi=10.1155/2021/5902824 |pmid=34539790 |doi-access=free |pmc=8448601 }}</ref><ref name="NCBI2021">{{cite journal |last1=Budday |first1=Silvia |last2=Raybaud |first2=Charles |last3=Kuhl |first3=Ellen |year=2014 |title=A mechanical model predicts morphological abnormalities in the developing human brain |journal=Scientific Reports |volume=4 |article-number=5644 |doi=10.1038/srep05644 |pmid=25008163 |bibcode=2014NatSR...4.5644B |pmc=4090617 }}</ref>

==Conception== thumb|400px|Highlights of human brain development from conception through adulthood.<ref name="Tau2010">{{cite journal |title=Normal Development of Brain Circuits |journal=Neuropsychopharmacology |volume=35 |year=2010 |pages=147–168 |doi=10.1038/npp.2009.115 |pmid=19794405 |issue=1 |pmc=3055433 |last1=Tau |first1=G. Z. |last2=Peterson |first2=B. S. }}</ref>|center {| class="wikitable" |- !Day !Event !Reference |- |33 || posterior commissure appears || Ashwell ''et al.'' (1996)<ref name="Ashwell1996">{{cite journal |doi=10.1159/000113225 |year=1996 |title=Ontogeny of the projection tracts and commissural fibres in the forebrain of the tammar wallaby (''Macropus eugenii''): timing in comparison with other mammals |journal=Brain, Behavior and Evolution |volume=47 |pages=8–22 |pmid=8834781 |issue=1|last1=Ashwell |first1=K. W. |last2=Waite |first2=P. M. |last3=Marotte |first3=L }}</ref> |- |33 || medial forebrain bundle appears || Ashwell ''et al.'' (1996)<ref name="Ashwell1996" /> |- |44 || mammillothalamic tract appears || Ashwell ''et al.'' (1996)<ref name="Ashwell1996" /> |- |44 || stria medullaris thalami appears || Ashwell ''et al.'' (1996)<ref name="Ashwell1996" /> |- |51 || axons in optic stalk || Dunlop ''et al.'' (1997)<ref name="Dunlop1997">{{cite journal |year=1997 |title=Development of primary visual projections occurs entirely postnatally in the fat-tailed dunnart, a marsupial mouse, ''nrnitnen'' |journal=The Journal of Comparative Neurology |volume=384 |pages=26–40 |pmid=9214538 |issue=1 |doi=10.1002/(SICI)1096-9861(19970721)384:1<26::AID-CNE2>3.0.CO;2-N|last1=Dunlop |first1=S. A. |last2=Tee |first2=L. B. |last3=Lund |first3=R. D. |last4=Beazley |first4=L. D. |s2cid=38381685 }}</ref> |- |56 || external capsule appears || Ashwell ''et al.'' (1996)<ref name="Ashwell1996" /> |- |56 || stria terminalis appears || Ashwell ''et al.'' (1996)<ref name="Ashwell1996" /> |- |60 || optic axons invade visual centers || Dunlop ''et al.'' (1997)<ref name="Dunlop1997" /> |- |63 || internal capsule appears || Ashwell ''et al.'' (1996)<ref name="Ashwell1996" /> |- |63 || fornix appears || Ashwell ''et al.'' (1996)<ref name="Ashwell1996" /> |- |70 || anterior commissure appears || Ashwell ''et al.'' (1996)<ref name="Ashwell1996" /> |- |77 || hippocampal commissure appears || Ashwell ''et al.'' (1996)<ref name="Ashwell1996" /> |- |87.5 || corpus callosum appears || Ashwell ''et al.'' (1996)<ref name="Ashwell1996" /> |- |157.5 || eye opening || Clancy ''et al.'' (2007)<ref name="Clancy2007">{{cite journal |year=2007 |title=Web-based method for translating neurodevelopment from laboratory species to humans |journal=Neuroinformatics |volume=5 |pages=79–94 |pmid=17426354 |issue=1 |last1 = Clancy|first1 = B|last2 = Kersh|first2=B |last3=Hyde |first3=J |last4=Darlington |first4=R. B. |last5=Anand |first5=K. J. |last6=Finlay |first6=B. L. |doi=10.1385/ni:5:1:79|s2cid=1806001 }}</ref> |- |175 || ipsi/contra segregation in LGN and SC || Robinson & Dreher (1990)<ref name="rob">{{cite journal |doi=10.1159/000115306 |year=1990 |title=The visual pathways of eutherian mammals and marsupials develop according to a common timetable |journal=Brain, Behavior and Evolution |volume=36 |pages=177–195 |pmid=2279233 |issue=4 |last1=Robinson |first1=S. R. |last2=Dreher |first2=B }}</ref> |}

Studies report that three primary structures are formed in the sixth gestational week. These are the forebrain, the midbrain, and the hindbrain, also known as the prosencephalon, mesencephalon, and the rhombencephalon respectively. Five secondary structures originate from these in the seventh gestational week. These are the telencephalon, diencephalon, mesencephalon, metencephalon, and myelencephalon; the lateral ventricles, third ventricles, cerebral aqueduct, and upper and lower parts of the fourth ventricle in adulthood originated from these structures.<ref name="Kim2008">{{cite journal|title=Three-dimensional sonographic evaluations of embryonic brain development|pmid=18096737 | volume=27 |issue=1 | date=January 2008|journal=J Ultrasound Med|pages=119–24|vauthors=Kim MS, Jeanty P, Turner C, Benoit B |doi=10.7863/jum.2008.27.1.119|doi-access=free}}</ref> The appearance of cortical folds first takes place during 24 and 32 weeks of gestation.<ref>{{Cite journal|last1=Budday|first1=Silvia|last2=Raybaud|first2=Charles|last3=Kuhl|first3=Ellen|author3-link= Ellen Kuhl |date=2014-01-01|title=A mechanical model predicts morphological abnormalities in the developing human brain|journal=Scientific Reports|volume=4|article-number=5644|doi=10.1038/srep05644|issn=2045-2322|pmc=4090617|pmid=25008163|bibcode=2014NatSR...4.5644B }}</ref>

==Childhood and adolescence== Cortical white matter increases from childhood (~9 years) to adolescence (~14 years), most notably in the frontal and parietal cortices.<ref name="Blakemore2012">{{cite journal|title=Imaging brain development: the adolescent brain|pmid=22178817|author=Blakemore, S.J. | doi=10.1016/j.neuroimage.2011.11.080|volume=61|issue=2|date=June 2012|journal=NeuroImage|pages=397–406|s2cid=207182527 }}</ref> Cortical grey matter development peaks at ~12 years of age in the frontal and parietal cortices, and 14–16 years in the temporal lobes (with the superior temporal cortex being last to mature), peaking at about roughly the same age in both sexes according to reliable data. In terms of grey matter loss, the sensory and motor regions mature first, followed by other cortical regions.<ref name="Blakemore2012" /> Though it is a controversial psychometric, adult IQ also begins to be tested around this age range, with the Raven's Progressive Matrices test beginning at age 14 and the Wechsler Adult Intelligence Scale test beginning at age 16, though scores between 14 and 16 on the Wechsler test have differences so small that they are considered unreliable. This may bring into question the effectiveness of brain development studies in treating and successfully rehabilitating criminal youth.<ref>{{cite journal |last1=Icenogle |first1=G. |last2=Steinberg |first2=L. |last3=Duell |first3=N. |last4=Chein |first4=J. |last5=Chang |first5=L. |last6=Chaudhary |first6=N. |last7=Di Giunta |first7=L. |last8=Dodge |first8=K. A. |last9=Fanti |first9=K. A. |last10=Lansford |first10=J. E. |last11=Oburu |first11=P. |last12=Pastorelli |first12=C. |last13=Skinner |first13=A. T. |last14=Sorbring |first14=E. |last15=Tapanya |first15=S. |year=2019 |title=Adolescents' Cognitive Capacity Reaches Adult Levels Prior to Their Psychosocial Maturity: Evidence for a "Maturity Gap" in a Multinational, Cross-Sectional Sample |journal=Law and Human Behavior |volume=43 |issue=1 |pages=69–85 |doi=10.1037/lhb0000315 |pmc=6551607 |pmid=30762417 |last16=Tirado |first16=L. M. |last17=Alampay |first17=L. P. |last18=Al-Hassan |first18=S. M. |last19=Takash |first19=H. M. |last20=Bacchini |first20=D.}}</ref>

In the 2010s and beyond, science has shown that the brain continues to develop until at least 30 years of age.<ref>{{cite journal |last1=Shafee |first1=R. |last2=Buckner |first2=R. L. |last3=Fischl |first3=B. |year=2014 |title=Gray matter myelination of 1555 human brains using partial volume corrected MRI images |journal=NeuroImage |volume=105 |pages=473–485 |doi=10.1016/j.neuroimage.2014.10.054 |pmc=4262571 |pmid=25449739}}</ref>

== References == {{Reflist|30em}}

== External links == * [http://www.translatingtime.net/ Translating Time] — a website providing translation of brain developmental times among different species

Category:Embryology of nervous system Category:Developmental neuroscience