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Today, The Visible Embryo is linked to over 600 educational institutions and is viewed by more than 1 million visitors each month. The field of early embryology has grown to include the identification of the stem cell as not only critical to organogenesis in the embryo, but equally critical to organ function and repair in the adult human. The identification and understanding of genetic malfunction, inflammatory responses, and the progression in chronic disease, begins with a grounding in primary cellular and systemic functions manifested in the study of the early embryo.

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Pregnancy Timeline by SemestersFetal liver is producing blood cellsHead may position into pelvisBrain convolutions beginFull TermWhite fat begins to be madeWhite fat begins to be madeHead may position into pelvisImmune system beginningImmune system beginningPeriod of rapid brain growthBrain convolutions beginLungs begin to produce surfactantSensory brain waves begin to activateSensory brain waves begin to activateInner Ear Bones HardenBone marrow starts making blood cellsBone marrow starts making blood cellsBrown fat surrounds lymphatic systemFetal sexual organs visibleFinger and toe prints appearFinger and toe prints appearHeartbeat can be detectedHeartbeat can be detectedBasic Brain Structure in PlaceThe Appearance of SomitesFirst Detectable Brain WavesA Four Chambered HeartBeginning Cerebral HemispheresFemale Reproductive SystemEnd of Embryonic PeriodEnd of Embryonic PeriodFirst Thin Layer of Skin AppearsThird TrimesterSecond TrimesterFirst TrimesterFertilizationDevelopmental Timeline
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Home | Pregnancy Timeline | News Alerts | News Archive June 11, 2013

 
Human brain hippocampus
"It was thought for a long time that we are born with a certain number of neurons,
and that it is not possible to get new neurons after birth. We provide the first evidence
that there is substantial neurogenesis in the human hippocampus throughout life,
suggesting that the new neurons may contribute to human brain function."

Jonas Frisén, senior study author, Karolinska Institute.

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Adults generate new neurons daily

The birth of new neurons in the adult brain sharpens memory in rodents, but whether the same holds true for humans has long been debated. Now, the dating of "heavy" carbon 14 has established that new neurons are born daily in the human hippocampus.

A study published by Cell Press June 6th in the journal Cell reveals that a significant number of new neurons in the hippocampus—a brain region crucial for memory and learning—are generated in adult humans. The researchers used a unique strategy based on the amount of carbon-14 found in humans as a result of above-ground nuclear testing more than half a century ago. The findings suggest that new neurons are born daily in the human hippocampus, offering the tantalizing possibility that they may support cognitive functions in adulthood.

"It was thought for a long time that we are born with a certain number of neurons, and that it is not possible to get new neurons after birth," says senior study author Jonas Frisén of the Karolinska Institute. "We provide the first evidence that there is substantial neurogenesis in the human hippocampus throughout life, suggesting that the new neurons may contribute to human brain function."


Due to technical limitations, until now it was not possible to quantify the amount of neurogenesis in humans. To overcome this hurdle, Frisén and his team developed an innovative method for dating the birth of neurons. This strategy takes advantage of the elevated atmospheric levels of carbon-14, a nonradioactive form of carbon, caused by above-ground nuclear bomb testing more than 50 years ago.


Since the 1963 nuclear test ban treaty, atmospheric levels of "heavy" carbon-14 have declined at a known rate. When we eat plants or animal products, we absorb both normal and heavy carbon at the atmospheric ratios present at that time, and the exact atmospheric concentration at any point in time is stamped into DNA every time a new neuron is born. Thus, neurons can be "carbon dated" in a similar way to that used by archeologists.


By measuring the carbon-14 concentration in DNA from hippocampal neurons of deceased humans, the researchers found that more than one-third of these cells are regularly renewed throughout life. About 1,400 new neurons are added each day during adulthood, and this rate declines only modestly with age.


Because hippocampal neurogenesis occurs to a similar extent in adult humans and adult mice, it could also play an important role in human cognition and psychiatric disease. "It has long been suspected that depression is related to reduced hippocampal neurogenesis, and our findings suggest that new and more effective antidepressants could potentially be developed to target this process," Frisén says.

Cell, Spalding et al.: "Dynamics of hippocampal neurogenesis in adult humans."

Original press release: http://www.eurekalert.org/pub_releases/2013-06/cp-ntf053113.php