After the first surgery, Dr. Weiner inserted a depth probe to about the middle of Evan's brain, where the two sides divide. He inserted grids on the surface of the brain too, but the depth probe goes in much deeper and has 8 points on it that collect seizure info. The advantage is that it is getting information from deep inside Evan's brain instead of from the surface. This was extremely important in Evan's case because Evan had three tubers in this area and Dr. Weiner was able to put the probe through all three. The probe ended in the tuber deepest in and this is where the seizure activity was originating in Evan's brain. Up until this trip, every doctor thought the seizure activity was coming from the largest tuber closest to the surface. The image below is of the depth probe in Evan's brain after the first surgery. The white area close to the center of the brain (where the depth probe ends) is the tuber causing all the trouble.
If you look really close, you can see a depth probe on each side of the area removed. They go deeper than what you can see in this image and are picking up additional seizure activity. The final surgery will be to remove a little more brain tissue to eliminate the rest of Evan's seizures and remove all the grids and probes.
The crazy thing is that Evan is completely normal after having this much of his brain removed. His spirits are effected by all this brain invasion, but you'd never guess by talking to him or interacting with him that he just had two pretty major brain surgeries.