I agree with Max Anstötz in general. Whole mammalian brain tissue requires continuous blood supply for temperature control, oxygenation, nutrient supply, and waste removal, if you want to study electrical activity that resembles physiological. I've not heard of anyone successfully maintaining an in vitro (removed from the body) brain alive for very long, even with in vitro perfusion, but I've not done a literature search on this. On the other hand, experiments can be performed for hours, possibly a day or longer, on animals that are anesthetized and the brain exposed by craniotomy for electrophysiology.

There are ways to keep brain slices in culture for up to several months, through the tissue "flattens out," and the neuronal phenotypes may drift over time as some synaptic connections are lost and others change. The neurons and other cell types in these slices are amenable to patch clamp. Whether the so-called organotypic brain slice culture is suitable to answer your experimental questions depends on the exact question. You may want to look at the work by the Gähwiler laboratory in Switzerland.

thank you Max Anstötz and Robert H Chow for such detailed explanation.