Question

Why electric impulse given to dead brain not stimulate life?

Answer 1

For one thing, there’s no such thing as a binary “dead / not dead” brain. Cells shut down and decay slowly, gradually, over time, leading to a smooth continuum of decreasing functionality. Formal medical declaration of death is I believe when the heart stops for some amount of time, but that by itself won’t kill all your brain cells right away. Minutes later, things will be in worse shape, an hour later, worse shape, a day later, worse shape.

But if I interpret your question to mean something like “Neurons that have no active blood supply and are not getting signals on their own anymore”, then the answer would depend on how long the person has been “dead”: after a short while, the neurons should still light up as normal, and propagate patterns through their networks, if artificially stimulated. They would quickly run out of oxygen and ATP though, to operate their proteins like ion pumps, and would no longer be able to fire action potentials after they used up their local supply of fuel, because blood isn’t resupplying them. So you’d get a temporary burst of normal looking activity, then it would go quiet. This is assuming they didn’t already use up their available local energy post-mortem from natural signals. I think that would depend on the situation and how they died.

if the person has been dead even longer and cell membranes are falling apart, chemicals aren’t being made, glial cells aren’t offering proper support or metabolism of leftover bits and pieces, etc., then nothing will happen, because the controlled environment needed for an action potential to fire won’t exist.