The brain is probably the most complex thing I've drawn. On one hand, it's squiggles of a certain shape. But on the other hand, I tried many times, and it turned out really bad. After a very large number of attempts, I finally got the hang of it. I'll try to explain how today.
The easiest way to draw a brain is to first draw a template of its shape. The template will need to be filled with convolutions, and then erased.
We begin filling the template with convolutions. One at a time. They shouldn't be too symmetrical or identical. That would look unnatural. They shouldn't be too different either. That would also look unnatural. The thickness should vary only slightly. And the curves shouldn't bend at different angles.
Look at a photo of a real brain and keep trying until you feel that it's starting to work out.
When the form is completely filled with curves, you just need to color in the spaces and add the brain stem and cerebellum at the bottom. You've got a brain. You're magnificent!