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Welcome to The Visible Embryo, a comprehensive educational resource on human development from conception to birth.

The Visible Embryo provides visual references for changes in fetal development throughout pregnancy and can be navigated via fetal development or maternal changes.

The National Institutes of Child Health and Human Development awarded Phase I and Phase II Small Business Innovative Research Grants to develop The Visible Embryo. Initally designed to evaluate the internet as a teaching tool for first year medical students, The Visible Embryo is linked to over 600 educational institutions and is viewed by more than ' million visitors each month.


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Pregnancy Timeline by SemestersFemale Reproductive SystemFertilizationThe Appearance of SomitesFirst TrimesterSecond TrimesterThird TrimesterFetal 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 HemispheresEnd of Embryonic PeriodEnd of Embryonic PeriodFirst Thin Layer of Skin AppearsThird TrimesterDevelopmental Timeline
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September 27, 2012--------News Archive Return to: News Alerts




Modified drawing of the neural circuitry of the rodent hippocampus.
Image: Santiago Ramón y Cajal (1911(1911)) [1909(1909)]
Histologie du Système nerveux de l'Homme et des Vertébrés, Paris: A. Maloine

WHO Child Growth Charts

       

Learning Requires Rhythmic Activity of Neurons

Scientists have discovered how the brain filters electrical neuronal signals through an input and output control, regulating learning and memory

The hippocampus represents an important brain structure for learning. Scientists at the Max Planck Institute of Psychiatry in Munich discovered the hippocampus filters electrical neuronal signals through an input and output control mechanism, to regulate learning and memory. Effective signal transmissions also need 'theta-frequency' impulses of the cerebral cortex.

The work was published in Frontiers in Neural Circuits.


With a frequency of three to eight hertz,
'theta-frequency' impulses generate waves of electrical
activity that propagate through the hippocampus.

Impulses measured at a different frequency evoke no
transmission, or only a much weaker one.


Signal transmissions through other areas of the brain using long-term potentiation (LTP), essential for learning, occur only when the activity waves take place for an extended period.

Scientists even have an explanation for why we are mentally more productive after drinking a cup of coffee, or in an acute stress situation: in their experiments, caffeine and the stress hormone corticosterone were seen to boost activity flow through the hippocampus.

Learning and recalling requires concentration on the relevant information and experiencing it again and again. Electrophysiological experiments in mice now show why this is the case. Scientists belonging to Matthias Eder´s Research Group measured the transmission of electrical impulses between neurons in the mouse hippocampus under a fluorescence microscope, and they were able to observe in real time how the neurons forward signals.

Jens Stepan, a junior scientist at the Max Planck Institute of Psychiatry in Munich, stimulated the input region of the hippocampus the first time that specifically theta-frequency stimulations produce an effective impulse transmission across the hippocampal CA3/CA1 region. This finding is very important, as it is known from previous studies that theta-rhythmical neuronal activity in the entorhinal cortex always occurs when new information is taken up in a focused manner.


With this finding, the researchers demonstrate
that the hippocampus is highly selective in its
reaction to entorhinal signals. It can distinguish
important and potentially recollection-worth
information from unimportant information
and process it in a physiologically specific manner.


One possible way the hippocampus distinguishes between important and unimportant information is in the formation of long-term potentiation (LTP) signal transmissions at CA3-CA1 synapses, which is often found to be essential for learning and memory.


The present study documents that CA1-LTP synapses
occur only when the activity waves through the
hippocampus take place for a certain time.

Translating this into learning behavior, to commit
for example, an image to memory, we should intently
view an image for awhile, as only then can we produce
activity waves long enough to store the image in our brain.


With this study, Matthias Eder and colleagues succeeded in closing a knowledge gap. Eder: "Our investigation on neuronal communication via the hippocampal trisynaptic circuit provides us with a new understanding of learning in the living organism. We are the first to show that long-term potentiation depends on the frequency and persistency of incoming sensory signals in the hippocampus."

Original article: http://www.mpg.de/6365232/learning-hippocampus