Perhaps as simple as fractal noise with a brain-shaped feathered mask. (Set to Dynamic Twist and Spline, then play with complexity, scale, brightness and contrast, and then animate evolution). Animating the mask path and feather might give you the effect you’re looking for.
More complex would be Trapcode form, which shares a lot of parameters with particular. I’d suggest a tutorial as I can’t go into detail here.
Anything extremely realistic means heading to a 3D app.
As far as timing issues, remember that you can always precomp such effects and then use time remapping to tweek the timing. Slow it down, speed it up, ramp it, reverse it. Lots of control.
Good luck.
Mac Pro 2 x 3 GHz 6-Core Intel Xeon
32GB Memory
Dual-channel 4Gb Fibre Channel PCI Express card
Dell Display (23″ flat panel)
Nvidia Quadro 4000
AJA Kona LSi SD/HD capture card
Rourke 16 TB
Flanders 2460
SOFTWARE
Mac OS X 10.8.4
FCP 7
Premiere CC
After Effects CC
Boris Continuum
Sapphire Plug Ins
All Trapcode Plugs
Zaxwerks Invig