The song goes “Pinky and the Brain, one is a genius, the other’s insane”, which, if it implies anything, implies Pinky is the genius and Brain is the insane one

Glial cells, not neurons.

https://www.scientificamerican.com/blog/guest-blog/human-brain-cells-make-mice-smart/

Human glia derived myelin sheaths are better, faster, and, in some mutants, can repair damaged sheaths better than rodent ones. Since myelin is what makes the action potential travel fast and efficiently along a neuron, this means smarter mice. Since there’s generally very little immune activity in the CNS, you have a much lower chance of rejection.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6700730/#ABS1title

Deleted because I should have scrolled down for “Narf!”

The beginning of Flowers for Algernon, or how I was introduced to the story through the movie Charly.

Wasn’t there a mutation in humans that increased the max. connections per neuron, with the cost of more, uh, faulty products?

Edit: asked ChatGPT, confirmed it somewhat but can’t search the net.

The study you are referring to might be related to research on the evolution of the human brain and the structural differences in neurons compared to other primates. One notable study published in 2012 by a team led by neuroscientist Suzana Herculano-Houzel found that humans have a higher number of connections per neuron in the cerebral cortex compared to other primates.