Why can't brain cells reproduce?

A typical mature neuron has a network of hundreds if not thousands of branches connecting it to other neurons, and these connections are what determine brain function.

These connections are also built up slowly over years and decades of experience and reinforcement signalling.

In order to divide itself, a neuron would have to retract all these connections back into its main cell body, thus losing all its accumulated normal function. The two new daughter cells would have no connections and would thus be useless.

Re-establishing such a complex network of connections to restore normal function is a staggeringly difficult task, and even if it could be done there would be a time gap in which the function would not be present.

And a single mistake in rewriting can have far reaching consequences, such as seizures.

Over evolutionary time as brains got ever more complex it just became more advantageous to maintain individual neurons for as long as possible, keeping their connections intact, and suppressing their self-replication, limiting it to just a few shall subsets in specialized locations in the brain.

Reference: Adam Wu