According to many estimates, 
the human brain contains around 100 billion neurons
(give or take a few 10's of billions).

So how many neurons are in the brains of other animals?

• Fruit Fly: 100 thousand neurons
• Cockroach: One million neurons
• Mouse: 75 million neurons
• Cat: One billion neurons
• Chimpanzee: 7 billion neurons
• Elephant: 23 billion neurons