Editing Adolescence (section)

===Changes in the brain===
The human brain is not finished developing by the time a person reaches puberty, or even finishes it. The frontal lobe of the brain has been known to shape itself well into one's 30s.<ref>{{cite journal | doi=10.1073/pnas.1105108108 | title=Extraordinary neoteny of synaptic spines in the human prefrontal cortex | journal=Proceedings of the National Academy of Sciences | date=August 9, 2011 | volume=108 | issue=32 | pages=13281–13286 | last1=Petanjek | first1=Zdravko | last2=Judaš | first2=Miloš | last3=Šimić | first3=Goran | last4=Rašin | first4=Mladen Roko | last5=Uylings | first5=Harry B. M. | last6=Rakic | first6=Pasko | last7=Kostović | first7=Ivica | pmid=21788513 | pmc=3156171 | bibcode=2011PNAS..10813281P | doi-access=free }}</ref> Neuroscientists often cannot agree precisely on when this developmental period ends or if there is an exact age for the end of brain development.<ref>{{cite journal | pmid=28009272 | doi=10.1016/j.neuron.2016.10.059 | title=Searching for Signatures of Brain Maturity: What Are We Searching For? | journal=Neuron | date=December 21, 2016 | volume=92 | issue=6 | pages=1164–1167 | last1=Somerville | first1=Leah H. | s2cid=207217254 | doi-access=free }}</ref> Below the age of about roughly 30, the human brain has been implicated in human behavior and [[Immaturity|social immaturity.]] However, there has been no empirical study indicating a causal relationship with the development of the prefrontal cortex in adolescence and into early adulthood with any irrational behaviors.<ref>{{cite journal | pmid=19699416 | pmc=2892678 | doi=10.1016/j.jadohealth.2009.05.016 | title=Adolescent Maturity and the Brain: The Promise and Pitfalls of Neuroscience Research in Adolescent Health Policy | journal=The Journal of Adolescent Health | date=September 2009 | volume=45 | issue=3 | pages=216–221 | last1=Johnson | first1=Sara B. | last2=Blum | first2=Robert W. | last3=Giedd | first3=Jay N. }}</ref> The brain reaches 90% of its adult size by six years of age.<ref name="Casey, B. J. 2008">{{cite journal |author1=Casey B. J. |author2=Getz S. |author3=Galvan A. | year = 2008 | title = The adolescent brain | journal = Developmental Review | volume = 28 | issue = 1| pages = 62–77 | doi = 10.1016/j.dr.2007.08.003 | pmid = 18688292 | pmc = 2500212 }}</ref> Thus, the brain does not grow in size much during adolescence.

Over the course of adolescence, the amount of [[white matter]] in the brain increases linearly, while the amount of [[grey matter]] in the brain follows an inverted-U pattern.<ref>{{cite journal|last1=Giedd|first1=Jay, N|title=Structural Magnetic Resonance Imaging of the Adolescent Brain|journal=Annals of the New York Academy of Sciences|year=2004|volume=1021|issue=1|pages=77–85|doi=10.1196/annals.1308.009|pmid=15251877|bibcode=2004NYASA1021...77G|s2cid=20947602}}</ref> Through a process called [[synaptic pruning]], unnecessary neuronal connections in the brain are eliminated and the amount of grey matter is pared down. However, this does not mean that the brain loses functionality; rather, it becomes more efficient due to increased [[myelin]]ation (insulation of axons) and the reduction of unused pathways.<ref>{{cite journal |author1=Giedd J. N. |author2=Blumenthal J. |author3=Jeffries N. O. |author4=Castellanos F. X. |author5=Liu H. |author6=Zijdenbos A. |author7=Rapoport J. L. | year = 1999 | title = Brain development during childhood and adolescence: a longitudinal MRI study | journal = Nature Neuroscience | volume = 2 | issue = 10| pages = 861–863 | doi = 10.1038/13158 | pmid = 10491603 |s2cid=204989935 }}</ref>

The first areas of the brain to be pruned are those involving primary functions, such as motor and sensory areas. The areas of the brain involved in more complex processes lose matter later in development. These include the lateral and [[prefrontal cortex|prefrontal]] cortices, among other regions.<ref>{{cite journal |author1=Gogtay N. |author2=Giedd J. N. |author3=Lusk L. |author4=Hayashi K. M. |author5=Greenstein D. |author6=Vaituzis A. C. |author7=Thompson P. M. | year = 2004 | title = Dynamic mapping of human cortical development during childhood through early adulthood | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 101 | issue = 21| pages = 8174–8179 | doi = 10.1073/pnas.0402680101 | pmid = 15148381 | pmc = 419576 | bibcode = 2004PNAS..101.8174G |doi-access=free }}</ref> Some of the most developmentally significant changes in the brain occur in the prefrontal cortex, which is involved in [[decision making]] and cognitive control, as well as other higher cognitive functions. During adolescence, myelination and synaptic pruning in the prefrontal cortex increases, improving the efficiency of information processing, and neural connections between the prefrontal cortex and other regions of the brain are strengthened.<ref>{{cite journal |author1=Segalowitz S. J. |author2=Davies P. L. | year = 2004 | title = Charting the maturation of the frontal lobe: An electrophysiological strategy | journal = Brain and Cognition | volume = 55 | issue = 1| pages = 116–133 | doi = 10.1016/S0278-2626(03)00283-5 | pmid = 15134847 |s2cid=16152759 }}</ref> This leads to better evaluation of risks and rewards, as well as improved control over impulses. Specifically, developments in the dorsolateral prefrontal cortex are important for controlling impulses and planning ahead, while development in the ventromedial prefrontal cortex is important for decision making. Changes in the orbitofrontal cortex are important for evaluating rewards and risks.

Three [[neurotransmitter]]s that play important roles in adolescent brain development are [[Glutamic acid|glutamate]], [[dopamine]] and [[serotonin]]. Glutamate is an excitatory neurotransmitter. During the synaptic pruning that occurs during adolescence, most of the neural connections that are pruned contain receptors for glutamate or other excitatory neurotransmitters.<ref>Weinberger, D.R., Elvevåg, B., Giedd, J.N. (2005). The Adolescent Brain: A Work in Progress. ''The National Campaign to Prevent Teen Pregnancy''.</ref> Because of this, by early adulthood the synaptic balance in the brain is more inhibitory than excitatory.

[[Dopamine]] is associated with pleasure and attuning to the environment during decision-making. During adolescence, dopamine levels in the [[limbic system]] increase and input of dopamine to the prefrontal cortex increases.<ref>{{cite journal | author = Spear L. P. | year = 2000 | title = The adolescent brain and age-related behavioral manifestations | url = http://faculty.weber.edu/eamsel/Classes/Child%203000/Adolescent%20Risk%20taking/Lectures/3-4%20Biological/Spear%20LV%20%20(2000).pdf| journal = Neuroscience and Biobehavioral Reviews | volume = 24 | issue = 4| pages = 417–463 | doi = 10.1016/S0149-7634(00)00014-2 | pmid = 10817843 | s2cid = 14686245 }}</ref> The balance of excitatory to inhibitory neurotransmitters and increased dopamine activity in adolescence may have implications for adolescent risk-taking and vulnerability to boredom (see [[#Cognitive development|Cognitive development]] below).

[[Serotonin]] is a neuromodulator involved in regulation of mood and behavior. Development in the limbic system plays an important role in determining rewards and punishments and processing emotional experience and social information. Changes in the levels of the neurotransmitters dopamine and [[serotonin]] in the limbic system make adolescents more emotional and more responsive to rewards and stress. The corresponding increase in emotional variability also can increase adolescents' vulnerability. The effect of serotonin is not limited to the limbic system: Several serotonin receptors have their gene expression change dramatically during adolescence, particularly in the human frontal and prefrontal cortex.<ref name="pmid24721318">{{cite journal | doi = 10.1016/j.euroneuro.2014.02.009 |author=Shoval, G. |author2=Bar-Shira O. |author3=Zalsman G. |author4=John J. Mann |author5=Chechik G. | pmid = 24721318 | year = 2014 | title = Transitions in the transcriptome of the serotonergic and dopaminergic systems in the human brain during adolescence | journal = European Neuropsychopharmacology | volume=24 | issue=7 | pages=1123–32|s2cid=14534307 }}</ref>