Building a Brain

How the brain and its neurons develop, from conception to young adulthood.

Week 3 after conception

≈ 5 weeks of pregnancy

How to use this page

Keep this guide open while you explore. Pick an age on the timeline, explore the model, and read what is happening at that age.

Move through development

Drag the slider, or press play, to move from the third week after conception to age 25.
The buttons under the slider jump to key moments, from the neural plate to age 25.
Ages are counted from conception. Weeks of pregnancy run about 2 weeks higher.

Move the model

Ways to move the model
To	With a mouse	On a touch screen
Turn it	Drag	Drag
Zoom	Scroll	Pinch
Move it	Right-drag	Drag with two fingers
Read about a part	Click it	Tap it

The tools above the model

Take apart: Spreads the parts out so you can see the deep structures. The slider sets how far, and Reassemble puts them back.
Cut: Slices the brain left to right, front to back or top to bottom. The slider moves the cut, and Flip switches which half is removed.
Color: Brain regions shows the lobes and structures. Embryonic origin shows which part of the early embryo each structure comes from. Maturation order shows the order in which areas of the cortex tend to mature. Natural tissue uses colors close to real tissue.
View from: Turns the model to a set angle: left, right, front, back, top or bottom.
Labels: Shows or hides the names on the model.
Reset: Turns the model back to the starting view.

Before about 10 weeks after conception the model is a simple embryo, so some of these tools stay off until the brain appears.

The panel next to the model

On smaller screens it sits below the model. It has three tabs.

This age explains what is happening at the age on the timeline and suggests something to try.
Selected part describes the part you chose: what it does, how it develops and where it comes from in the embryo.
Parts list shows or hides each part, hides one side of the cortex, or shows only the deep parts.

Further down the page

Inside the cortex at this age shows what the cells are doing at the age you picked.
When the main processes happen and when different measures peak: hover over or tap a row to see its source, or show either chart as a table.
About this model explains how the model was made and what it simplifies.
References lists every source cited on the page.

Sources

Every fact has a citation. Tap or click one to see the full reference, then choose See in reference list to find it in References.

Easier reading

The Display button at the top of the page switches between light and dark, or turns on larger, plainer text. On a small screen it is the round button with two sliders.

Prenatal ages are counted from conception. Weeks of pregnancy are counted from about 2 weeks earlier, so they run about 2 weeks higher.

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Embryo model · schematic

Loading the brain model…

Drag to rotate · scroll or pinch to zoom · right-drag or two-finger drag to move · click a part for details.Drag to rotate · pinch to zoom · two-finger drag to move · tap a part for details.

Inside the cortex at this age

What the cells are doing. Illustration, not to scale.

Zones of the wall: VZ ventricular zone · SVZ subventricular zone · IZ intermediate zone (future white matter) · MZ marginal zone (future layer I). Layers II–VI appear as the cortical plate matures.

When the main processes happen

Darker bars mark the most intense periods. The age axis matches the timeline above. Hover or tap a row for its source.

Different measures peak at different ages

Peak ages from postmortem synapse counts and from brain charts built on more than 100,000 MRI scans.

Building a Brain

Move through development

Explore the model

Take it apart, cut it, recolor it

Read about this age

Look inside the cortex

Check the sources

Inside the cortex at this age

When the main processes happen

Different measures peak at different ages

About this model

References